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Astronomy 101 - Solar System - Sun

Lesson 8: Visiting Close to Home


Image of our sun, Sol.

Image of our sun, Sol.

What is a solar system?

It consists of a star, orbited by planets or smaller rocky bodies. The gravitational pull of the star holds the system together. Our solar system consists of our sun, which is a star called Sol, nine planets including the one we live on, Earth, along with the satellites of those planets, a number of asteroids, comets, and other smaller objects. For this lesson, we'll concentrate on our star, the Sun.


While some stars in our galaxy are nearly as old as the universe, about 15 billion years, our sun is a second-generation star. It is only 4.6 billion years old. Some of its material came from former stars.

Stars are designated by a letter and a number combination roughly according to their surface temperature. The classes from hottest to coolest are: W, O, B, A, F, G, K, M, R, N, and S. The number is a subcategory of each designation. Our Sun is designated as a G2 star. Astronomers describe Sol as a very ordinary star. It acts just as would be expected from a star of similar size.

Star masses typically range from 0.3 to 3.0 times the mass of the Sun with most stars having masses similar to that of the Sun.

Our solar system is part of a larger system known as a galaxy. The name of our galaxy is the Milky Way. The Milky Way contains about 100 million stars, all revolving around a point known as the galactic center. We are located in the outer part of the galaxy, approximately 1.6 × 1017 miles from the Galactic center. At our current orbital speed of 140 miles/second, our solar system takes about 250 million years for one orbit around the Galactic center.

Since its creation, our star has used up about half of the hydrogen in its core. Over the next 5 billion years or so, it will grow steadily brighter as more helium accumulates in its core. As the supply of hydrogen dwindles, the Sun's core must keep producing enough pressure to keep the Sun from collapsing in on itself. The only way it can do this is to increase its temperature. Eventually it will run out of hydrogen fuel. At that point, it will go through a radical change which will most likely result in the complete destruction of the planet Earth.

The sun should never be viewed directly, either with or without a magnifying device. Permanent damage can be caused in a fraction of a second unless proper precautions are taken. There are filters which can be utilized with many telescopes. (SUNGLASSES ARE NOT ADEQUATE!) Consult someone with a lot of experience before attempting Solar viewing.

Sun Statistics:

  • diameter: 1,390,000 km.
  • mass: 1.989e30 kg
  • temperature: 5800 K (surface) 15,600,000 K (core)
A very interesting phenomenon associated with the Sun is called an eclipse. It happens when our own moon passes between the Earth and the Sun, blocking out all or part of the sun from view. Even though a portion of the sun is blocked, it is even more dangerous to view the sun during an eclipse than during a normal day.

In our next lesson, we'll take a closer look at the Inner Solar System.


Read more about Star Color Classification, The Milky Way, and Eclipses. Don't forget the discussion Forum.

Ninth Lesson > Visiting Close to Home: The Inner Solar System > Lesson 9, 10

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