Precision Software Appli…tions Silver Collection 4/Precision Software Applications Silver Collection Volume 4 (1993).iso/stats/solarvga.exe/CGSS.OVR

Turbo Pascal Overlay | 1991-06-22 | 273KB | 1,470 lines

The Moon's
Orbit
MotionU
Earth Year:U
Earth
CONTINUE
The motion of the Moon in
its orbit is somewhat com-
plex.  As if in a cosmic
carnival ride, it is like
riding on a small merry-go-
round out on the edge of a
much larger merry-go-round!
This display will show the
Earth and Moon in orbit a-
round the Sun.  The sizes
of the Earth and Moon and
their orbits are exaggera-
ted.  However the relative
periods of their orbits are
precise, and may be studied
by toggling the Calendar.
THE MOON'S
ORBIT MOTION
(View from above
the Solar System)
Press  F:  for FASTER display
Press  D:  to toggle DELAY
Press  S:  for SLOWER display
Press  C:  to toggle CALENDAR
TRACKING THE MOON'S ORBIT
They say that "seeing is
believing".  Having just
seen the Earth and Moon in
their orbit around the Sun,
do you think you now know
the "actual shape" of the
Moon's orbit?  We know it
is an ellipse with respect
to the Earth.  But what is
its shape with respect to
to the Sun?  If you know
already, then you are one
person in a thousand!  But
if you don't, then this
will surprise most of you!
TRACKING THE
MOON'S ORBIT
Press  R:  to RESET trackingU
    THE EARTH
THE MOONU
Moon's Diameter:  3,475 km
Moon's Diameter: 2,160 milesU
The Moon's
Size and
CONTINUE
THE SIZE OF THE MOON
At close to 3,475 km, the
At nearly 2,160 miles, the
Moon's diameter at its equa-
tor is only slightly less
than the breadth of the con-
tinental United States.
Therefore the total surface
area of the Moon is very
close to the combined land
areas of Africa and Aus-
tralia, yet still somewhat
less than the land area of
Asia.  (Perhaps one day
we will refer to the Moon
as the Earth's eighth con-
tinent.)
Though the Moon is close to
a perfect sphere, careful
measurements have revealed
slight deviations.  For in-
stance, due to gravitation-
al and tidal forces, the
side of the Moon toward the
Earth bulges toward us .81
kilometers.  Likewise, the
Earth bulges toward us a
half mile.  Likewise, the
Moon's far side dips inward
by a similar amount.  Thus
the Moon is actually very
slightly egg-shaped, though
so slightly as to be imper-
ceptible without sensitive
instruments.
If the Earth were represen-
ted by a basketball, the
Moon would be the size of a
baseball.  Thus compared to
the Earth, the Moon seems a
much smaller world.  How-
ever, except for Pluto's
moon Charon, our Moon is
closer in size to its par-
ent planet than any other.
In fact, some astronomers
elect to refer to the Earth
and Moon, and Pluto and
Charon, as double planets.
While other planets are a
thousand or more times lar-
ger than their moons, . . .
. . .the Earth has only 49
times the volume of our
Moon, and only 4 times its    diameter.
   Though it varies slight-
ly due to the eccentricity
of the Moon's orbit, the
Moon's angular size as seen
from Earth is about a half
of a degree.  This is the
same size as a dime held
about 2 meters away.  In
about six feet away.  In
an odd cosmic coincidence,
the Sun's angular size as
seen from Earth is very
near the Moon's.  (We'll
study this in ECLIPSES.)
EARTH
81 MOONS
THE MASS OF THE MOONGThe mass of 81 Moons would be required to equal the Earth's mass, whileHit would only require 49 Moons to equal the Earth's volume.  This is be-Ccause the Moon is less dense than the Earth.  Weighing 15.2 billionCcause the Moon is less dense than the Earth.  Weighing 16.7 billionDbillion tons, the Moon has an average density of 3.34 times the den-Asity of water, or about 2/3 the average density of the Earth. . .GThe size and mass of the Moon determine its gravity, which at the lunarJsurface is only 1/6 as strong as the Earth's.  This means that if on EarthDyou weighed 45 kg, you would weigh only 7.7 kg on the Moon.  It alsoFyou weighed 100 lb., you would weigh only 17 lb. on the Moon.  It alsoFmeans that things fall slower on the Moon.  In fact, if you dropped anGegg on the Moon from waist-height, it would fall slowly enough to prob-
ably keep from breaking! . . .GThe escape velocity of the Moon is only about 8,700 km/h.  The velocityIrequired to stay in orbit around the Moon is only about 6,100 km/h, or asFThe escape velocity of the Moon is only about 5,400 mph.  The velocityHrequired to stay in orbit around the Moon is only about 3,800 mph, or asGfast as a high-velocity bullet!  Thus, if you were on a mountain on theFMoon and horizontally fired a high-powered rifle, you had better duck!GThe bullet would go into orbit and return to your vicinity in less than8two hours!  Perhaps lunar gun control laws are in order.U
The Earth's
Size and
MassU
 Diameter: 12,756 km
 Diameter: 7,926 miles
EQUATOR
CONTINUE
THE SIZE OF THE EARTH
With an equatorial diameter
of 12,756 kilometers, our
of 7,926 miles, our planet
Earth is not quite a perfect
sphere.  Rather, since it
spins on its axis, it bul-
ges slightly at the equator,
resulting in a globe that
is flattened at the poles.
This flattening is not very
great.  In fact, the Earth's
diameter at the equator is
only 43.5 km more than its
only 27 miles more than its
diameter from pole to pole!
The Earth also deviates from
being a perfect sphere in at
least one other way. . .
Because the Southern Hemi-
sphere bulges slightly more
than the Northern Hemisphere,
the Earth is actually a tiny
bit "pear-shaped"!  But a-
gain this distortion is very
slight; and if you were out
in space, you would not be
able to detect it with the
naked eye.  As small as the
distortions of the Earth's
shape are, they are still
able to be measured with
sensitive instruments.  Many
can be measured by determin-
ing the deflection of satel-
lites passing over them.
Here compared to the Moon,
(shown much closer than it
would ever be), the Earth
seems a large world.  With
a diameter equalling about
4 Moon diameters, the Earth
is the largest of the inner
planets.  And if you could
somehow wrap a tape-measure
around the Earth at the e-
quator it would stretch some
40,060 km.  Therefore if it
24,900 miles.  Thus if it
were possible to drive all
the way around the Earth
at the equator at 88 km/h
at the equator at 55 mph
without stopping even once,
it would take 19 days!
THE SUN
EARTH
While the Earth might seem
large compared to the inner
planets and the Moon, it is
quite small when compared to
the Sun and its features.
Even sunspots can be larger;
and you might recall that
one sunspot could have swal-
lowed more than a hundred
Earths!  Solar prominences
dwarf the Earth like a jet
airplane dwarfs a sparrow!
And the Sun itself is so
large by comparison, that it
would take over 110 Earth's
set side-by-side to make up
just one solar diameter!
332,270
EARTHS
THE MASS OF THE EARTHHSo small is the Earth compared to the Sun, that it would require 332,270HEarths to weigh as much!  And this is despite the fact that the Earth isIalmost 4 times more dense than the Sun!  The Earth has an average densityFof about 5.5 times the density of water.  Still, the Earth seems to be0no "light-weight" when compared to the Moon. . .
81 MOONSFThe mass of 81 Moons would be required to equal the mass of the Earth!GWith an average density of about 1.5 times the density of the Moon, theFEarth weighs approximately 1.23 billion trillion tons.  This is enoughFEarth weighs approximately 1.35 billion trillion tons.  This is enoughFmatter to produce a line of automobiles that would stretch far outside!of our own galaxy, the Milky Way!U
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B Ring
C Ring
D Ring
Cassini
Division
Encke
A Ring
F RingU
 S A T U R N
  THE RINGED WONDER
CONTINUE.Saturn, the sixth planet from the Sun, is sur--rounded by a system of rings so intricate and-dazzling, that the planet has been called the/"most beautiful sight in the Solar System!"  As/the second-largest planet, Saturn is a slightly-smaller and more tranquil version of Jupiter./Like Jupiter, it radiates more heat than it re-/ceives from the Sun.  Also, Saturn's atmosphere.spawns large cyclonic storms.  One in 1933 was.almost as large as Jupiter's "Great Red Spot"!/But Saturn is farther from the Sun.  Its colder/atmosphere is "quieter" and its storms are more0short-lived.  Further, an upper-level haze tends/to hide much of the atmosphere below it, making.Saturn's bands of circulation appear much less0colorful and less defined than those on Jupiter..Saturn has the lowest density of any planet in/the Solar System.  In fact, its average density-is only about 2/3 the density of water!  Thus/it is often noted that Saturn could float . . .0if one could find a large enough cosmic ocean in/which to place the ringed wonder.  The planet's0low density results in a surface gravity that is0low considering Saturn's immense size.  In fact,.Saturn has a lower surface gravity than Earth!/Thus its rapid spin makes the planet bulge con--siderably at its equator, more than any other,planet!  As we shall see shortly, it is this/equatorial bulge caused by Saturn's low density-which helps to produce its magnificent rings.0Saturn posseses at least 21 moons, more than any/other planet!  Some of these are among the most/intriguing bodies in the Solar System.  For in-/stance, Titan is larger than Mercury and Pluto,0and has a true atmosphere.  Some scientists even-suggest that life may be found on Titan!  The.two moons known as 1980-S3 and 1980-S1 dance a/cosmic waltz around Saturn, actually exchanging-their orbits in mid-step!  And the "shepherd"/moons help to maintain Saturn's ring structure!
THE STRUCTURE OF SATURN.Despite its lower density, Saturn has a struc-.ture very similar to Jupiter.  Composed mostly0of hydrogen and helium, Saturn possesses a small.iron-rich rocky core surrounded by a vast zone0of "liquid metallic hydrogen".  But this zone is0proportionally smaller than that of Jupiter, due0to Saturn's lower mass and weaker gravity.  Even0so, it manages to produce a magnetic field 1,000 times stronger than the Earth's!-Above Saturn's zone of liquid metallic hydro-,gen lies an immense "spherical ocean" of mo-.lecular hydrogen, still compressed to a liquid0state.  This is surrounded by Saturn's thick at-/mosphere, where prevailing winds with speeds of/1,450 km/h have been detected near the planet's.900 mph have been discovered near the planet's/equator!  As on Jupiter, Voyager 2 verified the-existence of vast aurorae on Saturn, some two.to five times more energetic than those of the'Earth's "Northern and Southern Lights".
