Saturday, October 23, 2010

Sky Lights Tutorial

Hey Space Placers!

I apologize if this is seemingly too basic, but a number of students and the public were not aware of the following.

When we look up at the night sky we see two basic type of objects - stars and solar system objects. The stars we see, just like the Sun, are visible because they are producing light and energy by the process of nuclear fusion. Nuclear fission, which is what powers our reactors and nuclear bombs, makes energy by breaking apart atoms. In nuclear fusion, the temperature and pressure at the core of a star is significant enough to fuse hyrogen atoms (and others) together and thereby make new elements plus energy.

All of the solar system objects except for meteors, are visible because they are reflecting sunlight off of their surfaces. Regarding meteors, we do not see the actual meteoroid body but rather the ionized trail in the atmosphere caused by the tremendous heat of entering the Earth's atmopshere.

The planets, their moons as well as ours, comets, and asteroids are all reflecting sunlight off of their surfaces. The measurement of their reflectivity is called albedo and the higher the number the brighter the reflected light.

Now when we see the Full Moon as we did last night, the Sun, Earth and Moon are aligned in a straight line. If the Earth passes in front of the Sun, we get an eclipse of the Moon.

When we look at the Moon it is reflecting sunlight even though we cannot see the Sun. So is brilliant Jupiter in the east at sunset. Because light travels at 186,000 miles per second, it takes about about 8 minutes for sunlight to illuminate the Earth and Moon having travelled roughly 93,000,000 miles. It takes another 1.25 seconds for the light from the Moon to travel to us - roughly 225,000 miles. Jupiter is is about 40+ light minutes away.

In case you are wondering, the stars (other than the Sun) are light years away - the closest is Proxima Centauri at 4.2 light years, or over 24 trillion miles distant. The most distant stars we can see with our unaided eyes are thousands of light years distant - they have to be very large and bright stars for us to see them. The farthest object we can see with our unaided eyes is the Andromeda Galaxy - visible in our night skies right now and about 2.5 million light years distant.

So all light we see in the sky is from the past. Whether it is the Sun, the Moon, or Andromeda Galaxy, we are looking into the past.

Take a trip into the past tonight.

Sky Guy in VA

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