It’s always easier to show someone a picture of something rather than to use 1,000 words to explain it. The people at NASA’s Scientific Visualization Studio (SVS) know this, and they’re experts. Every year they release a simulation of the Moon that shows what the Moon will look like to us each day.
NASA’s Moon simulator uses images and data captured by the Lunar Reconnaissance Orbiter (LRO) to recreate the Moon on each hour of each day of each month in 2018. You can input any date and time to view the Moon (Dial-a-Moon) as it will appear at that time. You can also watch a video of the Moon over the course of the entire year. Along the way, you might learn something.
the geocentric phase, libration, position angle of the axis, and apparent diameter of the Moon. Image: NASA SVS/Ernie Wright.
NASA’s Moon Simulator relies on the Lunar Reconnaissance Orbiter. The LRO has been in orbit around the Moon since June 2009. The LRO has two missions: The first is to map the surface of the Moon and identify possible future landing sites close to in-situ resources. That was called the Exploration Mission, and that was completed in September 2010. After that, the Science Mission began, and is ongoing.
Throughout its time at the Moon, the LRO has relied heavily on two of its instruments. The Lunar Orbiter Laser Altimeter (LOLA) generates a high-resolution 3D map of the Moon’s surface, including slope and roughness. LROC, the Lunar Reconnaissance Orbiter Camera, captures hi-res black and white images of the surface, down to 1 meter resolution. It also captures color and ultraviolet images.
NASA/GSFC/Arizona State University
The result of all the LRO’s work is a detailed map of the surface of the Moon. And rather than hog all that data just for selecting landing sites for future missions to the Moon, NASA has created a simulation of the Moon for all to enjoy. And while enjoying it, you can learn a few things.
The Moon Always Shows Us the Same Face (Sort Of)
Most people know that the Moon is tidally locked to Earth. It doesn’t rotate on its axis, and we always see the same face. That’s why there’s a Pink Floyd album called “The Dark Side of the Moon.” But it’s not absolutely true.
The Moon actually shifts a little up there, showing us a slightly different face over time. It’s called “libration,” and it’s caused by the Moon’s tilt and the shape of its orbit. In the Moon simulator, you can see it wobble. The wobble is the libration.
The Moon isn’t Always the Same Distance From Earth
This may be a little more obvious to us. Nothing is static in space, certainly not the Moon and the Earth. The distance between the two bodies varies by up to 14%. When they’re furthest apart, that’s called the apogee, and when it’s closest, that’s called the perigee. When the internet heats up with talk of a “Super Moon”, that means the Moon is near perigee.
The Moon also rock and rolls a little up there. In the animation, it looks like it’s rolling back and forth on the sub-Earth point. According to NASA, “The roll angle is given by the position angle of the axis, which is the angle of the Moon’s north pole relative to celestial north.”
The Phases of the Moon
It’s the phases of the Moon that stare us right in the face. As the Moon orbits Earth, the angle of the Sun shining on the Moon changes, and a differing amount of its surface is illuminated. The phases of the Moon change according to what’s called a “synodic month,” which is about 29.53 days. That’s about 2.2 days longer than a sidereal month, which is how long it takes the Moon to orbit the Earth. (A sidereal month is about 27.3 days.)
Everything in space is moving, so there really is no single measurement of what a “month” is. It depends on where you’re observing it from. Told you you’d learn something, Einstein!
As the Sun’s angle changes, the phase of the Moon changes. It starts with a waxing, or growing, crescent Moon. You can see it in the West as the Sun sets.
When the Moon reaches first quarter, with a quarter of its surface illuminated, the Moon is higher in the sky at sunset, and sets at around midnight. When full Moon phase arrives, the Moon rises at sunset (everyone’s seen that and it is amazing!) and is high up in the sky at midnight.
The third quarter Moon can be seen in the daylit western sky long after the Sun has come up.
According to the simulation of the Moon, this is what the next Full Moon will look like to us, on January 20th, 2019. (When you look at a Full Moon with a telescope, you almost need sunglasses, it’s so bright.)
If you’ve got a hankering to visualize the Moon on some future date in the upcoming year, check out the Simulation of the Moon. If you have a backyard telescope, or even a pair of binoculars, the simulation can help you plan and understand your observations. Or if it’s way too cloudy to see the real Moon, the simulator can help.
The guy responsible for all this mesmerizing brain candy is Ernie Wright. He’s almost famous for his fantastic work. You can check out his other NASA space visualization work at the NASA SVS page right here.
Here’s one of my favorites, a five-minute 4K tour of the Moon. Enjoy!