Finding Neptune

October 10, 2020  •  Leave a Comment

Recently I have been pursuing a few more esoteric projects with my astrophotography setup, one of which is to photograph all the planets and other Solar System objects. Most of them are so far away that they don't show much detail since I don't get a lot of magnification with my equipment. So the photos aren't especially exciting visually, but it's something of a personal challenge.

Neptune is the outermost of the large planets in the Solar System. (Pluto is now formally known as a dwarf planet, one of the many such objects in the outer Solar System's Kuiper Belt.) Neptune is bright enough that it's clearly visible in photos with moderate exposure. In the photo above it's a medium brightness green star near the bottom-center. When I looked more closely at the image, I also saw another, much fainter dot to the lower right of Neptune. Looking in my trusty sky simulation software (SkySafari) it turns out to be Triton, Neptune's largest moon, about 20% of Earth's diameter, smaller than our Moon. This is a composite of seven exposures with a Nikon D850 and 200-500mm f/2.8 lens at 500mm, each exposure was 2 minutes at f/8, ISO 2000. They were processed in Lightroom and combined in Starry Sky Stacker.

Not only that, but I noticed some fuzzy patches toward the upper right in the image. These are distant galaxies, identified in star charts as NGC 7576, 7585, and 7592 (from the New General Catalog of Nebulae and Clusters of Stars, originally compiled in the 19th C. and revised up to the present). They are 150-350 million light-years away. 
Finally, looking a the separate exposures, there were a lot of satellite trails in a couple of frames. Most of these are from the new Starlink constellation of satellites being launched by SpaceX to provide global broad-band internet. They are the parallel streaks at the bottom of this composite photo, produced by several separate satellites orbiting fairly close together. There's also another unrelated satellite at upper right.

This photo is also a composite of the same exposures making up the previous photo. It was combined in Photoshop in a way to preserve the brightest value in each frame rather than the first photo, which was combined in a way to average out the brightness between the frames to make a clearer image. There are so many of these satellites that their trails show up in a surprisingly large number of photos of the night sky. And more are being launched all the time, so we're in for an interesting time in astronomy. Fortunately for the kind of astrophotography that I have been doing, the trails disappear when multiple exposures are combined, as with this example.

 


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