THE RINGS OF SATURNHThough rings are now known to exist around other planets, none can matchJthe awesome beauty of Saturn's rings.  Composed of rock, dust and ice par-Iticles, as small as dust specks to as large as a car, the rings exhibit aIdefinite intricate structure.  The A and B rings are brightest and can beLseen from Earth, bisected by the Cassini Division.  The C ring is faint. . .
F RingIand is only visible through powerful telescopes.  The neighboring almost-Jtransparent D ring stretches down to Saturn's surface!  The A-D rings con-Jstitute the main rings, and consist of thousands of concentric "ringlets"!JBut the small F ring has few components; and these are braided!  InitiallyIthis seemed to defy the laws of orbital mechanics.  But now it is thoughtHthat the gravities of two "shepherd moons" braid the F ring like a rope!HBecause Saturn is tilted in its orbit, we see its rings oriented at dif-Kferent angles in various parts of its orbit.  For example, roughly every 15Iyears, we see the rings "edge-on" and they are almost invisible.  This isKbecause the rings are so thin.  In fact, 99% of the ring material lies in aIzone only as thick as the Statue of Liberty is high.  Thus the rings haveHthe proportions of a circular sheet of paper the size of a soccer field!
PLANE OF RINGS
(Equatorial
 Plane)ISaturn's rings are believed to be the remains of a shattered moon, or theLcomponents of a moon that never formed.  Either way, it is Saturn's equator-Iial bulge(exaggerated below), which pulls the particles into a thin ring.JIf particles stray from equatorial orbits, they are pulled more by gravityHfrom the bulging equator than from the flattened poles.  Over time, theyBare thus "nudged" back into orbits very near the equatorial plane.
  Max.
 Temp.
  Min.
ATMOSPHERIC
  TEMPERATURE/Like the other gas giants which rotate rapidly,.Saturn's heat is distributed very efficiently..The difference between the temperatures of its0sunlit side and dark side is only a few degrees.
EARTH
 Volume:  1
 Mass:    1
 Gravity: 1
 Inclination: 23.5
SATURN
 Diameter: 12,756 km
Diameter: 120,000 km
 Diameter: 7,926 mi
Diameter: 74,566 mi
Volume:    752.00
Mass:       95.15
Gravity:      .93
Inclination: 26.73
SATURN: Compared to Earth%Though slightly smaller than Jupiter,#Saturn is still immense compared to"the Earth. Flattened more than any"other planet by its rapid spin and#low density, Saturn could hold over#750 Earths in its volume!  Plus, it%is a massive planet, though its rings$only contribute a mass equal to that!of a small moon to Saturn.  As we$have already seen, the ringed wonder$is less dense than water.  Therefore$its surface gravity is actually less$than that of Earth, despite Saturn's%greater size and mass.  Regardless of%all these differences, Saturn has al-#most the same inclination as Earth.
Saturn
Earth
Orbit inclined 2.5
TOP VIEW    SIDE VIEW
SATURN'S ORBIT AND ROTATION!On average, Saturn's slightly ec- centric orbit is 9 times further from the Sun than is the Earth's!orbit.  With its distance varying"between 1.35 and 1.51 "billion" km!between 835 and 934 million miles from the Sun, Saturn's orbit has"about the same eccentricity as Ju-!piter's orbit.  It is also tilted or inclined to the Ecliptic (the"Earth's orbital plane), in approx-"imately the same amount as the or-!bit of Venus.  As we have earlier"noted, Saturn spins rapidly on its!axis, causing it to bulge notice-!ably at its poles.  In fact, only
Jupiter rotates faster. . ."Saturn rotates on its axis once in
10.25 hours.  Therefore, as on Jupiter, objects weigh consider- ably less at the equator than at!the poles.  This is precisely why the planet bulges.  We have also#previously noted that roughly every!15 years, Saturn's rings face the
Earth "edge-wise".  This is be-!cause one Saturn year is equal to 29.46 Earth years.  Thus, as one"would expect, we can see the rings edge-wise from opposite sides of
Saturn's lengthy orbit.
Rotational Period: 10.25 hours
Orbital Period:    29.46 years
Orbital Velocity:   34,750 km/h
Orbital Velocity:   21,600 mphU
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CometU
Period
CometU
C O M E T S
ICY VAGABONDS AMID THE PLANETS
CONTINUECObserved since ancient times, comets are spectacular interplanetaryAvagabonds.  Once considered omens, they have been both feared andBhailed, even until recently in history.  In the early 1900's, manyDpersons believed that the 1910 arrival of Halley's comet would spellBthe end of the world!  But now comets are recognized to be members@of our Solar System, moving in highly elongated orbits which mayBtake millions of years to complete - IF they complete them at all.CSome move from beyond Pluto's orbit to well inside Mercury's orbit!DAs a comet moves deeper into the central Solar System, it encountersDthe solar wind and a transformation begins. The small once-invisibleBcomet may develop a brilliant tail (or more than one tail!), whichBmay stretch half way across the sky!  Pushed by the solar wind and@sunlight, the tail always points away from the Sun, and precedesAthe comet as it leaves the inner Solar System.  The tail is quite>insubstantial.  Several times in recent history, the Earth has
passed through one unharmed.
NUCLEUS
THE STRUCTURE OF COMETS>Comets have been called "dirty snowballs".  A core of dry ices=and rock forms the NUCLEUS, usually small and irregular.  For>example, the nucleus of Halley's comet was found to be potato->shaped: barely fifteen km long and eight km wide.  The nucleus>shaped: only nine miles long and five miles wide.  The nucleus@is thought to be a remnant which survived the birth of the Solar>System virtually unchanged.  Thus comets may contain important*information regarding our stellar origins.@As the comet moves into the inner Solar System, the Sun's warmth?causes material in its nucleus to "evaporate" away, forming the=COMA and the TAIL.  The coma is the loosely defined "head" ofCthe comet, and like the tail is composed of dust and ionized gases.@The spacecraft which rendezvoused with Halley's comet found this?material to leave the nucleus in "jets", rather than to evapor-7ate from it uniformly, another surprise to astronomers!@The most spectacular part of the comet is its tail.  Many cometsAhave two, one dust tail and one gas tail, which leave the nucleus@at slightly different angles.  This is due to slightly different?"radiation pressures" on the two materials.  Comet tails may be@huge.  The Great Comet of 1843 possessed a tail whose length wasAgreater than the distance from the Sun to Mars!  But as the cometAleaves the inner Solar System, the tail shrinks, then disappears.
THE ORBITS OF COMETS"While some comets have nearly cir-"cular orbits, most travel in paths
that are extremely elongated or!eccentric.  For example, Halley's!Comet travels from beyond the or-!bit of Neptune, to within the or-
bit of Venus, in a path highly-"inclined to the Ecliptic.  A group of clock-wise moving comets, the
"sun-grazers", swings closer to the Sun than one solar diameter!
Many in this group are believed"to be fragments of a larger comet,
torn apart by tidal and thermal forces encountered near the Sun. Since a comet crosses the orbits"of so many planets, it may be dis-"turbed considerably by their grav-
ities.  In fact, several comets have been perturbed by Jupiter's"massive gravity into nearly circu-
lar orbits.  These may complete
their orbits in 10 to 60 years, at "fairly constant" velocities. But many comets swerve deep into!the Solar System, accelerating to!fantasic speeds.  The Great Comet of 1882, swung around the Sun at 1.6 million km/h!  Other comets,"over 1 million mph!  Other comets,"pulled into the Sun, have achieved
even greater speeds than this!
In the most remote portions of their orbits, some comets wander
so far from the Sun, that they even leave distant Pluto far be-
hind!  These comets lose their
tails completely, and then be-!come invisible from Earth.  Their
orbits may be so large, that it"may take millions of years to com-!plete one circuit around the Sun!
These are known as "long period!comets", and their incredible or-
bits may stretch out to a vast!cosmic cloud of comets thought to!envelop the Solar System, the in-"triguing, immense Oort Cloud . . .
Radius: 1.5 light years
THE OORT CLOUD
An incredible accumula-
tion of comets is thought
to exist in a huge spher-
ical cloud 1.5 light
years from the Sun.  This
is more than 2,500 times
farther from the Sun than
Pluto!  The Oort Cloud is
believed to be the home
of 100 BILLION comets,
with a total mass twice
as great as that of Ju-
piter!  Thus comets make
up a sizable portion of
the Solar System's mass.
Astromoners believe that
the comets in the Oort
cloud are left over from
the time when the matter
closer to the Sun formed
the planets.  From time
to time, some of these
comets are "nudged" from
their orbits by the grav-
ities of passing stars.
Some may be pushed out of
the Solar System.  But
others may be urged sun-
ward, eventually to be
seen by us from Earth.U
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N E P T U N E
MOST REMOTE OF THE GAS GIANTS
CONTINUE+Neptune, the eighth planet from the Sun, is/the outermost of the gas giants.  Discovered in-1845, its existence had been predicted due to0irregularities in the orbit of Uranus, its near-.twin in both composition and size.  But in one0way, Neptune resembles Jupiter more than Uranus.,Neptune, like Jupiter, gives off more energy
than it receives from the Sun!*Though Neptune is difficult to observe be-.cause it is so far from Earth, it appears as a-blue-ish disk through a telescope.  So it was.appropriately named after the Roman god of the,sea.  Little was known of Neptune before the/summer of 1989, when Voyager 2 sent back infor-/mation and photographs, revealing the planet to*be somewhat different than expected! . . ..First, Neptune's deep-blue atmosphere was dis-.covered to be far more dynamic than predicted.0White clouds of methane gas strung out in finely0spun bands.  And several great storms like Jupi-.ter's "Great Red Spot" circled Neptune at dif--ferent latitudes.  One storm, "The Great Dark0Spot" is as large as the Earth.  In an eerie co--incidence, this is proportionally as large to'Neptune, as the Red Spot is to Jupiter!-As with Uranus and Jupiter, Neptune was found-to possess 5 extremely faint rings. The inner-ring has a continuous, nearly "solid" appear-.ance, while the outer ring is composed of tiny,icy moonlets.  The middle rings are so faint/that they were barely visible, even in the best"of Voyager's stunning photographs.-Before Voyager's "close-encounter", two moons,were known to orbit Neptune: both in strange0paths unique in the Solar System.  Triton orbits-opposite to the direction that Neptune spins!1And it is so close to Neptune that it may eventu-0ally be broken up by tidal forces to form rings /like Saturn's!  Nereid has an orbit more ellip-.tical than any other moon in the Solar System!/Experts theorize that perhaps an ancient cosmic-collision may have caused these weird orbits./Some theorists propose that Pluto may have once1been a Neptunian moon, ejected by this collision!*Six newly discovered moons bring the total/number of known Neptune moons to eight.  But by,far, the most intriguing is Triton, which is#larger than both Pluto and Mercury!
