Try Answering This

1. At a temperature of 37 C (98.6 F), your body radiates mostly at infrared wavelengths. Imagine that you visit a strange planet where the creatures' body temperature is so cold that they radiate mostly at radio wavelengths. Their sun, however, is just like ours. Would you be able to see them? Why? hint: You radiate at infrared wavelengths that our eyes are not sensitive to, yet you can see your friends. Why?

   Answer: Well, people here on Earth radiate mostly in the infrared but our eyes do not see infrared light, yet we see our friends with no trouble--thanks to the Sun. Sunlight reflects off things. That's how we see people, mountains and cars. On the strange planet, as long as your eyes were sensitive to visible light and the strange planet's Sun radiated visible light, you'd see the creatures, no problem.

2. The clothes you are wearing today probably have lots of colors: red, green, blue. Does that mean that that they have different temperatures? For example, if you're wearing a red sweater does that mean it has a different temperature than your green socks? Does your red sweater put out red light like a red star does?

   Answer: There's a difference between reflected light (sunlight reflecting off your clothes) and light that a body radiates because of its temperature. You see a red sweater as red because the sweater reflects red wavelengths better than yellow, orange or blue wavelengths. But if the sweater is at body temperature (like when you wear it!) then it radiates its own light mostly in the infrared.

3. Most people would say that stars are very hot. However all stars do not have the same temperature. Some stars are much hotter than others. Scientists use color as one way to tell the temperature of a star. Why is it that our Sun sometimes appears to be different colors (yellow, red, and orange)? Does this mean that it changes its temperature?

   Answer: No, the Sun does not change its temperature from sunrise to sunset! The changing color of the Sun is due to a change in the thickness of the atmosphere that the sunlight travels through. At noon, the Sun is right overhead and the sunlight goes through the least amount of atmosphere to reach us on the ground. At sunset, the sunlight travels through the greatest amount of atmosphere. The more atmosphere the light travels through, the more dust particles there are. Dust particles absorb short wavelengths of light (the blue end of the spectrum) and scatter them out of our line of sight. The redder wavelengths pass through unhindered by the dust. Since blue wavelengths are being removed due to scattering, the Sun appears red to us!