Archive for August, 2012


Observing report: An entirely different kind of virtual star party

August 28, 2012

If you’ve been following this blog or have trawled the recent archives then you know about virtual star parties on Google+, where astrophotographers put up real-time video images of celestial objects and a mixed group of professional and amateur astronomers and interested laypeople chat it up.

Tonight I got to experience a virtual star party of a completely different sort: a binocular tour of the night sky as projected on the dome of the Samuel Oschin Planetarium at Griffith Observatory. I was invited along by Steve Sittig, a good friend who works at the Webb Schools here in Claremont, where he teaches science, serves as chapel director, and runs the observatory. It is a curious lapse in my blogging that I haven’t covered any of the times that Steve and Andy Farke and I have passed an evening playing around observing with the big orange C14 in the observatory dome at the top of the Webb campus. We’ve chased comets and supernovae and had all kinds of fun–but those are stories for other posts.

Anyway, Steve hooked Andy and me up with tickets to this evening’s virtual star party, and a little before 7:30 we marched into the big dome, took our seats, and got our binoculars ready. I also got a few snaps, including this slightly-better-than-Bigfoot-level handheld portrait of the three of us not looking dorky at all.

I really didn’t know what to expect when the lights went down. I didn’t know whether the projector would project actual images of deep-sky objects, or just little groups of star-points that would mimic deep-sky objects, or maybe just the regular asterisms and constellation outlines.

All that uncertainty was dispelled as soon as the lights went down and the stars came out. The presenter directed us to Orion with his red laser pointer and went into some well-rehearsed patter about how it’s a big molecular cloud where new stars are being born. I was off and running. From the first view of the Orion Nebula (M42), it was clear that this was going to be a lot of fun. The nebula was big and detailed and looked pretty darned similar to its actual appearance through binoculars under dark skies.

I have to confess, I didn’t hang around for the whole Orion speech. I had stuff to see. I scanned south into Canis Major to look for the open cluster M41–and it was there, and looked legit. Followed the dog’s tail north and east to look for the closely paired clusters M46 and M47. There was only one glowing thing at their location, but there was something there and it was clearly supposed to be a star cluster, or maybe two close together. M35 in Gemini: there. Up to Auriga for M36/37/38: all there.

And so it went. The presenter did give us a pretty good tour of the northern sky, and he got to a lot of the stuff that I had raced ahead to find, but there was always more. I was shocked at the detail and fidelity of the images. Now, to be honest, not everything was there. A lot of the smaller or dimmer Messiers were not there–I looked in vain for M78 and M79. But I was often pleasantly surprised. M44, the Beehive, was an actual swarm of projected stars, not a hazy picture, just as it should have been. Better still, M67–hardly what one would call a showpiece object–was also there, just a bit to the south. And all of these things were not mere blobs of light, but were individually different and looked pretty much like they actually do through binoculars. It was pretty darned impressive.

I don’t know why I didn’t see this coming, since it was obviously technologically possible: the highlight of the evening was a tour of the Southern Hemisphere skies. We saw the Southern Cross and the Coalsack, the Jewel Box Cluster and the Eta Carina Nebula and the Southern Pleiades. I had seen these things before in binoculars, lying on the beach in Punta del Este, Uruguay, almost exactly two years ago. It was unexpectedly moving to get to visit them again, with binoculars, lying in much the same position in the reclined chair in the planetarium.

After that we came back to the northern skies for the summer highlight objects, which were very familiar since I just saw them last week. We hit the usual suspects: M4, M6, M7, M8, M20, M24, M25, M17. I popped up to the tail of Aquila and bagged M11 (actually in Scutum for any pedants in the audience, but it’s most easily found by following the eagle’s tail). All in all, by the end of the night the presenter had pointed out about two dozen deep-sky objects, and I had found another dozen or so that went unremarked. It’s weird to think that the projector is presumably putting up images of these faint fuzzies all the time, even though most of them are below the threshold of naked-eye visibility. I am going to start sneaking my binoculars into the planetarium on a regular basis.

When it was over, we all went out onto the observatory veranda to see what we could see in the real sky. Between the waxing gibbous moon, the regular LA light pollution, a bit of haze, and the modest aperture and magnification of our instruments, what we could see turned out to be “not very much”. We tried going right up to the fence and putting all the local lights behind us to try for the Andromeda galaxy and M13, but neither was in evidence. Oh well: the observatory staff did warn us that the real (Los Angeles) sky would be an unpleasant shock after the pristine projected sky. Steve said the projected sky was like what you see up in the Sierras, where the sky background is so black and there are so many  stars that it’s easy to lose your way; the bright stars that mark the constellations are simply lost in endless fields of distant suns.

