The Herschel 2500

 

H27-4, "The Ghost of Jupiter"

In the final decades of the 1700's, the German-British astronomer William Herschel and his sister Caroline conducted a survey of the heavens. Together they discovered and produced a list of 2500 star clusters and nebulae that they published in three separate catalogs. Night after night, using a telescope of 18.7 inches in aperture and 20 feet in length, William, making his discoveries at the telescope eyepiece in the garden, called out the positions and descriptions of his celestial objects to his sister through an open window of their house, and she wrote down all the details by candlelight. It was a colossal effort that took them 19 years to complete, and meanwhile, William continued to build telescopes and conduct other scientific experiments in the daylight hours. 

You can read all about the Herschels on Wikipedia, so I needn't repeat any more of their story here. However, in modern times, their 2500-object survey still manages to attract the interest of amateur astronomers around the world. After buying a telescope to look at the moon and planets, these amateurs wonder what else there is to see in the night sky. Typically, they start by going after Charles Messier's 110 objects. After that, they're left wanting more. The Herschels' list of 2500 objects would appear to offer enough targets to keep backyard astronomers busy for a lifetime. Indeed, the list of 2500 targets is so daunting that a subset of the list was created a few decades ago, dubbed the "Herschel 400." Observers often start out on the 400, and if they make it that far, some of them carry on with the rest of the 2500.

Before there was such a thing as a computerized "Go-To" telescope, a list of 2500 objects probably would require a lifetime for amateur astronomers to seek out. Hunting for deep-sky objects the old-fashioned way wasn't easy. Especially if the objects are dim. You'd find the right area with the help of a sky chart, but sometimes you'd search for an object by looking through the eyepiece and moving the scope back and forth, up and down, and you'd go right past the target every time, without spotting it. For inexperienced observers, just trying to find one object could sometimes take 30 minutes or longer. 

In 1980 (when I first became interested in astronomy), commercial telescopes were not computerized. The more advanced telescopes had only a clock-drive (synchronous motor) that was optional. When properly aligned to the North Celestial Pole (for those of us in the northern hemisphere), a telescope with a clock-drive could keep up with the diurnal movement of the stars, but it had to be aimed by hand at celestial targets. There wasn't a set of high-speed motors on each axis to "slew to" an object. The telescope user would need to know where the object is in the sky, disengage the gear clutches, point the telescope at the correct spot, then center the object in the eyepiece and lock down the clutches again. After that, the telescope could hold the object in the eyepiece field of view by keeping up with the earth's rotation. Aiming such a telescope at the moon or bright planets and stars is a trivial thing, because we can see those targets with our unaided eyes. We can simply aim the telescope by sighting along the tube. But the fainter stars, star clusters, nebulae, and galaxies are unseen by the naked eye. If we hadn't ever tracked them down before, we'd need to find a set of coordinates and a star chart to know where to aim our telescopes. 

In those years it wasn't just the telescopes that weren't computerized. Star charts were not computerized, and neither were the lists of celestial objects. In 1980, we didn't have PC's. There was no internet (for us non-university types). There were no internet service providers. We couldn't Google anything. We couldn't download a list of the Herschel 2500. The word "download" was not in our vocabulary. Every document was printed on paper (or stored on microfiche). If we wanted to get our hands on a list of William Herschel's discoveries, our best chance of finding it was by taking a trip to the public library and using their card catalog (also on paper) and the Dewey Decimal System. That is, if our local library even had a book or periodical that contained said list! Even if it did, how could we make a copy of it to plan our observations? By writing it down on paper with a pen? Re-typing the list using a typewriter? If our local library had a Xerox machine, we might be permitted to make photocopies of the Herschel 2500 list. But that would be 50 pages or more. We would have to get a hole puncher and put those 50 pages into a 3-ring binder. 

The next problem was that there were no pictures of the Herschel 2500 available for us to use as a reference. How could we verify our observations of the Herschel objects without knowing what they were supposed to look like? A lot of Herschel's open star clusters, for instance, are not very obvious in the eyepiece. You could be aimed at the correct coordinates, but the view in the eyepiece looks like a random star field. "Where's the cluster?" you'll ask. There were a few books and magazines available to amateur astronomers, but these were very sparsely illustrated with only a small fraction of the objects we could observe with our telescopes. Even the classic, three-volume Burnham's Celestial Handbook didn't cover all the Herschel objects. There was no bookstore or library anywhere that we could go to and get a picture of every celestial target we asked for. The all-sky surveys made by professional astronomers were on glass plates and locked away from the general public. 

The worst part of it all, though, was not the lack of available information and pictures, it was that the Herschel 2500 was fraught with errors, despite William and Caroline's best efforts. Many of the objects were missing. Observers would look in the correct position in the sky, but no object was found. Over the years since the Herschels published their lists, astronomers have solved some of those little mysteries and made corrections to the list, but in the process, they added some of their own errors. It was a mess! Anyone hoping to tackle the Herschel 2500 would have to realize from the start that it would be impossible to complete their task. Technically, there are not even 2500 objects to find. 

