Archive for the ‘Open cluster’ Category

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My article in the March 2017 Sky & Telescope

January 27, 2017

jan-2017-st-cover-wedel-article-highlighted

This is one was an easy write-up, because it had been in my head and in my notebook for a long time. Way back when I first got tapped to write for S&T, I pitched a tour of the winter Milky Way from Puppis to Gemini. I’d never written for a magazine before and I had no idea how much sky it would take to fill 1600 words. Turns out, all I got through on the first attempt was Canis Major, Puppis, and a couple of odds and ends like M48. That was my article in the December 2015 issue.

Right after that came out, I pitched the unfinished second half, and now it’s out. Like that first article, it’s a tour of the winter Milky Way pitched at binocular users, but hopefully useful for telescopic observers, too. This piece runs from Monoceros through northeastern Orion to southern Gemini. The March issue of Sky & Tel is probably hitting newsstands this week. If you get a copy, I hope you enjoy the article.

If you’re thinking that Gemini is a pretty arbitrary place to stop cruising the Milky Way, you’re not wrong. I can say no more for now, but stay tuned…

Update: whoops, I originally put January in the post title instead of March! This is, of course, the March issue, it just came out in January. Sheesh.

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Sunday night on Mount Baldy

November 3, 2015

Moon through trees 2015-11-01

Sunday night I went up Mount Baldy for a solo session. I was rolling with the C80ED, which has become my default grab-n-go rig.

One of my goals was to test a couple of new eyepieces. Several astro retailers had a big sale on Meade wide-angle eyepieces last month. I was torn between the 20mm and the 5mm Series 5000 Mega-Wide 100-degree EPs (man, is that a mouthful or what?). The 20mm would have been a great low-power, widefield scanner, which is something I’ve gotten progressively more interested in this fall. But for a long time I had been without an EP shorter than my 6mm Expanse, which is not without its problems, so I sprung for the 5mm instead.

In the meantime, thanks to this thread on Cloudy Nights I had become aware of the VITE eyepieces. These odd little birds come in only 3 focal lengths (at least so far): 23mm, 10mm, and 4mm. They are three-element EPs with one aspheric plastic element and plastic bodies. They’re about $17 apiece on Amazon, or $9 apiece on eBay. I ventured my nine bucks and got the 4mm from eBay, thinking it would make an interesting comparison with the 5mm Meade 100-degree. I had done a quick comparo late Saturday night from my driveway on the moon and the Orion Nebula – more about that in a bit.

Sunday evening on mount Baldy I cruised through the highlights in Lyra, Cygnus, and Sagitta. I did a quick, rough sketch in my notebook of the open cluster NGC 6823. It has a curl of stars wrapping up around it like a fiddlehead fern.

NGC 6823 sketch

After that a couple of high school kids and their little brother drove up nearby, and I spent about an hour showing them around the sky – the Dumbbell Nebula (M27), the Double Cluster, Pleiades, Andromeda galaxy, Polaris, M15, 61 Cygni (aka Piazzi’s Flying Star), and finally the Messier open clusters in Auriga – M37, M36, and M38.

The kids left about 10:30. Since I was in the area I had a look at M1, and then cruised down to Orion. The constellation was slowly crawling over the ridgeline to the east, so I started visiting the bright stars, and in some cases splitting them. First up was Meissa, which was elongated at 68x and cleanly split at 120x in the 5mm MWA and 150x in the 4mm VITE.

Mintaka was an easy wide split at only 25x. Seeing was not good, but Eta Orionis appeared to be elongated east-west at 120x and 150x. The view in the VITE was kind of a mess, so I spent a few minutes just cruising around Orion’s belt and sword with the 5mm MWA. Alnitak and its dim companion were widely split. I turned south to Sigma Orionis. I’ll have to check my notes, but I don’t believe I’d ever split this star before. It’s pretty great, with a group of three fairly bright stars and a second group of three much dimmer ones. I backed down to 68x and all six stars were still nicely split, and frankly looked a bit sharper, although that might have been down to bad seeing.

Sigma Orionis sketch

So, here are my thoughts and observations on the 6mm Expanse, 5mm MWA, and 4mm VITE. These don’t count as an actual review, as I didn’t have equivalent focal lengths to compare, and I’ve only spent a couple of nights with the two newer eyepieces, observing only a handful of objects. Still, I tried them on a variety of things – the moon, globular and open clusters, the Orion Nebula, double stars – and the strengths and weaknesses were consistent. All of these observations are with the C80ED, so the chromatic aberration (CA) with certain EPs is particularly interesting.

6mm Expanse – Has a small but noticeable amount of CA on bright stars. Eye placement is a bit tricky – I get some kidney-bean and full-aperture blackouts until I get my eye placed just so. Comfortable enough once I get my eye in the zone, though. Halos on some bright objects.

5mm MWA – Sharp from edge to edge. No detectable CA, but the edge of the field does look blue until I get my eye centered. No detectable field curvature. Eye relief is pretty tight – when I move in close enough to see the entire field, my eyelashes brush the lens about half the time (I do have long lashes, but still). I have to move my head around to focus on objects in different parts of the field. Very immersive – I feel like I could climb through the eye lens and into space. The rubber eyecup is annoyingly loose – it frequently comes off with the dust cap.

4mm VITE – Can’t focus the whole field at once. Center of the field is sharp enough, but objects start getting blurry halfway to the edge of the field and are entirely defocused at the edges. ‘Sweet spot’ is pretty small. Considerable CA – makes an ED refractor perform like a short fast achromat! Strong internal reflections from bright objects on the edge of the field, or just out of the field. Almost impossible to focus on the lunar terminator if it’s centered – a big bright glow from the lit side of the moon fills the center of the field. Eye relief is tight – eyelashes scrape most of the time.

