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Subject: SPACE Digest V12 #691

SPACE Digest                                     Volume 12 : Issue 691

Today's Topics:
                Vulcan
         GLOSSARY OF SOLAR TERRESTRIAL TERMS

Administrivia:

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----------------------------------------------------------------------

Date:         Fri, 14 Dec 90 16:05:29 EST
From: Leonard Abbey <[e-mail]>
Subject:      Vulcan


                            The Story of Vulcan

                       by Leonard B. Abbey, F.R.A.S.
                        The Atlanta Astronomy Club


The great impetus given to planetary astronomy by the discovery of Uranus
in 1781, the major asteroids in 1801--4, and Neptune in 1845 spurred many
astronomers to turn their attention to this field.  Theoretical work done
by the great French mathematician Leverrier had been a prime factor in the
discovery of Neptune by Galle in Berlin.  In fact, his calculations had
been the sole cause of that discovery.  (Of course, the English
mathematician John Couch Adams had made similar calculations which
pro-dated the Frenchman's work, but Adams' predictions were ignored by
Astronomer Royal Airy until after Galle had discovered Neptune -- using
Leverrier's work.)  A little taste of the fame associated with the
discovery of a new planet goes a long way, and Leverrier began to look for
new possibilities.

The unexplained advance of Mercury's perihelion soon attracted him.  He
deduced that this advance could be explained by either assuming Venus to be
1/10th more massive than had been thought, or by postulation an
intra--Mercurial planet.  By this time the relative masses of all known
major members of the solar system had been worked out to a reasonably
accurate degree, so Leverrier began to investigate the possibility of
another planet. In 1859 he published his preliminary findings. In response
to Leverrier's paper, a physician and amateur astronomer named Lescarbault
announced that he had observed the passage of an object, which he took to
be the new planet, across the sun's disk.  A minor earthquake shook the
astronomical world.  Many observers wrote excitedly to the reticent doctor
seeking further information, but he was reluctant to reply to such
correspondence pending more definite results.  Being unable to communicate
with Lescarbault in any other way, Leverrier journeyed to Eure-et-Loire to
seek a personal interview.

At that time Leverrier was the lion of the European intellectual community,
and was highly aware of his fame and achievements.  As a matter of fact, he
was known to be rather egotistical and pompous.  Imagine Lescarbault's
surprise upon answering his door when he was confronted by this arrogant
and angry man, who refused to identify himself, and began as follows: "It
is then you, sir, who pretend to have observed the intra-Mercurial planet,
and who have committed the grave offense of keeping your observations
secret for nine months.  I warn you that I have come here with the
intention of doing justice to your pretensions, and of demonstrating that
you have been dishonest or simply deceived.  Tell me then, unequivocally,
what you have seen."  Lescarbault then proceeded to show his equipment to
Leverrier.  This consisted of a small refractor (the typical, and very
expensive, amateur instrument of the day), a pocket watch showing only
hours and minutes and a seconds pendulum (the equivalent of our modern
stop watch).  All calculations had been made on a wooden board, the surface
of which was cleared for new calculations with a small hand plane.  Despite
the modesty of the equipment Leverrier came away convinced the observations
had been accurately made, and that the suspected planet had been observed.
He congratulated Lescarbault on his discovery and named the new planet
Vulcan. From Lescarbault's single observation, Leverrier obtained the
following data:

              Longitude of Ascending Node 12* 59'
              Inclination of Orbit 12* 10'
              Semi-major Axis (Earth=1) 0.143
              Daily Heliocentric Motion 18* 16'
              Period 19 days 17 hours
              Mean Distance from Sun 13,082,000 miles
              Apparent Diameter of Sun from Vulcan 3* 36'
              Greatest Possible Elongation 8*

Leverrier's work was now ready for its final test:  a second, predicted,
observation.  Astronomers at major observatories were alerted and anxiously
awaited the great event.  Alas, Vulcan failed to show up for its scheduled
passage across the sun's disk.

After 127 years Lescarbault's observation remains unconfirmed.  Numerous
sightings of unexplained objects transiting the sun have been reported
since 1860, but none of them appear to be consistent with an
intra-Mercurial planet. Sightings of unexpected star-like objects in the
immediate region of the sun during solar eclipses have been reported,
notably by Watson and Swift in 1878, but these observation agree neither
with theory nor with each other.

