Partial Eclipse, Partial Results

November’s astronomical events led me to plan for a week-long marathon astrophotography session. The catch was that it had to be around the full Moon, normally a frustratingly unproductive time for astrophotographers.

For this particular week, fortunately/unfortunately, the annual Leonid meteor shower was going to happen just a few days before the full Moon, which also happened to be when a partial lunar eclipse (just short of a total eclipse) was to occur. A couple of comets, including the promising Comet Leonard (see a previous article), were promising potential targets. In addition, I had a new IDAS hydrogen-alpha filter in hand, which I intended to try out under near worst-case lunar illumination conditions. Taking an i7 laptop would allow some image-processing to be done in the daytime. If I was lucky, even the Sun would be a good target to photograph with the increase in sunspot and prominence activity starting to happen this year. All in all, this was to be a pretty productive week under the moonlight.

Reality Sets In

As any outdoor photographer knows, the weather can be a big problem, so it’s always prudent to have a plan B, other than the last resort of just heading home. In my case, clouds moved in, blanketing most of southern California, though fortunately for me, the sky was not completely covered. Only the mandatory endless optimism, required of all landscape and travel photographers, kept me from packing up and heading home.

A lunar ring, caused by very high-altitude ice crystals, aircraft contrails, shadows, and lower levels of haze characterized the days leading up to the November lunar eclipse.

Meteors and Comets

The Leonid meteor shower has yielded some bright meteors in past years, so despite the moonlight interference and cloud cover, I ran a wide angle (Sigma 15mm fisheye) on a Nikon D600 on several nights, hoping to get lucky and catch a bright meteor between or through light clouds. On moonless nights, I use exposures of 15 to 20 seconds. Unfortunately, because of the moonlight, I had to reduce my exposures to 5 seconds (ISO 1,600, lens at f/2.8). I kept my frame rate at two shots per minute to keep from being overwhelmed by the number of shots to look through for meteors as well as to minimize having to attend to the camera and reset the intervalometer, which has a limit of 999 frames. The aperture was kept wide open, as closing it down affects the sensitivity to point (or linear) objects, such as meteors and stars. 

In the end, the meteor net caught only a couple of meteors, and they were from the Alpha Monocerotid meteor shower instead of the Leonid shower!

Alpha Monocertotid meteor under moonlight.

The comets were a complete bust, as they were only up in the sky during cloudy periods.

H-alpha Filtered Shots

Trying out my new IDAS narrowband H-alpha filter went reasonably well, considering the weather conditions. I managed to find some windows of opportunity in directions that were cloud-free for a few hours. The narrow-band filter is centered on the hydrogen line of glowing ionized nebulae in the deep red part of the spectrum. By filtering out all other light, it’s possible to photograph details even through heavy light pollution (e.g. moonlight).

H-alpha shot of the Horse Head and Flame nebulae in the belt of Orion. This was taken on a Canon RP mirrorless camera, modified for enhanced red sensitivity and converted to a black and white image in Lightroom. It is a stack of 41 five-minute exposures at ISO 1,600.

This H-alpha shot was taken five days before the full Moon, with the Moon 76 degrees away. The additional benefit of the H-alpha filter is to suppress the bright blue light from the bright belt stars of Orion, which tend to wash out H-alpha nebula details and/or cause internal lens reflections.

Technically, the use of a color-matrix camera such as a DSLR, mirrorless, or one-shot color astronomical camera is “wasting” three quarters of the pixels of the camera. A specialized monochrome (and cooled) astronomical camera works best, but my encouraging result shows that you don’t have to exclude the use of narrowband filters with your color camera.

Lunar Eclipse Finale

The finale of the week under the moonlight was to be the partial lunar eclipse. Even though the eclipse was partial, most of the Moon would be in the umbra of the Earth’s shadow, making the bulk of the Moon turn into a reddish-orange hue. Unfortunately, the evening of the lunar eclipse was looking as poor as all of the nights leading up to this one, but luck was with me, and the sky (mostly) cleared in the direction and at the time of maximum eclipse. At my home, my wife reported that the clouds were so thick, she couldn’t even locate the Moon, so I was indeed lucky!

The wide angle time-lapse sequence was shot at a fixed exposure of five seconds per frame throughout the eclipse and shows the dramatic darkening of the sky during even a partial eclipse. This is why I always recommend that a lunar eclipse be viewed from a dark location even though it is technically visible from a city location. Note that the sky looks blue in these long exposures, but the sky looks only slightly blue to the naked eye, being at the edge of color detectability for the human eye.

Since I wanted to include the landscape in my wide, fisheye view of the sky, I used my Skywatcher Star Adventurer tracker set with its polar axis pointing straight up to keep the panning parallel to the horizon. The view is to the South, with the tracker panning from East to West at ½ sidereal rate.

The reddening of the Moon is because at maximum eclipse, only the red light from the sun makes it around the Earth to the moon, having been bent and filtered through the Earth’s atmosphere. In a true total lunar eclipse, the bright white edge of the Moon seen in this partial eclipse would also be red. In a total eclipse, the Moon is only being illuminated by all of the golden hour sunrises and sunsets of the Earth.

Composite image of the lunar eclipse illustrates the Moon’s movement through the Earth’s shadow. Hazy skies prevented getting a clean composite.

The composite shot above was created to highlight the Moon’s movement through the Earth’s shadow. The shadow that is obvious here is the umbra of the Earth’s shadow. The penumbra is much wider and has a poorly defined edge. A wide field of view is best for creating this sort of composite shot.

The next lunar eclipse photo op is in May 2022.

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