Moonrise above the snow-covered San Francisco Peaks

March 6, 2015

Here are a few recent images of the nearly-full moon rising above the San Francisco Peaks in northern Arizona. The day before the full moon is often the most photogenic time as the landscape is still bathed in sunset light while the moon has already climbed well above the horizon.

But if only it was that easy! Earlier in the day I had used The Photographers Ephemeris (TPE) to find a location. I decided that a position on SR64 north of Williams, Arizona, would work and at that distance the moon would appear quite large juxtaposed against the mountains. Unfortunately, when I arrived at my predetermined spot I was not able to see the mountains. Numerous cinder cones and small hills completely blocked my view. I wish TPE was more intelligent than this photographer and would let me know of obstructions.

With less than 15 minutes until moonrise and one-half hour until the moon would be above the peaks, I had to find a new location quickly. I backtracked south on SR64 and then east along Route 66 but hills and trees continued to block my view. When I did finally get a clear view I was too far south and the moon would rise south (right) of the peaks. I stayed around for a few minutes to get a few consolation images of the moonrise then headed east again. Arriving in Parks, Arizona, I turned north and kept looking for a location with the moon above the peaks and a clear view. Finally, I found this location.

Although these were not the images I thought I was going to get I’m still happy with the result.

Note: No speed limits were broken while trying to reposition!

Photographing the night sky with the iOptron SkyTracker

March 1, 2015

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.

Orion and M42. (ISO1600, f/4.0, 120s exposure)

More Comet Lovejoy

February 20, 2015

Comet C/2014 Q2 Lovejoy continues to be a fascinating object to photograph in the evening sky. It is now located high in the sky at sunset and sets in the northwest overnight. It is, however, growing fainter and this requires longer exposure times to bring out the details. As noted in a previous post, I have been photographing the comet without an equatorial mount and this has limited my exposures to a few seconds. That has changed as I now have a tracker mounted on my tripod (iOptron SkyTracker) and this allows much longer exposures. It takes a bit of practice to properly align the device but I’ve gotten pretty good with a few sessions. With good alignment, it is possible to take exposures of 5–10 minutes without getting star trails.

On another night, I was again taking a sequence of images when some high, thin clouds moved in. Rather than shutting down, I continued to capture images. The result of the high clouds was to create a colored area around the brighter stars.

Cloudy skies have returned to northern Arizona and that will be the end of comet photography for at least a few days.

Comet Lovejoy and the Pleiades

January 22, 2015

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.

From the DeepSkyStacker pages on the theory of stacking:

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.

Comet C/2014 Q2 Lovejoy and Pleiades: 19 January 2015.

Comet C/2014 Q2 Lovejoy: 08 January 2015

Comet C/2014 Q2 Lovejoy: 27 December 2014

Comet C/2014 Q2 Lovejoy and Orion above Cathedral Rock, Sedona, Arizona: 28 December 2014

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.

Happy viewing!

Star trails and moonrise at Cathedral Rock

January 12, 2015

A few days ago I headed down to Sedona to try getting another set of images of Comet C/2014 Q2 Lovejoy. Although I did get the images, I was unable to create a final product that showed the stars and the comet well. I suspect there was too much light pollution and it overwhelmed the delicate tail.

Star trails above Cathedral Rock, Sedona, Arizona.

I also shot star trails with the camera pointed toward Cathedral Rock. The moon was still below the horizon when I started the sequence of images but rose above the horizon and illuminated the rock at the end. The result, after stacking and compositing the images was pretty good. But I was interested in trying out a popular technique of making the star trails look more like, well, comets. There is software available to do this but I was willing to do it the old-fashioned way using manual labor—at least this one time. The result came out well. If only the night sky actually looked like this!