I think it was in the year 2017 that I was looking over the list of certificates on the web site of the Astronomical League, and I saw among them the award for observing the Herschel 2500. My first reaction was, "Who in the world would attempt to observe 2500 targets, just to get a piece of paper from the AL?"

However, before dismissing it outright, I thought, "Wait a second. Most of the Herschel objects are probably galaxies. Since I'm a supernova hunter, and since I've taken pictures of all of the NGC galaxies north of -40 degrees declination, I'm probably already halfway through the list. Whoa!"

To "check off" objects, I used the highlighter tool in Adobe Reader

I downloaded the PDF of the Herschel 2500 and took a quick look at it by scrolling down through its many pages. Fifty-two pages, to be exact, each containing about 48 objects!

Okay, let's put this in proper perspective. I may have images of a lot of these objects on my computer but proving it will take some time! I can't assume that I didn't make any mistakes in all those years of shooting thousands of galaxies. I have to find all the pictures I've taken of potential Herschel objects, bring them up one at a time on my computer and compare them to some standard image of a Herschel object. Where do I find standard images of Herschel objects?

Nowadays, the logical choice to get images of every celestial object in the heavens is the Digitized Sky Survey. But have you ever used it? Yeah, the web site is a little awkward to use if you're trying to look up a couple thousand galaxies! It takes more than a few seconds to enter an NGC object or type in its coordinates, then select the image size you want, the instrument you wish to get it from, and whether you want a FITS image or GIF. To look at 2500 objects using the DSS interface would take forever!

But that's only the half of it! I still needed to find all the images on my computer. And I needed to open each one, mirror it (my images taken with the HyperStar lens are mirror-reversed) and rotate it (shooting with an altazimuth mounting causes my images to be somewhat rotated if they aren't taken on the meridian, and upside down if they're north of the zenith) so that they match the DSS view.

Lucky for me, I'm a computer programmer, so I wrote a combination of C++ programs and MS-DOS batch files to speed up the processes of getting DSS images and finding specific files on my computer to compare. It's difficult to calculate how much time I saved but suffice it to say that I could enter the NGC number at the MS-DOS prompt, and within seconds the DSS image would appear in my web browser. Then I could type another command and get a list of every image I've ever taken of that NGC object. A quick copy and paste brings up any one (or all) of those FITS files into my FITS viewing program. Using those homemade computer shortcuts, it still took me about an hour to verify 10 objects. 

If it takes 1 hour to verify 10 objects, I'm looking at 250 hours to verify 2500! What with work and family commitments and supernova hunting (not to mention getting enough shuteye to function the next day), I might be able to spend an hour here or there working on the Herschel 2500 verifications. And I couldn't do it every day. If I could give it 1 hour of my time only every other day, it would take me 500 days! Oh, well. It's not like there was a deadline to meet. It will just have to take as long as it takes. 

Before launching into the verification process, and just to give myself a feel for what lay ahead, I parsed the list of Herschel objects to find out how many of them were galaxies, and how many were star clusters and nebulae. According to the list that I downloaded, this worked out to 2110 galaxies, 148 open clusters, 37 globular clusters, 36 planetary nebulae, and 31 emission nebulae. All the rest were other types of objects (single, double, and triple stars) or else they were nonexistent (which would require further investigation and time).  

Indeed, verifying all the objects was daunting. But I pushed forward. What had initially sounded easy (my plan to kickstart the Herschel 2500 by quickly checking off the objects I had already shot) took me several months.

Getting the rest wasn't trivial, but it amounted to a few hundred objects that I knocked out within about a year or two. It was rather painless to follow my plan of working in some Herschel objects while shooting galaxies each night for supernova hunting.

Since there aren't truly 2500 Herschel objects, I had to make a decision on how and when to call it "finished." I read a lot of favorable online reviews of Mark Bratton's book, The Complete Guide to the Herschel Objects. So, I bought it and chose to use it as my "authority" on the Herschel list. Bratton researched the list and trimmed it down to 2433 objects that can be verified. Bratton's list became my goal. I decided that I did not need to be a literalist. Getting images of and verifying 2433 objects is close enough to still refer to them as "the 2500"! 

Now you might ask, "Wait a minute. You used a camera to take pictures of all the objects, and you used a Go-To telescope instead of finding them by yourself. You didn't even go outside to hunt for them. You sat at your computer, commanding your telescope in the back yard to aim at and shoot each object. Isn't that cheating?"

Yes, I must confess to slightly altering the game plan! The original concept of "going after the Herschel 2500" implied that you would do it the old-fashioned way of using your star chart and pointing your telescope by hand at each of the 2500 Herschel objects, and then looking at them through the eyepiece. But let's face it: That isn't even the way William Herschel did it! 

