Archive for October, 2015


My article in the December Sky & Telescope

October 31, 2015
SnT Dec 2015 cover - marked up

Einstein has my article on his mind!

Here’s the exciting news I teased back in September: the December 2015 issue of Sky & Telescope, which is available online and should be hitting newsstands about now, has an observing article by yours truly. It’s a binocular tour of the southern stretch of the winter Milky Way, from Canis Major through Puppis to end in Hydra.

SnT Dec 2015 contents - marked up

The road that led here started back in December, 2014, when I got a very nice email from S. Johnson-Roehr, “JR”, the observing editor for Sky & Tel. JR had stumbled across this very site (possibly because I’d just recommended the newly-reprinted Caldwell Objects?) and asked if I’d be interested in contributing an observing article. We batted some ideas back and forth and quickly settled on the winter Milky Way. I had been through this area of the sky before but I wanted to give it one more pass, both to flesh out my notes and to road-test the star hops I had in mind. I made those observations this spring, wrote the article over the summer, and now it’s out in the world.

I have one favor to beg of anyone who reads the article – I need feedback. This is my first time writing about astronomy anywhere but a blog, forum post, or club newsletter, and I’d like to know (1) what worked, (2) what didn’t, and (3) what you’d like to see in the future. The comment field is open.

There’s a lot more to like in this issue of S&T, some of which will be of particular interest to regular readers of this blog. Tony Flanders has another inexpensive telescope shoot-out. Back in 2011 he and Joshua Roth looked at $100 scopes, in particular the Orion SpaceProbe 3, GoScope 80, and SkyScanner 100 (that article is a free download here, and a follow-up comparing the SkyScanner to the StarBlast is here). This time Tony considers three scopes in the $200 range: the Meade Infinity 90mm refractor and alt-az mount, the Orion StarBlast 4.5, and the Astronomers Without Borders OneSky. I won’t give away any spoilers, except to note that he finds all three to be capable scopes, which I’m sure is no surprise around here.

Another nice review in this issue is Alan MacRobert’s look at the first two volumes of Jeff Kanipe’s and Dennis Webb’s Annals of the Deep Sky, from Willmann Bell. As a deep-sky junkie who likes to read himself to sleep with Burnham’s Celestial Handbook and Stephen James O’Meara, I have been curious about these new books, but I hadn’t heard anything about their quality before reading MacRobert’s article. Sounds like I need to make space on my Christmas list.

There’s loads more interesting stuff in this issue – cover articles on Einstein and gravitational waves, great observing articles by Alan MacRobert, Fred Schaaf, Gary Seronik, and Charles A. Wood, a very nice piece by Sue French looking at some neglected open clusters and double stars in Cassiopeia (an area I thought I knew well)…you get the picture. If you’re not a subscriber, you can find the December issue of Sky & Telescope on your local newsstand, or order a print or digital copy online here.

If you’re new here, welcome! Have a look around, and feel free to comment.


Digiscoping with the GoSky universal cell phone adapter

October 30, 2015

Bird on a stick - 50x

As I mentioned in the moon video post, I recently got a GoSky universal cell phone/eyepiece adapter. So far I’ve tested it on some birds during the daytime, and on the moon after dark. Here’s a Northern mockingbird at 50x, about 125 feet away.

C80ED set up for digiscoping

I did most of the digiscoping with my C80ED and a 12mm Plossl (50x). I tried other eyepieces but for my purposes the 12mm Plossl delivered the best balance of magnification, true field, and image brightness.

