Thursday, February 4, 2016

Dawn Alignment of Planets

For the first time in over a decade all of the bright solar system objects are visible in the sky at the same time. Even my Pebble watch is celebrating the event. With the moon approaching crescent and a forecast of clear skies, I dragged myself out at 5AM this morning in the below freezing weather to do some imaging of the planets. Earlier in the week I had scouted some sites that afforded a low southeast horizon with minimal light dome in that direction. This was to give me a better chance of imaging Mercury which is easily washed out. I chose a spot northeast of Georgetown on CR-150, about 20 minutes from home.

Since I do not have a fish-eye lens, I had to resort to creating a mosaic using my widest lens, a Canon EFS 18-55mm f/3.5-5.6 IS. I set up a tripod with a Vixen Polarie tracker to allow me to take longer exposures without star trailing so that I could keep the ISO low. I spent a half hour or so setting up, aligning the tracker and taking test shots. I used Astrophotography Tool to focus the lens and capture the images. Without using a computer, it is nearly impossible to get critical focus with this lens.

The final mosaic below consists of three frames, the first centered on the moon, the second on Spica, and the third on Regulus. I took an additional image of the eastern horizon with the tracker turned off to get the trees in focus. Each frame was taken with the Canon 7DII set at ISO-200. I decided to not create spiky stars so left the lens wide open at f/3.5. Each frame was exposed for 120 sec. The images started in the east at 6:15AM and progressed westward ending at 6:25AM. There was a fairly narrow window of time when Mercury was above the horizon muck but not yet washed out by the dawn light.

I used Photoshop to align the frames into a mosaic, performing a bit of distortion on the center image to align stars along the joins. Using adjustment layers, I tweaked the exposure, gamma, and color balance of each frame to get a smooth transition. The adjustments were especially necessary because the lighting conditions changed noticeably between the first and last frames. I added labels to show the position of the planets and nearby reference stars. At the left of the image, you can make out the Milky Way and a number of star clusters.

To see the image in detail, navigate here and use the viewer to zoom in and pan around. You can also navigate here and see a version with all of the constellations labelled stretching along the zodiac from Sagittarius at the left to Cancer at the right.

As another processing attempt, I rotated the image vertically, and cropped off the uneven borders. I use the Photoshop plugin GradientXTerminator to help reduce some of the sky glow gradient. I also used the Photoshop plugin StarSpikes Pro 2 to give the brightest stars a bit of extra punch. The planetary symbols took a bit of hunting. I found them in the DejaVu Sans font.

My brother-in-law, Ross Cunniff, braved the cold Colorado dawn to create some interesting images.

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