The downside to virtual stargazing is just that: the endless fields of distant suns are not really endless. Using the binoculars allows you to see the projected stars and DSOs more clearly, but not the stars and DSOs between them. You can’t go very deep; there’s an inevitable limit and you hit it pretty fast. The Milky Way does not break up into a visually exhausting never-repeating parade of clusters, nebulae, asterisms, and rich fields of stars; it’s just a bunch of cloudy light projected overhead. You’re not really out there; the marvel is not at natural splendor but at human ingenuity, and you are, in the end, sitting in a big dark room using the world’s biggest sky app. Fun and interesting, for sure, but not nearly as rewarding as the real thing.

But I think that’s okay. Tonight’s exercise was an outreach, designed to get people who have never used their binoculars for anything other than spying on birds and neighbors to turn them skyward and see a few of these awesome things for themselves, and for real. Based on a wholly unscientific sample of personal eavesdropping, I think it was a success.

One final note. I had come across the idea of indoor stargazing before, in a blog post by Stephen Saber. He wrote,

darksky arenas…

I’m going to have some Superdome-sized Bortle-class 8 planetariums built with a projection accuracy to match. Really, really accurate. Open 24/7.
Peaceful outdoors sounds. Always a clear sky waiting. No more frozen fingers. No skeeters. Lunatic Happy Hours. Southern Sky Sundays and Messier Marathon Mondays.
Such an idea might offend a lot of hardcore Purists. Many might come just for the experience. But I really can’t see also faking the observation making any difference to goto users. *sorry. old habits.*
Or maybe night sky coliseums. Huge fields with perimeter walls rising to block local light pollution and outlying city lightdomes.

Would you come?
How far would you drive?
How much rain and cloudcover would it take?
Will preserving an area’s dark skies eventually come to this?

Having now done a light version of this, my answers are:

  • Apparently I would.
  • Um, 45 miles at least.
  • None, just good company.
  • I sure hope not.

So, virtual stargazing: weird, no substitute for the real thing, but still highly recommended. Go if you ever get a chance.


Observing report: Mt Baldy again, with friends

August 23, 2012

I did a short run up Mt Baldy last night, with some of my former students from the summer anatomy program. One of them, Kevin Zhao, brought along his Canon DSLR and got this awesome 30-second exposure. Kevin waved a little flashlight around during the exposure, which had the cool effect of making me look like I’m just beaming down here. This is looking east; if you click through to the big version, you can see that stars in the upper left corner, near the celestial pole, are little pinpoints, whereas those in the upper right corner, near the celestial equator, were already starting to trail.

And you can see some clouds. I thought these were going to be the end of the enterprise. We got up there about 8:45 and the sky was halfway clouded out. Over the next 20 minutes the clouds continued to congregate, until all that was left was a little sucker hole extending from the handle of the Big Dipper to Arcturus. So our first object was the double/multiple star Mizar and Alcor. I had along the XT10 and 15×70 binoculars, and people had fun cruising the skies with the big binos while waiting for their turn at the eyepiece.

Happily, by the time everyone had a look at Mizar and Alcor the sky had started to clear overhead, so we moved on to the Dumbbell Nebula (M27), the Ring Nebula (M57), the beautiful color-contrasted double star Albireo. By then the sky was almost completely clear, and it stayed that way, except for a stubborn bank of clouds to the south and west that kept us from seeing Mars and Saturn and almost denied us the moon.

By now we were rocking and rolling on summer sky highlights: the Great Globular Cluster in Hercules (M13), the Wild Duck Cluster (M11), a fine globular in Sagittarius (M22), the Lagoon Nebula (M8), the Swan Nebula (M17), and the M24 star cloud. We probably would have observed all of the clusters and nebulae that form the ‘steam’ rising from the teapot of Sagittarius, but the light pollution was worst in that direction so I stuck to a handful of the best and brightest objects. Sadly, the open clusters M6 and M7 were buried in the top of the southern cloud bank, so we missed them.

Speaking of that cloud bank, about 10:45 the crescent moon emerged from the flat bottom of the cloud deck and set over LA. Distance and haze dimmed its light somewhat and colored it orange, but we still got good looks at 50x and 86x. As the last person got a look at high mag, the horizon started to nibble away at the moon, and soon it had set.

After that we turned 180, to the northeast, and looked at the Double Cluster (NGC 869/884), the Andromeda galaxy (M31) and one of its satellite galaxies (M32). Then a couple of nice asterisms: Brocchi’s Coathanger, and the Engagement Ring around Polaris. Polaris itself was nicely split in the telescope (not surprising, a good 3-inch scope will split it, and it’s pretty easy prey for scopes of 4 inches and up).

Our final object of the night was the Cat’s Eye Nebula (NGC 6543), which was a bright round glow at 200x, and–as I had hoped–noticeably blue-green in the eyepiece.

By then it was 11:20 and we were all winding down, so we packed up and came down. It’s a fun drive, coming down the mountain–steep and twisty enough that you can really pour through the turns, but not so bad that you worry about burning out your brakes or sailing into a canyon. And the cool mountain air was most welcome after the 110-degree heat we’ve been sweating through for the past month.

Unfortunately with the moon waxing there won’t be much point in going out to dark skies for the next couple of weeks; last night was about the last night we could have gone and gotten skies dark enough to be rewarding. I’m glad it worked out.


