Star Points for July 2010 by Curtis Roelle Our Hot Summer Sun Summer has hit the ground running with its hot sticky days. So, the last thing you might want to think about is that blazing sun up in the sky. But the sun is a marvelous life-giving machine. Pour something cold to drink while we have a discussion about our closest star. Our sun is an oblate gas sphere with an equatorial diameter of 865,000 miles. Oblate means farther around the middle than around the top and bottom. In comparison, the diameter is 3.6 times the earth-moon distance of 240,000 miles. And it would take about 340 earths side-by-side to make a belt around the sun. The sun's distance away from us is 93 million miles, or nearly 400 times farther than the moon. Inside, the sun has the volume of 1.3 million earths. However, due to its lower density, the sun's mass is only 333 thousand earths. As far as mass, the sun contains 99% of the mass in our entire solar system of planets, moons, asteroids, comets, and dust. These numbers are truly astronomical. Not only is the sun big, it is bright and hot. The surface we see is called the photosphere, radiating at a temperature of 11,000 degrees Fahrenheit. Farther beneath its surface, the temperature and pressure both increase. At its core, the sun is said to be around 27 million degrees Fahrenheit. It is in this core where the sun's energy is created through a process known as fusion. The pull of the sun's gravity crushes several hydrogen atoms together, fusing them in a several-step process, to form helium and excess energy. Because of the high density at the sun's core, energy will travel only a tiny distance before being absorbed and re-emitted over and over again by other gas molecules. Convection forces eventually carry the energy to the surface, where it is released as light and heat. The journey from core to surface is said to take a million years. Each second the sun converts 700 million tons of hydrogen into helium. Also, each second several million tons of energy is released. The conversion of matter into energy means that the sun is gradually losing weight. Above the photosphere is a layer known as the chromosphere because of its ruby red color. We don't see it except during total solar eclipses or using special hydrogen-alpha telescope filters. These filters show features such as prominences and flares rising from the sunspot regions. The sunspots themselves are depressions in the photosphere beneath the chromosphere. These spots are visible through telescopes equipped with approved, safe, white-light filters. Care must be taken when selecting or building a solar filter for a telescope. It would be best to consult reliable sources such as Sky & Telescope magazine or a local telescope store such as Hands On Optics in Damascus. A local astronomy club such as the Westminster Astronomical Society can also offer advice on choosing optical filters for many different astronomical targets. Extending above the sun and beyond the chromosphere is a tenuous gaseous region known as the corona. Here the temperature spikes to more than three million degrees Fahrenheit. However, its low density means that the heat is not as bad as it sounds. The corona streams outward from the sun and its beautiful pearly streamers are a favorite target of eclipse photographers. The sun is an interesting object for observing. But great care is needed because carelessness or improperly filtered telescopes can lead to damaged vision. A million years after its creation, the light energy leaving the sun takes only about eight minutes to speed through space and reach your body. You use sunscreen to protect your skin. Even more care should be taken of your precious vision.