Alan Johnson, age 12, of Louisville, Kentucky, for his question:

How hot is a star?

All of them are seething nuclear furnaces. But as stars go, some are hot, others are cool and many like our sun have medium temperatures. Young stars tend to be coolish and old timers tend to be fiery hot. However, some stars burn faster than other, using their hydrogen fuel at a great rate. These extravagant ones may be very hot, even as young adults. Naturally, their starry life expectancy is rather short. Sooner or later, every star consumes all its hydrogen fuel. Then its nuclear furnace subsides, grows cold and finally dies.

The hottest stars have surface temperatures of 50,000 degrees centigrade    and even higher. Even a medium star such as our sun has a surface temperature of 6,000 degrees centigrade. The coolest stars are around 2,000 degrees centigrade. We can duplicate their temperatures in non nuclear furnaces here on earth. Astronomers take a star's temperature by estimating its magnitude, or brilliance, and by the color index revealed in the spectrum of its blazing gases. Young red giant stars tend to be too1lsh. Ancient white dwarfs tend to be super hot.