The Sun, Stars, and Galaxies

The Sun, Stars, and Galaxies — page 5 — THE SUN THE CENTER OF THE SoLAR SYSTEM lthough the Sun is a rather ordi nary star it is very important to the inhabitants of Earth The Sun is the source of virtually all Earth’s energy 6 approximate size of Earth A huge cloud of gas erupts from the Sun The image is in false color and was taken in extreme ultraviolet light An image of Earth has been superimposed to show how enormous the Sun is in comparison SOHO ESA NASA Io

The Sun, Stars, and Galaxies — page 6 — THE SUN TuE CENTER OF THE SOLAR SrsTEM It provides the heat and light that make life on Earth possible Yet Earth receives only about half a billionth of the energy that leaves the Sun The Sun is a huge ball of hot gases Like other stars it produces enormous amounts of energy by converting hydrogen to helium deep within its interior PosITION IN SPACE The Sun lies at the center of the solar system It contains more than 99 percent of the sys tem's mass The immense pull of its gravity holds the planets dwarf planets asteroids comets and other bodies in orbit around it The average distance between the Sun and Earth is roughly 93 million miles 150 million kilometers Light travels through space at about 186 282 miles 299 792 kilometers per sec ond so a ray of sunlight takes only about 8 minutes to reach Earth Light from other stars takes much longer to reach Earth light from the next nearest star Proxima Centauri takes more than four years to arrive The Sun is in the outer part of the Milky Way galaxy Light from the center of the galaxy takes many thousands of years to reach Earth II

The Sun, Stars, and Galaxies — page 7 — THE SUN STARS AND GALAXIES An illustration of the solar system with the Sun at its center Shutterstock com 12

The Sun, Stars, and Galaxies — page 8 — THE SUN TuE CENTER OF THE SOLAR SrsTEM Because the Sun is so close to Earth it seems much larger and brighter than other stars It is the only star whose surface details can be observed from Earth BASIC PROPERTIES Stars vary greatly in size and color They range from giant stars which are much larger than the Sun to dwarf stars which can be much smaller than the Sun In color they range from whitish blue stars with very high sur face temperatures more than 30 000 Kelvin or 53 500° F to relatively cool red stars less than 3 500 K or 5 840° F The Kelvin tem perature scale uses degrees of the same size as Celsius or centigrade degrees but it is numbered from absolute zero 273 15° C The Sun is a yellow dwarf star a kind that is common in the Milky Way galaxy It has a surface temperature of about 5 800 K 10 000° F Its diameter is about 864 950 miles 1 392 000 kilometers which is about 109 times the diameter of Earth Its volume is about 1 300 000 times Earth's volume and its mass or quantity of matter is some 333 000 times as great as Earth s mass More than 90 percent of the Sun's atoms are hydrogen Most of the rest are helium 13

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