Belief in Vulcan began to wane by 1880. It is possible that some of these
sightings were transits of the nuclei of sun-grazing comets.  Many comets
which encounter the sun are never observed from earth because they both
approach and recede from that part of the sky which is behind the sun from
our viewpoint. This is evident from the fact that many comets have been
observed during solar eclipses but are never seen otherwise. However there
is no authenticated observation of the transit of a cometary nucleus across
the sun's disk.

Leverrier maintained his belief in Vulcan for the rest of his life.
Shortly before his death in 1877 he wrote: "There is, without doubt, in the
neighborhood of Mercury, and between that planet and the sun, matter
hitherto unknown.  Does it consist of one, or several small planets, or of
asteroids, or even of cosmic dust?  Theory cannot decide this point."

Theory did decide the point, though not in a manner which Leverrier, in
spite of his undisputed genius, could have conceived. The Theory of
Relativity, first published in the early years of this century, has special
meaning for the Vulcan problem.  As with other planets, the orbit of
Mercury is essentially a perfect ellipse.  The direction in which this
ellipse is tilted rotates slowly about the sun.  The shape of this orbit,
as well as the rate at which it rotates around the sun, is determined by
the mass of the planet, the mass of the sun, the planet's distance from the
sun, and by the perturbations caused by the other bodies of significant
mass in the solar system.  Astronomers of the late 19th century thought
that they were aware of all these factors to a great degree of accuracy,
and thus the positions of the planets could be predicted fairly precisely,
well in advance.

This was true with one exception.  The exception was Mercury, where the
rate of advance for the perihelion could not be reconciled with the most
careful predictions.  According to Einstein, the presence of a strong
gravitational field requires the addition of new terms to the equations
describing space and time, which were unknown to Newton and the other
founders of celestial mechanics.  Mercury is the only planet whose orbit
lies sufficiently close to a very massive body (the sun) for these new
considerations to be measurable. The net effect is that the Newtonian
formulas, when refined by the relativistic terms, predict an advance of
Mercury's perihelion exactly equal to that observed over the centuries.  In
fact, this is one of the three classical tests of the theory of relativity.

Once again our knowledge of the solar system had been advanced by a man
sitting at a table, working with only a pencil and paper!  Nevertheless,
the lure of such an appealing subject as an undiscovered planet, even
within the orbit of Mercury, will probably never die out.  It is possible,
even probable, that there are very small bodies (or cinders!) revolving in
the hellish intra-Mercurial region.  Some of them are most certainly
man-made.  What is definite, however, is that they will never be observed
from earth, whether in transit across the sun, during a total eclipse, or
at elongation.

The case book for Vulcan is closed.  Leverrier and Lescarbault are not to
be criticized for their honest and scientific approach to a very serious
problem. Though they did not live to see their theory disproven, they
realized, as we do, that failure to seek is the destroyer of progress.

------------------------------

Date:    Thu, 13 Dec 90 22:10:42 MST
From: [e-mail] (Cary Oler)
Subject: GLOSSARY OF SOLAR TERRESTRIAL TERMS
X-St-Vmsmail-To: ST%"[e-mail]"

                      GLOSSARY OF SOLAR TERRESTRIAL TERMS
                      -----------------------------------


     The solar terrestrial forecasts which are being distributed over the
networks contain some language that may not be very clear to many people
unfamiliar with solar terrestrial terms.  Since the reports are intended to
be intelligable by the general public, this glossary of terms has been
compiled to help provide some explanations for terms which may be used in
the reports. This glossary is not meant to be exhaustive, but is rather meant
to provide people with a well-rounded vocabulary and a basic knowledge of some
of the terms and classifications used in the reports.

Definitions are not in any particular order.


Solar Flux:

     The 10.7 cm (2800 MHz) radio flux is the amount of solar noise that is
emitted by the sun at 10.7 cm wavelengths.  The solar flux is measured and
reported at approximately 1700 UT daily by the Algonquin Radio Observatory at
Ottawa, Canada.  Values are not corrected for variations resulting from the
eccentric orbit of the Earth around the Sun.  The solar flux is used as a basic
indicator of solar activity.  It can vary from values below 50 to values in
excess of 300 (representing very low solar activity and high to very high solar
activity respectively).  Values in excess of 200 occur typical during the peak
of the solar cycles.  The solar flux is closely related to the amount of
ionization taking place at F2 layer heights (heights sensitive to
long-distance radio communication).  High solar flux values generally provide
good ionization for long-distance communications at higher than normal
frequencies.  Low solar flux values can restrict the band of frequencies
which are usable for long distance communications.