William Herschel discovered all of these objects, so he didn't use a star chart to show him where they were! And his 20-foot long telescope was too difficult for one person to aim. He had to hire a couple of employees to point the telescope for him, while he stood on a platform to look into the eyepiece. His discoveries were made by making what he called "sweeps." This was done by having his helpers aim the telescope at a bright star near the meridian. The workers would take a break and let the sky carry objects through the telescope's field of view for several minutes. William, watching closely through the eyepiece, would patiently wait for a nebula or star cluster to come into view. Using a clock, he noted how many seconds it took for the object to appear after the bright star drifted away from center.

Thus, technically speaking, if you wish to claim that the only proper way to do the Herschel 2500 is to use star charts and aim the telescope by hand, then you also are not finding the objects the way Herschel himself did it! He didn't use a star chart. And he didn't aim his own telescope. His helpers did!

And to address the issue of taking pictures of all 2500 objects versus looking at them through the eyepiece, I can only say that this comes down to a matter of personal preference. It's probably a safe bet to say that, in the 21st century, the majority (I don't know the actual ratio) of backyard telescope enthusiasts have swapped out their eyepieces and replaced them with cameras. City light pollution has forced us to do that. Electronically Assisted Astronomy (or EAA) has become increasingly popular, and EAA is often considered synonymous with "observing." When I am searching for supernovae, for example, my pictures are closer to eyepiece observations than they are to resembling the beautiful astrophotographs you'll find on the internet. My pictures are 22-second exposures, revealing only about as much detail as perhaps what can be seen in a 32-inch Dobsonian telescope that you may encounter at a dark-sky star party, where observers stand precariously on stepladders, peering through the eyepiece to hunt down, among other faint targets, the Herschel objects. I can't drive to a dark-sky site every night, and I don't like climbing up stepladders in the dark! And goodness knows I have no place to store a 32-inch Leviathan! My Celestron CPC-1100 with HyperStar and camera is the way I do my "observing." And even though I don't delete any of my 22-second exposures, for all practical purposes they can be considered "throw-away" images. Like looking through the eyepiece, after I examine the latest image coming into my computer from the camera out in the back yard, I've gotten what I needed from it. I may never look at that picture again, except when I wish to collect a bunch of my exposures of a certain target and stack them up to create a "pretty picture." 

Some people like to cozy up to the idea that if you look at each of the Herschel 2500 objects through the eyepiece of your telescope, then you're seeing all the objects the same way that William Herschel saw them. There's something special about knowing that you're looking at the same thing that Herschel first saw centuries ago, and that, essentially, the through-the-eyepiece view of Herschel's discoveries hasn't changed at all! 

But once again, there is a difference between the instruments Herschel used and what is available to us today. Herschel used a modified Newtonian reflecting telescope. We refer to his telescope as a Herschelian reflecting telescope, because he didn't use a secondary mirror like Newton did. Not only that, but Herschel's objective mirrors were made of speculum metal, not aluminum-coated glass like modern reflecting telescopes. So, we modern backyard observers, looking through the eyepiece of our modern reflecting telescope designs, are not seeing the Herschel 2500 objects like he saw them. Nor can we even imagine what these objects looked like to Herschel through his telescope. 

Therefore, let's be honest. The only way for us 21st century astronomers to conduct the observation of Hershel's star clusters and nebulae in the exact same way that Herschel did it, would be for us to use a meridian telescope with a mirror made of polished metal, with no secondary mirror, and by pointing our scopes at bright stars and allowing the Herschel 2500 objects to drift into our field of view. 

Bottom line for me here is, if you didn't complete the Herschel 2500 list in the exact way that Herschel did it, then don't criticize me for using a Go-To telescope and camera! 

After shooting all the Herschel objects and verifying them myself, which was an enormous undertaking, I tried to imagine what it would be like for me to submit my observations to the Astronomical League in order to get one of their certificates. Would I send my FITS images to them on a CD or thumb drive? Wait. What if they required that my images be in JPG or some other format? Now I have to convert 2000+ FITS images to JPG? How long will that take? And when they received my images, how long would it take them to open each one and compare it to some standard Herschel object image and verify that I got them all? 

And then I thought, "What if I hadn't taken pictures of them? What if I had done it the so-called "proper way" and observed the objects through the eyepiece and wrote a description of what they looked like or drew sketches of them in my logbook? How long would it take the AL to read my descriptions and look at the sketches of each object and verify that I had actually observed all of them?"

But wait. I'm just one person! What if a thousand amateur astronomers sent a CD of their 2500 photos or sketches to the Astronomical League in the same week? How would they possibly look at a thousand times 2500 objects and verify them in any reasonable period of time?

