Space Facts

Facts About the Sun

Center of the Solar System

Our sun, Sol, with detailed closeup. Hydrogen alpha photo courtesy www.SunGazer.net, taken October 27, 2005 1600UT, Rockville, MD, USA. Click on the image for a full-size view of the original solar portrait.

Like campers around a fireplace, the planets of the Solar system huddle around our sun. The light in our daytime skies is an ordinary star — one of hundreds of billions in the Milky Way galaxy. It is a single parent to 8 full-size planets, perhaps dozens of dwarf planets, and millions of smaller bodies.

Of course, we think it is special because it is our sun. Its formal name is "Sol." From this, we get the word "solar," as in "our Solar system." It is roughly 4.5 billion years old (4.5 × 10⁹). It is a bright, yellowish star still in its "main sequence," and thus has been given the spectral class G2V.

In recent years, we have found that Sol is even more ordinary because other stars have planets, too. Oh yes, but do they have life? Some day soon we may find out.

Our sun has an absolute magnitude of 4.83. It stands approximately 24,800 light years (~7,600 parsecs) from the Milky Way center, and takes roughly 230 million years to orbit the galactic hub. It has a diameter of about 864,000 miles (1,390,000 kilometers or 10⁹ × Earth). In about 5 billion years, our sun will leave the main sequence and enter its old age, first as a sub-giant, and later as a red giant — swelling in size until its surface extends beyond the Earth's current orbit.

Like all main sequence stars, our sun is gradually getting brighter with age. One estimate places the rate of brightening at roughly 10% per billion years. Professor James Kasting, at Pennsylvania State University, calculates that Earth's oceans will disappear in about a billion years' time, long before Sol's old age sets in. But we won't need to be looking for a new home any time soon. A billion years is a long time.

Another factor that might affect the useful life of our Solar system has to do with our Milky Way galaxy. Mark Reid of the Harvard-Smithsonian Center for Astrophysics performed a study that seems to show that our galaxy is larger and more massive than previously thought — now a virtual twin to the nearby Andromeda galaxy. He reported his findings at the January 5, 2009 meeting of the American Astronomical Society's convention in Long Beach, California. One side-effect of this, if the study proves to be correct, is that our galaxy and Andromeda will crash into each other a lot sooner than expected and with a lot more than a glancing blow. Such a "collision" could disrupt billions of star systems. And this might occur in 2-3 billion years. There's a good possibility that the Solar system won't easily enter old age.

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