A quick observation about aperture

August 22, 2012

I had an epiphany last night. The busier I am, the less often I get out to observe, the more likely I am to use the XT10. The rationale: if I’m only getting out once or twice a month, I want to enjoy myself as much as possible, and that means using the biggest available scope. The only exceptions are (1) truly quick peeks, under half an hour, where I’ll usually grab the 90mm Mak, (2) sidewalk astronomy, where I use the 90mm Mak just because it’s the most portable, and (3) double star work, where I prefer the slightly cleaner, sharper views provided by the Maks. Any other small-scope observing is a luxury, for stretches when I’m already getting plenty of dark-sky time with a bigger scope–not my current situation, unfortunately. But fall is coming, and that’s traditionally my season for getting out to the desert on dark weekends. I can’t wait.

Maybe this would not even be worthy of comment for most observers, but I’ve always had a thing for small scopes. I still do, and probably always will. But now that I’m sort of settling into my current lineup and not especially wanting or needing another (small) scope, I’m spending more time thinking about the scopes I have and their strengths and weaknesses. Although every one of my current scopes fills a need, I am finding that the overall enjoyment they provide correlates with aperture more than anything else. It’s one thing to hear that aperture rules, another thing to really understand why, and still another thing to discover that for yourself, out of your own experience.


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, which I just learned about.

What does it look like to you?


Why aperture matters

August 15, 2012

Most people who have gotten as far as even doing research on buying a telescope can probably rattle off the two benefits of aperture: greater diameter allows increased angular resolution–the ability to resolve fine details–and greater collecting area simply gathers more light. But what do these advantages really mean? Just in the past month I’ve read a couple of explanations that gave me new ways to think about this, and that I think need to be more widely read.

The first comes from Richard Panek’s fine little book, Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Heavens (page 111):

Double the diameter of the aperture, and its light-gathering capacity increases fourfold; triple it, and the capacity goes up ninefold. At the same time the brightness of the object under observation depends on the square of the distance. Double the distance of a light source, and its brightness decreases fourfold; triple it, and the brightness drops off ninefold. The implication was clear: Double the diameter of the aperture, and you double the distance the mirror can see. Herschel understood that for the purpose of investigating the starry depths the major advantage of a reflecting telescope wasn’t in greater magnification, but in gathering more light–wasn’t in seeing more detail, but in seeing farther.

Okay, cool stuff. I knew that light grasp increases proportional to the square of the diameter, and that brightness drops off proportional to the square of the distance, but I’d never thought to put those two thoughts together.

Still, deep sky observers usually start with the bright stuff, like the Messier objects, and with sufficiently dark skies even the Herschel 400 are within reach of a 2-inch scope. Given that you’re already looking out more than 60 million light years to see the most distant Messiers, does seeing father really help?

There’s another piece to this, and it’s one I’d never considered until I read a very clear explanation of it by Ed Moreno (CN username Eddgie) on Cloudy Nights. Here’s the link to the CN post, but it’s so good I’m just going to copy and paste the whole thing here:

Make no mistake here. If you want to see more structure or detail in any kind of extended target such as nebula, galaxies, or planets, there is absolutely no substitute for clear aperture.

Almost all of the design discussions totally omit the function of image brightness/image scale that is offered by a larger aperture. We tend to discuss equipment like we don’t have eyeballs.

But we do have eyeballs… Or Cameras.

The image brightness and the ability to trade it for image scale is a huge part of the value of a larger aperture.

Keep in mind that a 16″ telescope and a 4″ telescope can both show the Orion Nebula with the exact same brigntness. Is all one has to do is use an eyepeice in each scope that has the same exit pupil.

For example, if I use a 16″ telescope at 100x, this will give about a 4mm exit pupil for the observer. In a 4″ scope, to get the same exit pupil (same image brightness), you will have to use 25x.

Now in the 4″ scope, the image is exactly as bright as in the 16″ scope, but the scale is only 1/4th as large.

Now is where it gets interesting. The structure inside the nebula is often very low contrast and very fine.

It is often stated on these forums that the human eye can resolve down to one arc minuted. This actually greatly overstates the eye performance of the scotopic eye for low contrast detail. This figure (one arc minute) is only achievable when the target is well illuminated and the contrast is 100%.

If the eye is in scotopic mode, and the contrast is very low, the eye may struggle to resolve detail that is smaller than about 3 or 4 arc minutes of apparent field unless the contrast is very high or the target is well illuminated.

There are two ways to increase the likelihood of the human eye (or camera) being able to resolve this very low contrast detail. They are to A: Make it bigger by magnifying it more, or B: make it brighter. Of course if you can make it slightly bigger and slightly brighter, this greatly enhances your ability to resolve fine, low contrast structure present in the extended target.

