Archive for the ‘Target of opportunity’ Category


My talks at RTMC this year

May 24, 2017

Quick note: I’ll be at RTMC again this year, and I’m giving two talks. On Saturday morning at 10:30 I’m giving a Beginner’s Corner talk on “Exploring the Universe with Binoculars”, and on Sunday morning at 10:00 I’m giving a Main Hall talk on “Observing the Scale of the Universe”. There are loads of other great speakers, including Mr. Eclipse himself, Dr. Fred Espenak, and plenty of cool events going on, so come on up and hang out with us. I hope to see you there.


Two binocular comets and a small-scope supernova

March 31, 2017

Comet 41P brightens – photo by Hisayoshi Kato, from Sky & Tel’s 41P news page.

This is a shorty, just posting links to some current events for easy reference:

  • Comet 41P is bright and easily visible in binoculars from dark skies for most of the night from mid-northern latitudes (link).
  • Comet C/2017 E4 Lovejoy – the sixth comet discovered by Australian amateur Terry Lovejoy – is up just before dawn, near the ‘nose’ of Pegasus (link).
  • Supernova 2017cbv in the spiral galaxy NGC 5643 is visible in Lupus in the middle of the night – it’s a few degrees north and about an hour east of Omega Centauri, so it transits the meridian around 3 AM right now (link).

Go see some fun stuff.


Kickstarter – the Great Lick Refractor

February 25, 2017

I have been very fortunate in getting to visit the Lick Observatory three times, and to look through the Great Lick Refractor (36″/914mm aperture, f/19) on two different occasions. On the second visit I even got a quick afocal snap of Saturn through this wonderful, 129-year-old instrument. Those stories and accompanying photos are on Cloudy Nights, here.

I bring this up because there’s a Kickstarter going on right now to sponsor a couple of experienced astrophotographers to use the Great Lick Refractor for one night (or maybe two, if they enough funding), and backers get copies of their pictures. The project will be funded – they’re already well over the target goal of $6500 and closing in on the $9000 they’ll need for a second night – so there’s no real risk here. I pounced as soon as I heard about it. If you’re interested, click on one of the links above and check it out.

This project will be funded on Monday, March 20, 2017, at 7:17 PM PDT.


Get $5 off your first purchase from

February 21, 2017

Hey, I was temporarily without a 10mm eyepiece (long story) and I have been sufficiently happy with the Bresser 20mm 70-degree that came with my AR102S Comet Edition that I plunked down thirty bucks for the 10mm version (sale price, down from $50). It was only my second-ever purchase from (after the Bresser Spektar spotting scope a couple of years ago), but they rewarded my ‘ongoing support’ with this deal. You can use this link and unique code:

to get $5 off your first purchase, and if you do, I’ll get a $5 kickback. As far as I know, there is no limit to how often this can be used by people making their first purchase there. So if you’ve been tempted by something at that store, here’s your chance to save a little dough. Happy shopping!


Unboxing the Bresser Messier AR102S Comet Edition

January 31, 2017


I’ve been interested in this scope since late 2014. The Celestron TravelScope 70 turned me on to the joys of refractors back in 2012, which led to the C102, which led to the C80ED, which got me firmly hooked on low-power, widefield scanning, which led to this.

This is the Bresser Messier AR102S Comet Edition, which I believe is a record for the longest name of any telescope I’ve owned. And you actually do need all of it, because there is another Bresser Messier AR102S that is a completely different scope. That other AR102S is a standard f/6 achromat. The AR102S Comet Edition is an f/4.5 rich-field scope. And as you can see from the photo, it’s built funny. Instead of having the focuser at the back end of the tube, the focuser is mounted on the side of the tube, as in a reflector, and a reflector-style secondary mirror* bounces the light from the objective lens to the eyepiece. This makes for a very short, compact scope, and theoretically for easy collimation via that secondary mirror (I haven’t tried that yet). Scopes like this are sometimes called “reflactors” because they combine an objective lens with a secondary mirror. I’ve seen ATM builds using this design, but I’ve never seen another one marketed commercially.

* Existential telescope question: is it still a secondary mirror if there’s no primary?


As far as I know, this scope has only ever been sold as part of a travel kit that includes the OTA, an eyepiece, an alt-az mount, 7×50 binoculars, and a backpack to carry it all. That package has a list price of $349, but the list price has been creeping downward. Explore Scientific’s online store and both carry the AR102S Comet Edition (man does this scope need a nickname) package for $299, but B&H Photo-Video has it for $249 with free shipping. Amazon used to have it for $249 as well, but I seem to have gotten the last of those – as of this writing, the price is hovering in the $340s.

I’ll have a first light report along soon, this one is mostly photos of the unboxing and the scope.


Outer box…


…contains the middle box…


…contains the inner box. That’s right, three boxes before you get to anything other than packing material and the instructions.


Inside box number three are the backpack and two more boxes.


Inside the backpack is the OTA in a plastic bag, and on the right you can see the eyepiece peeking out of the side pocket.


Oh, also in the backpack are the 7×50 binos. Everything bagged.


And inside the bags, the telescope OTA with wrapping paper, the binocular case with the binos in yet another plastic bag inside that, and the eyepiece bolt case with the eyepiece in yet another plastic bag inside that. Oh, and a couple of hex wrenches inside the bag with the bolt case, for collimating the OTA.


And here’s everything finally outside of the various bags, bolts, and cases.


The OTA is 20″ long and 4″ in diameter, with a 4 1/4″ diameter dew shield. In the shots before this one, you can see the dovetail on the right side of the OTA, and here you can see the shoe for a finder (not included) on the left side of the OTA. Having the dovetail on one side and the finder shoe on the other is convenient, because it means the OTA can’t roll over and bang the focuser if you set it down on a flat surface.