C80ED digiscoping business end

If you haven’t seen one of these cell phone adapters, it has a diamond-shaped, padded clamp that screws down around the eyepiece, and another padded clamp to hold the phone. The bracket for the phone can slide up and down and rotate relative to the eyepiece clamp, so you can get the phone’s camera centered over the exit pupil of the eyepiece. As you can see here, the phone bracket is wide enough to hold an iPhone 5 with a heavy Otterbox case. I prefer to leave the case on while shooting – it’s rubber, so I can crank down the adapter bracket and make sure the phone is truly secure. Plus, it’s one less thing to do during setup and teardown.

iPhone earbuds remote shutter release

You may be wondering why I have earbuds hooked up to the phone. It’s because of a very nice feature with the iPhone 5 and 6 (don’t know about other iPhone models or other brands of smartphones) – the volume buttons work as shutter release buttons, which is often handier than trying to press the button on the screen, AND this functionality extends to plug-in volume buttons like those on the earbud cords. So you can plug in your came-with Apple earbuds and use the volume control there as a remote shutter release for hands-free, no-shake photography.

Fanned tail feathers - 50x

That mockingbird again, fluffing its tail feathers.

Waning gibbous moon 2015-10-28

Here’s one of the moon. The seeing was punk last night so I know the system was not performing anywhere near its limits. I’ve done far better holding the phone by hand on nights with better seeing, but only by dumb luck, taking loads of pictures, and throwing away all but the best. Using the adapter I get much more consistent results, even if the seeing makes them all consistently lousy on a given night.

The biggest problem with this setup so far is that the lens of the iPhone camera is bit fish-eyed and that introduces some kind spherical distortion (I believe it is positive or pincushion distortion – feel free to educate me in the comments) in the image. It’s not so bad in this cropped picture:

European Starling x4 - 50x

But check out the diverging power lines – which are parallel in real life – in the unmodified original:

European Starling x4 - raw shot

These are European starlings at 50x, again with the 12mm Plossl, from about 250 feet.

I did lots of back-and-forthing between camera and the various eyepieces to confirm that the distortion was in the camera and not in the telescope or eyepieces. It’s a fairly minor annoyance for me – I’m not expecting world-class results out of my smartphone camera. Just something to be aware of.

European Starling - 100x

I tried going up to 100x with the 6mm Expanse on this starling. It caused a lot of vignetting – even in this severely cropped photo, you can see that the corners are dark. I’ve had this problem with using too much magnification with handheld afocal photography as well. I think that as magnification goes up and the exit pupil goes down, it’s progressively harder to fully illuminate the camera’s CCD.

This may seem like a lot of caveats and complaints – distortion, vignetting, etc. – but they’re all problems that come along with doing afocal photography with a phone. The adapter itself is dandy. It holds the phone and eyepiece securely and without stressing either one or leaving a mark, it’s easy to put on or remove, and it adjusts easily. I wish now I’d gotten one a lot sooner. There are lots of interchangeable brands on these things – if you want the GoSky verison, it’s here.


Video: Moon and clouds

October 29, 2015

After much helpful prodding by Doug, I finally broke down and got a cell phone/eyepiece adapter. I had some Amazon credit and I was looking at some cheap astro gear by VITE. In particular I was checking out their cell phone adapter when I saw the link for a similar piece of gear by GoSky. The GoSky model cost a little more but the build quality looked more substantial and the reviews were better, so I bit. Got it out after work this evening for some digibirding and then some moon shots. More about that, and about the mount, in another post.

Shot this video from my driveway using the C80ED, a 12mm Plossl, the GoSky camera adapter, and my iPhone 5C. I know a horizontal aspect ratio works better on most computer screens, but I deliberately wanted it vertical to catch as much of the moon rising as possible without moving the scope. These were the last clouds of the evening, so at least for now, the New Gear curse has lifted.



Double stars and the Double Cluster: a short observing run in bright skies

October 17, 2015

I completed a major lecture Thursday so I treated myself a short stargazing run in the driveway that evening. Transparency was rotten – it was so humid here that even with the temps in the low 70s I was still sweating, and with all that water vapor to bounce back the city lights, the sky was bright to about 45 degrees above the horizon. I did a quick turn around the sky with my old 7×35 binoculars, which I’d not used in ages, and all I could see were the major constellation outline stars. I decided to see what the C80ED could do, in part because it’s my best grab-n-go scope and I knew it would be a short run, and in part since I’d just had it out under much darker skies.