Now, lets take our 16″ scope and our 4″ scope and use the 16″ scope with our 4mm exit pupil. Remember, the illumination (determined by the exit pupil) is the same, but the angular size of any detail in the target will be four times as large. Detail within the target that does not have the angular magnification to be resolved in the smaller scope is now presented as four times as large. This means that there is now a lot more detail that has been magnified enough to be seen in the much bigger scope. Of course I can make the detail larger in the smaller telescope but this comes at the expense of loosing illumination (smaller exit pupil) which makes it harder for the eye to see the detail.

The other option is to make the image bigger and brighter in the bigger scope. Suppose I use the bigger scope with a 6mm exit pupil. Now, the exit pupil being larger gives me a brighter image. Once again, the eye likes illumination as one of the two ways to improve the ability to detect detail. When I make the image brighter in the larger scope, I see the extended target as extending over more area. The added brightness expands the extent of a nebula or galaxy. And guess what…. With the 6mm exit pupil in the 400mm scope, the magnification is 66x, so every detail present is still presented at almost 2.5 times the image scale as it would be in the 4″ aperture!!!!!! So now I have an image that is both bigger AND brighter in the larger aperture. I don’t care what kind of scope this is… It can be a refractor, a reflector, or a compound scope. If I make the image bigger and brighter, even if the contrast of the detail is exactly the same, my eye will have a better chance of seeing that detail if I make it bigger or brighter, or both at the same time.

Again, make no mistake about it… For seeing the most detail in extended targets of all types, clear aperture is king. You cannot isolate the telescope from the detector, and when the human eye is the detector, with a larger aperture you usually get both increased scale AND better illumination of the target and all of the structure present in the target.

I have owned perhaps 40 telescopes in the last 10 years, and for all classes of extended targets I would rank them in terms of performance in almost 100% agreement with the amount of clear aperture the scopes provided. I personally have never compared two telescope (even of different types) that the scope with the most clear aperture didn’t equal or exceed the performance of the smaller clear aperture.

There is no substitute for aperture. That is why the Hubble is a 2.4 meter instrument and not a 4″ refractor.

Aperture gives you image scale and illumination. It doesn’t even matter how you get that aperture (design). It is only important to have a lot of it.

Big telescopes simply show more. At the end of the day, if you want to see more structure in all class of extended targets, or if you want to see these extended targets at their maximum size, the best way to do this is to use as much aperture as you can manage.

The problem with refractors is that to get any meaningful amount of clear aperure (I recommend 8″ to 10″ for seeing a lot of structure in most deep sky extended targets) the expense becomes impractical as does the physical size of the instrument.

Everyone gets to use what they like, but the physics of image formation give clear aperture the best image formation, and lots of aperture gives the human eye the best chance of seeing any existing detail that might be present in the target.

There really isn’t any substitute for clear aperture. The more you apply to almost any target in the sky, the more structure or detail you will be able to see.

Now, I had experienced this, but I hadn’t thought about it–in fact, hadn’t known about it–in terms of brightness and image scale. And now that I have,  I agree with Ed completely.

I like small scopes. A lot. Maybe more than is healthy. But I will readily admit that my XT10 blows away all of my smaller scopes, on almost every target. Maks are often described as being fine planetary scopes, and they are. My 5″ Mak rocks on planets. But the XT10 just annihilates it on max detail. Even on the moon–I will put one of the smaller scopes on the moon and think I’m getting a good view, and then I put the XT10 on the moon and BAM! It’s the same field of view, but not the same view–suddenly everything is just bursting with details that I couldn’t see before. And now I know why–it’s not just angular resolution and not just light grasp, but rather the ability to get an image that is bigger, brighter, and more detailed, all at the same time.

Fortunately, I didn’t buy the Mak under the illusion that it would outperform the dob–I bought it because it fits in a space only a little bigger than a gallon milk carton, for those times when I don’t have room for anything bigger. And there is in fact one class of targets where I strongly prefer the Maks, and that is double and multiple stars. Oh, there’s no doubt that the XT10 will split closer doubles, period, and split wider doubles more easily, but I have not (so far) been going after doubles that are at the limit of resolution of a 10″ scope. And for things the Maks can split, they provide a more pleasing image than the dob, with no diffraction spikes. There is something entrancing about seeing a just-barely-split star as two clean little balls of light separated by the thinnest of black lines, surrounded by nice concentric diffraction rings but with no other visual noise to clutter the view.

So, dobs are cheap, but people end up buying other scopes for other reasons, and probably the two most important of those reasons are portability and aesthetic “cleanness” of view. Those are, in fact, the very reason that I own scopes other than dobs. BUT if you are interested in the deep sky–or pretty much anything else up there–and you’re on a budget, then clearly it is in your best interest to get as much aperture as you can afford. So this post is a deliberate follow-up to the last one; that one showed which scopes provide the most bang for the buck, and this one explains why you want as much bang as possible.

All of this is just part of an extended run-up to the Suburban Messier Project. I’m not ready to get started on that, not yet. I’m too busy with teaching, and my skies are lousy right now anyway. But I am thinking about the SMP, and when and how to best get started, and what information you may want or need if you’d like to tackle the project with me.