THE STRUCTURE OF NEPTUNE(Neptune is believed to be very much like)Uranus in structure.  A rocky Earth-sized'core is probably surrounded by a frozen*mantle of water, methane and ammonia ices.(Neptune's mantle is believed to be about(10,000 km deep, and in its outer regions*6,200 miles deep, and in its outer regions'it is thought to become an ocean of icy&"slush".  Above this, an atmosphere of*hydrogen, helium and methane swirls around)the planet.  Variations in the brightness*of radiation at different wavelengths have*been observed.  This suggests a continuing'climatic cycle in Neptune's atmosphere,(like the constant formation, dissipation#and reformation of clouds on Earth.
Min. Temp.
Max. Temp.
ATMOSPHERIC TEMPERATURE5As on the other gas giants which rotate fairly rapid-3ly, Neptune's heat is well distributed.  Also since3its atmosphere further helps to distribute its heat2very evenly, Neptune has little difference between2its dark side and sunlit side temperatures.  For a4given altitude, Neptune's temperature varies little.
 EARTH
NEPTUNE
 Volume:  54.00
 Mass:    17.23
 Gravity:  1.19
 Inclination: 29.6
 Diameter: 49,500 km    12,576 km
 Diameter: 30,758 mi
7,926 mi    Diameter:
Volume:         1
Mass:           1
Gravity:        1
Inclination: 23.5
NEPTUNE: Compared to Earth#Like Uranus, Neptune is a gas giant%with a diameter of about 4 times that&of the Earth.  Its mass being equal to$over 17 Earth masses, Neptune is the!Solar System's third most massive%planet.  It is even more massive than%Uranus, which is slightly larger.  In%spite of its high mass, Neptune still"is not very dense.  Therefore, the$pull of gravity at Neptune's visible&surface is only 19% greater than it is$at the Earth's surface.  Inclined to&the perpendicular of its orbital plane%by 29.6
, Neptune "leans" on its axis"slightly more than does the Earth.
NEPTUNE'S ORBIT AND ROTATION#Neptune's orbit is almost a circle!#In fact, only the orbit of Venus is#more circular.  Neptune's orbit av-!erages close to 4.49 "billion" km!erages about 2.79 "billion" miles#from the Sun.  This is 30 times the#distance from the Sun to the Earth."Neptune has a 1.77
 orbital incli-"nation, and usually is the second-"furthest planet from the Sun.  But#every 248 years, Pluto moves closer#for 20 years, (in the last instance#between 1979 and 1999.)   But since"their orbits are synchronized, and"since Pluto crosses over the orbit"of Neptune like one person passing
over another on a bridge, . . .!there is virtually no chance of a!collision.  (See PLUTO section of!program.)  Like the other gas gi-!ants, Neptune rotates on its axis"fairly rapidly.  Thus it completes#a single rotation every 15.8 hours.
Also, because Neptune is so far"from the Sun, it moves more slowly"than the inner planets and takes a"long time to complete a full orbit!around the Sun.  One Neptune year#is thus equal to 164.8 Earth years!!Neptune's orbital velocity around the Sun is close to 19,100 km/h.
the Sun is close to 11,880 mph. This is roughly half the maximum
velocity achieved by the Apollo!astronauts during lunar missions.
Rotational Period:  15.8 hours
Orbital Period:    164.8 years
Orbital Velocity:   19,100 km/h
Orbital Velocity:   11,880 mphU
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J U P I T E R
THE GIANT OF THE GIANTS
CONTINUE,Jupiter, the largest planet and fifth planet/from the Sun, is a mysterious "gas giant".  Re-1flecting relatively high amounts of the solar en-1ergy it receives, Jupiter is bright, usually out-,shined by only the Sun, the Moon, and Venus.,Even by planetary standards Jupiter is huge,0over twice as massive as the rest of the planets/combined!  This is doubly impressive because it/is composed almost entirely of hydrogen and he--lium, the two lightest gases!  In fact, these1gases exist in the same ratios as in the galactic0clouds which form stars.  Jupiter retained these/stellar "building-blocks", because it was mass-1ive enough and far enough from the Sun.  The same.gases "boiled away" from the inner planets un-1der intense radiation during the Sun's formation.)Hydrogen has combined with less plentiful.elements on Jupiter to form multi-hued clouds,,which race in gigantic bands parallel to the/planet's equator.  On the edges of these bands,/"atmospheric shear" produces immense eddies and1whirlpools, savage storms that would swallow hun-0dreds of Earth hurricanes!  The largest of these-is the puzzling "Giant Red Spot", observed to-rage now for over 300 years!  More than twice0the diameter of Earth, this long-lived "cyclone"+may be caused by something unseen below it.,Oddly, Jupiter gives off more than twice the0energy it gets from the Sun!  This may be due to/an extremely gradual planetary contraction, for!it would need to shrink less than
2.5 cm each
an inch each-year to produce this puzzling energy surplus!*Possibly, Jupiter will be the most hostile0of all the planets for man to explore!  Its mag-1netic field, thousands of times stronger than our.Earth's, produces radiation powerful enough to2kill astronauts in minutes.  In fact, some plasmas/in this field millions of miles above Jupiter's)surface are "hotter" than the Sun's core!+Jupiter's immense gravity holds at least 160moons in its grasp.  Four are larger than Pluto,-and two are the size of Mercury!  It is as if.Jupiter and its retinue form a miniature solar#system within our own Solar System./In 1979, the Voyager spacecraft detected a ring0system around Jupiter!  But unlike Saturn's very-prominent rings, Jupiter's are so sparse that they are not visible from Earth.
THE STRUCTURE OF JUPITER*Jupiter's structure is different from that+of the inner planets.  While Jupiter is be-*lieved to have a rocky, iron-rich core the,size of the Earth, the planet is mostly com-*posed of hydrogen and helium.  Outside the+core is a vast globular ocean of liquid hy-+drogen, compressed so tightly that it takes)on the properties of a metal!  It is this*"liquid metallic hydrogen" that helps pro-)duce Jupiter's tremendous magnetic field.)Further out, Jupiter's hydrogen loses its(metallic properties, but still remains a+liquid more dense than lead!  It is unknown'whether this liquid forms a surface. It)might just diminish in density, until fi-)nally blending with the thick atmosphere.+Although the atmosphere of a gas-planet may*not be as clearly defined as on one of the+inner planets, evidence suggests a definite*structure.  Just above the liquid hydrogen(near the "surface",  clouds of ice crys-*tals and water vapor are covered by clouds(of ammonia compounds.  In this turbulent(atmosphere of Jupiter, vast auroras have&have been observed over polar regions.)And in the upper atmosphere, "superbolts"(of lightning continually rip through the'"cloudscape".  These bolts are huge.  A*single superbolt may pack enough energy to)literally vaporize a city!  Even with its(forbidding conditions, the atmosphere of)Jupiter may harbor some form of life, ac-#cording to some hopeful scientists!
Min. Temp.
Max. Temp.
ATMOSPHERIC TEMPERATURE0Of all the planets, Jupiter has perhaps the best/"air-conditioning" system!  Because it spins so.rapidly on its axis, and also because its wind/spread out its heat so efficiently, Jupiter has-nearly the same "sunlit side" and "dark side".temperatures at a given latitude and altitude.
EARTH
 Volume:  1
 Mass:    1
 Gravity: 1
 Inclination: 23.5
JUPITER
 Diameter: 12,756 km
Diameter: 142,857 km
 Diameter: 7,926 mi
Diameter: 88,770 mi
Volume:   1323.00
Mass:      317.89
Gravity:     2.54
Inclination:  3.12
JUPITER: Compared to Earth$The diameter at its equator stretch-$ing 142,857 km, Jupiter is gigantic!%ing 88,770 miles, Jupiter is immense!%Its poles noticeably flattened by its$rapid spin, it could hold over 1,300%Earths in its volume.  But Jupiter is$not as dense as Earth.  In fact, its"average density is only 1/3 higher$than water!  Still, 318 Earths would$be required to equal Jupiter's mass.$Such mammoth size and mass produce a$surface gravity which would strain a$champion athlete!  A person weighing$50 kg on Earth would weigh 127 kg on%100 lb on Earth would weigh 254 lb on%Jupiter!  With an inclination of only$3.12
, this giant is the second most%"upright" planet in the Solar System.
TOP VIEW
Jupiter
Earth
Orbit inclined 1.3
JUPITER'S ORBIT AND ROTATION"Jupiter's slightly eccentric orbit#is over five times further from the!Sun than our Earth's orbit.  This#is far beyond the inner planets, at"an average distance of 778 million"km from the Sun.  It thus requires"an average distance of 483 million"miles from the Sun.  It thus takes!Jupiter some considerable time to"make its way once around the Solar!System.  Every 11.86 Earth years, the gas giant completes a single!orbit of the Sun.  With its orbit"inclined 1.3
 to the Ecliptic, Ju-!piter travels at an average speed"of 46,350 km/h.  This is interest-!of 28,800 mph.  This is interest-!ing because many of its moons or-"bit Jupiter at much higher speeds!$The rotation of Jupiter is the fast-"est in the Solar System!  And this$is true in two ways.  First, Jupiter#rotates once on its axis every 9.84"hours!  Second, due to such a high#rotational rate, the "linear speed"#at Jupiter's equator is fastest, at#over 45,060 kp/h!  You might recall
Orbital Velocity:   46,350 km/h"over 28,000 mph!  You might recall
Orbital Velocity:   28,800 mph that this is very near the speed at which Jupiter itself moves in
its orbit around the Sun!  Also noteworthy is that this speed is about 10% higher than the escape
velocity of the Earth!
