Phases of the Moon
Gregory Gross

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.

Imaging the Moon on April 14, 2014
Imaging the Moon with a Standard Questar on April 14, 2021.

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.

Waxing crescent Moon, 4% illumination
Waxing crescent, 4% illumination, May 13, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/3 second exposure at ISO 6400.
Waxing crescent Moon, 7% illumination
Waxing crescent, 7% illumination, April 14, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/6 second exposure at ISO 400.
Waxing crescent Moon, 13% illumination
Waxing crescent, 13% illumination, April 15, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/30 second exposure at ISO 1600.
Waxing crescent Moon, 20% illumination
Waxing crescent, 20% illumination, April 16, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/30 second exposure at ISO 1600.
Waxing crescent Moon, 24% illumination
Waxing crescent, 24% illumination, July 14, 2021. Canon EOS M200 on 102mm Orion Maksutov-Cassegrain telescope, 1/20 second exposure at ISO 400.

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.

Waxing crescent Moon, 28% illumination
Waxing crescent, 28% illumination, April 17, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/8 second exposure at ISO 200.
Waxing crescent Moon, 31% illumination
Waxing crescent, 31% illumination, May 17, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/8 second exposure at ISO 200.
Waxing crescent Moon, 34% illumination
Waxing crescent, 34% illumination, July 15, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/8 second exposure at ISO 200.
Waxing crescent Moon, 37% illumination
Waxing crescent, 37% illumination, April 18, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/3 second exposure at ISO 100.
Waxing crescent Moon, 45% illumination
Waxing crescent, 45% illumination, July 16, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/10 second exposure at ISO 200.

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.

Waxing gibbous Moon, 51% illumination
Waxing gibbous, 51% illumination, January 20, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/10 second exposure at ISO 200.
Waxing gibbous Moon, 59% illumination
Waxing gibbous, 59% illumination, June 18, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/8 second exposure at ISO 100.
Waxing gibbous Moon, 67% illumination
Waxing gibbous, 67% illumination, April 21, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/8 second exposure at ISO 100.
Waxing gibbous Moon, 73% illumination
Waxing gibbous, 73% illumination, March 23, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/10 second exposure at ISO 100.
Waxing gibbous Moon, 77% illumination
Waxing gibbous, 77% illumination, April 22, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/13 second exposure at ISO 100.

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 with a problem, and it does a good job with capturing the ray systems that emanate most conspicuously from Tycho and Copernicus craters.

Waxing gibbous Moon, 82% illumination
Waxing gibbous, 82% illumination, May 22, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/13 second exposure at ISO 100.
Waxing gibbous Moon, 90% illumination
Waxing gibbous, 90% illumination, May 23, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/20 second exposure at ISO 100.
Waxing gibbous Moon, 93% illumination
Waxing gibbous, 93% illumination, July 21, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/15 second exposure at ISO 100.
Waxing gibbous Moon, 95% illumination
Waxing gibbous, 95% illumination, March 27, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/20 second exposure at ISO 100.
Waxing gibbous Moon, 99% illumination
Waxing gibbous, 99% illumination, May 26, 2021 (image taken minutes before the beginning of a total lunar eclipse). Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/25 second exposure at ISO 100.

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.

Waning gibbous Moon, 91% illumination
Waning gibbous, 91% illumination, January 1, 2021. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/50 second exposure at ISO 400.
Waning gibbous Moon, 83% illumination
Waning gibbous, 83% illumination, November 4, 2020. Canon EOS M200 on 89mm Questar Maksutov-Cassegrain telescope, 1/80 second exposure at ISO 1250.
Waning gibbous Moon, 79% illumination
Waning gibbous, 79% illumination, August 26, 2021. Canon EOS M200 on 102mm Orion Maksutov-Cassegrain telescope, 1/25 second exposure at ISO 100.