Until next time, clear skies!


What aperture costs

August 14, 2012

Just for the heck of it, I decided to find out which telescopes are the best deals in terms of light grasp. My comparison group consists of widely available commercial dobsonian reflectors ranging from 3″ to 16″ in aperture. Sometimes I included two models at the same aperture to show the effect of differing features, like the finder scope and better eyepieces on the Orion Funscope versus the Celestron Firstscope, or the collapsing truss-tube design on the Meade Lightbridge scopes. Prices are street, not list, as of this writing. Each entry follows this layout:

Brand Model – mirror diameter (mm) – mirror area (in^2) – price – cost per in^2

Celestron Firstscope – 76mm – 7.065 in^2 – $38 – $5.38/in^2

Orion Funscope – 76mm – 7.065 in^2 – $50 – $7.08/in^2

Orion SkyScanner – 100mm – 12.56 in^2 – $100 – $7.96/in^2

Orion StarBlast 4.5 – 114mm – 15.89 in^2 – $200 – $12.59/in^2

Bushnell Ares 5 – 127mm – 19.63 in^2 – $165 – $8.41/in^2

Orion StarBlast 6 – 150mm – 28.26 in^2 – $280 – $9.91/in^2

Orion XT6 – 150mm – 28.26 in^2 – $280 – $9.91/in^2

Orion XT8 – 200mm – 50.24 in^2 – $350 – $6.97/in^2

Orion XT10 – 250mm – 78.5 in^2 – $580 – $7.39/in^2

Meade 10″ Lightbridge – 250mm – 78.5 in^2 – $700 – $8.92/in^2

Meade 12″ Lightbridge – 300mm – 113 in^2 – $1000 – $8.85/in^2

Orion XT12i – 300mm – 113 in^2 – $1100 – $9.73/in^2

Orion XX14i – 350mm – 154 in^2 – $1700 – $11.04/in^2

Meade 16″ Lightbridge – 400mm – 200 in^2 – $2000 – $10.00/in^2

Interestingly, there are two low points where the price dips below eight bucks per square inch: at the low end, with the 3″ scopes, and in the middle, with the 8″ and 10″ solid-tube dobs. It’s also interesting to note that the StarBlast 4.5, which is an extremely popular scope, is the most expensive in this group in terms of cost per square inch.

I only included dobs because everything else is more expensive–tripod-mounted Newtonians, catadioptrics, and refractors alike. Here are some comparative costs for beginner instruments of those other designs; for fairness, I only picked models with mounts included.

Orion SpaceProbe 3 Alt-Az (reflector) – 76mm – 7.065 in^2 – $100 – $14.15/in^2

Orion GoScope 80 (refractor) – 80mm – 7.74 in^2 – $100 – $12.92/in^2

Orion StarMax 90 Tabletop (catadioptric) – 90mm – 9.85 in^2 – $200 – $20.30/in^2

The difference here is that there is no mid-aperture dip as there is for the dobs, or if there is, it doesn’t bring the price per square inch near the $10 mark, let alone under it. Indeed, one would be hard-pressed to find a new, high quality 4″ achromatic refractor for less than $300-400, which is up in the neighborhood of $30/in^2. Similar prices obtain for mounted 5″ Maks and 8″ SCTs. That’s why I didn’t bother to account for the effect of the central obstructions in calculating the costs of the reflectors and catadioptrics; even what seem to be large secondary obstructions are usually less than 10% of the total collecting area, and dobs cost anywhere from a half to a fifth as much as other popular, “everyman’s” scopes in terms of collecting area.

Now,  I’m not saying that dobs are objectively superior to other scope designs. They’re cheaper. We all knew that, I’ve just quantified it, snapshot style, using currently available models and prices. I did it because I had a gut feeling that 8″ and 10″ solid-tube dobs were in sort of a sweet spot, price-wise, and that actual costs (per square inch of collecting area) rose a bit on either side. And they do.

Finally, these numbers put some classic deals into perspective. When the SkyWatcher 130N was on sale for $100, its cost was just a hair over five bucks per square inch–better than any of the models listed above by a considerable margin. The SkyWatcher 70AR was at one point selling for $36 shipped, or just a hair rover six bucks–a bit more expensive, per square inch, than the Celestron Firstscope, but for a much more capable instrument. I think the  only refractor deal in history that has ever equalled that was the Galileoscope. With 50mm of aperture and an introductory price of $15, it was originally selling for $4.78/in^2, but that was without a mount. Similarly, the value of buying used is now apparent–when I got my XT10 for $350, that was a cost per square inch of $4.46, much less than any of the new scopes, even the cheapies.

What should you buy? That’s a more complicated question, and it can only be answered by reference to your situation and your observing goals. I own a mid-sized Mak because sometimes it’s nice to have 5″ of light grasp in a package a foot long, and I bought it new because sometimes it’s nice to have something fresh off the line. But if you’re interested in deep-sky work, where every photon counts, and you’re on a budget, then you might find the numbers above useful in considering which scope will give you the most bang for your buck, or for evaluating future scopes.

