Mars at Opposition July 30, 2018
During the last weekend in July, at 36 million miles, Mars was closer to earth than at any other time between 2003 and 2035. Backyard astronomers hoping to have a great look at the ice caps and surface details under these optimal conditions were frustrated by a raging dust storm on the Red Planet. For most of June and early July, viewed through a telescope the planet was just a featureless orange disk. I saw a few images online, however, just before that weekend that showed signs of the dust storm abating. We had good weather on Friday and Saturday nights, so I took a stab at imaging each night during the hour that the planet passes through a treeless portion of my yard.
On Friday, I overexposed the images and on Saturday I underexposed them. Finally on Sunday night I shot 32 GB of properly exposed movie files using a ZWO ASI 120MC planetary camera through my Questar 3.5” telescope with a 2X Televue Powermate. Planetary imaging uses different techniques than deep sky imaging: each exposure is a short fraction of a second and it is easiest to collect the images in a movie format. In my case, at 20 frames per second. At this rate, after 5 minutes, the accumulated 6000 frames vary widely in quality thanks to atmospheric turbulence. I put a trio of free software tools to work processing the movies down to one still image. PIPP is a great image file handling program which I used to center the planet in each frame, score the images on quality (automatically) and select the best 300.
This top quality group was stacked into one image using AutoStackert 3, and the image was sharpened using the “wavelet” processing in Registax 6. Final sharpening and contrast adjustments were made with PixInsight and ACDSee. For the full weekend’s worth of attempts, I’d say that I spent about 3 hours of camera/telescope time and 8 hours of processing time until I figured out the best way to handle all the data. But this reflects how rusty I’ve been at planetary imaging. If I were to try it again tonight, I’d say 20 minutes with the camera and 1 hour of processing would do the trick. During the weeks since the opposition, plenty of decent Mars images have been appearing online as the impact of the dust storm wanes. But I’m glad I persisted so I could get one decent shot while Mars was so close!