Comet Lovejoy and the Pleiades

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 and Pleiades: 19 January 2015.
Comet C/2014 Q2 Lovejoy: 08 January 2015
Comet C/2014 Q2 Lovejoy: 08 January 2015
Comet C/2014 Q2 Lovejoy: 27 December 2014
Comet C/2014 Q2 Lovejoy: 27 December 2014

 

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

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.
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!

Comet C/2014 Q2 Lovejoy visible in the night sky

Comet C/2014 Q2 Lovejoy has been climbing northward and is now well above the horizon for easy viewing in the northern Hemisphere. Sky and Telescope magazine has a good article showing where the comet is located each night in the sky through January.

With inclement weather approaching and threatening to eliminate any chances of photographing comet C/2014 Q2 Lovejoy for the next week (or more), I took advantage of one last clear, chilly night. The comet was easily visible in 7×50 binoculars and faintly visible as a naked-eye object.

The first image shows the well-known Cathedral Rock in Sedona, Arizona, with the comet visible in the lower left. Shot with a wide-angle lens, the tail is barely distinguishable in this image. In the upper center of the image stands Orion. (ISO 1600, 28mm, f/2.8, 15 seconds.)

20141228_0018_DBP_3743The second image clearly shows the tail extending up and to the left. (ISO 1600, 85mm, f/1.8, 8 seconds.)

20141227_2213_DBP_3504The third image is a composite of 100 images each of 8 seconds duration and stacked with Deep Sky Stacker and shows a much longer and more detailed tail. (ISO 1600, 85mm, f/1.8 100×8 seconds.)

Picture saved with settings applied.All images were taken using a fixed tripod with no tracking. I would like to try a equatorial tracking device so that I might be able to take longer exposures without the stars developing trails. Perhaps that will be my next photo equipment purchase.

A partial solar eclipse

There was a partial solar eclipse October 23, 2014, that was visible across most of North America. Patches of cirrus clouds moved across the sky all day but the sun was always visible. To safely view the eclipse, we donned our solar eclipse glasses and sat back to enjoy the show. At our location, the maximum coverage was about 50% of the solar disk.

20141023_1528_P1030528This photo was taken using a Panasonic Lumix FZ150 zoomed to 600mm (equivalent) focal length with an ND3 neutral density filter. The ND3 reduces incoming light by 10 stops. Even with the filter, I had to shoot at f/8 (the smallest aperture for this camera and a shutter speed of 1/2000 second at ISO 100 to get a reasonable exposure.

The large sunspot near the center of the solar disk is AR2192—the largest sunspot in several decades. The combination of solar eclipse and massive sunspot made for an interesting image.

Another planetary conjunction

Another planetary conjunction occurred yesterday (31 Aug 2014) with the close placement of Mars, Saturn, and the Moon in the evening sky. It’s only been a few weeks since the planetary conjunction of Venus and Jupiter in the morning sky so we’ve had an interesting few weeks for sky watching.

Mars and Saturn were joined by the crescent Moon to form a triangle in the evening sky. Using “The Photographers Ephemeris” I was able to determine that I could get a photograph of the triplet as they hung in the sky above Cathedral Rock in Sedona, Arizona. But if only it were that easy. After arriving at my predetermined spot I still had to move around to get a good setup. A bit of travel southward along the Templeton Trail…followed by some climbing up…then down…then back to the north…and finally I get a few minutes where they lined up with the spires of Cathedral Rock. Whew!

Conjunction of Mars, Saturn, and the crescent Moon.
Conjunction of Mars, Saturn, and the crescent Moon.

With that done, I retreated back down to the parking lot before it got too dark and spent another few hours photographing the Milky Way as it lined up with Cathedral Rock.

Milky Way and Cathedral Rock.
Milky Way and Cathedral Rock.