Mean orbital velocity per second (in millions):N/A
Inclination of axis: unknown
Orbital eccentricity: N/A
Orbital inclination: N/A
Diameter at equator: unknown miles (1,392,530 km)
Escape velocity per second: unknown mph
Mean temperature: Core: 27,000,000 ╩F / 15,000,000 C / 15,000,000╩K
Surface: 10,000 ╩F / 5,500╩C / 5,500╩K
Mass (Earth = 1): 1.9891x1030 kg
Volume (Earth =1):1.414 x 1027 m3
Density (water = 1):
Entire sun 1,410 kgm m-3
Interior (center)1.6 x 105 kg m -3
Surface gravity (Earth = 1): unknown
Maximum apparent diameter as seen from Earth (seconds of arc): unknown
Planet composition
The Sun, which is really a star, dwarfs the other planetary bodies. It represents approximately 99.86 percent of all the mass in the solar system. All of the planets, moons, asteroids, comets, dust, and gas add up to only about 0.14% of the mass of the Sun. This 0.14% represents the material left over from the Sun's formation. One hundred nine Earth's would fit side-by-side across the Sun's disk, and its interior could hold 1.3 million Earth's.
The visible surface of the sun is known as the photosphere ("sphere of light"). The photosphere is a shell of gas about 400 km thick. With the exception of a tiny fraction, all of the Sun's light is emitted from a 100 km thick slice of the photosphere. The photosphere is covered by the chromosphere, which is several thousands of kilometers thick. That, in turn, is overlaid by the region known as the corona, which is generally about 200 km thick. Beyond that layer lies the magnetosphere and the solar wind.
Topography
The chromosphere of the Sun (considered to be the surface) changes rapidly. There are, however, several frequent phenomenon that could be considered topographical features of the Sun.
The edge of the sun appears to be made up of many flame-like protrusions, known as spicules. Spicules are vertical columns of gas that follow the directions of the local magnetic fields and rise to about 10,000 km. They typically have temperatures ranging from 10,000 to 20,000 K. The average spicule lasts from 5 to 10 minutes.
A longer-lived version of the spicule is known as a prominence. Prominences appear in the upper chromosphere and inner corona as flame-like clouds. Some (known as quiescent prominences) maintain their form and volume for as much as a full year before breaking up and disappearing. The mass of a prominence is about 100 times greater than the surrounding material, but the temperature is much lower. Though they seem to be comprised of material surging up from the chromosphere, the great majority consist of material condensing from the corona and flowing downward.
The Sun also exhibits sun spots, which consist of a dark central region (the umbra) surrounded by a lighter region (the penumbra). On the whole, these spots are relatively cool. Although there is no completely satisfactory theory on the origin of sunspots, the Babcock-Leighton theory has gained the greatest acceptance.
Magnetic field and gravity
The Sun produces a strong magnetic field and streams of charged particles (known as solar wind), both of which extend far beyond the planets. The magnetic field strength varies according to the location and feature being measured: Sunspots exert 3,000G; polar fields 5G; prominences 10 to 100G; and chromospheric plages 200G.
Orbit and rotation
Because it is the center of our solar system, the Sun does not have an orbit. It does, however, rotate once on its axis every 26.8 days.
Mythology
For many years, people thought the Earth was the center of our universe (as described by the theory made famous by Claudius Ptolemy). People also believed that the Sun was the creator of the Earth and dispensed all light, life, and power. The Sun, in essence, was the king and many civilizations developed rituals to honor the deity (such as the Christian habit of resting on Sunday).
Discovery and exploration
Many spacecraft have explored the Sun's environment, but none have gotten any closer to its surface than approximately two-thirds the distance from Earth to the Sun. Pioneers 5 - 11, the Pioneer Venus Orbiter, Voyagers, 1 and 2, and other spacecraft have all sampled the solar environment. The Ulysses spacecraft, launched October 6, 1990 as a joint solar mission of NASA and the European Space Agency, will fly over the Sun's polar regions during 1994 and 1995 to perform a wide range of experiments.