Rotational Period:  9.84 hours
Orbital Period:    11.86 yearsU
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   M A R S
   THE RUSTY DESERT PLANET
CONTINUE,Mars, the fourth planet from the Sun and the/first past the Earth, glows so red in the night0sky that it is easy to find and identify.  It is0so bright at its brightest, that the only planet.brighter is Venus!  And since its strong color/invoked images of bloody battlegrounds, the an-+cients named Mars for the Roman god of war.-Since some Martian features have been visible0through telescopes for centuries, early theories.explained markings as vast canals and areas of0vegetation.  But close-up photos from Mariners 4-and 9 contradicted such ideas.  Instead, Mars1was revealed to be a dry, lifeless, desert world,0covered with iron-rich compounds which have oxi--dized to a planet-wide blanket of rusty dust!)This is what gives Mars its unique color.+The most prominent features of Mars are its1polar ice caps, the only others in the Solar Sys-1tem in addition to Earth's.  Consisting of "water1ice" and "carbon dioxide ice" (dry ice), the caps.seasonally advance and retreat, and are easily0observed through a telescope.  Also visible from2Earth through a telescope are Martian dust storms.0Usually seen during the Martian summer, they ob-1scure surface details and may grow to cover near-
ly half the planet!-But usually, Mars's thin atmosphere is trans-2parent, and to orbiting spacecraft it reveals geo-2logical features of immense proportions.  "Olympus2Mons", perhaps the Solar System's largest volcano,0rises 3 times higher than Mt. Everest and is the-size of France!  Other volcanic craters . . .-and impact craters, lightly scar vast plains!/The canyon "Valles Marineris" stretches as wide2as the continental United States!  Huge systems of2dry riverbeds extend over much of the Martian sur-1face, indicating that prodigious amounts of water
may have been present ages ago!,But now, Mars appears dry and lifeless.  Its0thin atmosphere of mostly carbon dioxide is over.100 times as dry as Earth's air!  Most Martian/water is frozen as polar ice, or combined chem-/ically in soils, or frozen beneath the surface.1Still, it does manage to snow on Mars!  The snow-0storms are composed mostly of dry ice particles,-the source of snow for Mars's polar ice caps..Mars has two small potato-shaped moons, Phobos-and Deimos, thought to be captured asteroids.
THE STRUCTURE OF MARS$The structure of Mars is believed to#be quite similar to the other inner%planets.  A relatively thin and rocky"crust encases an Earth-like mantle$and an iron-rich core.  But a weaker%Martian gravity suggests that Mars is#less dense than the Earth, and that&probably its core is relatively small-$er.  Because of the immense sizes of%volcanoes on Mars, geologists surmise#that the Martian crust is extremely#stable compared to the Earth's.  In%fact, some suggest that all continen-"tal plate activity may have ceased eons ago on the Martian surface.
Min. Temp.
Max. Temp.
SURFACE TEMPERATURE1Due to its inclination and the length of its day,/Mars experiences seasons similar to Earth.  But.with its thinner atmosphere, and being farther/from the Sun, Mars is generally colder than the0Earth.  The mean surface temperature of the Mar-
tian landscape is about
EARTH
Volume:  1
Mass:    1
Gravity: 1
Inclination: 23.5
Diameter: 12,756 km
Diameter: 7,926 mi
MARS    Diameter:
Volume:      .15
Mass:        .107
Gravity:     .38
Inclination:  24
MARS: Compared to Earth
6,794 km%With a diameter of 6,794 km, Mars has
4,221 mi%With a diameter of 4,221 mi, Mars has'a surface area nearly equal to the land'area on Earth.  In fact, since Mars has'no liquid water, we might say that both&planets have equal land areas!  Having%a density of 2/3 that of Earth, and a(volume only 15 percent as large, results%in a lower mass and gravity for Mars.&With the Martian gravity only a little&more than 1/3 as strong as Earth's, on'Mars you would weigh almost exactly the&same as you would on Mercury!  One way'Mars is very similar to Earth is in the&tilt of its axis.  With an inclination&of 24
, Mars tilts only 1/2
 more than%the Earth: an intriguing coincidence!
Earth
Orbit inclined 1.8
ORBIT AND ROTATION OF MARS!Mars orbits the Sun at a distance
which varies between 205.5 and
248.5 million km.  Its average
distance is 227.7 million km.
which varies between 127.7 and!154.4 million miles.  Its average distance is 141.5 million miles.
In such an eccentric orbit, and!because their orbits are not syn-"chronized, Mars reachest its near-!est distance to Earth every 15 to 17 years.  Its orbit is inclined
only 1.8
 to the Earth' orbital#plane, the Ecliptic.  Being further#from the Sun, Mars moves more slow-!ly in its orbit.  Its longer year"is equal to 687 Earth days, making
the seasons on Mars last almost twice as long as those on Earth!!And since the orbit of Mars is so!eccentric, climatic condtions be-#tween its hemispheres are more pro-"nounced than on the Earth.  In yet another cosmic coincidence, Mars rotates on its axis to produce a"day that is nearly the same length#as the Earth day!  Once every 24.62!hours, Mars completes its day, as"if some giant celestial hand wound
both Mars and the Earth to the
same tick of the clock! With so many similarities to our Earth, and presenting less harsh"challenges than the other planets,"Mars may be the first other planet"to be visited by man!  Perhaps you
yourself may one day leave your
footprints on its surface!
Rotational Period:  24.62 hours
Orbital Period:     687 days
Orbital Velocity:   86,320 km/h
Orbital Velocity:   53,640 mphU
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M E R C U R Y
A SCORCHED AND BATTERED WORLD
CONTINUE-Mercury, the second-smallest major planet and0the nearest planet to the Sun, is a scorched and.battered world!  So near the Sun, it is diffi--cult to view from Earth.  In fact, Mercury is.only visible when the bright Sun is just below0the horizon, immediately before sunrise or after/sunset.  Even through a telescope, Mercury only,reveals phases, like the phases of the Moon.+In 1974, Mariner 10 sent back the first de--tailed photos of Mercury, revealing a surface/scarred by thousands of craters.  In fact, even+experts have mistaken photos of Mercury for.those of the Moon!  Unlike the Lunar surface's/large open areas (the maria), Mercury's surface.is almost totally covered with craters, formed-when billions of meteorites fell sunward. . .%during the youth of the Solar System.-Mercury's only large area comparable to a Lu-0nar sea is the Caloris Basin, itself filled with0smaller craters.  But unlike lava flows in Lunar1maria, the Caloris Basin is believed to have been1in diameter, it is ringed by mountains and cliffs thrust up by the ancient impact!.Also unlike the Moon, Mercury possesses large,0caused by a huge impact eons ago.  Over 1,340 km.unusual cliffs up to 3 km high and over 450 km1caused by a huge impact eons ago.  Over 835 miles/unusual cliffs up to 2 miles high and 300 miles0long.  These cut through craters and basins, in-0dicating they are geologically relatively young.0Experts think these cliffs are evidence that the/planet is shrinking!  This shrinking has caused,great crustal faults to be raised on much of
Mercury's cratered surface.
THE STRUCTURE OF MERCURY
Since Mercury is so much smal-
ler than the Earth, its lower
gravity is less able to com-
press its matter to higher den-
sities.  Thus it was a surprise
when Mercury's density was de-
termined to be very close to
that of Earth.  At 5.4 times
the density of water, the den-
sity of Mercury suggests a
very large core in relation to
the size of the planet itself.
Scientists believe that almost
2/3 of Mercury's mass forms a
core rich in iron and nickel,
and about the size of our Moon!
This large core makes Mercury
the most mineral-rich body in
the Solar System!  The outer
regions of the planet are be-
lieved to be composed of high-
temperature silicates, forming
a crust very similar in nature
to the crusts of the Earth and
the Moon.  With regard to an
atmosphere, Mercury resembles
the Moon more than the Earth.
With its low gravity, Mercury
is thought to have lost any
atmosphere long ago.  All that
remains is an EXTREMELY thin
presence of helium gas, thought
to originate in the Solar Wind.
Min. Temp.
Max. Temp.
SURFACE TEMPERATURE4Mercury's surface temperature varies greatly because3the planet rotates so slowly.  Its sunlit side gets3as hot as      .  This is hotter than an oven!  Yet3despite Mercury's nearness to the Sun, its slow ro-2tation gives its dark side plenty of time to cool.1Dark side temperatures plunge to a frigid       !
EARTH
Volume:  1
Mass:    1
Gravity: 1
Inclination: 23.5
Diameter: 12,756 km
Diameter: 7,926 mi
MERCURY    Diameter:
Volume:      .06
Mass:        .055
Gravity:     .38
Inclination:  0
MERCURY: Compared to Earth
4,878 km$With a diameter of 4,878 km, Mercury
3,031 mi$With a diameter of 3,031 mi, Mercury is nearly a perfect sphere.  Its!volume is approximately 6 percent!of the Earth's, while its surface"area is very close to the combined#areas of Asia and Africa!  Further,$Mercury has a mass of 5.5 percent of!the Earth's, and a gravity only a#little more than 1/3 as strong.  So!if you weighed 50 kg on Earth, on#Mercury you would weigh only 19 kg."if you weighed 100 lb on Earth, on#Mercury you would weigh only 38 lb."Mercury is also the Solar System's"most upright planet!  Its axis has!no inclination or "tilt" from the#perpendicular to its orbital plane!%By comparison, Earth's axis is tilted#23.5
 from the perpendicular to its own orbital plane, the Ecliptic.
Earth
Mercury
TOP VIEW
Orbit inclined 7
MERCURY'S ORBIT AND ROTATION The orbit of Mercury is somewhat!eccentric.  Its distance from the Sun varies between 45.9 and 69.7 million km, averaging about 57.9
million km.  Mercury's 88-day Sun varies between 28.5 and 43.3!million miles, averaging about 36 million miles.  Mercury's 88-day orbit around the Sun is inclined!7
 to the Ecliptic, more than any"other major planet's except Pluto.
Since its orbit lies inside the
Earth's orbit, Mercury presents different portions of its sunlit
surface to us as it orbits the
Sun.  Thus, like the Moon, Mer-
cury exhibits phases, as viewed"from Earth.  Also, Mercury rotates on its axis, though very slowly! Mercury rotates only three times!for every two times it orbits the!Sun!  Also, since its orbit is an!ellipse, Mercury slows down as it
moves farther from the Sun, and
speeds up as it moves closer. This combination of motions pro-!duces one of the strangest "days"!on any planet.  The Sun first ri-!ses slowly in the east, then pro- gresses gradually westward until it begins to slow down!  Finally!it slows to a complete stop!  La-
ter, it begins moving slowly to
the west again, finally setting
on the western horizon.  This
"snail's-paced" day is somewhat!ironic, as Mercury's proximity to
the Sun makes it the fastest of
all the planets!
Rotational Period:  58.7 days
Orbital Period:     88 days Orbital Velocity:   172,200 km/h
Orbital Velocity:   107,000 mphU
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    The Solar
Life Cycle
CONTINUE    THE CLOUD
Over five billion years ago,
the cloud which would beget
our Sun existed in the dark
silence of space, as it had
for billions of years.  The
cloud was gigantic, over 480
trillion kilometers across,
cloud was gigantic, over 300
trillion miles in diameter,
so large that light required
fifty years to travel across
it once!  The cloud was not
very dense, containing less
than a thousand atoms in each
cubic cm of space.  (Air at
sea level contains over 30
very dense, containing only a
few thousand atoms in each
cubic inch of space.  (Air at
sea level contains over 500
billion billion "molecules"
in the same volume!)