Why you want as much aperture as you can get is the subject of the next post–and for a contrary view, see this post.


What’s on your bucket list?

August 7, 2012

First off, many thanks to everyone who has responded about the Suburban Messier Project. I’m going to do it, sooner or later, and I’ve started a draft outlining how my thinking has moved forward, thanks to your answers, but I haven’t had time to work on it much. I’ve been in summer teaching mode and anything not directly related to human anatomy has had to be fitted into the scraps of leftover time. Exhibit A: this post, which I started writing weeks ago, and only just finished.

Actually, work bears on this post in a way, in that it was work-related stuff that got me thinking along these lines. We’ve had a lot of discussions lately about goal-setting, and our annual reviews are shifting to be based more on the goals we set for ourselves. I’ll be honest, at first I thought this was one of the fairly pointless exercises of the kind that have made “academic” a curse word (“it’s all just academic”, etc.). But I’m warming up to the idea, now that evaluation is tied to it, because it means I can sort of set my own criteria for advancement (within reason).

ANYWAY, this has sort of spilled over in my stargazing. As you may have noticed, I am a bit of a gearhound, and I especially like to try out new (to me) scopes. About two dozen telescopes have passed through my hands since I first got into amateur astronomy in the fall of 2007. About two thirds of those were purchased used, and I sold most of them for about what I paid for them, which is a nice way to audition telescopes without spending a bundle. This summer I’ve been on a kick to thin the herd a bit, and cut back to just those scopes that I actually use. And I’ve realized that I’m pretty happy with my current scope lineup. I’d like to have a bigger, ultralight dob someday, and I’d like to try out an ED or APO refractor, but I no longer feel compelled to pounce on every affordable scope that comes over the horizon.

Free from the constant distraction of ten-night stands with hot little scopes, I’ve been thinking more and more about–gasp!–observing, and specifically my long-term goals as an observer. Either a bigger dob or an APO will require saving up dough for quite a while, possibly years. If I’m going to invest in a scope on that level, I should be pretty darned sure that it will show me stuff I want to see.

So, what do I want to see?

My imagination has been fired by the achievements of observers I idolize. Steve Coe observed something like 2000 deep-sky objects over a couple of decades–all of those visible from his latitude (in southern Arizona) that are listed in Burnham’s Celestial Handbook (see this sidebar page for a similar list). Uncle Rod just finished the Herschel 2500–all of the deep sky objects catalogued by William Herschel and his sister Caroline. And Jay Reynolds Freeman’s essay “10,000 Objects” has been lurking out there like Mount Everest.

(I should say here that some people dismiss observing thousands of objects as a form of celestial stamp collecting. I can’t speak for everyone, but for me it’s quite the opposite. These things are really out there. They are part of our universe, and I want to see them for the same reason that I want to visit as many countries as I can in my lifetime, and see as many earthly splendors as possible. The universe is very big, human lifetimes are very short, and there is just so much to see.)

But the observing list that has stuck most firmly in my head is one posted by Don Pensack on Cloudy Nights, in a thread on telescope aperture. It’s worth quoting at length, so I will:

For years I thought an 8″ scope was a “lifetime” scope. Probably around 15000 DSOs are reachable, and pretty much all star clusters. You could spend a lifetime with one and become quite an accomplished observer.
But my interests shifted more to galaxies so I moved up “a magnitude” to a 12.5″. And while I certainly can see more galaxies and details therein, the biggest difference in appearance came with the mundane, easily visible, brighter objects.
I’ve seen (and it wasn’t possible in an 8″):
–individual stars in M31 (NGC206 stars)
–stars across the face of M14
–tons of H-II regions in most of the nearer galaxies
–white swirls inside the GRS on Jupiter
–brightness variations on Ganymede
–differential colors in the Galilean moons
–the Keeler Gap in Saturn’s rings
–the outer spiral arms of M81 and NGC7331
–to-the-core resolution on M15
–red giants in M13
–dark lanes in tons of edge-on galaxies
–M17 and M16 as part of the same nebula
–wonderful striations across the face of NGC6888
–B33 (Horsehead), both with and without a filter
–galaxies in some faint Abell Galaxy clusters
–several Abell planetaries

I sit when I observe except at the zenith.

The next logical step (to gain a magnitude): 20″
But it’s too big to easily carry by one person and transport in a small, high-mileage, car. I regularly observe at dark sites frequented by others with larger scopes, and I’ve learned that, by and large, most big scope observers don’t go after targets any fainter than I do.
And I hate standing or using a ladder to observe.
A 20″ f/3 would work, but the issue of lifting the scope would still remain.

So, for me, though I’m tempted by larger apertures, MY serious aperture is 12.5″. I guess the key is, if you observe a lot of things, and use the scope quite a bit on a variety of targets, that constitutes serious observing. And, no matter what aperture is used, by extrapolation that’s serious aperture.