I started on M57, the Ring Nebula, which is obvious even at low power under most conditions. This time out, the Ring was just a ghostly blob in averted vision at any magnification, even when Lyra was still quite high. But the seeing was rock-steady. Epsilon Lyrae, the famous double-double star in Lyra, was very elongated, like a pair of 8s, at 68x, and cleanly split – juuuuust barely – at 100x, although I had to go up 136x to easily hold the split in direct vision. After that I bopped over to Cassiopeia/Perseus to split some doubles (Eta Cass was nice) and look at the Double Cluster. Didn’t attempt a sketch, I was just rolling for aesthetic appreciation, but I did use a lot of magnification and spent more time on the clusters than I usually do. I had not noticed before that NGC 884 has an empty center. I mean, under dark skies there are plenty of stars in the middle, but the bright stars form a series of arcs around the edge, and under so-so skies those outer bounding arcs of stars are all you can see. NGC 869 is the opposite, it just gets more and more concentrated toward the center, albeit unevenly.

Double Cluster from SEDS

The Double Cluster: NGC 884 (left) and 869 (right). Photo borrowed from SEDS.

At 11:20 the clouds suddenly thickened up – in the space of five minutes I went from pleasant observing to totally socked in. After I got everything stowed, I went inside and looked up Stephen O’Meara’s entry on the Double Cluster in his Caldwell Objects book. His observations were gratifyingly similar to mine, but I learned some interesting stuff about the clusters. They are BIG and they are distant: 7300 light years, compared to less than 4000 light years for most Messier open clusters, and dimmed by about 1.5 magnitudes by intervening dust clouds. One shudders to think about how much more impressive they’d be if they were only half as far off and not obscured by interstellar dust.

Anyway, a good run. We’re clouded out this weekend, so I’m glad I got it in.


A tour of Big Bear Solar Observatory

October 13, 2015

BBSO from up high

The gleaming white domes of the Big Bear Solar Observatory sit at the end of a causeway that projects from the north shore of Big Bear Lake – they draw the eye from almost any point in Big Bear Valley. And as I mentioned in my last post, the Pomona Valley Amateur Astronomers got to visit the BBSO on Friday, October 9.

BBSO causeway

We were greeted at the gate by Claude Plymate, Chief Observer and Telescope Engineer at BBSO, and Teresa Bippert-Plymate, who is not only a professional solar astronomer but also the president of the Big Bear Valley Astronomical Society. As pros who are also enthusiastic amateur observers, Claude and Teresa did a great job of pitching the tour with just the right balance of necessary background, technical detail, and the hands-on practicality of managing big scopes and the complicated hardware and software necessary to run them.


The first thing you come to on the causeway is a big white storage container with a coelostat (sun-tracking mirror) – this is one of the six Global Oscillations Network Group (GONG) installations spaced roughly equally around the world. The GONG telescopes track the sun around the clock for helioseismology research, mapping the acoustic pressure waves that propagate around and through the sun.

PVAA group outside BBSO domes

The smaller dome just short of the end of the causeway holds two telescopes on a common mount. One is a 10cm full-disc hydrogen-alpha solar telescope, the other is a second smallish refractor for Project Earthshine, which tracks the Earth’s albedo by measuring the intensity of the earthshine that falls on the moon’s unlit side.

London with BBSO New Solar Telescope

The observatory’s ‘big gun’ is the 1.6-meter New Solar Telescope, an off-axis Gregorian. One-point-six meters is 63 inches, which means this scope has a slightly larger aperture than the famous 60-inch reflector on Mount Wilson (which I’ve been fortunate to visit – see here and here). Here’s the light path of the NST (an unmodified version of this image is at the bottom of the post):

BBSO New Solar Telescope light path

And here’s a view on the right side of the scope showing the mask that rejects the light from most of the sun (which bounces onto the back wall of the dome, landing at about the same intensity as natural sunlight). The mask has a small hole which allows light from a small part of the sun to pass through to the chain of lenses and mirrors that bounce the beam to the research instruments on the next floor down.