Despite its low density, the
cloud was massive, so massive
that it possessed the bulk of
numerous Suns!  And the cloud
was cold!  Chilled by inter-
stellar space, its temperature
was -230
C, so cold that it
was -450
F, so cold that it
radiated almost nothing.  So
low was its radiation pres-
sure, that the cloud was in a
very fragile equilibrium.  If
it were disturbed, it would
either dissipate or condense.
Inevitably, a chance outside
influence disturbed it.  And
so, under its own gravity the
cloud BEGAN TO COLLAPSE!. . .
GLOBULES Thousands of years later, random
concentrations of matter called "globules" formed in the immense
collapsing cloud.  Their tem- peratures had risen, but only to!a still-frigid -205
C!  Thus they!a still-frigid -400
F!  Thus they
radiated no visible light, and
were only apparent as very dark!masses against a lighter backdrop of gas and stars.  Our "pre-sun"
globule was one of medium size.
Still, it was the width of more
than a hundred solar systems!!The globule continued collapsing.
But in order to go on, we must
first magnify our view. . .
Globules
Magnifying. . .
1.6 trillion km:
1 trillion miles:
 = (width of over 100
solar systems)     Original
 Globule     Diameter
GLOBULE
Now (with our view of it great-
ly magnified), the globule con-
tained the mass of perhaps 25
suns!  But spread out over such
incredible distances, its den-
sity was still so low that it
would be considered a vacuum on
Earth.  Nonetheless, its gravi- ty pulled constantly on the mat-
ter within it; and trillions
upon trillions of tons of dust
and gas continued to fall from all directions toward the center
of the globule.  Thus the tem-
perature of the globule contin-
ued to rise.  Soon it would be
hot enough to radiate strongly
in the infrared. . .    PROTOSTAR
Diameter: 24 billion km
Diameter: 15 billion miles
(more than twice width
of solar system)%Within 100,000 years, the globule had%contracted to a millionth of its ori-%ginal volume; still it was over twice#the width of the solar system!  Its"core, heated by the contraction of#its matter, now internally radiated#substantial amounts of energy which%began to slow the collapse.  Its core#was stable and well-defined; and it$could no longer be called a globule.#Now it was a PROTOSTAR!  The proto-%star continued to collapse.  But now,"in order to go on, we must magnify%our view again.  For we must remember#that the small red dot shown at the%right represents our protostar, which%now was still more than two times the width of the solar system! . . .
24 billion km:
15 billion miles:
 = (twice the width of
solar system)    Protostar
ORIGINAL
Mid-stage Diameter:
360 million km
225 million miles
Diameter of
Orbit of Mars:
460 million km
285 million miles%Now the protostar's evolution was ad-$vancing relatively rapidly.  In only&a few thousand years, it had collapsed%to just less than the diameter of the'orbit of Mars!  Its central temperature)the atoms at the core of their electrons!%had risen to over 56,000
C, stripping&With its 1,650
C surface so large, the&had risen to over 100,000
F, stripping&With its 3,000
F surface so large, the%protostar was now radiating much more&light than would the Sun.  But the red&light its surface emitted was not pro-$duced by nuclear fusion, but only by$gravitational contraction; and so it$was not yet a star!  For its stellar%birth as our Sun, it would first have%to contract even further!  And so for&a final time, we must magnify our view
of the collapsing protostar!
  =   360 million km
= 225 million miles:    Mid-Stage    MID-STAGE
THE SUN
Diameter: 1,392,000 km
Diameter: 865,000 miles)Finally the protostar contracted down un-+til it was smaller than Earth's orbit, then*smaller than Venus's and Mercury's orbits,*and then even further until it was no more(a protostar!  For somewhere in this last(stage of contraction, the core had risen&to several million degrees, hot enough(for hydrogen nuclei to fuse into helium!
And thus as a star,
OUR SUN WAS BORN!&As the nuclear reactions began to pro-(duce vast amounts of energy, the Sun was(an unstable star, varying in temperature%and luminosity due to the creation of(tremendously violent convective currents'in its gases.  Then after 25 to 30 mil-(lion years, its structure stabilized in-'to its form of today, some five billion&years later.  Since it stabilized. . .'the Sun has grown slightly in both size(and output.  But these changes have been$extremely gradual and will continue.'(See "Built-In Safety Valve" in NUCLEAR(CYCLE portion of program.)  Further, the(Sun possesses enough nuclear fuel in the)form of hydrogen to keep shining steadily%for another five billion years.  This(means that we on Earth are now experien-'cing the benevolent "middle age" of our)Sun.  But after ten billion years of sta-%bility, violent unstoppable processes(will begin in our Sun, which will herald)the onset of its "old-age", and eventual-&ly its death as a star.  So let us now(peer five billion years into the future!%As we look forward, remember that the(small yellow dot at the right represents%the immense body that is today's Sun.
Orbit of Mercury
Orbit of Venus
Orbit of Earth
Orbit of Mars    RED GIANT
In five billion years, all the
hydrogen in the Sun's core will
have been converted to helium,
and nuclear fusion will cease!!With no heat from nuclear fusion,
the core will begin to collapse under its own weight.  But soon,
the gravitational energy from
collapsing will be converted to
heat: in fact, more heat than
had been produced by fusion!
Signaling the end of the Sun's
long stability, the added heat
will cause its outer layers to
swell drastically.  The Sun
will have become a red giant! For a few hundred million years, the expansion will continue, and
the Sun will engulf the planet!Mercury!  Though its surface will have become cooler, the Sun will!have become so large that it will!produce 500 times more light than
it did as a stable star!  Venus!and the Earth will be baked!  And
probably all life left on our planet will be destroyed!  Mean-
while in the Sun' core, new nu-
clear processes will begin to!trigger more violent death throes!for our star, as the core temper-
ature rises to over 85 million
degrees C!. . .
ature rises to over 150 million
degrees F!. . ."Now the core will be hot enough to"fuse helium into carbon and oxygen!nuclei, producing more heat!  But
a helium-rich core is unable to!lose heat fast enough.  In just a
FEW HOURS, it will get too hot!and explode!  Outer layers of the
Sun will absorb the blast; but!the core, less dense after explo- ding will drop in temperature a-
gain.  Too cool for fusion, the
core will no longer be able to
support the matter above it.
Contracting again, the Sun may
repeat the cycle several times!
Shrinking and swelling, shrink-
ing and swelling!. . ."Finally enough carbon will accumu-
late in the core to prevent the!core explosions.  Now with helium fusion continuing to add heat to"the outer layers, the Sun will ex-!pand a final time.  So great will!be this swelling that after about!30 million years, it will swallow
Venus and the Earth!  Then the outer layers will keep expanding
outward, finally fast enough to escape into space.  With as much
as half of the Sun's mass torn
from it, this will leave behind only the core!  Still fusing he-
lium, the core will shrink, now
very close to its end!. . .
Remaining Solar Core
WHITE DWARF
 Diameter: 12,900 km
 Diameter: 8,000 miles*Eventually, all helium in the core will be)exhausted.  Now out of fuel and unable to(produce the radiation that would support'its outer layers, the Sun will lose its)long battle against gravity.  All its re-(maining matter will collapse down into a'small body the size of the Earth!  Thus)the Sun will have become a "white dwarf",)a body so dense that a teaspoonful of its&matter will weigh over a ton!  With no'fuel to produce further nuclear fusion,&the white dwarf will still continue to(shine, as it radiates away the energy of'its collapse.  But eventually even this)energy will be spent, and the white dwarf&will begin to cool, starting to go out
like a dying ember. . .
YELLOW DWARF    RED DWARF
BLACK DWARF
(no visible disk)(As the last vestige of the Sun cools, it'will emit yellow light, then red light,)and then no light at all.  Its atoms will'be packed as tightly as physically pos-(sible; and it will be unable to collapse(any further.  With no more energy avail-)able to it, (not even gravitational ener-%gy), it will continue to cool like an)Earth-sized burnt-out cinder.  Finally it'will become as cold as the space around'it, emitting nothing.  As a carbon-rich'black dwarf, it will continue invisibly)through the voids of space.  It will give(no indication of its violent beginnings,(nor of its benevolent middle age, nor of(its final death throes.  But someday, by)pure chance, it may in its cosmic wander-"ings encounter another huge cloud.    collapses
expands
cools
CLOUD
WHITE
DWARF
BLACK
stable for 10
billion years
LIFE CYCLE OF THE SUNEThe above illustrates the major stages of the Sun's Life Cycle.  How-Dever due to the vast sizes of the various bodies, it would be impos-Esible to show all of them to scale.  For example, let us take the SunDshown at 1/3 cm in diameter as a reference.  If the white dwarf wereFshown in the same scale, it would be about 1/34 mm in diameter, almostAwould be almost 84 cm in diameter - the size of a beachball!. . .Bshown at 1/8" in diameter as a reference.  If the white dwarf wereEshown in the same scale, it would be about 1/900" in diameter, almostEwould be almost 33 inches in diameter - the size of a beachball!. . .Binvisible to the naked eye!  The red giant shown in the same scaleEGoing further, the protostar shown in the same scale as the Sun wouldCbe over 55 meters in diameter!  The globule would be almost 4 kilo-Emeters in diameter!  And largest of all, the interstellar cloud would@be about 1100 km across, almost the distance between Chicago andDbe over 180 feet in diameter!  The globule would be almost two and aDhalf miles across!  And largest of all, the interstellar cloud wouldBbe about 700 miles across, almost the distance between Chicago andEWashington, D.C.!  Thus the scale of space and time for the life of aDstar like our Sun is truly incredible.  And yet, our Sun is only oneCof billions upon billions of stars in the vastness of our universe.U
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G r a v i t y
The Attraction of the
Solar System
CONTINUE&While nuclear forces operate at the a-&tomic level, GRAVITY is the force that%shapes the Solar System on a far more$grand scale.  Whenever we see a ball&bounce or an airplane land or anything&fall, we are seeing gravity's effects.&Moreover, when we see the Sun and Moon%and all the other objects in the sky,%we see the elegant order that gravity%imposes on the universe.  All objects$we perceive are under its influence.%The most obvious effect of gravity we%experience on Earth we call "weight".&Weight is an indication of how strong-%ly gravity pulls two bodies together.&Moreover it is a measure of the gravi-$tational force between one celestial"body and an object at its surface.%Though it is common knowledge now, it$was not always known that a planet's%gravity depended on the planet's size
and mass. . .%Thus an object's weight on some other$planet would be quite different from&its weight on Earth.  For example, as-%tronauts descending by craft into the&clouds of Jupiter had better be in ex-&cellent physical shape.  Jupiter's in-%tense gravity will severely tax their
skeletons and muscles!&Now let's determine your weight on the%other bodies of the Solar System. . .
