L2

StarDate: April 7, 2009

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To see the universe in all its glory, it's best to get outside Earth's atmosphere. The air blurs the view of stars and galaxies, and it prevents some types of energy from reaching the surface.

But even getting into space doesn't eliminate all the problems. Earth reflects a lot of sunlight, and it produces a lot of heat. There's also interference from all the gizmos that send out radio signals.

One way to avoid these problems is to shoot a space observatory a million miles away from Earth, in the opposite direction from the Sun. At that spot, a spacecraft can shield itself from the Sun and Earth at the same time. But it stays close enough to Earth to keep in easy contact.

This point in space is known as L2. It's named for European mathematician Joseph-Louis Lagrange, who found that the gravitational pull of two objects creates stable points in space.

Normally, anything that orbits farther from the Sun would quickly fall behind Earth. But anything at L2 is pulled along by the gravity of Earth and Sun, so it stays at the same point in space relative to Earth. L2 isn't completely stable, though, so a spacecraft actually goes into orbit around the L2 point in space.

A NASA spacecraft that studied the afterglow of the Big Bang operated from L2. The replacement for Hubble Space Telescope will head there, too. And so will two European probes that are scheduled for launch this month. We'll talk about one of those probes tomorrow.

Script by Damond Benningfield, Copyright 2009

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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