BBSO New Solar Telescope right side optics

It took me a while to wrap my head around how this works. If the mask rejects most of the sun’s light, doesn’t that mean that most of the telescope’s 1.6-meter aperture is wasted? The answer is no – the mask functions as a field stop, not an aperture stop. If I put a mask across the front of my 10″ Dob and let only a 4″ beam of light through, that’s an aperture stop – it effectively turns a 10″ f/4.7 obstructed system into a 4″ f/12 unobstructed system (which may be desirable for sharp planetary and lunar views, where light-gathering is not so important). But imagine I left the front of the scope uncovered and instead masked down the field stop at the bottom of one of my eyepieces, so that I could only see a tiny hole in the center. If I put the scope on Jupiter, I’d see Jupiter in the center of the field but nothing else – I’d be getting the full benefit of the 10″ mirror’s light-gathering and resolution on Jupiter, but rejecting the light from the surrounding starfield, which would reflect off the mask at the bottom of the eyepiece. That’s more or less what happens with the New Solar Telescope, only “the rest of the field” is the rest of the sun, and the small area that the scope focuses on is not a planet but a small patch of the sun’s surface. But that patch can be imaged with the full benefit of the 1.6-meter primary mirror’s angular resolution.

BBSO burnt light shield

Now, a 1.6-meter mirror focusing the light from the full disc of the sun onto an area about 3cm across is a hell of a lot of energy. That beam could fry electronics, melt metal, and start fires if it got off-course. There are multiple redundant systems to prevent that from happening – the dome can close, the primary mirror has a cover that can activate quickly, and if all else fails a 1/16″ steel plate slides into position in front of the field stop. A few years ago – before Claude’s tenure as Chief Observer! – there were not so many safeguards in place. The software that allows the telescope to track the sun briefly got confused by some passing clouds, and the scope stopped tracking properly. That allowed the concentrated beam of sunlight to slide off-target. The steel plate did its job and slid into place, and the scope melted two holes in it in the space of about 30 seconds. The folks at the observatory keep the melted metal plate as a visible reminder that they are in a very real sense playing with fire.

BBSO sunspot image

This sunspot is a bit larger than our planet.

Our last stop on the tour was the telescope control room, where another professional astronomer was driving the scope and taking data. There was a minor mechanical hiccup at one point and Claude had to swing into action, running back and forth from the control room to the instrument room to get everything back on track. It was amazing to see live images coming in in real time. I’ve been fortunate to tour a lot of observatories but never while they were working. At one point Claude and the other astronomer put the scope on a sunspot group which was just swimming in atmospheric distortion. Once the computer had enough data to engage the adaptive optics, they switched on the AO and the view instantly settled down to nearly rock-solid, like it was painted on the monitor.

BBSO New Solar Telescope

The NST is currently the largest, best-equipped solar telescope in the history of humankind, and it is producing the sharpest images of the sun ever taken. BBSO joins Mount Wilson and Palomar in continuing the long, proud history of world-class astronomy in southern California. And it’s 65 miles from my house. Many thanks to Claude and Teresa for being such gracious hosts and letting us see their beautiful machines in action.


Observing report: Deep and dark in Big Bear

October 12, 2015

Big Bear Lake

This past weekend I was up in Big Bear for a few days’ vacation. The proximate reason was the PVAA tour of the Big Bear Solar Observatory on Friday, Oct. 9 – more on that in another post. London and I went up Thursday evening with Steve Sittig, who runs the Hefner Observatory at the Webb Schools here in Claremont. Thursday evening Steve took us out to one of his favorite dark-sky observing sites a few miles east of Big Bear. (I didn’t get any pictures from the observing site, so you’re getting pictures of London and me hiking instead.)

We had hoped to get an early start but a succession of minor things kept us from getting set up and going until about 10:15 PM. By that time astronomical twilight was long over. There was a noticeable light dome from the LA metro area but it only badly affected the last 15-20 degrees above the local horizon, and only in the southwest.

Oh, speaking of the ‘local horizon’ – the site is in a shallow bowl with low hills fairly close on three sides and a bit more distant on the fourth. We could occasionally see lights from vehicles on a bend in the road about a mile off, but other than that, no artificial lights were visible from the site. None. The altitude is around 6700 feet.

