Monday, August 11, 2008

Around and around and around it goes...

Hubble celebrates 100000 orbits

This morning, at 7:42am EDT, the Hubble Space Telescope reached a new milestone by completing it's one hundred thousandth (100,000) orbit around the Earth.

The Hubble orbits the Earth in what is known as a "low-Earth orbit," or "only" 600 kilometers (375 miles) above Earth's surface. While this sounds very high, it's not, in space terms. The space station and space shuttle also orbit this low. In low-Earth orbit, it takes a satellite about 90 minutes to orbit the Earth. But at these altitudes, the Earth's atmosphere is still present (although very, very tenuous), and if you don't put a booster rocket on your spacecraft, it will fall back to Earth in just a few years or decades.

In order to stay in orbit, the Hubble has to move at a speed of about 7.5 kilometers per second, or almost 17,000 miles per hour. When the space shuttle goes to repair Hubble, it is also moving this fast. How can the astronauts safely catch the Hubble? It's all relative speed. Although both spaceships are moving at 17,000 miles per hour, compared to one another, they are moving only a few miles per hour (more when the shuttle is moving in to catch it, and much less when the shuttle sticks out its arm to grab Hubble). It's like passing a car going slightly slower than you on the road. Although you are both moving at 65 miles per hour, you can take several minutes to pass each other. Plenty of time to see what their kids are watching on the DVD, get a good look at the driver, and perhaps even try to pass some Grey Poupon.

In the 18 1/3 years it took Hubble to go around the Earth 100,000 times, it covered a distance of 2.7 billion miles. That sounds like a lot, especially if you are moving at 17,000 miles per hour! But, in space, 2.7 billion miles is only about the distance from the Earth to Neptune, and only 1/10000th the distance to the nearest star. We have four space probes (Pioneer 10 and 11, and Voyagers 1 and 2) that have travelled much further. And many other satellites around the Earth have been longer-lived, and have logged many more miles than Hubble.

Basically, Hubble hasn't set any records. It's just reached a nice, round number that is kinda fun to celebrate. So, in that line of celebration, NASA has released some colorful new pictures of a star-forming region in the Large Magellanic Cloud (LMC), one of the Milky Way's own satellite galaxies. And the LMC has only completed one or two orbits around the Milky Way in the 13 billion years its been around. So, our Hubble has an entire galaxy beat! (Of course, instead of an altitude of 600 kilometers, the LMC is at a distance of about 160,000 light-years, and it is travelling about 40 times faster than Hubble).

Also, NASA has a contest where you can win a nice print of a picture from the Hubble; look on the Hubble's home page for that contest (which ends after this week).

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