Okay, so his list wasn’t presented as a list of observing targets per se, more like some highlights from his move up in aperture. But I still read them and thought, “Damn, I’d like to see that stuff for myself.”

In that spirit I’ve been working on a list of stuff I want to see; an astronomical bucket list. Some things that might be on a general astro bucket list are not on my specific list, in some cases because I’ve already observed them. So as I was making up the bucket list, I made a parallel list of my favorite observations to date. Not all of them were challenging, but all were memorable. They delighted me, and the chance to possibly recapture that delight is my major motivation for going out to observe.

On to the lists! Both are arranged roughly from the center of the solar system out toward the edge of the observable universe.

My Favorite Observations to Date

My Astronomical Bucket List

  • Chart sun’s rotation using sunspots
  • Total solar eclipse
  • Transit of Mercury
  • Night sky from a ship in the mid-ocean
  • Southern hemisphere skies with more than 50mm of aperture
  • Up-close rocket launch–okay, so this isn’t technically an astronomical observation. But hey, it’s my list.
  • Phobos
  • Major asteroids
  • Zodiacal light–this is supposed to be an easier catch than the Gegenschein, which I have seen. Possibly I have seen it and not known what it was.
  • Jupiter or Saturn being occulted by the moon
  • One or more moons of Uranus and Neptune
  • Pluto
  • A great comet (this one is up to the universe)
  • Barnard’s star
  • Track a high proper-motion star as it moves in front of background stars (will take 2 or more observations some years apart)
  • Sirius and the Pup
  • Herschel 500 double stars
  • Detail in the Crab Nebula (M1)
  • Central star in the Ring Nebula (M57)
  • “Pillars of Creation” in M16
  • Horsehead Nebula (B33)
  • Bright, naked-eye nova or supernova (again, this is up to the universe)
  • “Propeller” in M13–apparently there are three dark lanes in M13 that form a propeller shape. I’ve never noticed them.
  • Globular clusters in the Andromeda galaxy (M31)
  • Jet in M87 (will definitely need a bigger scope!)
  • All 110 Messiers in a Messier Marathon
  • Herschel 400, Herschel II 400, and Herschel 2500–I’m not quite a third of the way through the Herschel 400, so I’ll be climbing this mountain for a long time. But the scenery is well worth it.
  • More, and more distant, quasars

I’m sure more things will occur to me in the future. In the meantime, quite a few things on my bucket list are achievable with the gear I’ve already got. I just need to get out and see more–and that is a goal I can work on anytime. May it ever be so.


Hell yes–wheels down on Mars again!

August 6, 2012

We all stayed up last night to watch Curiosity land on Mars. It was amazing, to be watching the live feed from Mission Control at JPL, hearing the live telemetry being relayed, and then just moments after touchdown get to see the first photo sent back by the rover (it’s grainy and blurry because the transparent lens cap is still on the camera to protect it from the dust kicked up by the landing).

As John Holdren, President Obama’s assistant for science and technology, said, “there’s a one ton automobile-sized piece of American ingenuity and it’s sitting on the surface of Mars right now.”

I was particularly engaged because I had gotten to see parts of the actual spacecraft, including the aeroshell and rocket skycrane, during a tour of JPL two and a half years ago. Strange and amazing to know that the same machinery I saw in the big white room at JPL is now on Mars.

During the landing, data were relayed  back by the Mars Odyssey spacecraft, which has been in orbit around Mars for 10 years, 9 months, and 13 days. This decade-old craft was never designed to function as a data relay, but, you know, engineers are smart. Curiosity joins the rover Opportunity, which is still going strong 3116 days into its 92.5-day mission.

Turns out, we weren’t the only ones watching the landing. The Mars Reconnaissance Orbiter got a photo of Curiosity on the way down, using its HiRISE camera.

This is the second time MRO has caught a Mars lander on the way down; it got a photo of Phoenix descending under its parachute back in 2008.

Happily, today’s xkcd explains why I’m blogging about space on a Monday morning:

Or, as my buddy Jarrod put it on Facebook, “We just landed a one-ton NUCLEAR ROBOT on another planet with a SUPERSONIC PARACHUTE and a FRICKIN’ ROCKET SKYCRANE.”

Good times.


Last week’s full moon

August 5, 2012

Ever since the full moon of January 29, 2010, I’ve been wanting to catch another that was perfectly full. Not a day or even half a day early or late, but right on the button. I came pretty close last Wednesday, August 1. Here’s my best shot, taken with the Nikon Coolpix 4500 shooting through my Apex 127 Mak and 32mm Plossl.

It’s hard to say if this moon is really perfectly full or not; in a way it is, and in a way it isn’t. I know that’s enigmatic, and I’ll clarify it at the end of the post. But first, compare last Wednesday’s full moon to the renowned (by me, anyway) January 29, 2010, moon.

Here, let me make that comparison easier for you. As always, click for the big version.

Two things here are worthy of note. First, there is a difference in illumination. On the left, the east side of the moon is better lit, and on the right, the west.