The combined effect of this was that the sky was dark right down to the horizon. There was none of the usual near-horizon crud that obscures objects for the first 10 or so degrees after they rise. The seeing was worse near the horizon but the transparency was still excellent. We looked at Orion virtually as soon as it was up, and although we really had to pour on the magnification to split the Trapezium, the nebulosity was already very extensive.

A word about gear. Steve had his ETX 125, a 5-inch f/15 Mak on a motorized base with a hand controller. London had his Orion 20×50 compact spotting scope – I have been regularly kicking myself for not snapping up one of those for myself while they were still available. I had my C80ED refractor on the SkyWatcher AZ4 mount (= Orion VersaGo II), as well as my trusty old Celestron UpClose 10×50 binos. The choice of the C80ED was driven by two things: my space on the drive up was limited, so it was either the C80ED or the Apex 127 (which would have basically duplicated Steve’s rig), and I knew I’d want to do some wide field, low power observing, which is the one thing the Apex 127 can’t do.

For eyepieces, I spent most of the night using the 24mm ES68, which in the C80ED gives 25x and a sprawling 2.7-degree field. When I needed more power – which is much less often than I had anticipated – I bumped up to the 14mm and 8.8mm ES82s (43x, 1.9-degree field, and 68x, 1.2-degree field), and on a couple of tough double stars, the 6mm Expanse and 2x Shorty barlow. Unusually for me, I didn’t even mount a finder. With a 2.7-degree field, I can usually get the scope on target just by sighting down the tube. On those occasions when I needed more accuracy, I could lay my green laser pointer into a couple of shallow v-shaped notches on the tube ring and just move the scope until the laser was pointing where I wanted to go.

London Big Bear hike

Within moments of hopping out of the car, we could see loads of detail in the Milky Way with our naked eyes. The Double Cluster and the Andromeda Galaxy were both easy as well. Later on, we also spotted the excellent open clusters M35 and NGC 752 without optical aid. I logged the seeing as 4/5 and transparency as 5/5.

Our first few observations were “best in class” objects – the Pleiades, the Double Cluster and Stock 2. At low magnification under dark skies, the Double Cluster looks not so much like a pair of isolated objects, but rather a couple of thickenings or condensations in an incredibly rich Milky Way starfield. So it was that evening. Seeing that far above the horizon was rock steady and even at low mag, the C80 focused the stars down to tiny pinpoints of brilliant light. One of the clusters has a pair of red giants near its center – these were visibly brighter and more yellow than the rest of the cluster stars, even at 25x.

After that I turned west to catch M13 before it got too low. Going up to 68x revealed tantalizing hints of resolution – not bad for an 80mm scope.

M57, the Ring Nebula, was an arresting sight. At 25x, I could get both of the ‘corner’ stars that mark that end of the Lyra parallelogram, with M57 as a small but crisp circle of nebulosity floating in inky dark space. Although we also looked at the nebula with more magnification, I found that lowest-power view delightful. It reminded me of spotting the Ring at 12.5x in the TravelScope 70 three years ago – the view that first infected me with refractoritis.

We didn’t try to split Epsilon Lyrae until a bit later, when it was lower in the sky. The seeing there was only so-so and I had to push the scope to 200x, using the barlowed 6mm Expanse, to get a clean split, although both pairs were visible elongated at much lower magnification.

We stayed out long enough to catch the leading edge of the Big Dipper rising. One of the best views in that part of the sky is the galaxies M81 and M82 in the same field of view. They are close enough to be nicely framed in the same field even in the 8.8mm ES82. At that magnification (68x), M82 was starting to show tantalizing hints of structure.