Surely all they can do is take a quick glance at each person's submissions and say, "Yeah, looks like they put forth a lot of effort. Good enough! Here's their certificate!"

As one who has completed the Herschel 2500, I was curious to read others' descriptions of "doing the Herschel 2500." And what I found online puzzled me. I read various accounts of people who had completed the Herschel 2500 list, but they didn't talk about the humongous effort of verifying their objects. They simply stated that they "completed the Herschel 2500," along with their other many accomplishments as amateur astronomers. As if it was no big deal. 

After my own experience, I am skeptical of anyone who claims they completed the Herschel 2500, if they don't also talk about how difficult it was to manage the administrative part of recording the observations and verifying each of the 2500 objects by comparing it to online pictures. How demoralizing it was to cross off all 48 objects on one page of the PDF, then scroll to the next page and find 48 more objects that needed to be checked off. And then to keep scrolling and reach page 25 and realize you're only about halfway there!

However, there are two paths to take when tackling a project as big as observing all of the 2500 Herschel objects. The first path is one like mine, where you observe many objects over the years, and then you apply those observations to a list like the Herschel 2500. When you have to go back and verify many years' worth of observations, it's a huge chore. And because it's so difficult, it's a very memorable chore. But the second path is to choose your list first, and then begin observing all the objects on that list. When you go down this path, you verify each object as you go. Maybe when you choose this path, it's not as difficult or memorable to verify your observations, since you're only verifying one observation at a time.

Based on my own experience, I'd have to say that if you're going to do the Herschel 2500, choose the second path that I mentioned above. Don't make my mistake! Observe and verify each object as you go. That way, when you observe your last object, you're done! I feel like I had to do the Herschel 2500 twice. Taking the pictures of all of them was the first time through. Making the Herculean effort to verify each and every one of them later was like doing the Herschel 2500 a second time. It was every bit as painful and took nearly as long as the first time! 

The first Herschel 2500 object I shot was planetary nebula NGC 3242, affectionately known as "The Ghost of Jupiter" because of its appearance in the eyepiece. My image was taken on April 25th of 2008, marking the beginning of my quest (which I didn't even realize I had started). The final image was an NGC galaxy that I had previously missed. It was on the night of April 16, 2020, when I realized that I still needed to get a shot of NGC 5672, in order to complete my version of the Herschel 2500. Fortunately, NGC 5672 was observable in April's night sky, so I was able to get an image of it. Thus, it took me nearly 12 years to finish imaging and verifying all the Herschels.

There is something else I want to mention here that was a motivational factor for me to do the Herschel 2500. And that is the pressure that I felt while looking back on my many years of amateur astronomy. There's a very different feeling that you have at the end of the road than what you felt at the beginning of your ride. The first 20 years of backyard astronomy were very enjoyable and relaxing. I took out my telescope whenever I felt like it, and I hunted down some random targets using a star atlas and my trusty Odyssey 1 Dobsonian telescope from Coulter Optical. There's nothing like the experience of being out under a clear, dark sky, chasing down faint fuzzies with a big light bucket. Then I dabbled in astrophotography with film for a decade. Driving out into the desert all alone, 50 miles from town. Sitting on my camera case for a chair and staring at a dim star through the guiding eyepiece for five or six hours, while my telescope was aimed at targets I couldn't see. During all that time, I never had much of a plan for my observing or astrophotography sessions. I made them up as I went along. Then, all of a sudden, I found myself in my 50's and I thought, "Man, I've been an amateur astronomer for 30 years. What do I have to show for it? A couple hundred astrophotographs? Is that all?" 

Can you imagine having spent 30 years exploring the night sky with your telescope and someone asks you, "Wow! Thirty years! You must have completed the Herschel 2500 by now, huh?" And you'd have to sadly admit, "Well, no. I guess I never got around to that." 

Thoughts like these can be a real wakeup call! Now in my 60's, I realize more than ever how few are my remaining years! 

After starting on the Herschel 2500, I went hog wild on the other lists, too! It wasn't as though I wanted to complete them. I felt as though I must! I had already bagged the 110 Messiers, so after completing the Herschel 2500, the next list that I tackled was the Caldwells. I took pictures of all of those that I could get from my back yard (some of the Caldwells are in the southern hemisphere and I can't see them from here). There were only about 85 of them. After going after 2500 targets, 85 was like nothing! Of course, some of the Caldwells are also Herschel objects, so I crossed a few of the Caldwells off the list right up front. Next up was the 100 Hickson galaxy groups, and then the 338 Arps. I also went after the first 100 numbered asteroids. I had already taken pictures of all the major planets (including Pluto).

I absolutely do not want to be known as a do-nothing amateur astronomer! Even if I don't have any certificates to show for my efforts, I have my images to prove all the observation lists I've completed, in case anyone would like to go through and verify them all.

H310-3, or NGC 5672