By Dr. Marc Rayman
Asked by young visitors to the Storer Planetarium in Prince Frederick, Maryland.
This is a good question. After all, the Sun is obviously the brightest light in the sky, but is it bright enough to light up all the distant stars? Well, the Sun actually is a star and it really is pretty much an average one, just one of about 200 billion stars in the Milky Way galaxy. But it is a special star for those of you who live on Earth, because you are so close to it that it appears extremely bright. All the other stars are so far away that they can only show up at night, when the sky is so dark that we can see their faint light as it reaches us after crossing unimaginable distances.
If you and some friends were outside at night with flashlights and were far away from each other, the light that would look the brightest to you would be your own, because it's so close to you. Suppose you held your own flashlight one foot away from your eyes; it certainly would look extremely bright. If you pretended that were the Sun, for another flashlight to be far enough away to represent the distance to the star nearest to the Sun, that flashlight would have to be about 50 miles from you, or in another city. That distant flashlight would appear faint only because of its great distance. Now when you think about it, perhaps it's amazing that you can see stars at all, they're so far away.
If you were lucky enough to travel to any another star, the Sun would look like just one of the many magnificent pinpoints of light in the sky, making it hard to imagine that it's the brilliant Sun that Earthlings depend upon.
Although the Sun doesn't light up the other stars, it does provide the daylight here on Earth; and the moon and planets we see are illuminated by that same sunlight.
All stars produce light (and other kinds of energy) through nuclear reactions, using the energy stored in the tiny nucleus at the center of atoms. These reactions make the star so hot that it glows—it's like an enormous ball of fire, giving out light and heat. Now maybe you have noticed that the color of hot objects depends upon their temperatures. Heating elements in the stove in your kitchen may get red hot, and flames that are hotter still may be yellow or even white hot. Stars are the same way. If you go outside on a crisp cold night this month to enjoy the beautiful views of the stars, look carefully and you'll see that they are different colors, like an assortment of the universe's treasures displayed proudly in the elegant blackness of space. When you come back inside, warm up with a nice drink and cookies the colors of stars.