One of my background projects, along with everything else that I’ve been involved with in the past couple of weeks, has been the attempt to capture images of comet C/2020 F3, mostly known as NEOWISE, which has been visible just before dawn for large portions of the northern hemisphere, and recently moved into being visible after sunset as well. The views are to the north, roughly at 30° at sunrise, and 235° at sunset (tracking diagonally and depending on your viewing latitude, so these are only rough directions.) Monday night I got out, but storm clouds on the horizon effectively prevented any views, so I tried again on Tuesday evening when the skies were much clearer. The comet is not terribly bright, but enough to be seen with binoculars (or a long lens or small telescope) once the twilight fades enough; basically, start watching for stars to appear in the region, and once they’re visible, the comet should be not far behind. Not seeing anything while I was out there Tuesday, I started to experiment, and shortened the focal length down to get a broader view of the sky, firing off a few long exposures at various regions to examine the image afterward. And then, there it was.
This is a 14-second exposure, f6.3, ISO 800, capturing the residual light about an hour after sunset. The horizon is just out of view below the bottom of the frame; between that and the phone app plot from someone who had chosen the same viewing area as I (an overpass above the interstate, about the best view of the horizon to the north within quite a few kilometers,) I’m pegging this at about 8° elevation. To give an idea, trees at a moderate distance tend to run between 5 and 20°, while common viewing around here never gets less than 25-40° – there really are a lot of trees and not very many open views here. I’d considered going down to Jordan Lake, but aiming north from there puts the city lights of both Chapel Hill and Durham into the sky, not the best of moves for a dimmer subject.
Now we go to 600mm, and cropped even tighter.
This is now 9 seconds, f6.3, ISO 1600, and the motion blur of both the comet and the stars is apparent. This is from the earth’s rotation, and not a lot can be done about it without more specialized equipment. For instance, I could shorten the exposure time down a little with an f4 lens, which at 600mm runs, oh, about $13,000. Not gonna happen on this paycheck.
Or I could pick up a new body with expanded ISO range, but I was doing several frames at ISO 3200, and even then the exposure times weren’t short enough, so it would have to be something that pulled down 6400 to 12800, and sharply at that. And this is about the only use I’d have for that kind of ISO range.
Or, I could make a tracking mount, as I’ve mentioned before, which counteracts the rotation of the earth by turning in the opposite direction. Which is another, much bigger project that any I’m working on now, and is even a project just to align it for each shooting session (which wouldn’t have occurred this time around because the comet became visible before Polaris, the star used for alignment.) Someday, someday – but since I’d use it perhaps twice a year (partially just from not wanting to fuss with the alignment each time, and feeling obligated to be shooting night sky shots for a couple of hours once I did,) it’s never been a high-priority project.
And then there’s software, which can edit out motion blur like this to provide a sharper image. But I don’t have it installed, and right now, it looks like it’s gonna be another hassle, so it’s waiting for another time – maybe within a few days.
I may also do a morning run and see if the conditions are better – it’s still a matter of free time and adequate sleep. But if you want to try it, the best resource I’ve found so far has been Stellarium Web, which will use your location (once you provide it) to show you how to find the comet – click on the clock in the lower right to adjust times and see what’s best.