200 kg
200 lb Move the scroll bar as indicated!below, until it shows your weight!on Earth.  Your weight on various other bodies of our Solar System!will automatically be calculated.!Now notice your weight on Phobos,!one of the two moons of Mars.  So weak is its gravity, that on its
surface your weight needs to be!measured in grams, not kilograms!
measured in ounces, not pounds!!On some of the smaller asteroids,
you would actually weigh less
than a feather weighs on Earth!
Sun:          kg
Moon:         kg
Mercury:      kg
Venus:        kg
Mars:         kg
Jupiter:      kg
Saturn:       kg
Uranus:       kg
Neptune:      kg
Pluto:        kg
Ceres:        kg
Phobos:        g
Sun:          lb
Moon:         lb
Mercury:      lb
Venus:        lb
Mars:         lb
Jupiter:      lb
Saturn:       lb
Uranus:       lb
Neptune:      lb
Pluto:        lb
Ceres:        lb
Phobos:       oz
Your Weight
On Other Worlds
"+/-" keys add/subtract  1 kg
" / " keys add/subtract 10 kg
"+/-" keys add/subtract  1 lb
" / " keys add/subtract 10 lb
Earth
The Moon
Jupiter
Gravity and
Falling Objects:
A THREE-EGG DISPLAY(We have seen that objects have different$weights on different worlds, because(gravity pulls on these objects with dif-&ferent strengths.  What does this mean(for falling objects on different worlds?(Let's imagine we have three eggs: one on(the Moon, one on Earth, and one on Jupi-&ter.  Now, what if we can somehow drop(the eggs simultaneously from about waist&height?  You probably have a good idea
will happen."Now press "ENTER" in order to drop&our eggs.  But get ready!  You'll need
to watch very closely!%As you probably guessed, the egg fell'the fastest on the planet with the most&powerful gravity, namely Jupiter.  And&on the Moon, with its gravity only 1/6&as strong as the Earth's, the egg fell%so slowly that it did not even break!&(This of course assumes no atmospheric'resistance on either Jupiter or Earth.)&On some of the asteroids, an egg would&fall so slowly that it would take days(to fall from waist-height to the ground!'Make your choice and press "ENTER".  If%you "DROP EGGS AGAIN", then press the'"SPACE BAR".  The eggs will continue to'drop until you press "SPACE BAR" again.
DROP EGGS AGAIN&A FEATHER, A PENNY AND A MISCONCEPTION.Just as a feather falls to Earth slower than a-penny, for thousands of years it was a common+misconception that all lighter objects fall0slower than heavier ones.  Yet this is not true!.Legend maintains that Galileo proved the truth.when he dropped two dissimilar weights off the,Leaning Tower of Pisa, then watched them hit.the ground at the same time.  You can prove it-to yourself by dropping a penny and a quarter*from overhead.  You will find that they DO,fall at the same rate!  In fact, on any par-*ticular world, if you can nullify all air-.resistance and buoyancy, all objects will fall,at exactly the same rate if dropped from the-same height!  The problem with the feather is+that it is so light and has so much surface+area, that air-resistance and buoyancy slow
it down substantially./The reason that objects of unequal weights fall.at the same rate is not so hard to understand./True, gravity does pull the heavier weight more.strongly.  But it also takes more force to get/the heavier weight to start moving in the first-place!  It is like trying to push a light car.and a heavy one.  The lighter car is easier to.make move than the heavy one.  In fact, the a-.mount of force it takes to make an object fall/is exactly proportional to the object's weight!/And thus, whether light or heavy, gravity pulls/on objects just enough to make them fall at ex--actly the same rate.  But what about the eggs-that dropped at different speeds on the Moon,-and Earth and Jupiter?  The reason is that on.the different worlds, gravity itself is weaker.or stronger.  An egg WILL fall faster on Earth.than on the Moon.  But without air resistance,.all objects, dropped from the same height on a-particular world, will fall at the same rate!.We have just seen the feather fall slower than-the penny again.  And we have said that it is.the air resistance and buoyancy which made the-feather fall slower.  Now let's prove this by/recreating an experiment.  Let's get rid of the,air, and drop the feather and the penny in a.vacuum!  This experiment is often repeated all,around the country in our schools by pumping-air out of a container, and then watching the/objects fall inside that container.  A far more,elegant demonstration of the same experiment+was made by Apollo astronauts.  They did in+fact drop a feather and a heavier object on'the Moon, where there is no atmosphere!-Now let's see what happens when we drop these,objects in a vacuum.  And afterward, you can,repeat the experiment.  Or you can even drop.the objects in the air again, and then compare
your results!
CREATING VACUUM . . .
VACUUM ACHIEVED !
Now use the ARROW KEYS to make!your choice.  Then press "ENTER".
DROP OBJECTS AGAIN
DROP OBJECTS IN VACUUM
DROP OBJECTS IN AIR
PUMPING IN AIR . . .
MORE MASSIVE PLANET
LESS MASSIVE PLANET
moon orbits faster
moon orbits slower
GRAVITY, MOONS AND RELATIVITY,Gravity is one of the most useful yardsticks,for astronomy.  For instance, when the grav-)ity of a planet can be measured, its mass+and composition can be deduced.  One of the*best ways to measure a planet's gravity is+to observe its moons.  Just as objects fall*faster on a more massive planet, so too do+its moons orbit faster.  This was precisely)why astronomers were so excited when they,discovered Pluto's moon, Charon.  By observ-+ing how fast Charon orbits, astronomers de-*duced how large and massive Pluto must be!,This kind of scientific deduction is typical+in astronomy.  Similarly, in the early part)of this century, Albert Einstein deduced.
Light "bends" more
Light "bends" less+that gravity can be thought of as curvature+of space-time!  While not all physicists a-,gree with him, many of the predictions about*gravity in his "Theory of Relativity" have+been confirmed.  For example, it seems that(gravity can actually "bend" light waves!,In its most extreme case, when gravity is so,strong, it can even keep light from escaping*from its source!  This produces the famous
"black-hole" phenomenon.*Whether you do agree with Einstein or not,*the subject of gravity provides one of the)most intriguing areas of study in science+today.  Who knows?  You may be one who con-,firms Einstein's theories.  Even better, you&might be the one who proves him wrong!U
T  i  m  e
Setting the Rhythm of
the Universe
CONTINUECTime is one of the most puzzling of all concepts.  From our own ex-Aperience, we all intuitively know what time is, but explaining itCis often confusing and frustrating.  As difficult as time is to ex-Cplain, it is quite easy to measure.  Measurements of time are basedCon recurring events, like the nuclear "tick" of an atomic clock, or@the march of a planet around the Sun (commonly called a "year").BIn fact, your age in "Earth years" can be thought of as the numberBof times the Earth has orbited the Sun since you were born!  SinceAthe different planets take different amounts of time to orbit the,Sun, their years are of different durations.BSo let's see what our ages would be on some of the other worlds in&our vast and varied Solar System . . .
100 yr Move the scroll bar as indicated!below, until it shows your age on!Earth.  Your age on other various
bodies of our Solar System will!automatically be calculated. Look!at Kohoutek.  This comet takes so!long to make one orbit of the Sun
(about 75,000 years!) that your!age does not even register at the
top of the scale!  "Long period!comets" can have orbits so large,!that one of their years can equal
over a million Earth years!
Mercury        yr
Venus          yr
Mars           yr
Jupiter        yr
Saturn         yr
Uranus         yr
Neptune        yr
Pluto          yr
Ceres          yr
Kohoutek       yr
Your Age
On Other Worlds
"+/-" keys add/subtract  1 yr
" / " keys add/subtract 10 yr
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Motions of the Inner Planets
CONTINUEKAbove, we see the relative distances between the Inner Planets and the Sun.HWhen you start the display, notice that our view is from above the SolarKSystem, looking down at about a 45
 angle.  This makes the planetary orbitsJseem more elliptical than they are.  This view is an "exaggerated perspec-Gtive".  Notice how the planets will get smaller when they go behind theISun.  Although the sizes of the planets and the Moon are exaggerated, allIorbital periods are as accurate as the screen allows.  (Because they can-@not be represented accurately, the moons of Mars are not shown.)BThe display begins with the planetary positions of January 1,1988.BAfter you CONTINUE on to the MOTIONS OF THE INNER PLANETS DISPLAY:'Press  F:           for FASTER Display.'Press  S:           for SLOWER Display.;Press  D:           to toggle DELAY and show planet orbits.:Press  W:           to toggle DELAY WITHOUT planet orbits..Press  C:           to toggle CALENDAR on/off.&Press  M:           to return to MENU.9Press  BACKSPACE:   to return to this information screen.
Earth Year:
Orbit ofU
Neptune
Pluto
Jupiter
Saturn
Uranus
Motions of the Outer Planets
CONTINUEKAbove, we see the relative distances between the Outer Planets and the Sun.HWhen you start the display, notice that our view is from above the SolarKSystem, looking down at about a 45
 angle.  This makes the planetary orbitsDseem more elliptical than they are.  This far out in space, all the Hplanets (and even the Sun!) would be but mere points of light, very muchFsmaller than the smallest dot which can be represented on this screen.HThus the sizes of the planets and the Sun are greatly exaggerated, and  Hno moons of the Outer Planets are shown.  Yet, if you look very closely,Cyou might just see the giant, mysterious Red Spot of Jupiter! . . .JThe "exaggerated perspective" of the display shows the orbital periods as Jprecisely as possible.  Notice Pluto's highly elongated orbit, inclined o-Hver 17
 to the Ecliptic.  Pluto's orbit brings it closer than Neptune toIthe Sun for about 20 years per orbit, (the latest case being between 1979Hand 1999)!  Notice also how Pluto and Neptune "keep their distance" fromGone another.  (See "PLUTO" for further explanation.)  As you watch the HMotions of the Outer Planets, remember that well within the orbit of Ju-Dpiter, the four Inner Planets are, in a comparative sense, whizzing Baround the Sun far more rapidly than their more distant neighbors!BThe display begins with the planetary positions of January 1,1988.BAfter you CONTINUE on to the MOTIONS OF THE INNER PLANETS DISPLAY:'Press  F:           for FASTER Display.'Press  S:           for SLOWER Display.;Press  D:           to toggle DELAY and show planet orbits.:Press  W:           to toggle DELAY WITHOUT planet orbits..Press  C:           to toggle CALENDAR on/off.&Press  M:           to return to MENU.9Press  BACKSPACE:   to return to this information screen.
