Moon Gets In The Way Of A Perfectly Good Pic Of Earth
NASA revealed recently my favorite picture in recent memory……a wonderful snapshot of the earth being partly eclipsed by the moon from a million miles away.
The image was captured as part of the test images of NASA’s Deep Space Climate Observatory (DSCOVR) satellite. In its lofty orbit, it will primarily be observing the Sun’s solar wind. Accurate and timely solar wind data is critical for warning us of imminent space weather events like geomagnetic storms that could have terrible effects on our power grids, telecommunications, aviation, GPS etc. Being so far away and closer to the sun could give us 15 minutes to an hour heads up before we’re hit with something nasty from the sun like a coronal mass ejection. Unless it’s weird and traveling close to the speed of light, then we’re screwed.
You may be wondering what the hell kind of satellite is a million miles away from the earth. The location of DSCOVR is a very special one. It’s called a Lagrangian point. These are points in space where the motion of objects is impacted by the mutual gravity of earth and the sun such that they can maintain stable or meta-stable positions relative to the earth and sun. These are called station-keeping orbits.
There are five L points in the earth/sun system. DSCOVR is at the L1 position, a million miles away between us and the sun. Orbital mechanics demands that objects orbiting closer to the sun do so more quickly than farther away objects. Mercury then has a much shorter year than we do. Mars has a longer one. If you’re at L1 though, the gravitational pull of the earth lessens the apparent pull of the sun causing you to orbit more slowly. So slow in fact that you orbit at the same speed as the earth and so you’ll always appear to be in the same place in the sky.
There’s 4 more Lagrangian points. It’s almost 3am and I’m too tired to write about all them. Check out the link below if you’re less lazy than I am.
Image Credits: (NASA/NOAA)