The Sun is really a star. It is a huge body of hot, glowing gases. Compared to other stars, the Sun is average in size. The Sun appears to us as a huge luminous disk because the Earth is the third planet closest to it. If we were several light years away, the Sun would appear as a small paint of light. The Sun is 30,000 light years (ly) from the center of the Milky Way. Many facts have been discovered about the Sun by studying it during solar eclipses. A solar eclipse occurs when the moon moves between the Sun and the Earth. In this position, the moon blocks the path of the Sun's light and casts a shadow on Earth.
In order for us to clearly understand our position in the solar system there are important facts we must keep in mind about the Sun. Its distance from the Earth is 93 million miles. It takes the sun's light 8 minutes and 20 seconds to reach Earth. The diameter of the Sun is about 864,000 miles and its rotation speed is 29km/sec, which equals to one complete revolution every 25 days.
Aristrachus, who lived in Samos (an island in the Mediterranean), estimated the relative size and distances between the Earth, Moon, and Sun. His calculations gave us a sense of their proportionate size and their relative distances from Earth. For example, by comparing the size of the Earth's shadow on the Moon during a lunar eclipse to the size of the Moon's disk, Aristrachus determined that the Moon's diameter was about one third the diameter of the Earth.
Aristarchus also calculated that the Sun is approximately 20 times farther from the Earth than is the Moon. These findings were determined by measuring the angle between the Sun and Moon when the Moon was exactly half lit. We now know the figures were inaccurate.
The Sun's rotation rate can be determined from the differences in the Doppler shifts. The Doppler method confirms that the Sun rotates faster at low latitudes than at high latitudes. At a latitude of seventy-five degrees the rotation period is about 33 days, and its direction of rotation is from West to East like the orbital revolution of the planets. It is possible for different parts of the Sun to rotate at different rates because of its gaseous composition, as opposed to the solid mass and slower speed of the terrestrial planets.