Phases of the Moon
Since I entered the hobby in the summer of 2014, full-disk lunar observing and imaging has remained a simple yet enduringly pleasing activity for me. No matter how bad the light pollution is, Luna never fails to shine brightly in the sky. In spite of one side tidally locked into place from our perspective here on Earth, the Moon wobbles slightly as a result of lunar libration. As a result, it offers subtly different things to see each time it makes its regular monthly appearance.
For years, I used eyepiece projection to capture images of the Moon. The technique is simple: bring the telescope to focus, aim a cell phone or point-and-shoot camera into the eyepiece, and snap a photo. Although holding the imaging device by hand can yield surprisingly good images, eliminating camera movement during exposure is best. Placing the camera on some kind of brace and using the self-timer to fire the shutter yields the sharpest results.
After using eyepiece projection for years, I am just starting to get more serious about imaging the Moon. With my Canon EOS M200 mirrorless camera attached to my 3.5-inch Standard Questar, I have been able to step up my game significantly. Although running the Questar’s motorized drive keeps the Moon in the field of view, I am continuously surprised to see what is possible by taking photos even at a relatively slow exposure speed with the scope’s tracking motor turned off.
Having built a collection of lunar images, I used data from the JPL HORIZONS data and ephemeris computation service to determine what percent of the Moon’s disk was illuminated when I took each photo. I was then able to sort my collection by that figure and pick out the best images.
Between New Moon and 25% Illumination
I have been finding that imaging the Moon when it simply appears as a thin crescent in the early evening sky is surprisingly difficult for a number of reasons. Trying to capture earthshine—the glow of the unilluminated side of the Moon from reflected sunlight off the Earth—is impossible without overexposing the illuminated areas of the Moon’s surface. Images often lack contrast. Poor seeing at low altitudes cause the Moon to appear as a boiling mess. And so on.
Between 25% Illumination and First Quarter
As the Moon’s illumination increases, it gets easier to image. But finding a good exposure time is still somewhat of a challenge. Still, a wealth of detail around the terminator appears more obviously.
Between First Quarter and 80% Illumination
This is my favorite time to observe and image the Moon. Satisfying detail along the terminator becomes visible and indeed quite obvious, but the Moon is not overwhelming bright, and the camera does not struggle with finding a good exposure. Ray systems become visible. And the Moon crosses the meridian at a convenient hour, enabling me to do some meaningful imaging and observing without having to deal with poor seeing.
Between 80% Illumination and Full Moon
As it approaches its full phase, the Moon starts to get quite bright. Surface features like craters are much less apparent with only minimal detail showing. But my camera seems to be able to settle on an exposure time without a problem, and it does a good job with capturing the ray systems that emanate most conspicuously from Tycho and Copernicus craters.
The Waning Moon
After Full Moon, the challenge becomes one of convenience: observing the Moon at a decent hour. One has to wake up very early before dawn or stay up late at night to allow the Moon to gain altitude.
