Although it’s fun to photograph the Full Moon, I actually prefer photographing a thin crescent Moon, usually just a day or two after the New Moon. The thin crescent is brightly lit while the remainder is softly lit by light reflected by Earth, hence known as Earthshine. It’s also known as DaVinci Glow. As well, the Moon does not overwhelm the night sky so that stars can also be in the photograph.
During late Spring and into early Summer the crescent Moon sets in the west-northwest and this makes it a good target for shooting at Upper Lake Mary. The long and narrow lake is aligned WNW–ESE so that the Moon casts a brilliant reflection that can run the length of the lake.
I’ve shot this several times over the last few years but never tire of it. All it requires is enough of a gap in the clouds for the Moon to shine and for light winds so that the lake surface is relatively smooth.
Orion is one of the most conspicuous and recognizable constellations in the night sky. It was named after Orion, a hunter in Greek mythology. Its brightest stars are Rigel (Beta Orionis) and Betelgeuse (Alpha Orionis), a blue-white and a red supergiant, respectively.
Hanging from Orion’s belt is his sword which contains the Orion Nebula, also known as M42. This is a spectacular object that can be clearly identified with the naked eye as something other than a star. It is one of the most easily photographed Deep Sky Objects and can be captured by most modern digital cameras.
The first image of Orion was taken last winter on an evening with a very thin layer of high clouds. This cloudiness was enough to cause a beautiful glow around the brighter stars in the constellation. Some nebulosity is visible in both the belt and sword of Orion. (Nikon D700, ISO 1600, f/5.6, 120 seconds, 80mm).
The second image was taken this spring (Nikon D700, ISO 1600, f/4, 10x120s, 200mm) and is zoomed/cropped on the Orion Nebula (M42).
I recently heard someone say that a reasonable goal of astrophotography is not so much to produce the best image, but to produce a better image than your previous best. In this case, I can claim some success.
And, for comparisons sake, here is a richly detailed image of the Orion Nebula captured by the Hubble Telescope and posted on the Astronomy Photo of the Day (APOD) site.
As mentioned in a previous post, I now have a tracker mounted on my tripod (iOptron SkyTracker). With this gadget, I can take longer exposures of the night sky without star trails. Exposures of 30 to 120 seconds typically give me the best results. Shorter exposures don’t gather enough light and the longer exposures may show a hint of star trails.
There was an evening a bit over a week ago with mostly clear skies. Very thin cirrus clouds were moving across the area. I was unable to see them while photographing but inspection of satellite imagery at the time showed that there was some high-altitude moisture moving across the area. The result? The thin clouds produced a faint glow around the brighter stars in the constellation Orion. I like the result.
Comet Lovejoy (known formally as C/2014 Q2) continues to put on an impressive show for sky watchers. In December it began to climb upwards from the southern horizon towards Orion, then passing to its west and climbing higher. In mid-January it was nearly overhead in the evening sky as it passed near Taurus and Pleiades. Many astrophotographers have taken advantage of this setting and there have been some beautiful photographs posted at various web sites.
To best capture the delicate details of the comet—and especially its tail—a tracking device is needed to guide your camera or telescope so that it matches the motion of the stars across the sky. This allows longer exposures without the stars streaking or creating star trails. Without a tracking device, exposure time is limited. This limitation can be partially overcome by taking numerous short exposure images and stacking them using any of the many applications available. Still, the laws of physics and the engineering of camera sensors will result in better images if you have, say, five 30-second exposures than thirty 5-second exposures—even though both are 150 seconds total exposure.
Are 100 x 1 minute and 10×10 minutes giving the same result? Yes when considering the SNR but definitely No when considering the final result. The difference between a 10-minutes exposure and a 1-minute exposure is that the SNR in the 10-minutes exposure is 3.16 higher than in 1-minute exposure.
Thus you will get the same SNR if you combine 10 light frames of 10 minutes or 100 light frames of 1 minute. However you will probably not have the same signal (the interesting part). Simply put you will only get a signal if your exposure is long enough to catch some photons on most of the light frames so that the signal is not considered as noise.
For example for a very faint nebula you might get a few photons every 10 minutes. If you are using 10 minutes exposures, you will have captured photons on each of your light frames and when combined the signal will be strong. If you are using 1 minute exposures you will capture photons only for some of your light frames and when combined the photons will be considered as noise since they are not in most of the light frames.
Since I don’t have a tracker (at least, not yet), I have no choice but to stack short-exposure images of the comet. Here are a few images of Comet C/2014 Q2 Lovejoy taken on several different nights. The quality of the images varies depending on how much light pollution was captured in the image, whether there was moonlight, and how clear the sky was.
There’s still plenty of time this winter to venture outside with a pair of binoculars and gaze at the comet. Here is a link to a sky chart provided by Sky and Telescope for the month of January. For February and beyond, try this chart hosted by UniverseToday.