Last night I spent about four hours photographing the Orion Nebula again. This time, I used my longest focal length, 840mm, and an intervalometer to capture over 100 shots. The sky was a little cloudy, and the light pollution is terrible (even worse than normal, thanks to the high reflectivity of snow), but I discovered a new stacking technique a little while ago that I decided to employ. I have to say, the results are nothing less than remarkable, at least given the conditions and other limitations I had to work with. Between the clouds, the light pollution, and my lack of any kind of tracking mount that would allow much longer, more detailed shots of deep sky objects…I think the image I am sharing is rather amazing.
The photo I am sharing today is an astrophotography “stack”. For most photography, you point the camera, focus, and press the shutter button. The camera does most of the difficult work of metering the light in the scene, identifying your subjects, actually adjusting the focus of the lens on those subjects, and exposing. When it comes to photographing the night sky, particularly deep sky objects like nebula, galaxies and star clusters, etc. a much greater burden is placed upon the photographer. Deep sky objects are very dim, usually barely visible to the naked eye if visible at all, and as such require either extremely long exposures measuring in hours to properly expose…or “stacking”. Stacking involves making multiple short exposures, short enough not to blur due to the motion of the sky or drift caused by a tracking mount, but long enough to capture as much light as possible…then aligning and blending those exposures in a tool like Adobe Photoshop to produce a richer, brighter, more detailed exposure.
I used a stacking technique to produce the image above, from a series of 50 shots of VERY SHORT exposures: 0.6 seconds, to be exact. Generally speaking, astro stacks are created from exposures that are several seconds at least, and often many minutes for those who are blessed with a high quality equatorial tracking mount with automatic guiding. Stacking ten ten minute exposures is always better than stacking any number of shorter exposures, however when push comes to shove, short exposures will do…with less detail and less clarity. That said, I never expected to be able to extract the amount of detail, particularly in the extremely dim dust cloud around the heart of the nebula, the Trapezium open cluster. Trapezium is a cluster of five primary stars, and three smaller stars. Four of these stars are usually visible with a moderately decent telescope (130mm aperture or larger), and I was able to see and sharply focus on all four with my lens (150mm aperture).
In addition to the Orion nebula itself, I also managed to capture some very faint detail in the first “star” of Orion’s sword. This is called Running Man Nebula, due to the shape of the dust obscuring part of this dim reflection nebula. This is actually another small cluster of stars, not a single star. Additionally you can also see Messier 43, also called De Mairan’s Nebula after it’s discoverer Jean-Jacques Dortous de Mairan, the small round sphere attached to the center top of Orion Nebula. I frequently see these stars when I’m looking through my lens, but I’ve never captured enough dim dust detail to have it show up in any of my photos. I’m quite happy it is clear enough to see in this shot.
The Orion nebula (M42) and its neighbors M43 and Running Man are part of the greater Orion Molecular Cloud Complex region of the sky, an expansive dust and gas nebula region that covers the entirety of the Orion constellation, and it permeates the entire image I have shown here. With longer exposures and truly dark skies, an astrophotographer can expose detail in the much dimmer dust that surrounds the Orion nebula, and reaches up to the Horse Head and Flame nebulas near Orion’s belt, and beyond. Once I acquire a tracking mount (I have a basic telescope on order), I’ll be promptly attaching my camera to it and aiming to expose as much of the region as I can, and hopefully I’ll be able to find some nice, deeply dark skies to do it in (the snow should be melting a bit soon as 50° weather is on the way, so light pollution should lessen a bit).
For those of you who are interested in astronomy, the great yearly show of the Geminid meteor shower is almost upon us. It usually peaks around the 13th through 14th. If you want to watch the show, be up and ready, under dark & cloudless skies, by 8:30pm or so this Friday night, and keep an eye on the sky until midnight (for US viewers…viewers in other parts of the world may have to adjust their time window.) The show should start around 9pm, and is supposed to peak around 10pm…which is kind of nice, a bit earlier than a lot of meteor showers which often peak in the wee hours of very early morning (3-4am). The Geminid meteor shower is one of the most reliable, usually having a ZHR (Zenithal Hourly Rate) of 100 to 160, which means you should see more than 1 meteor per minute.
The Geminids source from a “main sequence” comet, or asteroid with a more elongated orbit that periodically takes it a bit closer to the sun, giving it cometary behavior. Earth crosses this asteroids dust trail every December, and the radiant source for the meteors is in the constellation Gemini. To get a bead on the source, and point your eyes (or cameras) in the right direction, find Orion, then look to the upper left over his shoulder (the bright orange star Betelgeuse) by maybe 8°. At this time of year, Gemini is high in the sky, almost directly overhead by midnight (it is a Zodiacal constellation.) A comfy chair that lets you lean back will offer the most convenient viewing (assuming you can withstand the cold!)
The Geminid meteors move relatively slowly compared to other major showers like the Perseids, Leonids, and Orionids. That makes them fairly easy to spot, and trails can often be quite long. Bolides (larger fragments that are much brighter in the atmospher) occur frequently enough, and often glow greenish. The moon will be waxing Gibbous, almost full, so while the hourly rate is supposed to be high (I think 120 is predicted for this year), the light of the moon may reduce the visibility of all but the brightest, so ZHR might be closer to 50.