The Green Comet

Well, the first thing that came to mind seeing news headlines about The Green Comet was a flashback to the 60s TV show The Green Hornet staring Bruce Lee. :-)

Seriously, this has been a newsworthy comet. While it wasn't bright enough to be seen except under very dark skies and/or with optical assistance like a telescope, as you know if you've followed the news, it is a singularly unique solar system visitor. Check out sites like EarthSky.org for more details and some of the more interesting images. 

For my part, I had hoped to capture comet C/2022 E3 (ZTF) with my rig (Evostar 72ED on a Star Adventurer tracker, using a Nikon D750). Unfortunately, the North Texas weather hasn't cooperated. Last week when it was at its closest to Earth (and at its brightest magnitude), we were in the throes of a winter storm. By the time we had a night with relatively clear skies on Friday night, we also had a nearly full Moon. It was also still very cold outside. If it had been a moonless night, I'd have packed things up and headed out east of town to darker skies to shoot but since I knew the Moon was going to make it hard to get really good shots, I just set up in my backyard. At least I could duck inside from time to time to warm up. 

Here is the result. See below for more on how it was created. 

Comet C/2022 E3 (ZTF) captured in my backyard
February 3rd, 2023

Between the light pollution and the glare of the Moon, it was hard for me to pull out much detail but you can at least see the dim fuzzball of the comet's core. The comet was in a region of the sky without any bright stars but the few brighter ones on the right side of the image are in the constellation Camelopardalis.

Still, it was time well spent. It was the first time I've gone through the process of capturing what are called calibration frames (bias, darks, flats), additional shots taken to improve astrophotography images by accounting for things like sensor noise and dust. It is also the first time I have processed using calibration frames; I took 100 images (20 seconds each) and post-processed them and the calibration frames using a software tool called Siril and then finished in Photoshop. 

Capturing a comet is often tricky since it is moving at a different rate than the stars. Using a star tracker (vs. a telescope mount), my only choice was to track the stars and hope to be able to post-process the comet and stars separately then combine them afterwards. I did that but it took a long time and many tries just to get the results above. I wish I had more data but longer exposures weren't possible since the histogram showed that any longer than 20 seconds at ISO 3200 would have resulted in clipping (i.e., the blue was almost lost to the right side at 30 seconds). On top of that, the comet would have blurred if I used too long an exposure given how fast it was moving.

One of the other tools I learned how to use is Astrometry.net which can do something called plate solving, taking an image and finding where in the sky it is a view of. Here is the results of plate solving using one of the images used to create the shot above. I find this raw, astrometrically-labeled view an interesting alternative version of my night's labors since the comet (though not green) stands out a bit more.

The three dots and labels represent stars in the constellation
Camelopardalis identified using plate solving on astrometry.net

Anyway, the next time I am shooting a dim fuzzy (hopefully without the Moon up and away from city light pollution), I'll have had some practice and expect to be able to produce much better results. 

Stay tuned...

Click on an image to see full-screen. 

Eaton Family Solarcan Project - Phase 3: Kaili

As covered in previous posts, late in 2021 I discovered a product called the Solarcan, a pinhole camera created using an aluminum can with a small hole in the side and photographic paper inside, all to capture long-period exposures (weeks, months, years) of the Sun as it moves across the sky each day, images called solargraphs. I bought a five-pack of Solarcans in December 2021 and gave four to my grandkids as Christmas gifts. 

In the Phase 2 posts, I covered helping my grandkids set up their Solarcans. The plan for each one was to have them up about 6 months. For the one Kaili and I put up (see this post), the plan was to leave it up till at least the winter solstice but she decided she wanted to leave it up longer. Here are views of her Solarcan taken in November including a view from the Solarcan. 

Kaili's Solarcan	View from the cul de sac
View from the Solarcan

Kaili took her Solarcan down today. Following the Solarcan instructions for developing solargraphs, I opened it and scanned the photographic paper contained in the can.

In the initial scan, the sky and the arcs traced by the Sun are dark and the foreground is light. The reason is that the photographic paper reacts to light by darkening, resulting in a negative image. The bright spot on the sides of the image are the result of tabs on the inside of the Solarcan that hold the paper in place; because they overlap the paper, they block the light, preventing the paper from darkening. 

The next step in the development process is to convert the image from negative to positive. After that, the goal of processing is getting an image in which some of the details come out (e.g., adjusting exposure and contrast) and adjusting color and other variables to get something that looks interesting. Here is the final result.

Like the solargraphs done by Olivia, Jack and Harper, the dominant feature is the arcs across the top representing the path through the sky of the Sun. Long, bold lines are from sunny days and thin lines or ones with gaps are from cloudy or partly-cloudy days. After the winter solstice, the Sun started passing a little higher each day so I think the fact that it was tracing back over the days leading up to the solstice is why the lower lines are so much brighter (i.e., twice as much exposure in those areas). 

The thing that is cool about this one is the basketball backboard. Of course, that was what we were hoping for (see photos of the view from the Solarcan). What we hadn't planned for is there being two. But there is just one backboard (at least on this side of the cul de sac) so what's up?

Notice that it's not just the backboard that shows up twice. So does the light post. And if you look closely, there are two images of other things too... the trees in the distance and the house across the street. What must have happened is that at some point during the time the Solarcan was active, it got bumped which left the pinhole pointing a little bit to the side. The "double-exposure" effect that resulted is similar to what happened with Jack's and Harper's. I imagine that it's not uncommon for a Solarcan left up for months (or years) to get moved, whether it's by an animal, the weather or maybe even a basketball. :-)

As always, click on an image to see it full screen.