Page 12 - Curriculum Visions Dynamic Book

The Sun is called a G2V star. G2 means that it is one of the second hottest stars in the (yellow) G class. V tells us that it is a main sequence, or dwarf star, which is
the most common kind of star. Dwarf, however, does not mean that the Sun is itself a small star. In fact,
it is within the top 5% of stars in its neighborhood and in the top 10% of
stars by mass in our galaxy. It is simply not one of the blue giants.
Why the Sun appears so bright
It is difficult to imagine some of the properties of
the Sun. For example, it is a mass of gas so hot that it lights up the sky. It contains no liquid or solid at all.
The temperature at the center of the Sun measures about 15,000,000°C, but it is “only” 6,000°C at the “surface.” Because we only see the surface, we see the Sun at a colour appropriate to 6,000°C—as a yellow-white colour.
The surface we see, and which we might take to be some kind of hot solid, is made entirely of gaseous atoms, mainly hydrogen, which heave around and constantly change shape. Gases also exist in a Sun “atmosphere” beyond the surface.
So, there is nothing special about our Sun. It is a yellow star known as a dwarf star. To us it is immensely bright, but that is simply because we are—at 149,600,000 km—
 The constantly changing surface of the Sun.
The Sun gives evidence of rotation
 At first glance the solar disk is featureless except for sunspots, visible on these images as dark blemishes.
By tracing the apparent path of sunspots across the solar disk from one day to the next, solar astronomers in the early 17th century could demonstrate that the Sun rotates. They could also estimate the length of the solar day at about 27 Earth days. The largest sunspots or sunspot groups are visible to the naked eye.
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