Q & A: Temperature of planets and the big bright center of the galaxy.

Q:
How do you measure the temperatures on different planets? Also what is at the "center " of the Milky Way?
- Nathan Krehbiel
Pleasant View Home School, Urbana, IL USA
A:
The easiest way to actually measure the temperature of a planet is, in fact, just look at it! Objects which are hot give off energy in the form of infrared waves. For example, when you hold your hands over a fire to warm them, your hands are feeling the infrared waves. These infrared waves are actually another form of light which are given off different depending on the temperature of the object.
Here is an exmaple of a picture of a man and a match taken with a camera which only sees these infrared waves.

You can tell that the match is hot because it looks very bright as does the man's body. But his tie, glasses, and the backgroud appear blue to show that they are cool.
Astronomers use this same procedure for planets to tell what their temperatures are. They use an infrared telescope to get an image of the planet and compare the colors of the plant to a scale. This also allows astronomers to find the temperatures of galaxy's, stars, and any other body in the universe.

Now, for the center of the galaxy. Like planets in the solar system, every body in the galaxy is currently rotating around a fixed center point. If look at the galaxy as a bigger verious of the solar system, then it would appear that there must be some large mass at the center of the galaxy. Like the sun's gravity pulling the plants into their orbits, this large mass pulls the solar systems in the Milky Way into their own orbits. But the Milky Way is HUGE! It takes light 100,000 years to cross it! So the mass at the center of the galaxy must be incredible. In fact, it is believe that at the center of the galaxy is an object so massive, that nothing, not even light can escape from it. This object is called a black hole. It is believed that at the center of the galaxy is a black hole which has a mass about 1,000,000 or more times that of the sun. These large objects give off huge jets of particles and waves which we can view on earth.

-Scott

(published on 10/22/2007)