Finding Ceres: astronomy in the time of the Coronavirus

This is the story of an asteroid, a challenge and a video. It describes why I decided to catch the dwarf planet Ceres, how I found it, how I photographed it, how I watched it make its way through the dark, and how it reminded me how little we are.

Astronomy in the time of the Coronavirus

The other night was the first night in weeks where it wasn't cloudy. Of course, there was a mad scramble when Melbourne-based astrophotographers were all running outside to take photos. Naturally, I was one of them.

We couldn't run far though. The Melbourne Coronavirus lockdown prevented anyone from leaving their homes.

The Moon was about three quarters full (waxing gibbous, if you're into that sort of thing), and not far from Jupiter and Saturn. Mars was up later. The Helix Nebula was around half way between Saturn. and Mars, and the Sculptor Galaxy followed.

The asteroid formally known as...

So I didn't go for the Helix or Sculptor. I decided to go for the dwarf planet Ceres.

I'd been thinking about getting a photo of Ceres, for weeks. I'd written about it previously, and my research had piqued my curiosity. Ceres was the first asteroid discovered: its official name is "(1) Ceres".

It was discovered in 1801, by Giuseppi Piazzi, as part of an actual effort to search for objects between Mars and Jupiter. Astronomers, notably Kepler, had noticed there was a sizable gap there and were convinced that something had to fill it. Piazzi spotted something and initially thought he'd found a comet, but decided it wasn't that, as its movements were wrong. It was something like a star, but not a star.

Pretty soon after Ceres was discovered, a heap of star-like things ("asteroids") had been found filling that void. We now know of over 800,000.

Signal-to-noise ratio

Ceres isn't exactly dazzling. After all, it's less than 1000km across (about the distance between Melbourne and Mildura) and it's orbiting between Mars and Jupiter. Currently, it's about 300 million kilometres away. So its signal was going to be low.

But the background wasn't going to be dark either. On the night, a three quarter moon was pretty close. What's more, Melbourne's light pollution is ... awful. The background noise was going to be high.

This was a challenge. It was going to be one of those images where you don't know if it worked until after processing the image.

I was reasonably confident, though. Ceres is magnitude 7.7, and I've taken a photo of Titania and Oberon (two of Uranus' moons) before, and they're magnitude 14 or so.


Catching Ceres

Finding something like that

Pointing a high magnification telescope at something you can't see is difficult. This is where having a go-to helps, obviously. But Ceres isn't in my NEQ6's database.

So I consulted a star map. These are pretty easy - I've got one on my phone as well as on my computer. I simply set the time to when I was going to be outside taking the photos, and searched for Ceres. This is what the star map looks like:

You can see a couple of catalogued stars (I've highlighted HIP 113024) and you can see Ceres as well as a little of the path it's taken over the past few hours. I found the closest star that had a catalogue number (in this case HIP 113024, which is also known as SAO 191467). There was a target I could hit.

The easy way

Most go-to handboxes will go to stars that have SAO catalogue numbers, so I could just go there. It's very Bourgeois.

I control my mount using my laptop and not the handbox, but setting up a photo of HIP 113024 in the program I use is simple. Just tell the mount to go there, it will take a photo, confirm it's in the right spot using a process called plate solving, move a little if necessary, and the job is done.

Scruffy, for sure, but I've got reason to call myself a lazy astronomer as well.

Old school

But if I have a manual telescope? My goodness.

Pointing a manual telescope at something that moves about but isn't visible is - and this is no exaggeration - one of the hardest, most frustrating things you can do in amateur astronomy. Comparing a map, and what you see in the telescope isn't easy. You don't know what's up and what's down, which stars are your landmarks, and worst, you don't really know what the scale of the map is in relation to your telescope view.

I've found dark targets using a telescope and a map before, moving from a star I know towards my target, before. It's called star hopping, and experienced owners of Dobsonian telescopes do it all the time. Honestly, these people have skills that make me stand in awe - that's real astronomy. I'm just mucking about.

Taking the photo

The way to take photos of things that move is to get a series over time. Once you're done, you can looking at the photos in sequence. If you've got it right, one of the dots will move.

Normally, when I'm photographing stars, especially clusters, I do 30 second exposures using red, green and blue filters on my monochrome sensor. This ensures I don't overexpose the bright dots, and as a result, I'm able to enhance their colours.

But I wasn't particularly interested in quality: I was groping in the dark. I didn't need colours or anything sophisticated, so I used my monochrome sensor with nothing but a luminance filter - plain glass, really. I stuck with 30 second exposures though. I guessed they'd leave the background dark, avoiding the light pollution and revealing just the stars. And, I hoped, Ceres.

I set my scope up in the back yard and located the target star. This was what I got.

Gathering the data

I watched the mount, scope and camera work for over five hours, taking 30 second exposure after 30 second exposure while tracking the star. It paused only to focus every hour.

My only duty was to watch a wiggly line on my computer screen which showed how well the mount was tracking, and how much the autoguider was intervening to keep it on target.

Shortly before 2am the telescope paused to do a "meridian flip" while I supervised. Ceres was passing overhead, moving from the eastern part of the sky to the western part of the sky. Once it reset itself, it made sure it was still on target and kept going, while I went to bed, leaving it to do its thing.

I woke the next morning and hurried outside to find the scope stalled. It had thrown in the towel when Ceres had disappeared behind our house. All up, it had taken 378 exposures.

Processing the image

When I started processing the next morning, I was worried to discover that all of the images looked the same. Out of the computer, they were all very dark, with just a few stars showing. I opened the first one again, and lightened it using Photoshop's levels tool until the black turned charcoal.

When I compared the first image with the last one, one of the dots had shifted. I breathed again. There it was. To save you the game of "Where's Wally" that I played, I've circled it.

But the job wasn't completely finished. I had a sequence of images, so I was able to make an animation. Using Deep Sky Stacker, I aligned every fifth image precisely, and crop so the movement was noticeable. Then I used Photoshop to open each one, brighten them and save them as files I could use in a video. Finally, I opened these in my video editing software, Shotcut.

And there it was

I watched Ceres making its lonely way through the darkness, so small, and so dim. In the 220 years that humans have known of this speck of dust, how many have actually watched it? Certainly, there's a good chance that I was the only human watching it at the time. 

Finally, I wondered about myself. Why is it so fascinating watching a white dot moving among white dots? The answer is that it's not simply a white dot - it's an asteroid - it's a solar system - it's a universe. Humans struggle and fail to understand our place here: the answer, both simple and complex, is just out of reach.