Sunspot Number:

     This term is basically self-explanatory.  It represents the number of
observed sunspots and sunspot groups on the solar surface.  It is computed
according to the Wolf Sunspot Number formula: R = k (10g + s), where 'g' is the
number of sunspot groups (regions), s is the total number of individual spots
in all the groups, and k is a scaling factor that corrects for seeing
conditions at various observatories.  Sunspot number varies in phase with the
solar flux.  Sunspot numbers can vary between zero (for sunspot minimum
periods) to values in excess of 350 or 400 (in the very active "solar max"
period of the sun's 11 year cycle).  Solar flux is related to the sunspot
number, since sunspots produce radio emissions at 10.7 cm wavelengths (as
well as at other wavelengths).


X-Ray Background Flux:

     This represents the average background x-ray flux as measured on the
primary GOES satellite.  This value basically represents the amount of x-ray
radiation that is being received at the Earth by the Sun.  Generally, active
regions emit more x-ray radiation than non-active solar regions.  Therefore,
this value can be of use in determining the overall state of the solar
hemisphere facing the Earth.


Proton Fluence:

     Although this term will seldom be referenced within the reports, it may be
of use to make a note of it.  Proton fluence is simply the total number proton
particle fluxes measured by the GOES spacecraft at geosynchronous altitudes for
protons of energies >1 Million electron Volts (MeV), >10 MeV and >100 MeV.  The
higher the proton fluence, the more intense proton bombardments are at
geosynchronous altitudes.  It can also be used implicitly to determine the
approximate amount of ionization occurring in the upper atmosphere, as well as
the proton penetration level into the atmosphere and possible satellite
anomalies caused by the solar proton bombardments.


Electron Fluence:

     Again, this term will seldom be referenced within the reports.  It is
analagous to "proton fluence" but is measured for electrons with energies
>2 MeV.


Magnetic A-Index:

     The geomagnetic A-Index represents the severity of magnetic fluctuations
occurring at local magnetic observatories.  During magnetic storms, the A-index
may reach levels as high as 100.  During severe storms, the A-index may exceed
200.  Great "rogue" storms may succeed in producing index values in excess of
300, although storms associated with indices this high are very rare indeed.
The A-index varies from observatory to observatory, since magnetic fluctuations
can be very local in nature.  The A-index for Boulder Colorado (the same value
reported on WWV and WWVH) will be the one referenced most often within the
reports.  Occassionally, the A-index for higher latitude stations may also be
referenced for purposes of comparison.  Magnetic fluctuations monitored locally
here in Southern Alberta will also be referenced, particularly during storm
periods for descriptive purposes.


Magnetic K-Index:

     The geomagnetic K-Index is related to the A-index.  K-indices are scaled
by comparing the H and D magnetometer traces (representing the horizontal and
declination magnetic components) to assumed "quiet-day curves" for H and D.
Each UT day is divided into 8 three-hour intervals, starting at 0000 UT.  In
each 3-hour period, the maximum deviation from the quiet day curve is measured
for both (H and D) traces, and the largest deviation (the most disturbed trace)
is selected.  It is then input into a quasi-logarithmic transfer function to
yield the K-index for the period.  The K-index ranges from 0 to 9 and is a
dimensionless number.  It is assigned to the end of the 3 hour period.  The
K-Index is useful in determining the state of the geomagnetic field, the
quality of radio signal propagation and the condition of the ionosphere.
Generally, K index values of 0 and 1 represent Quiet magnetic conditions and
imply good radio signal propagation conditions.  Values between 2 and 4
represent Unsettled to Active magnetic conditions and generally correspond to
less-impressive radio propagation conditions.  K-index values of 5 represent
Minor Storm conditions and are usually associated with Fair to Poor propagation
on many HF paths.  K-index values of 6 generally represent Major Storm
conditions and are almost always associated with Poor radio propagation
conditions.  K-index values of 7 represent Severe Storm conditions and are
often accompanied by "radio blackout" conditions (particularly over higher
latitudes).  K-indices of 8 or 9 represent Very Severe Storm conditions and are
rarely encountered (except during exceptional periods of solar activity).
K-indices this high most often produce radio blackouts for periods lasting in
excess of 6 to 10 hours (depending upon the intensity of the event).