London and Matt hiking above Big Bear Lake

The most memorable observations of the night were of the Auriga Messier clusters and the other Local Group spiral galaxies. Auriga clusters first – M38, M36, and M37 (from west to east, in the order that they rise) are seasonal favorites and fun to compare. We swept them up easily in binoculars and then scrutinized them in the scopes at progressively higher powers. I had a good laugh at M36 – at the orientation we saw it in this weekend, it looked like a short, fat stick figure, the bobble-head version of the Stock 2 stick-man. But M37 was my favorite, just an incredibly dense swarm of tiny pinpoint stars.

Fairly early in the evening we had a look at the Triangulum galaxy, M33. I was tracing out the constellation Triangulum with the GLP when we noticed a naked-eye glow that turned out to be the fine open cluster NGC 752. Neither of us could make out M33 with our naked eyes but it was dead easy in binoculars, and at 25x in the C80ED it showed considerable structure in averted vision, including what both of us independently took to be one of the spiral arms. Incredible.

We closed the session with another great view of a local galaxy. All through the three-hour session we’d been saying that we’d look at Andromeda, and then one thing or another would capture our attention and we’d get sucked into some other part of the sky. We finally got around to M31 and its companion galaxies a little after 1:00 AM. By that point they were basically at the zenith. Even with the tripod extended as high as it would go, we had to kneel to look in the eyepiece. But when we did, the view was astounding. M31 stretched all the way across the field, with only the very outer edges clipped by the eyepiece’s field stop. The little companion galaxies M32 and M110 were dead easy, of course, but what amazed me was that we could both see structure and detail with the main galaxy. I’d never seen those dust lanes in anything smaller than a 5-inch scope.

We knocked off after three solid hours of observing, exhausted but giddy. It was one of those transcendent nights that makes my heart sing, and also makes it really hard to go back to observing from suburbia. The most surprising thing for me was how much observing I got done with the 24mm ES68. “Small telescope at low power” does not scream satisfying deep sky observing, but under sufficiently dark, clear skies, I rarely needed anything else. I’m already looking forward to the next run.


Guest post: Whys and hows of astronomical sketching, by Doug Rennie

October 11, 2015

Doug Rennie first opened my eyes to the value of sketching for the visual observer. I’m very happy to host his thoughts on the subject – and his sketch of the Alpha Persei association.

Rennie Alpha Persei association - curved and inverted

Sometime in the late-1990s, I wrote an essay on bibliophila, the love of books, for a literary journal. Thinking back, I recall two quotes I cited in that essay, one from an anonymous French book collector in 1851, the second from renowned literary critic Edmund Wilson – and both relate to the reasons why several years ago I made sketching a regular component of my observing routine.

“Owning a book puts it in your possession,” the Frenchman wrote. “But only reading a book makes it yours.”

For me, the same principle applies to stargazing. Locating and observing a celestial object, be it Messier, NGC, IC, asterism, whatever, produces a visual experience – and another box checked on your Objects Seen list. You now “own” it. Then, too often, you move onto the next one in the catalog, and just as quickly, the one after that. And so on. The impressions and mental images of the object you just minutes ago observed are already dim and vanishing fast in your memory’s rear view mirror.


Not so if you regularly sketch what you observe. Because now you have to slow down, actually study what you see in the FOV, look at it through various eyepieces, seeing it both up close and large and bold – its own entity – and smaller and more subdued and part of a larger celestial context, the latter being what I personally prefer.

Then you put pencil to paper and sketch it.

One star dot at a time. Or perhaps you sketch it twice: Once at high magnification to capture all the detail and maximum star count, a second time pulled back to see both object and surrounding star field, the total celestial tapestry. By the time your sketch is done, you will have spent a half hour, sometimes more, in the company of this one single object. Moreover, you will have a permanent and personal hard copy of what you observed.

In the spirit of that anonymous Frenchman, you will have made the object yours.

The second quote, from Edmund Wilson, is this:

“No two persons read the same book.”

Think about it.

And this, too: Astronomical sketching is exactly the same. No two observers see the same exact object. If you want confirmation, hit a sketching site such as Deep Sky Archive and go to any object, say NGC 6633, and you will see a dozen sketches, often more, by different observers – and no two even look REMOTELY alike. I mean, you would think you were looking at sketches of 12 different objects. Sue French turned me onto this site over a year ago and I thought, Wow this will be great as I would now have a sense of what pattern(s) to look for in future first time searches. Nope.

