By Rich Lynch: We had a prominent celestial visitor back in mid-October – a bright comet with the unwieldy name of  “C/2023 A3 (Tsuchinshan-ATLAS)” .  Didn’t take very long for observers to more simply refer to it as “Comet A3”, especially since most of us had no idea how to correctly pronounce “Tsuchinshan”.

The news media referred to it as “the brightest comet in 27 years” – in other words, all the way back to Comet Hale-Bopp.  That made for some big expectations and for the most part the new comet met them.  For us here in the northern hemisphere A3 was quite the sight not long after sunset.  Where I am in the never-completely-dark skies of suburban Maryland it was easily visible to the naked eye the early evening of October 14^th, even with a waxing gibbous moon that was worsening the light pollution that was already present.

I’ve always been somewhat of an amateur astronomer, so for me the urge to view and photograph the comet had been pretty much overwhelming.  The previous time a supposedly naked-eye comet had graced our skies was back in 2020, during the pandemic, and long story short, it wasn’t.  There was nothing at all to see with the naked eye.  I was able to capture it on pixel, but it took a bit of post-processing to get a usable image.  This time was different.

A brief beginners’ guide on how to photograph a comet: You don’t need very expensive equipment.  Nope, not at all – a stationary camera works just fine.  I used my dependable Nikon D‑3100 digital camera, a bottom-of-the-line model that they don’t even make anymore, with a 50-mm manual-focus lens.  (A manual focus lens is much simpler to use than an autofocus one for night sky photography because of the necessity to set the lens to ‘infinity’ focus, which an autofocus lens seems incapable of easily doing.)  Almost any F-stop will work, and the lower you go the more light gathering power the lens has.  (I compromised at F4 to reduce the effect of light pollution on the image.)  For ISO (the film/pixel ‘speed’), I’ll save you some trial-and-error: ISO-1600 is as ‘fast’ as I could go, here where I live, without light pollution fogging over the image.

So, with all that out of the way, you set up the camera on your trusty tripod and point it at the comet.  And then comes the critical question: What’s the correct exposure time?

Here’s where a bit of math creeps in.  For stationary camera night sky photography, exposure is determined by the so-called “Rule of 500”.  Simply put, the maximum exposure time (in seconds) is 500 divided by the focal length of the lens.  (More than that and you get noticeable star-trailing instead of crisp points of light.)  For my 50-mm lens, that works out to be 10 seconds.  I never push it that far, though, because if you want to enlarge the image it will in effect increase the lens focal length.  And at some point star-trailing (or in this case, comet-trailing) will become evident.

But enough tutorial.  As I mentioned, this time was different than what happened in 2020 because the comet was much, much brighter.  On that night it was bright enough that it was plainly visible even before twilight had completely faded.  And I wasn’t the only one who thought so.  A short distance from where I live is a middle school which has an expansive athletic field with a mostly unobstructed view of the western horizon.  And best of all, there’s a paved basketball court which provides a nice, level surface devoid of any animal droppings (specifically geese and deer) – a perfect place for comet viewing.  Three other people must have thought the same thing, as they joined me there before I even finished setting up my tripod.  Two of them were using hand-held binocs and the other guy had a camera so much nicer than mine that it figuratively made my mouth water.

It was a chilly evening and I was there only for about 45 minutes or so.  In that time I got about a dozen photos of the comet, but unfortunately all but one of them were largely ruined from photobombing by earth satellites and airplanes.  That one is spectacular – it shows a long primary tail and a much shorter and fainter opposite-pointed secondary tail, with the comet partially framed by clouds that reflect light from suburbia.  It’s maybe the best astrophoto I’ve ever taken.

Before I left, just for the hell of it, I decided to see what would happen if I took a photo with my iPhone’s camera.  I had no idea what the focal length was, so I just held the phone firmly against the camera tripod and pressed the virtual button, hoping for the best.

I’m actually amazed that it worked!  The comet is easily visible on the image, and so are Venus (to its left) and the bright star Arcturus (to its right).  And in the foreground the pattern of lines on the paved area adds to the interest of the photo.  All in all I’ve decided it’s maybe the second-best astrophoto I’ve ever taken.

I guess the moral of the iPhone story is: Forget everything I told you about comet photography with a stationary camera.  You don’t need it!  A late-generation mobile phone seems to work just fine!

I’ve read that there’s going to be another really bright comet in January.  The good news is that Comet C/2024 G3 (ATLAS) – and let’s just call it “Comet G3” – will be so bright that it reportedly may become visible even in the daylight sky.  But the bad news, at least for me, is that it will be entirely a southern hemisphere event.  Feh!

There’s not expected to be another northern hemisphere naked-eye comet for at least the next three years.  But nobody knows for sure.  Comet A3 was discovered only 20 months before it became a very bright object, and there are all kinds of icy objects out there from the Oort Cloud that could be dive bombing their way toward the inner Solar System.  So when – not if – that happens I’ll be ready.  And until then I’ll keep watching the skies!