Earth Year:
Orbit of
Orbit
of Neptune
Orbit    of Uranus
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AAs the Earth rotates, friction between the ocean floors and waterDis constantly slowing down the Earth, as if the tidal bulges are im-Bmense brake shoes.  As a result, the length of an Earth day is in-?creasing by a fraction of a second each century.  Also, gravity>between the Moon, the Sun and the tidal bulges is slowing down@the Moon and causing it to move slowly away from the Earth.  The;net result will occur billions of years in the future . . .U
BAt that time, the length of the Lunar month and the Earth day willBhave increased to the same measure of time, and will then be equalDto about 47 of our present days!  Then, just as the same side of theBMoon always faces us, the Earth will likewise always have the same?side facing the Moon.  In this "tidally locked" position, . . .Bthe Moon will always occupy the same relative place in the Earth's@sky!  Thus the Moon will no longer romantically rise and set forAEarth's young lovers.  However, the tides will continue.  But, noDlonger compelled by the Moon, these future tides will only be causedBby the Sun.  As such, compared to the tides of today, future tidesAwill be far smaller and less frequent, barely recognizable as the<heirs to the tides which once helped shape the planet Earth.U
@Now, instead of looking at the Earth/Moon system from above, let?us look at it from the side.  This illustrates why the two high<tides each day can be of different heights.  As we know, the@Earth's axis is inclined 23.5
 from the vertical; and thus it is.also inclined to the axis of the tidal bulges.?In the example above, the Earth's Northern Hemisphere is facing?the Sun, so it is experiencing summer.  An observer at a middle=northern latitude would notice a "very-high" high tide during<the day, when he is on the side of the Earth facing the Sun.>But during the night, 12 hours later, when his position on the=Earth had rotated under the Moon, the high tide would be much'lower, due to inclination of the Earth.U
>Of course, all our examples so far have assumed an ideal Earth<that is completely covered with water.  And in most cases on>Earth, the tides do behave according to the stated principles.<However, in reality land masses get in the way of the moving2tidal bulges, sometimes to a very striking effect.;Especially where the tidal flow of water is funneled into a?narrow or V-shaped inlet, the difference between high tides and?low tides will be large.  The Bay of Fundy, between Nova Scotia?and New Brunswick, experiences tides that will sometimes exceedB15 meters!  For similar reasons, many places on Earth may only ex-@50 feet!  For similar reasons, many places on Earth may only ex-7perience one high tide a day, instead of the usual two.U
AThe solid portions of the Earth also respond to tidal forces, and?produce what are known as "land tides" when continents face theAMoon.  Though the Earth's solid crust resists the tidal pull moreAthan the ocean, the crust still allows the continents to flex to-Award the Moon by about 15 centimeters!  This flexing of the Earth=ward the Moon by about six inches!  This flexing of the Earth@under the Moon's muscle is thought to contribute to earthquakes!>Similarly, there is evidence that the Earth's tidal effects on4the Moon contribute to increased moonquake activity!U
Daily Tides:>As the Earth is rotating, once each day your area of the globeAmoves first under one tidal bulge, then under one non-bulge, then?under the second bulge, and finally under the second non-bulged?area.  This produces two high tides and two low tides each day.>Since it rotates in the same direction that the Moon revolves,Athe Earth must rotate a little more than 360
 each day to "catch-=up" again with the moving tides.  Therefore, the time between7successive high tides is about twelve and a half hours.U
TideU
At other times of the
month, the Moon and Sun
are at right angles with
respect to the Earth,
and their forces tend
to have a canceling ef-
fect.  High tides are
about 20% lower than
normal, and low tides
are about 20% higher
than normal.  The
tides which occur at
these times are known
as NEAP TIDES.U
BTwice every month the Sun and Moon work in unison to produce high-Aer than usual tides.  These occur 1) when the Sun and Moon are on=opposite sides of the Earth, and 2) when they are on the same=side.  Tides occurring at these times are called SPRING TIDES<because they "spring forth", and are 20% higher than normal.U
?The Sun also produces tidal effects on the Earth.  However even>though the Sun is so much more massive, it is so far away thatAthe solar tidal forces are less than half as strong as those pro-Bduced by the Moon.  As indicated in this display (greatly exagger-:ated in scale), the tides follow the Moon and not the Sun.U
Spring
TideU
    T I D E S
UNDER THE CONSTANT
TUG OF THE MOONU
gravitational
forceU
observer
nightU
CONTINUE
Lunar Tides:
EARTH
MOONCPerhaps the Moon's greatest effect on Earth is experienced daily inEthe form of Tides.  Tides help to shape the coastlines of continents,Eaffect shipping and commerce, and have even determined the outcome ofGmajor naval battles.  Despite our everyday familiarity with them, tidesEremain one of the least understood of astronomical phenomena.  In theDabove greatly exaggerated illustration, we see the Sun at the right,?and the Moon and Earth (with its tidal bulges) on the left. . .ETwo things create the tidal bulges:   First, since gravity diminishesFwith distance, the Moon pulls harder on the near side of the Earth andFweaker on the far side.  It pulls with medium strength on the Earth inFbetween.  Since the oceans are liquid, they are free to respond to theDdifferent strengths of the Moon's gravity as indicated by the arrowsBin the illustration.  But this is only half the story.  The second7cause of the tidal bulges involves the Barycenter . . .
centrifugal
forceFAs we have seen, the Moon does not orbit the center of the Earth.  In-Cstead both orbit their collective center of mass, the Barycenter, aBpoint 1,600 km below the Earth's surface, on the line between bothEpoint 1,000 miles below the Earth's surface, on the line between bothDbodies' centers.  As the Earth swings around the Barycenter, centri-Efugal force is strongest on the side opposite the Moon.  Thus gravityDand centrifugal force act together to make the Earth's surface bulgeCoutward in two directions: away from the Moon and torward the Moon.
Solar Tides:
observer
night
Future Tides:!Press  D:  to toggle DELAY on/offU
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    Penumbral
Partial
TotalU
ECLIPSES
COSMIC  GAMES  OF
HIDE  AND  SEEK
CONTINUE
Solar EclipsesEDuring a Solar Eclipse, the Moon moves "directly" between the Sun andFEarth, and prevents all or a portion of the Sun's rays from reaching aDpart of the Earth's surface.  As the Moon's shadow sweeps across theEEarth in one of the most awesome of cosmic events, the Sun may be to-Ftally blotted out, as if hiding behind the Moon.  The air suddenly be-Fcomes cooler, and birds halt their singing.  It is not surprising that7Solar Eclipses were feared by peoples of ancient times.
Total and Partial
Umbra:(dark shadow)
Penumbra:(medium shadow)DWhen the cone-shaped "umbra", the dark portion of the Moon's shadow,Ftouches the Earth, a Total Solar Eclipse occurs.  Since the umbra justFbarely reaches down to the Earth's surface, the shadow it casts on theDEarth is usually smaller than 242 km across.  This sweeps across theGEarth at about 1,600 km/h: faster than most jet airliners!  Because theDEarth is usually less than 150 miles across.  This sweeps across theFEarth at about 1,000 mph: faster than most jet airliners!  Because theFshadow cast on the Earth is so small and moves so quickly, Total SolarFEclipses usually last only a few minutes, never more than 7.5 minutes.GUsually occurring over oceans, most are not seen by the average person!DA Partial Solar Eclipse occurs when the "penumbra" of the Moon fallsCupon the Earth's surface.  Only part of the Sun's rays are blocked,Fand from Earth it appears as if the Moon bites into the Sun, but neverFcompletely covers it.  The sky darkens, but not nearly as dramaticallyDas during a Total Eclipse.  Because the penumbra is so large, a Par-Ctial Solar Eclipse can be seen over wide areas of the Earth and mayClast for more than 2 hours!  Partial Solar Eclipses occur more fre-"quently than Total Solar Eclipses.
Annular EclipsesEAn Annular Eclipse is a special kind of Partial Solar Eclipse.  SinceEthe Moon's orbit is an ellipse or oval, the Moon is sometimes fartherDfrom the Earth than at other times.  If a Solar Eclipse happens whenEthe Moon is farthest from the Earth, its umbra does not reach all theEway down to the Earth's surface.  Look closely above, and notice thatDnow the umbra is not touching the Earth!  Thus, even though the MoonCis directly between the Earth and the Sun, only the Moon's penumbra
falls on the Earth. . . DAt these times, when the Moon is farthest from the Earth, the Moon'sDapparent diameter in the sky will be smaller than the Sun's apparentGdiameter.  Thus, even when the Moon is exactly in front of the Sun, theFSun's outer rim will remain visible.  Like a bright, shining ring, theDSun's outer portions will surround the black disc of the Moon.  ThisBgives us the name Annular (meaning "ring-like") Eclipses.  AnnularAeclipses happen slightly more often than do Total Solar Eclipses.
TOTAL SOLAR ECLIPSE
PARTIAL SOLAR ECLIPSE
ANNULAR SOLAR ECLIPSEBNow you may view a Total or Partial or Annular Eclipse from out inBspace and simultaneously from on the Earth.  Use the ARROW KEYS to*make your selection, and then press ENTER.=     During the Eclipse Displays:  Press  D: to toggle DELAY.>    When you wish to move on, select CONTINUE and press ENTER.
View From Earth    (dayside)
Lunar EclipsesCWhen the Moon, the Earth and the Sun line up, such that the Moon isD"directly" behind the Earth relative to the Sun, a Lunar Eclipse oc-Dcurs.  At such times, the Moon enters the Earth's shadow and darkensBnoticeably.  The Moon moves through the Earth's shadow at close toF3,200 km/h; and as the shadow's edge moves across the Moon, it is dis-E2,000 mph; and as the shadow's edge moves across the Moon, it is dis-Ftinctly circular.  This was first noted by the Greeks over 2,000 yearsAago, leading them to conclude that the Earth was indeed a sphere.