If anything, more confusing (So, is This what it looks like? Or is it this one? Or . . . maybe . . . this? . . .)

Just as no two persons read the same book, it seems that no two observers see the same object. Even something as “clear cut” an image as, say, the Pleiades will have as many variations as there are observers/sketchers. So one more reason to make every object yours by laying out on paper the testimony of your visual senses for each object you observe on THAT night in THOSE skies with THAT instrument with THAT/THOSE eyepieces.

Now I’ve been observing for just over 3 years, and my background is all humanities, my hard science expertise zero. Or close to it. I am primarily an aesthetic observer who just enjoys drinking in all the beauty up there and, sad to say, pays scant attention to RA and Dec #s, Bortle Scale assessments of my sky that night, recording AFOV and TFOV, etc. I just go out and hunt down what I want to observe, and once I have what I’m after in the EP, I hang around it for a while. Most of the time, but not always, doing a sketch.

I began to sketch almost as soon as I started observing, and my early sketches are, well, “pitiful” would actually be kind. I was going to include one here to illustrate, but in the end could not bring myself to post one. Bad. These things are terrible. Third graders would laugh.

So here’s how I now go about it, and produce some decent-to-me results.

I have an artist’s sketchbook, spiral bound so it lies flat when opened, 8 x 10 inches, hard black cover. Cost under $10. My wife is an artist, so I initially used her drawing pencils, but quickly bought a set of my own at a local artist supply store: 2B, 4B, 6B, 8B, etc. Cheap. I store them in a plastic travel toothbrush case. I also use her recommended eraser, some artists’ gray plastic eraser, “Prismacolo” thing and it works superbly.

I have a scraggly small lined notebook that I use at the telescope and record in it a very rough first draft, focusing on accurate positions and spatial relationships among the stars, and taking care to use different size “dots” for individual stars commensurate with their brightness/dimness and size. I do a fair amount of erasing to get this draft, which is REALLY ragged, as accurate a reflection as possible of what I see.

I first do the outermost stars in all 4 directions just to make sure that I get the entire image I want in, then sketch in the anchor/biggest/brightest stars to get the main pattern. Once this is done, I work outward from there, one quarter section at a time. Seems to work.

The next day, I transfer the image into my sketchbook, now taking time to create perfectly round dots for every star and, often, using one of those plastic architect’s templates (3 bucks at Office Depot) for the larger stars, insuring that I get perfectly round dots for each. On the smaller stars, this is generally not a problem. See the attached sketch of the Alpha Persei Association. The two largest star sizes were done with the template.

Rennie Alpha Persei association - curved

A soft 2B pencil works best for most stars, but for the really tiny dim ones, of which there are generally quite a few, I go to a 2H or HB harder lead pencil which creates a lighter gray hue. When I have completed the entire sketch, I then take a very soft/dark 6B pencil, freshly sharpened and pointy, to go over the larger and darker stars to set them off, as they are through the eyepiece in “real time”, more dramatically from the background stars.

For open clusters, by far my favorite object to observe, I much prefer the look I get through one of my refractors (Explore Scientific AR102, Stellarvue SV80ED, Orion ST80) vs either of my Dobs, the largest of which is a StarBlast 6. With a Celestron 8-24mm zoom eyepiece in place for the first observation, I can go in and out, seeing the object large and up close with maximum stars, then widest field possible which puts the object at the center and gives it more context, and various degrees of both in between. Once I find the sweet spot, to me the ideal meld of object and context, I can go to one of my fixed focal length eyepieces, often an ES 16mm or Agena flat field 19mm. Some objects, such as the Double Cluster, look best in my ES 24mm/82 afov.

That’s it. Nothing more to see here. And, as you can deduce from the foregoing, sketching is NOT all that difficult. I mean, c’mon, it’s not particle physics. So if you’ve not already included sketching as a regular part of your observing, why not give it a test drive next time out?