More importantly, these pictures do not show the same stretch of moon! Check out this overlapped composite, with a few prominent landmarks labelled.

All of the offsets are consistently in the southeast-northwest direction, and the two moons are perfectly overlapped at the periphery. The difference between the images is not because the photographs are rotated in two dimensions, but because the moon was differently rotated in three dimensions. This effect is called libration, and because of it we can see almost 60% of the lunar surface from Earth.

Here’s the comparo again, this time with some of the limb features labelled.

On January 29, 2010, the northwest limb of the moon was tipped toward us, allowing a good view of the “shore” of Oceanus Procellarum and some prominent rim craters like von Braun and its equally-spaced outriders Lavoisier A and Harding. Another useful landmark is the bright crater Seleucus, just to the east of the much larger, dark-floored Eddington. On the opposite limb, Mare Marginis and Mare Australe are barely visible, and Mare Smythii is just a dark patch on the limb itself.

Now compare to last week’s fully moon. The northwest limb is rotated so far away that von Braun is completely lost, along with the rest of the shore of Oceanus Procellarum, and Eddington is a barely perceptible dark streak. On the other hand, the southeast limb shows excellent detail in Mare Australe, especially around the very dark-floored craters Lyot and Oken, and farther north we can see all the way across Mare Smythii to the lighter terrain beyond.

Now, as to the “perfection” of the fullness: there is some terminator-like shadow and detail visible in my  photo from last week, but not on the eastern limb where one might expect it. Instead, all of the visibly shadowed craters are around the south pole. This is where the story gets complicated.

There are three widely-discussed causes of libration: (1) the moon leading or lagging, relative to its own rotation, along its eccentric orbital path; (2) the tilt of the  moon’s axis relative to the plane of its orbit; and (3) rotation of the Earth, which from moonrise to moonset carries an Earthbound observer almost 8000 miles from west to east (which is why everything in the sky rises in the east–that’s the direction we’re constantly headed here on the surface). The moon is only 240,000 miles away, so this daily (or nightly) trip equals 1/30 of the distance from Earth to the moon. How much difference does that make? The average interocular distance for a human is 6.5 cm (2.5 inches), so look at something 30 times farther away (195 cm or just over 6 feet) first with one eye and then with the other. You just simulated diurnal libration.

Now, as I noted above, the eastern limb of the moon is darker than the western side in last week’s photo. The Sky & Tel online almanac said max fullness would be at 8:37 PM, PDT. But the moon was just rising then, about four hours before it would cross the local meridian. In other words, at max fullness the moon was dead overhead for people 4000 miles west of me, but the turning Earth wouldn’t carry me directly under the moon for another four hours–and by the time I got there, it wouldn’t be perfectly full anymore. I took the picture I used in this post at about 11:30–three hours too late for a perfectly full moon. I took other pictures at 8:37 and other times in between, but they turned out poorly–seeing near the horizon was rotten and my scope wasn’t properly cooled yet.

So I’m pretty sure that diurnal libration–the effect of the turning Earth–accounts for the less-than-even illumination from east to west in my moon shot. But that doesn’t explain why there are shadows at the south pole. I assume that the alignment of the moon and Earth was such that I was looking up the moon’s skirts, so to speak–so far south, relative to the moon, that I could see past the illuminated area and into the shadowed highlands beyond. If that’s true, then observers in the Southern Hemisphere, being even farther “below” the moon, should have been able to see even farther into the shadowlands.

The moral of the story is that if you want a good photo of the perfectly full moon, it’s not enough that the moon be visible in the sky at the moment of max fullness–you should also be right underneath it (it should be as high in the sky as it is going to get). Even if you get good enough seeing to get a clean shot of the moon low in the sky, you’ll be several thousand miles to one side or the other, and you won’t be seeing it face-on. On the flip side, if you catch the rising full moon a few hours before max fullness, or the setting full moon a few hours after, you might still get a fully-illuminated disk, because Earth’s rotation will put you along the same line as the incoming light. Sounds a bit hairy, but as Timothy Ferris wrote of making chancy observations, “You can’t catch any fish if you don’t get your line wet.”

Anyway, I had a lot of fun, and got a good look at some southeast limb features that I’d never seen before. I’m anxious to see what libration will bring me next.


Curiosity arrives at Mars this weekend!

August 2, 2012

Our newest and largest Mars rover, Curiosity, will arrive at Mars Sunday night or Monday morning, depending on your time zone (image from Wikipedia). I say “will arrive at Mars” because we won’t know if it landed safely or just hit Mars until 7 minutes after the fact. As you can see from this nifty calculator, the distance between Earth and Mars is currently 152 million miles and growing. The landing is scheduled to occur at 10:31 PM, PDT, on August 5, or 1:31 AM EDT, or 5:31 AM UT/GMT.

This video about the landing explains something of the difficulty and complexity of landing a BIG rover on Mars, and some (but not all) of the justification for going with the never-before-attempted skycrane landing method.

Fingers firmly crossed!