Total, Partial and PenumbralDA Total Lunar Eclipse occurs when the Moon enters the "umbra" of theDEarth's shadow.  Though this is the darkest part of the Earth's sha-Edow, the Moon still does receive some sunlight.  This is because someAof the Sun's rays are refracted or "bent" around the edges of theDEarth by its atmosphere.  Since the Earth's atmosphere scatters muchEof the blue wavelengths in sunlight, the resulting light reaching theFMoon contains higher-than-normal proportions of red wavelengths.  This9makes the eclipsed Moon appear a dull-red, coppery color.EA Partial Lunar Eclipse occurs when the Moon enters the "penumbra" ofEthe Earth's shadow, and then only partially enters the umbra.  DuringFthis time, only the portion of the Moon within the umbra will be dark-Eened substantially.  While instrumentally that portion of the Moon inBthe penumbra can be measured to darken, it is often not detectableDwith the naked eye.  For this reason, Penumbral Lunar Eclipses oftenCgo unobserved, even by astronomers.  Penumbral Lunar Eclipses occurBwhen the Moon enters only the Earth's penumbra, but not the umbra.CThe illustration in the above right shows (in an exaggerated scale)Da cross section of the Earth's shadow, where the Moon passes throughCit during Lunar Eclipses.  Paths of the types of Lunar Eclipses areDalso shown.  Here, the umbra and penumbra are 9,200 km and 16,000 kmDalso shown.  Here, the umbra and penumbra are 5,700 and 10,000 milesFacross respectively.  Thus Total, Partial and Penumbral Lunar EclipsesClast considerably longer than solar eclipses, sometimes for severalFhours.  Since Lunar Eclipses are visible anywhere the Moon is visible,>they can usually be observed from half of the Earth's surface.
TOTAL LUNAR ECLIPSE
PARTIAL LUNAR ECLIPSE
PENUMBRAL LUNAR ECLIPSEANow you may view a Total or Partial or Penumbral Eclipse, as seenCfrom the surface of the Earth.  Use the ARROW KEYS to make your se-
lection, and then press ENTER.
(nightside)!Press "F":    for FASTER display.
Press "D":    to toggle DELAY.!Press "S":    for SLOWER display.
Earth
ECLIPSE SEASONS!Ecliptic:(plane of Earth's orbit)GFrom what we have just learned about eclipses, it might seem that thereIshould be one Solar Eclipse and one Lunar Eclipse each month, as the MoonFmoves in front of and behind the Earth.  But in reality, eclipses onlyHhappen about every six months during "eclipse seasons".  The reason liesFin the fact that the Moon's orbit is tilted about 5
 to the Ecliptic, Fthe plane of the Earth's orbit.  This means that for most of the year,Fthe Moon is either above or below the Ecliptic, making eclipses impos-Fsible.  Like one person crossing a bridge above another, the Earth and0the Moon stay well clear of each other's shadow.GThough the Moon is usually above or below the Earth's orbital plane, itHdoes cross through this plane twice a month.  The points where it passesEthrough are called "nodes", and the line between the points is calledDthe "line of nodes".  As we can see, when the line of nodes does notHpoint toward the Sun, no eclipse can occur because the Moon's orbit car-Gries it too far above or below the Ecliptic.  However, as the Earth andGMoon orbit the Sun, the line of nodes points toward the Sun about twiceGeach year, (approximately every six months).  At such times, the cosmic,stage is set for the occurrence of eclipses.
node A
node B
Here, the line of nodes does
point toward the Sun.  Now,
when the Moon passes through
the Ecliptic, eclipses will
occur.  When the Moon rises
through node A, its shadow
will fall on the Earth, and
a Solar Eclipse will result.
When the Moon moves down
through the Ecliptic at node
B, it will be in the Earth's
shadow, and a Lunar Eclipse
will result.  Because of the
motion of the line of nodes,
no more than seven eclipses,
(Solar and Lunar Eclipses
combined), can occur in any
single calendar year.
THE FUTURE OF ECLIPSES
As noted in the Moon's ORBIT
FACTS portion of the program,
the Moon is slowly moving a-
way from the Earth.  Thus the
Moon will slowly look smaller
and smaller, able to cover
less of the Sun during Solar
Eclipses.  More ANNULAR Solar
Eclipses will occur, instead
of TOTAL Solar Eclipses.  In
millions of years, no matter
where the Moon is in its or-
bit, it will not be able to
fully eclipse the Sun.  To-
tal Solar Eclipses will be
events of the past, replaced
by less dramatic, but equal-
ly beautiful Annular ones!U
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The Earth's
Orbit
MotionU
Earth Year:U
Earth
CONTINUE
The motion of the Earth in
its orbit describes a near-
ly circular ellipse with
the Sun residing at one of
the foci.  Like the other
planets, the Earth orbits
the Sun from west to east,
or counter-clockwise when
viewed from above the Solar
System.  Like so many nat-
ural phenomena, this seems
elegantly simple, when ob-
served in the right way!
But in a moment, we shall
see that things are not
always quite as simple as
they seem!
THE EARTH'S
ORBIT MOTION
(View from above
the Solar System)
Press  F:  for FASTER display
Press  D:  to toggle DELAY
Press  S:  for SLOWER display
Press  C:  to toggle CALENDAR    "to Vega"
EARTH'S "TRUE" MOTION?
If the Sun were stationary
then the motion you just
saw would be all there is
to it.  But the Sun is in
motion in the galaxy.  It
presently is moving toward
the star Vega at a speed of
about 69,000 km/h!  And so
about 43,000 mph!  And so
it drags all the planets
with along with it!  Let
us track this more com-
plex motion now, with our
view from the side of the
Solar System, just above
the plane of the Ecliptic.
(View from near plane
of the Solar System)
Press  R:  to RESET display
Venus
Mercury
Thus the Earth is spiral-
ing toward Vega!  And this
does not take into account
that our galaxy is also
spinning, and that it is
moving toward other galax-
ies, and so on!  So, it is
the relative motion of bod-
ies which is complex, even
though the natural laws
governing this motion are
so elgantly simple.  To
close, let's watch the
relative motions of the In-
ner Planets, as they move
continually toward Vega.
Tracking the orbits
of the Inner PlanetsU
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GThe "proton-proton cycle" begins when, once in 7 billion years, a givenGproton (red) will collide with another proton with the proper energy toHbind to it.  But the 2-proton nucleus is unstable and immediately decaysLinto a deuterium nucleus consisting of 1 proton (red) and 1 neutron (white).GThe decay releases a neutrino (small white), which speeds off at nearlyGthe speed of light, and a positron (small red).  The positron moves offGand eventually strikes a free electron (small yellow), at which instantAboth are annihilated in a burst of gamma ray energy (wavy lines).U
GThe deuterium nucleus produced in the first collision continues on; butDit is very highly prone to reacting with other atomic nuclei.  It isJonly a few seconds before it collides with another nearby proton!  A high-Jenergy gamma ray is released, and a new element is born in this collision.IA rare kind of helium called "helium-3", weighing only 3/4 as much as or-Hdinary helium, the new element consists of 2 protons and only 1 neutron.U
DThe third and last collision of the proton-proton cycle occurs aboutF400,000 years later!  At that time, the helium-3 nucleus collides withDanother helium-3 nucleus which has been built-up in exactly the sameDway.  The net result of the collision is two free protons and an or-Fdinary helium-4 nucleus, consisting of 2 protons and 2 neutrons.  The C2 free protons move off, now at liberty to strike other protons and
begin the entire cycle again.U
Solar Nuclear Cycle
CONTINUE
   +    +   +    =       +
                 =          +"  Four Protons     Helium
Energy
THE PROTON-PROTON CYCLEHThe nuclear fusion process by which the Sun produces its energy is a se-Iries of 3 collisions between atomic particles.  Called the "proton-protonHcycle", it is the process by which 4 hydrogen nuclei (protons) are fusedHinto one helium nucleus, releasing energy.  The steps in the process areFnot of equal interval because there is a different probability of eachGcollision occurring.  In fact, given a single proton, the likelihood isDthat it will make the first type of collision only once in 7 billionHyears!  Yet, since the number of protons in the Sun is so enormous . . .9the fusion process continues constantly and steadily. . .FLet us now examine this nuclear cycle of the Sun, this fusion reactionHwhich is a close relative of the explosive processes of a hydrogen-bomb.FWe must first enter the sub-microscopic world of atomic nuclei deep inESun's core.  Here the temperature is measured in millions of degrees,Dso hot that atoms of hydrogen and helium have been stripped of their?orbiting electrons and wander through the core unattended . . .2Watch closely!  Nuclear events occur VERY QUICKLY!
RERUN 1st COLLISION
RERUN 2nd COLLISION
RERUN 3rd COLLISION
 7 Billion Years
 A Few Seconds
 400,000 Years
Proton
Neutron
Electron
Positron
Neutrino    Gamma Ray
Proton-Proton CycleDThe net effect of each proton-proton cycle is that 4 hydrogen nucleiH(protons) are converted into one helium nucleus.  However the helium nu-Gcleus is only 99.3 percent as massive as 4 protons!  Where then is the Gmissing mass?  It has been converted to energy in the form of the gammaFrays and neutrino which were the end-products of the three collisions.HThe energy, converted from the missing mass, has been produced accordingDto Einstein's famous equation: E = mc
.  The neutrino produced is soInon-reactive that it quickly passes out of the Sun and into space.  Mean-Gwhile, the gamma rays will continue to bounce around the solar interiorFfor thousands to millions of years, before reaching the Sun's surface!
 HOW MUCH ENERGY?<The scale at which the Sun produces energy is truly stagger-<ing.  Each second     million tons of hydrogen is converted 7into       million tons of helium.  The missing mass of;million tons is converted to energy!  Each second!  That is/equal to the mass of a line of automobiles over;long!  Likewise the number of proton-proton-cycle reactions;concluding each second in the Sun is equally mind-boggling.4Let's suppose that every person on Earth today has a
587.9
4.1    20,000 km
50 kg
652.5
12,000 miles
100 lb.;bag of fine sand.  The number of grains of all that sand is<still much less than the number proton-proton reactions end-4ing their long cycles EACH SECOND in the Sun's core!;So how much energy does the Sun produce?  In everyday terms9each second it produces 13 million times more energy than;the annual consumption of electricity in the United States!9This is a staggering CONTINUOUS solar radiative output of(383 billion billion MEGAWATTS of energy!
     CONTINUOUS SOLAR OUTPUT
             EQUALS
  383 BILLION BILLION MEGAWATTS
A BUILT-IN SAFETY VALVE<What is it that keeps this immense flood of energy contained<in such an orderly solar furnace?  Gravity and heat work to-=gether as a "built-in safety valve".  If the Sun suddenly be-:gins to produce more energy because more reactions are oc-:curring, then more heat is generated and the Sun begins to<expand.  This means that there is more space between nuclear:particles, so the reactions begin to slow down.  When they:slow enough for the temperature to drop, gravity draws the8Sun back down so the particles are close enough to react<again.  Scientists estimate that this safety valve will keep7the Sun shining steadily for billions of years to come!U
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