Photographing the 2015 Total Lunar Eclipse

Lunar eclipses aren't that rare - certainly not as rare as some uninformed sections of the media would have you believe, but I hadn't photographed one since March 2007, so I stayed up till stupid o'clock the other week to get some images of the so-called Super Blood Moon eclipse. The wind was a little gusty, but fortunately the clouds didn't interfere.

One thing the photos don't convey is just how much the moon dims during totality. (The reason it doesn't go completely dark is because it's illuminated by sunlight refracted through the earth's atmosphere. Or to put that in a slightly more lyrical way, an observer standing on the moon during an eclipse would see all of the earth's sunrises and sunsets compressed into a beautiful ring of light.) The first image in the sequence above (the barely eclipsed moon) was shot hand-held with a 1/1600 second exposure at ISO 800. The last shot (fully eclipsed) was taken on a tripod with a cable release, with the mirror lock-up function enabled; exposure time 1/2 second, ISO 1600. At long focal lengths (400 mm and above), these slow exposure times can be problematic. Shoot for anything longer than about half a second and the earth's rotation will start to smear the image.

So, as is often the case in astrophotography, there's a trade-off to be made. Do you under-expose and increase noise, or do you expose correctly and lose detail? A tracking mount which will correct for the earth's rotation is one way around the problem, but the good ones don't come cheap. Another method (if you find high ISO noise objectionable) is to shoot lots of under-exposed images one after the other, stack them in RegiStax or AviStack to increase the signal-to-noise ratio, and then push the exposure in Photoshop. I did think about doing this, but it was late and I was tired and it seemed like a lot of effort given that I still had several hundred photos from the Camargue to sort through (a post on that is coming soon).

Maybe it's something I'll try for the next eclipse in 2018; or maybe by then cameras will have progressed so much that high ISO noise won't be a big deal... Anyway, to tide us over till then, here's an uncropped view of the eclipse taken at ISO 6400, and carefully pushed in PS to bring out the background stars. A red full moon surrounded by stars; now that's a sight worth staying up for.

Ocean of Storms

At first glance Oceanus Procellarum (the Ocean of Storms) appears to be one of the less interesting regions of the Moon, presenting to the casual observer nothing more than a vast, monotonous plain of dark grey lava, dotted with the occasional impact crater. But look closer and you'll find evidence of ancient volcanism on a huge scale, unlike anywhere else on the lunar surface.

Here's a 100% crop showing the Aristarchus plateau - an diamond-shaped block of uplifted terrain dominated by the dazzling crater Aristarchus and the 160 km-long Schröter's Valley:

Easily visible in a small telescope, the valley is the largest and perhaps most dramatic example of a lunar rille, a sinuous channel cut (a very long time ago) by fast-flowing lava.

Follow the terminator south and you come to the Marius Hills, a complex of some 300 volcanic domes and hills that - through a small telescope - look like pimples on the lunar surface:

Lunar Orbiter 2 photographed the complex from an oblique angle, giving an idea of the relative height of the domes, and a few decades later the Japanese SELENE/Kaguya mission discovered an intriguing dark pit in the area (shown here in a high-resolution image taken by the Lunar Reconnaissance Orbiter).

Incidentally, if you move your mouse over the cropped images you can compare the finished versions with one of the original photos, illustrating the dramatic improvement that image-stacking can make to lunar photography.


See also:
Procellarum: The Biggest Basin?
Shooting the Moon: Lunar Photography with a DSLR and a Small Refractor

Photographing Earthshine

I generally try to avoid going back and tinkering with old photos because - as with any creative endeavour, whether it's writing a story, composing some music, or making a film - there comes a point where you have to say, "Enough's enough," and walk away from it. However, I was recently contacted by a production assistant at Popular Photography magazine saying they were interested in using my image "Crescent Moon with Earthshine" for a "How-to" feature in the June 2012 issue*.

The original image was composed back in April 2007 and close inspection shows quite a lot of noise and signs of oversharpening (as well as some obvious artefacts from where the two stacks were spliced together). I've learnt a lot about processing since then - and newer tools have become available - so I decided I could do a much better job if I went back to the source files and reprocessed them from scratch.

For those who are interested in the technical nitty-gritty, the images were taken using a Canon 350D (Rebel XT) DSLR connected to a Vixen SP-102 achromatic refractor (focal length 1000mm). Earthshine (which is the reflected sunlight from the earth illuminating the shadowed part of the moon) is easy enough to capture on camera, but normally results in a severely over-exposed crescent. To retain the detail on the crescent I shot 31 images at 1/60 sec, ISO 200, and to expose the earthshine I took 11 images at 0.5 sec, ISO 800. I then stacked and sharpened these images separately using the freeware tools AviStack and RegiStax, before combining them in Photoshop using a layer mask to create the finished version you see above.

This new "redux" version is a big improvement on the original, and is probably the best I could do given the quality (and quantity) of the original 350D image files. Some flaws are still apparent: the dark band between the earthshine and the crescent is a little distracting and the earthshine itself could be brighter. These are issues that could be fixed by capturing more images at a wider range of exposures - and then combining them using HDR software.

But that's a project for another day...

*And in case you're wondering, yes they did use it, and yes they did pay me.

See also:
Shooting the Moon: Lunar Photography with a DSLR and a Small Refractor
Earthshine (NASA Science)
Planetshine (Wikipedia)

Venus and the Moon

If the weather is clear later today (which doesn't seem very likely at time of writing), Venus and the crescent moon should make a nice pairing in the evening sky. Venus of course has been at its brilliant best in recent months, so brilliant in fact that you can see it in daylight if you know where to look. It helps if the sun is shielded by a building or a tree, but the real trick is getting your eyes to focus to infinity while staring at an apparently featureless blue sky.

The moon and Venus, June 2007

Your chances of seeing Venus during the daytime are greatly improved if something prominent like the Moon is nearby, as it was during the occultation of 18 June 2007. The image above was taken at half past four in the afternoon, shortly after Venus emerged from behind the moon's limb.

Venus will continue to dominate the evening sky for the next month, before passing in front of the sun's disc on June 5th-6th (the last such transit until 2117!).