Believe it or not, the Sun is just a star, just like those we see twinkling at night. The Sun, however, is so much closer to us on Earth that it looks much bigger, much brighter, and we can even feel heat coming from it.
Scientists know great deal about the stars that shine at night. Compared to these other stars, the Sun is actually quite average. Many of the stars that appear so small in the night sky are actually much bigger than our Sun. Others, however, are quite tiny in comparison. Some are much hotter, and some are so cool and dim we can barely see them. But for us on Earth, the Sun is just right!
The Sun is made of hot gases, containing many of the same materials we find here on the Earth. These materials, called elements, include hydrogen, helium, calcium, sodium, magnesium, and iron. You can find all of these on any periodic table of elements.
The Sun is HUGE! Even though it looks small in the sky it is actually bigger than you might imagine. It only looks small because it is 93 million miles away. (That's about 150 million km.) The Earth is very tiny compared to the Sun. In fact, if you think of the Sun as a basketball, the Earth would only be the size of the head of a pin - a mere speck.
The Earth is about 13 thousand kilometers (8000 miles) wide, whereas the Sun is roughly 1.4 million kilometers (900,000 miles) across. This means it would take more than 100 Earths to span the width of the Sun! If the Sun were a hollow ball, you could fit about one million Earths inside of it!
The Sun is very FAR from Earth. In fact, it is 93 million miles away. (That's about 150 million km.) If the Sun were the size of a basketball, and Earth the size of the head of a pin, the basketball and the pin would be separated by about 100 feet - a third of a football field (30.5 meters). If you were standing at the basketball (and didn't have a telescope to help you), you wouldn't even be able to see the pinhead Earth.
Another way to understand the distance is to think of driving to the Sun in a car. If you actually could do this, and drove really fast, say 60 miles an hour (80 km/hr), it would take you 176 years to get there! Light from the Sun takes about 8 minutes to reach the Earth. If you understand how fast light travels, you can recognize that the Sun must be very far away.
Although we cannot actually weigh the Sun with a scale, we can compute its weight by studying the way it affects other objects, like the Earth. We do know that it contains virtually all the mass in our solar system! We can also understand this better by making some comparisons. Since the Sun is so much more massive than the Earth (over 300,000 times heavier) its gravitational pull is also much larger. A child that weighs 75 pounds on Earth would weigh about a ton on the Sun. The weight increases by a factor of 30. (Of course, we cannot really stand on the Sun, for it is too hot and has no solid surface.)
The Sun is about 4 1/2 billion years old. Humans have only been around for a tiny, tiny fraction of this time. As a comparison, if you think of 4.5 billion years as the length of a 12 inch ruler, then the time humans have existed wouldn't even be the width of the lines marking the inches. (Metric equivalent is 30.5cm and it would still be just the width of the markings.)
The Sun will remain more or less the way it is now for about another 5 billion years. After that, it will exhaust the hydrogen it currently "burns" and will enter a new phase of existence. During this phase the Sun will begin "burning" helium and will expand to about 100 times its current size and become what is called a red giant. Once it runs out of helium it will collapse into a much smaller object called a white dwarf.
The Sun is extremely HOT! The middle of the Sun is at least 10 million degrees. The "surface" of the Sun (what we see) is only 5800 degrees. This is cool for the Sun, but is actually about 16 times hotter than boiling water (ouch!). The outer atmosphere of the Sun (which we don't really see with our eyes) gets extremely hot again, about 1.5 to 2 million degrees. These huge temperature changes are very interesting to scientists.