Sudden Storm Commencement or SSC:

     An SSC is the magnetic signature of an interplanetary shockwave most often
produced by solar flares.  It is always a precursor to increased geomagnetic
activity, most often followed within 3 to 8 hours by a Minor to Major
geomagnetic storm.  It appears on the H (horizontal) trace of magnetometers.
This phenomenon is detectable at almost all magnetic observatories world-wide
within 4 minutes of eachother.


Sudden Impulse or SI:

     A sudden magnetic impulse is similar to an SSC.  It represents a rapid
momentary fluctuation of the geomagnetic field over a period of only a few
minutes.  It is generally associated with interplanetary shockwaves produced by
energetic solar events and can (but need not always) be followed by increased
geomagnetic activity.


Satellite Proton Event:

     Proton events are almost always associated with energetic solar activity
such as major flares.  They are periods of increased proton bombardments at
satellite altitudes.  They can affect satellite transmission/reception if
intense enough and can cause other satellite anomalies.  Proton events may
affect the ability of a HAM operator to establish contact with a satellite, and
may affect the quality of television signals received by satellite (ie. cable
tv may be affected).  Satellite proton events occur within a few hours of a
major proton flare.  They are also often followed by a PCA event (see below).


Polar Cap Absorption Event or PCA:

     A PCA is almost always produced by an intense solar proton flare.  PCA's
are the result of copious quantities of high-energy solar protons penetrating
the Earth's atmosphere to levels of the order of 50 km, producing intense
ionospheric ionization.  The result is a complete (or near-complete) radio
blackout over polar latitudes.  A typical PCA lasts from 1 to 5 days and can
severely effect the propagation of radio signals near or through polar regions.
In intense, long-lasting events, direct entry of the high-energy solar protons
to the upper atmosphere can extend equatorward as far as about 50 degree's
geomagnetic latitude.  They occur almost coincident with satellite-level proton
events, maximize in intensity within a few hours and then begin a slow decay
that can last up to 10 days for intense events.  A PCA is often followed within
48 hours by a SSC and a subsequent Minor to Major geomagnetic storm about 3 to
8 hours later.


Sunspot Classifications:

     Sunspots are classified according to size, shape and spot density.  They
are classified using a set of three coded letters (Zpc) as follows:

        Z - Modified Zurich class, labelled A through F plus H.
               A - Single small spot (single magnetic polarity).
               B - Very small distribution of small spots.
               C - Two or more small spots, at least one of which has a
                   detectable penumbra.
               D - Moderately sized group of spots, several of which may have
                   noticable penumbrae.  Magnetic complexity of D-type regions
                   are usually capable of producing C and low-intensity M-class
                   flares.
               E - Moderate to large area of a fairly complex system of
                   sunspots, several of which have noticable penumbrae and
                   good definition.  Often capable of producing minor C-class
                   as well as major M-class flares.
               F - Large to very large area of a complex system of sunspots.
                   These regions are often capable of producing major X-class
                   flares as well as numerous major M-class and many C-class
                   events (depending on their magnetic complexity).
               H - Single large to very large sunspot (not usually capable
                   of producing significant energetic events).  This type of
                   sunspot is usually manifest in the dying phase of a sunspot
                   group.

        p - Penumbra type of the largest spot in the group.
               x - Single spot.
               r - Rudimentary.
               s - Small symmetric.
               a - Small asymmetric.
               h - Large symmetric.
               k - Large asymmetric.

        c - Relative sunspot distribution or compactness of the group.
               x - Single spot.
               o - Open group (separated by quite a wide space).
               i - Intermediate (moderate sunspot compactness in the group).
               c - Compact (very dense and complex spots within the group).

Example:  A sunspot group classified as type DKO would be of moderate overall
size (that is, the region encompassing all of the sunspots within the group
would be of moderate size), the penumbra of the largest spot within the group
would be large and asymmetric in shape, and the group would be "open"
indicating that the sunspots within the region are not notably close together.