Verdict – The 5mm MWA is a keeper. The eye relief is short but tolerable, and totally worth it for the huge, flat, well-corrected field. As for the VITE, I’m glad I didn’t spend more than $9. I’ve read that these perform better in longer focal ratio instruments, but at f/7.5, the C80ED isn’t exactly fast. So how long does the light cone have to be for the VITE to perform well – f/10? f/15? At those focal ratios, it would take an exceptionally still night for a 4mm EP to be useful. I will try the thing in my Mak and probably in my C102 but I am not expecting much. People on CN seem pretty happy with the 23mm, so maybe there’s some variation within the line.

Back to the observing report. By midnight I was tired and my feet were cold. I had just resolved to pack up and head home when I saw that the hillside behind me was lit up by moonlight. The moon was coming up behind the ridgeline to the east. It had been a long time since I’d had a chance to shoot the moon rising behind trees, so I quickly set up the camera adapter and got to work. My best still shot is at the top of this post. And here’s a video:

I went for the sideways aspect ratio this time, but I didn’t quite get the camera square on to the view. Guess I’ll just have to try again next month.

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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.

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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.

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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.

But.

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?

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Sketching NGC 6633

October 7, 2015

Wedel NGC 6633 2015-10-06 - inverted and cropped

As long-time readers will recall, I have been bully on the idea of sketching DSOs for a long time. I have been inspired by the careful observations and sketches of Doug Rennie and Terry Nakazono in particular. So I made up a blank observing form (which is now up on the sidebar here), printed out some copies, and decided to finally give it a shot. I was going to do M57 first, and kick off my much-discussed, long-delayed Suburban Messier project. But I’d just been emailing with Doug and he’d recommended NGC 6633 as a rewarding open cluster for visual observation, and as I was flipping around in my Pocket Sky Atlas I noticed that it was well-placed high in the southeastern sky.

I was rolling with the XT10. I figured that whatever target I went for, I’d want to capture as many background stars as possible, and the XT10 has much better light grasp and angular resolution than anything else I own.

I started at moderate magnification with the 8-24mm zoom but kept backing out to try to get more context for the cluster, and I ended up with my trusty old 32mm Plossl. The transparency here was appalling. The sky looked clear, in that there was no naked-eye-visible haze or clouds, but it was very humid, and all of that water vapor in the air was bouncing back the city lights like crazy. The sky was about as bright as I have seen it without actual clouds up there. Here’s a measure of how humid it was – all of my exposed stuff dewed up! I don’t think that has ever happened to me here in Claremont.

Wedel NGC 6633 2015-10-06

As far as my method – I was using a 0.5mm mechanical pencil and a click eraser. I started out by trying to frame the field of view with some bright ‘anchor’ stars and then interpolate between them to flesh things out. This proved frustrating – inevitably I’d get one region ‘starred in’ to my satisfaction and then see that its geometry was off compared to a neighboring section. So I did a fair amount of erasing and repositioning. On the first pass I was mainly trying to get the positions of the stars correct.

Then while I was still at the eyepiece I went back and ‘brightened’ up some of the stars by drawing over them with slightly larger circles. I tried to sort them into about five bins, from the bright star south of the cluster, through the brightest anchor stars, the major cluster members, the minor cluster members, to the barely-theres.

Finally, when I brought the drawing inside I touched up a few stars that were noticeably out-of-round.

So the drawing you see here is the ‘rough’ drawing, but with about three layers of revision layered on top. I don’t know if this is good practice or not, it’s just what I did this time, pretty much making everything up as I went along.

As for the cluster, NGC 6633 has a fairly recent nickname: the ‘Italy cluster’. Here’s a diagram from this blog, with my sketch inverted and rotated to match:

NGC 6633 comparo

I can buy it. I wouldn’t have ever picked out that by myself, but I can see the shape in my drawing, and I didn’t know it was there when I was drawing it.

So, I have rather mixed feelings about all of this. While I was doing the sketch, all I could think about was how difficult it was, and how badly I was screwing it up. But I’m fairly happy with the result – it is at least recognizable as NGC 6633 – and I know that I know that cluster and the surrounding starfield a lot better now. Probably better than I know any other single object. I can’t think of another time that I invested so much time and energy on a single observing target.

Maybe this is the beginning of wisdom.

UPDATE October 26, 2015

Here are a couple of sketches of NGC 6633 sent along by Terry Nakazono with permission to post. Thanks, Terry!

NGC 6633 at 31X (7-19-12)

From July 9, 2012.

NGC 6633 at 44X (6-28-13)

From June 28, 2013.

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NGC 6645–the cosmic maw

August 19, 2012

I was out hunting Herchels last night and observed the open cluster NGC 6645 for the first time. From my notebook:

Fairly large open cluster. Not sparse, loads of stars, but all are about equally dim–none really jump out. Has an unusual dark spot in the middle like a mouth or the entrance to a cave. That plus five radiating chains of stars make it look like a howling monster.

This didn’t occur to me until today, but I finally realized which monster it put me in mind of–the Beholder from D&D. This sketch gives a sense of its appearance, although it does vary a bit with aperture–that artist saw “a pretty faint unresolved gray haze with about 30 dim stars visible” whereas the 10-inch resolved it completely, with mini-clusters around the central hole and long chains of stars radiating away like nerve endings from a cartoon neuron.

Anyway, this open cluster is well-placed in the early evening, it’s not hard to find, and it has a lot of character. Well worth tracking down. You can even generate a custom finder chart for it using the interactive star chart at NGC891.com, which I just learned about.

What does it look like to you?