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HOW HOT ARE THE STARS?

Stars in the night sky always look cold. They probably are
quite hot, but what do I know? Astronomers use several
techniques to determine the temperatures of stars.

Use a pair of pliers to hold an iron nail, pin, or needle in a flame. Observe and note what happens to the color as it gets hotter. In an analogous way, astronomers compare the colors of stars to colors of heated objects on earth to
estimate temperatures.

The "hottest" stars are a blue-white color; "cooler" stars
are yellow; and the "coolest" stars are red.

Another method suggests you hold a thermometer about 1 foot
away from an unshaded light bulb. Record the temperature
reading after three minutes. Now hold a magnifying glass so that the light focuses on the bulb of the thermometer. After three minutes, record the temperature again.

Repeat the measurement by moving the thermometer greater
distances from the bulb. You will realize that as the distance increases, more sensitive instruments are needed.

Graph the relationship between the distance in inches and
degrees of temperature. In a similar way, astronomers use
the lenses of telescopes and other sensitive instruments to
measure the temperatures of stars.

The following is from the Concise Columbia Encyclopedia:
A star is defined as "A hot incandescent sphere of gas
(usually more than 90% hydrogen) that is held together by its own gravitation and emits light and other forms of electro-magnetic radiation whose ultimate source is nuclear energy. The universe contains billions of galaxies, and each galaxy contains billions of stars, which are frequently bunched together in star clusters of as many as 100,000. The stars visible to the unaided eye are all in our own galaxy, the Milky Way. The visible stars are divided into six classes according to their apparent magnitude. Stars differ widely in mass, size, temperature, age, and luminosity. About 90% of all stars have masses between one tenth and 50 times that of the sun. The most luminous stars (excluding supernovas) are about a million times more powerful than the sun, while the least luminous are only a hundredth as powerful. Variable stars fluctuate in luminosity. Red giants, the largest stars, are hundreds of times greater in size than the sun. At the opposite extreme, white dwarfs are no larger than the earth, and neutron stars are only a few kilometers in radius. The central region, or core, has a temperature of millions of degrees. At this temperature, nuclear energy is released by the fusion of hydrogen to form helium. By the time nuclear energy reaches the surface of the star, it has been largely converted into visible light with a spectrum characteristic of a very hot body. The theory of stellar evolution states that a star must change as it consumes its hydrogen in the nuclear reactions that power it. When all its nuclear fuel is exhausted, the star dies, possibly in a supernova explosion."

Yes, I guess stars are hot. Until I read that, I had no idea that stars were so big. Obviously, they are a long distance away from us. When you look up into the sky at night, they still look cold!

At our house, we like to lie out in the back yard late at
night, looking up at the sky. We have watched satellites
buzz across the sky, we have looked for the dippers, we have watched "shooting stars." Imagine the surprise of this brilliant writer, when driving out in the night to a really dark place to watch the meteor showers in mid-August. Once we were out of the influence of city lights and street lights there were bazillions more stars visible!

We need to find out how far away they are.

 

 
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