Magnetic Class:

     The magnetic class of sunspots is important in determining how potentially
volatile particular active regions may be.  Sunspots are regularly observed
using instruments capable of determining the magnetic polarity of sunspots and
active regions.  By also applying laws which have been formulated over the
years, visual observations can also be used to establish the magnetic polarity
and complexity of spot groups.  There are basically 7 magnetic types of
sunspots that are classified.  They are described as follows:

       Type A   - Alpha (single polarity spot).
            B   - Beta (bipolar spot configuration).
            G   - Gamma (atypical mixture of polarities).
            BG  - Beta-Gamma (mixture of polarities in a dominantly bipolar
                  configuration).
            D   - Delta (opposite polarity umbrae within single penumbra).
            BD  - Beta with a Delta configuration.
            BGD - Beta-Gamma with a Delta configuration.

Example:  A region labelled as having a magnetic classification of BG
indicates that the sunspot region contains a mixture of magnetic polarities,
but the dominant polarity of the group is bipolar.

Potentially very powerful and potent regions are those which have
classifications of BG, BD and BGD. As magnetic complexity increases, the
ability of an active region to spawn major energetic events likewise increases.


Solar Activity Description:

     Solar activity is described (also applicable on WWV and WWVH) according to
the number of flares which occur during the day.  Activity is basically
classified as follows:
        Very Low :  X-ray events less than class C.
             Low :  C-class x-ray events.
        Moderate :  Isolated (one to 4) M-class x-ray events.
            High :  Several (5 or more) M-class x-ray events or isolated
                    (1 to 4) M5 or greater x-ray events.
       Very High :  Several M5 or greater x-ray events.


Flare Classifications:

     Flares are classified using one of two different systems.  The first
classification ranks the event by measuring its peak x-ray intensity in the 1-8
angstrom band as measured by the GOES satellites.  This x-ray classification
offers at least two distinct advantages compared with the second system of
classification (optical): it gives a better measure of the geophysical
significance of the event and it provides an objective means of classifying
geophysically significant activity regardless of its location on the solar disk
or near the solar limb.  The classification scheme is as follows:

        Class           Peak Flux (1-8 Angstroms in Wm^-2)
          A                < 10^-7
          B                < 10^-6 but > class A
          C                < 10^-5 but > class B
          M                < 10^-4 but > class C
          X                            > 10^-4

The letter designates the order of magnitude of the peak value.  Following the
letter the measured peak value is given.  For descriptive purposes, a number
from 1.0 to 9.9 is appended to the letter designation.  The number acts as a
multiplier.  For example, a C3.2 event indicates an x-ray burst with a peak
flux of 3.2 x 10^-6 Wm^-2.  Since x-ray bursts are observed as a full-Sun
value, bursts below the x-ray background level are not discernable.  The
background drops to class A level during solar minimum; only bursts that exceed
B1.0 are classified as x-ray events.  During solar maximum, the background is
often at the class M level, and therefore class A, B and C x-ray bursts cannot
be seen.  Bursts greater than 1.2 x 10^-3 Wm^-2 may saturate the GOES
detectors.  If saturation occurs, the estimate peak flux values are reported.

The second system of classification involves a purely optical method of
observation.  A flare event is observed optically (in H-alpha light) and is
both measured for size and brightness.  This classification therefore includes
two items of information: a descriptor defining the size of the flare and a
descriptor defining the peak brightness of the flare.  They are listed below:

          Importance
          ----------
               S          -  Subflare area <= 2.0 square degree's.
               1          -  2.1  <= area <= 5.1  square degree's.
               2          -  5.2  <= area <= 12.4 square degree's.
               3          -  12.5 <= area <= 24.7 square degree's.
               4          -          area >= 24.8 square degree's.

          Brightness
          ----------
               F          -  Faint.
               N          -  Normal.
               B          -  Brilliant.

Example:  A major flare rated as a class M7.4/2B event indicates that the flare
attained a maximum x-ray intensity of 7.4 x 10^-5 Wm^-2. The "2B" portion of
this specification indicates that the flare was an importance 2 flare
(>= 5.2 and <= 12.4 square degree's) and was optically Brilliant.  This sample
flare is a powerful event.  Flares that reach x-ray levels in excess of class
M4 can begin to have an impact on the Earth.  Likewise, flares rated 2B or
greater are generally capable of influencing the Earth, particularly if
accompanied by Type II and IV radio sweeps (discussed below).


