Tale of two comets

 

You may have seen the online hype this month over two comets that are currently gracing our nighttime skies. We backyard astronomers are, of course, enjoying the views of these comets using our binoculars and telescopes, but we also know that they are far from being "Great Comets," much less being worthy of such widespread coverage by the news media. After all, any comet that one can only barely see with a pair of binoculars is not a comet that non-astronomers will appreciate. I, for example, might look at these comets using my 8x42 binoculars, and say, "Nice!" But if I were to hand my binoculars to a neighbor who knows nothing about backyard astronomy, they would do their best to follow my instructions as to where to look, and ultimately say, "I don't see anything," before handing the binoculars back to me.

Now, you take, for instance Comet Tsuchinshan-ATLAS that was in our skies almost exactly one year ago. That was a much better comet than either of these two that are currently visible in the night sky. Comet Tsuchinshan-ATLAS was at least visible (if only barely) to the naked eye! It wasn't a "Great Comet," either. My neighbors may not have been able to spot Comet Tsuchinshan-ATLAS with their unaided eyes, but I could easily have taken a picture of it with my smartphone, showed it to them, and they would have been amazed! 

In truth, my neighbors (who never venture outside at night without first turning on their super-bright LED lights) didn't care about either the comet or the starry host, and it's no surprise that they weren't outside after dark when I was out there taking pictures of Comet Tsuchinshan-ATLAS.

So, what makes a "Great Comet"?

Well, it's a very simple distinction. A Great Comet is a comet that is as easy to spot as the sun or the moon in the sky. If there's a Great Comet in the sky and you walk outside at night, you likely will see it before you notice anything else in the sky! You won't need to be told about it in the news media. Nobody will have to point it out to you. It will command your attention all by itself.

My photo of Hale-Bopp in
1997 taken with a 200 mm
camera lens on Konica 3200.

We haven't seen a Great Comet since Hale-Bopp was cruising through the inner solar system back in the spring of 1997. Even if you didn't hear about Comet Hale-Bopp on the news, you would simply go outside after dark, look up in the sky and say, "Whoa! What the heck is that?" 

Yeah. That's a great comet!

To give you a sense of scale for my photo of Hale-Bopp, the little star cluster situated where the two tails split apart is Messier 34, in Perseus. And the brightest star at the top edge (center) of the photo is HD 16780. That star is 5-1/2 degrees away from M 34. Five-and-a-half degrees is the area subtended by slightly more than the width of your three fingers (index, middle, and ring fingers, as in the "Boy Scouts Honor" gesture) held up to the sky at arm's length. 

Three fingers?  That's a good glass of whisky, but how does that make a Great Comet? 

Well, for a little more perspective, 5-1/2 degrees is the width of 11 full moons! And Hale-Bopp wasn't just a dim little comet that required binoculars to see. It was so bright, you could see its two tails naked-eye! It looked nearly as good to my naked eyes as it looks in my photo. 

For comparison, in my photo up there at the top of this page, Comet Lemmon's tail fades rapidly as you look away from its nucleus. From the front tip of the coma to the end of the faintest part of the tail that can be seen in the photo, it measures only 8/10ths of one degree. In binoculars, I could see only about half of the tail that shows up in my photo. So, using binoculars, the comet appeared to be about half a degree in length. With my naked eyes, I could see nothing!  

But as far as amateur astronomers are concerned, any comet that can be seen with a pair of bird-watching binoculars is a "decent comet." If it's visible through binoculars, then it is at least as good a target as any Messier or other famous deep-sky object. Any object that can be spotted with binoculars is an object that will look even better through the eyepiece of a telescope. And we backyard astronomers have plenty of telescopes! So we love it when any comet gets bright enough to be seen in a pair binoculars, even if just barely. That's because we know our way around the night sky, and if a comet is passing through, even the not-so-great ones, we have the knowledge, skills, and instruments to go outside and track it down. It's what we've been doing for years! But non-astronomers? They aren't prepared to go outside at night and spot non-great comets.

