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Sun

The sun - it's a star, but it seems brighter than other stars in the sky because it's much nearer.

Ideas such as "near" and "far" in astronomy are relative, as the sun is 93 million miles from the earth, which might not sound near, but that's only 8 light-minutes, whereas the next nearest stars are many light-years away.

The sun is much bigger than the earth. The earth is about 8 thousand miles across, but the sun is more like 800 thousand miles across. To see a comparison of the size of the sun with that of an earth-sized planet, see Xyroth's transit of venus photos.

It's a globe of boiling liquid/gas, heavier than water. The actual mass (weight) of the sun is 2x10³⁰ Kg (exponential notation), or in old money that's 2000000000000000000000000000000 kilograms. It's kept together by its own gravity.

The power of the sun is 3.9x10²⁶ watts, or 390000000000000000000000000 watts, or 390 yottawatts. The power, in light and heat, comes from fusion where hydrogen is turned into helium. It's burning away by e=mc² at four million tons per second, but this is no cause for alarm as there is plenty of sun remaining and it's not going to run out soon. It's estimated that there is enough sun to last for thousands of millions of years.

The sun has an "apparent magnitude" of about minus 26. I wonder if I should explain apparent magnitudes.

The earth goes around the sun. Galileo was right, and the Church was wrong.

Curiously, if you divide the mass of the sun by the power of the sun, you can get an idea of the power-to-weight ratio of the sun. It turns out that for every watt of output there is about five tons of sun! That seems initially a very odd idea, as you might suppose that even a tiny amount of sun, if teleported to the earth, would explode as a huge amount of energy. But on the sun, every watt of output is represented by five tons of fuel. Like a scaled-up five ton candle with a tiny wick on the top. How can this be? The answer is to be seen in the fact that it's very large, so in effect most of it is inside, in the middle, rather than being on the surface.

Cups of tea which are bigger than normal don't go cold as fast as normal cups of tea. A gallon cup of tea is twice as wide as a pint of tea, has eight times as much tea (volume) as a pint, but has only four times as much surface area. (see surface area and volume explanation). Therefore it cools down twice as slowly. Extending this to an extreme example of starshine coming off the sun, it has insulation provided by geometry which is like a super-Thermos Flask!

Another thing about the sun is that it can be thought about as a giant planet with liquid oceans of fire. The sun rotates on its axis and takes about 30 days to complete one revolution, but it doesn't all rotate at the same rate, because it's fluid. Also, whereas the Earth rotates once per day and has its magnetic poles flip once every few tens of thousands of years, the sun has its poles flip every eleven years or thereabouts (coinciding with solar maximum of sunspot activity). See http://science.nasa.gov/headlines/y2001/ast15feb_1.htm . Also, now that there's a new spacecraft getting spectacular improved movies and photos of the sun, it's worth looking at this: http://science.nasa.gov/science-news/science-at-nasa/2010/21apr_firstlight/

The sun is fairly typical of a star, and there are a great many of these. Stars tend to have planets around them. Some planets have life on them. Planets tend to have advanced life on them if they are the right sort of distance from the source of heat, and are there for long enough. There is no reason to assume the sun is unique in any way.

Despite recent successes with manned landings on the moon, there are no current plans for manned landings on the surface of the sun as there are technical difficulties.

Other stuff: Very basic astronomy , Orbits explained , the Speed of Light , Weather , Venus , Lighting , Optics , and Earth / Moon / Sun orbits (which goes around which), etc.