Sweep Frequency Events (Type II, III, IV and V events):

     Energetic solar events often produce characteristic radio "bursts".  These
bursts are generated by solar material plunging through the solar corona.  Type
III and type V events are caused by particles being ejected from the solar
environment at near relativistic speeds.  Type II and IV events are caused by
slower-moving solar material propagating outward at speeds varying between
approximately 800 and 1600 kilometers per second.  Type II and IV radio bursts
are of particular importance.  These sweep frequency radio events are
signatures of potentially dense solar material which has been ejected from the
solar surface.  If the region responsible for these events is well positioned,
the expelled solar material may succeed in impacting with the Earth.  Such an
impact often causes an SSC followed by Minor to Major geomagnetic storm
conditions and significantly degraded radio propagation conditions.  It is
therefore interesting to pay attention to events which cause Type II and/or IV
radio sweep events, since they may indicate the potential for increased
magnetic activity (and decreased propagation quality) within 48 hours.  It
should be noted, however, that predicting degraded terrestrial conditions is
significantly more complex than simply observing whether the energetic event
had an associated Type II or IV radio sweep.  Flare position, proton spectra,
flare size, event duration, event intensity and a host of other variables must
be analyzed before a qualitative judgement can be made.
     It should also be noted that sweep frequency radio events are capable of
producing Short Wave Fades (SWF's) and Sudden Ionospheric Disturbances (SID's).
Depending on the severity of the event, the duration of SWF's and SID's may
last in excess of several hours with typical values being approximately 30
minutes.  SWF's and SID's cause absorption of radio signals (due to intense
ionization) at frequencies up to and well in excess of 500 MHz.  Microwave
continuum bursts can affect frequencies up to 30 GHz.  Frequencies in the HF
region can be completely blacked out for a period of time during intense
energetic events.


Classifications of Auroral Activity used in the Reports:

     Auroral activity is rated as either not visible, low, moderate, high,
very high or extremely high.  These classifications are defined according to
the brightness achieved by auroral activity, visual activity (ie. changes of
form or structure), whether the aurora is pulsating, and according to the
intensity and fluctuations of color in the aurora.  The various levels of
activity are defined below:

  - Not visible:  Self-explanatory.

  - Low:  Low intensity aurora consisting mostly of diffuse, dim, and
lifeless activity.  Generally no rapid changes in form or structure are
discerned with auroral activity that is classified as "low."

  - Moderate:  Moderate intensity auroral activity which consists of diffuse
aurora intermixed with curtain aurorae or other forms of relatively-low
activity aurora.  Moderate activity may include beams or rays of aurorae
which travel either east or west with time.  No color fluctuations or
significant brightenings of aurorae are associated with moderate intensities.

  - High:  High intensity auroral activity is activity associated with very
bright, active displays that may exhibit changes of color and rapid
pulsations.  High activity is generally confined to curtain aurorae and
moderate-intensity pulsating aurorae.

  - Very High:  Very high intensity auroral activity is usually only
experienced over the high latitude regions where zenith aurorae and
significant auroral displays occur.  Activity classified as very high consists
of most auroral forms of activity, but the activity is always very bright and
extremely active.  Curtain aurorae may change form and color rapidly.  Zenith
aurorae may become exceedingly bright and colorful.

  - Extremely High:  Extremely high auroral activity is only rarely
encountered.  Activity at this level of intensity is most often experienced
within the middle and/or low latitude zones during significant periods of
geomagnetic activity.  The expansion of the auroral zone equatorward produces
the intense activity over regions equatorward of the normal position of the
auroral oval.  This activity usually consists of exceedingly bright, rapidly
fluctuating, strongly pulsating, color-varying auroral activity.  Levels of
auroral activity this high are usually only associated with "rogue flares",
which may occur only once or twice during a solar cycle.



-----------------------

For a good discussion on the topic of solar flares and terrestrial impacts,
consult the book "Solar Flares" by H.J. Smith and E.V.P. Smith (publisher:
Macmillan, New York).  Although this book is a few years old (1963), it
provides an excellent knowledge base to build upon and a wealth of information
on flares in general.

------------------------------

End of SPACE Digest V12 #691
*******************