Sometimes it’s cloudy for so long you’re surprised at the change in the moon’s phase since it was last clear. Thanks to almanacs and apps we can always know and see the moon’s phase. I suppose that will have to do for now, since clouds stubbornly remain in the forecast.
Tonight the moon will be a near perfect “half” as it enters first quarter phase. You may also notice that the moon is much higher in the sky than a few months back at this phase. That’s because the angle of its path up from the western horizon in December and January is much steeper – it gets high in a hurry. Higher altitude also makes this 2,160 mile wide ball of rock all that more inviting for observation.
Did you get a new telescope for Christmas? Yes? The first thing you should point it at is the moon. The next few nights are the best for seeing hundreds of craters and craggy peaks along the terminator, the boundary marking the line of advancing lunar sunrise. Here the sun is low and shadows long, and even low magnification will reveal a stunning amount of detail. Crater forms and mountain ranges are even visible in 7x binoculars.
The moon is the apple of NASA’s eye this weekend as the twin Gravity Recovery And Interior Laboratory (GRAIL) spacecraft make their way to lunar orbit. GRAIL-A should enter orbit sometime today with GRAIL-B following on New Year’s Day at 4:05 p.m. CST. Once at the moon, each of the twin probes’ orbits will be refined until they’re nearly circular and only 34 miles high. You could never get away with a 34 mile-high-orbit around Earth; the satellites would quickly burn up in our atmosphere. On the airless moon, it’s possible to come down very close to the surface. And the closer you get, the more detailed the measurements and photographs you can make.
The purpose of the mission is to map the moon’s gravity field to determine what’s going on beneath the moon’s crust. When the science phase begins in March 2012, the spacecraft will transmit radio signals to each other precisely defining the distance between them as they orbit in formation. Subtle variations in the pull of gravity over different areas of the lunar globe will change the distance between the GRAIL probes. Measuring those changes will help scientists create a map of the moon’s interior.
One of the biggest questions NASA hopes to answer is why the lunar farside crust is thicker and the surface more saturated with craters than the nearside. The mission also has a fun participatory side. GRAIL will carry four “MoonKAMS“, which middle school students can use in collaboration with their teachers to take pictures of the moon. Students choose a specific location on the moon’s surface and request the GRAIL satellites to snap a photo of it. They sure didn’t have stuff like this when I was in junior high.
MoonKAMS stands for ‘Moon Knowledge Acquired by Middle school students’. The project is being led by Sally Ride, America’s first female astronaut. Ride joined NASA in 1978 and flew aboard the space shuttle Challenger in June 1983 on the shuttle program’s 7th mission. She was also the first woman to use the robotic arm in space to retrieve a satellite.
Some 2,100 schools have already signed up but there’s room for more. Teachers can click HERE to register to participate. And yes, it’s free. More information HERE. Tomorrow I’ll have an update on GRAIL’s progress. Meanwhile, as you gaze at tonight’s first quarter moon, consider the excitement of this next mission to “see” into its dark innards.