While I enjoy looking at and taking pictures of comets with my telescope, I must confess that I am by no means a skilled astrophotographer amongst today's community of astrophotographers! I don't use any of the sophisticated image-processing software that can turn either of these current comets into the amazing APOD-quality pictures that you'll find all over social media. I'm rather old-school in my methods, and my pictures above are representative of my goals for astrophotography: I'm not going for the sensational or over-hyped imaging results that require hours of exposure time and many more hours of image-processing time. I just want a quick and dirty picture of what's out there. 

My exposures of deep-sky objects (to include non-naked-eye comets) are relatively short (a few minutes, at most). I don't process the comet separately from the stars or super-enhance my images using sharpening and color-enhancing algorithms. I just take a few exposures and stack them. The result is something that is not much more fantastic than what these objects look like in the telescope eyepiece. And I would bet that anyone who has seen Space Telescope pictures of celestial objects would be extremely disappointed to look at those same objects through the eyepieces of small backyard telescopes!

This is an important subject matter to talk about, though, so let's do it! Scroll up and take another look at my pictures at the top of this page. If you were to go outside and try to find either of these comets in your backyard telescope, they will probably look worse than they do in my photos! But only a little worse! You probably won't see as many stars as in my photo of Comet SWAN. And you probably won't see any of the colors that you see in my photo of Comet Lemmon. 

It's a sad truth: Eyepiece views of celestial objects don't look nearly as good as the super-enhanced astrophotographs that you see in the news media. It's very deceiving! The news media will show you a picture of a blazing comet with amazing color and swirling-tail details, but if you go out at night to try and see the comet for yourself, you will be sorely disappointed with what you see in your binoculars or telescope eyepiece!

My advice? Well, I think you should go outside at night and see what you can see. Pay attention to the location of these comets, because you won't be able to see them with your naked eyes. Use their celestial coordinates, finder charts, and a good star atlas (or software) to track them down with binoculars or a telescope, if you own one. Forget about the super-enhanced photographs you saw in the news articles. These comets won't look anywhere near as spectacular as the news article photographs made them appear. What you'll likely see instead will be uninteresting and colorless "fuzz balls." If all you can see are fuzz balls, then you have succeeded in finding them! And if you are happy with your ability to at least find them and see them as fuzz balls, maybe then you'll be inspired to upgrade your equipment so that you can see them better or maybe even take your own long-exposure photographs of comets some day!

One interesting scientific fact that I'd like to point out here, as you look at my pictures above, is that, as comets reach the inner solar system, the sun's intense energy causes their frozen surfaces to warm up and break up a little. During this breakup as they get closer to the sun, dust and gas escape to produce spectacular "tails" that can be millions of miles long. Comet tails usually point away from the sun, because the solar wind (charged particles flowing outward from the sun in all directions) pushes the gasses of a comet's tail away from the sun. And the comet's gravity tends to keep the escaping dust close to the comet's orbital path around the sun.

To this point, my image of Comet SWAN (top left) was taken soon after sunset when it was low in the southwestern sky. A tiny gas tail can be seen pointing toward the upper left (north and east), away from the setting sun. And note in my picture of Comet Lemmon (top right), taken not long after sundown when it was low in the northwestern sky, that its tail was pointed toward the upper right (north and east), also away from the sun.

Why do I mention this?

Because as backyard astronomers and astrophotographers, it's important to keep our directions straight! If you were taking a picture of the sun setting over the ocean, you would want the water line in your photo to be perfectly level (horizontal), wouldn't you? Well, for space photos, people tend to think that there's no up or down, so they have some kind of artistic license to do whatever they wish with their astrophotos. Astrophotographers will sometimes rotate their cameras on the telescope to frame their celestial subjects in an arbitrary or aesthetically pleasing way. 

But when it comes to comets, their tails are like the ocean water lines in sunset photos. They must be pointed away from the sun. That is, if you're shooting a comet in the northwest just after sundown, then your picture shouldn't be oriented so that the tail of the comet points straight downward. Neither should it point straight upward. For a comet in the northwest just after sundown, its tail should point to the upper right (northeastward), if your photo is going to look realistic. And if the comet is nearly due south in the sky at sundown, its tail should point to the upper left (also northeastward). 

Comet tails aren't arbitrary. And we're supposed to be astronomers, aren't we? Well, then, let's get it right! All I'm sayin'.