The Sun: Our Star Chaisson & McMillan, Ch. 16

• The Sun is a hot ball of self-luminous gas. It has neither a solid surface nor a solid interior and yet it appears to have an edge. Why?

• The Sun is a G2 V (Main Sequence) star. The Sun is a little above average in mass for a star in our Galaxy (the average stellar mass is 30 % of the mass of the Sun), but overall, it is a fairly typical star.

• It resides in the large grouping of stars referred to as the Milky Way (optical, DIRBE). The Milky Way is a spiral galaxy (e.g., M101, M104) composed of ~ 100 billion stars. The Sun lives in one of its spiral arms of the Milky Way, roughly 2/3 of the way out from the center of the galaxy, whizzing around the center of the galaxy at a speed of around 200 kilometers per second.

For the next few lectures, we will consider the Sun in detail. We will look at the following three topics:

I. The Structure of the Sun II. The Quiet vs. the Active Sun