Re: What makes some stars brighter than others?

Hello, Andrea,
The stars in the sky have different brightnesses because different kinds of stars give off different amounts of light, and because they are all different distances away from us.

Let's think about that distance reason first. Imagine that you are in a room with many 100-watt light bulbs. They are all the same kind of light bulb, so they all give off the same amount of light. But, the ones that are closer to you would appear to be brighter than the ones that are farther away. Go ahead and try this. Find a light bulb that is turned on and walk up real close to it and then walk very far away from it. You should notice that the bulb is very bright close up and not so bright farther away. It's the same for stars. Stars of the same kind that are closer will be brighter than those farther away.

Now, stars are not all alike. Some stars are bigger and hotter than others. The bigger and hotter the star, the more light it gives off. Imagine two different kinds of light bulbs, a 60-watt bulb and a 100-watt bulb. If they are both at the same distance from you then the 100-watt bulb will look brighter than the 60-watt bulb. So, if there are two stars that have the same distance from us, but one is bigger and hotter than the other, it will appear brighter.

When you look at stars at night, it is impossible to know if one star is brighter than another because it is bigger and hotter, or because it is closer to us. To know this we need to know the distance to the stars or know what kind of stars they are. We can learn that information using special instruments on telescopes.

I hope that helps answer your question.

I hope your interest in astronomy continues,
Bryan Méndez, UC Berkeley Space Science Lab