Here’s the lens cap. If you’re thinking it looks like a Meade, you’re not wrong.


And way down inside the dewshield, 4 1/4″ in, is the objective lens, with its dark green anti-reflection coatings. The achromatic doublet is fully multicoated. The dewshield has an outside diameter of 4 1/4″, and an inside diameter of 4 1/8″. Past the objective lens you can also see the single baffle inside the OTA, which is otherwise just painted flat black inside.


Remember those other two boxes? The long one has the tripod and the short one has the alt-az head.


The alt-az head, which is metal, and the eyepiece tray, which is plastic.


The mount assembled. The alt-az head looks like my SkyWatcher AZ-4/Orion VersaGo II, but it lacks the adjustable tension knobs.


Here’s a feature that I really like: the eyepiece tray goes solidly onto the spreader bars with no tools. It threads over a central bolt, and then rotates to snap into position. This is super-handy at the end of the night, because I can unlock and rotate the eyepiece tray without taking it off, and fold the tripod legs in just enough to get through the door.


The whole rig set up. The tube looks not quite square here, but that’s just field distortion from the iPhone camera, which we’ve seen before here.

The OTA weighs 6.2 lbs, the mount weighs 6.8, so the whole rig clocks in at 13 lbs even. That’s pretty portable, although certainly at least flirting with being undermounted. More on that in the first light report.


User end. The eyepiece is a Bresser 20mm 70-degree model, which is currently on sale for $40, down from $60, at If you’re thinking that $60 seems like not much money for a new fully-multicoated 70-degree eyepiece, I agree, and I am likewise suspicious. I assume it’s some kind of Erfle, but I haven’t taken it apart to confirm. The size, form factor, and even barrel detailing are very similar to Orion Sirius Plossls, but the eye lens is just slightly too big for Sirius dust caps to fit (which is a shame, since it gets in the way of me stuffing this thing in my pocket while I swap Plossls and Expanses around). It gives 23x and a 3-degree true field of view.


Here’s the left side of the back end, showing the finder shoe, the collimation bolts for the secondary, and another look at the focuser. The focuser is an all-metal rack-and-pinion job. Oddly enough, the focuser drawtube is 2″ in diameter but the 1.25″ adapter at the top is permanently mounted. So it’s a 2″ focuser that only accepts 1.25″ eyepieces. I think there’s a reason for this – the focal plane is 6-7 inches (150-175 mm) away from the center of the OTA, which means at least a third of the 459-mm light path occurs after the light hits the secondary. I think a 1.25″ drawtube would cut into the light path and stop down the scope.

The finder shoe is not one I’m familiar with. Almost all of my experience is with gear made by Synta (Orion/Celestron/SkyWatcher), which uses the same mostly-but-not-quite industry standard dovetail shoe for finders. This is a weird square rig that is outside my experience. I probably won’t use a magnifying finder – I can get by okay just dead-reckoning, and when I feel like cheating I can lay a laser pointer along the dovetail shoe or the square edge of the focuser and get on target very fast. But I might put a counterweight there, to get the balance point a little farther back so the eyepiece height would change less going from horizon to zenith. Or here’s an interesting thought: I bet I could gin up an eyepiece rack that would attach to the finder shoe. That would be cool, convenient, and a counterweight.

Here’s the focuser again, with the axis drawn in blue. This is to make a point. I’ve seen one or two folks on Cloudy Nights alleging that this is a “leftover scope” – that Bresser/Explore Scientific had some leftover tubes, leftover secondaries, and leftover focusers, so they cobbled it all together into this Frankenscope. But that doesn’t hold up. The focuser is a single-piece aluminum casting with two features of note. First, it wraps tight to the 4″ diameter tube, which if it was leftover from a reflector would have housed a smaller-than-4″ mirror. There are 3″ reflectors out there, like Orion’s SpaceProbe 3, but no-one puts 2″ focusers on them. Second, and more importantly, the focuser knobs point across the tube on this scope – that’s what the blue line shows in the image above – as opposed to down the length of the tube as in all mass-produced reflectors. Again, the focuser is a single chunk of aluminum – the 2″ tube can’t be separated from the base, or rotated relative to it. So I’m confident that this focuser was purpose-built for this scope.

The “leftover scope” idea was pretty dumb anyway. The most expensive part of any refractor is the objective lens, which has to be figured to a tolerance of a millionth of an inch. The rest is just steel, aluminum, plastic, and fasteners, which cost peanuts by comparison. As far as I’ve been able to tell, neither Bresser/Explore Scientific nor their parent/partner Jinghua ever sold a 4″ f/4.5 scope before. It doesn’t make any sense to figure a bunch of bespoke objectives – the expensive part, especially after full multi-coating – just to sell the cheap hardware.

So, somebody decided that a fast, 4″ reflactor was a good idea. Were they right? Tune in next time and find out.


A little piece of Mars

July 21, 2016

Mini Museum no 3614 DSCN1469

This is my Mini Museum: a collection of tiny samples of rare and interesting specimens from the history and prehistory of Earth and the solar system. There’s a lot of stuff in here that is very satisfying as both a paleontologist and an amateur astronomer. Highlights for me are the preserved woolly mammoth meat, the fiberglass casts of Diplodocus bones used as the Krayt Dragon skeleton in Star Wars: A New Hope, and, above all, the tiny piece of the Martian meteorite Zagami. It’s labeled “Martian atmosphere” because the meteor is known to contain tiny bubbles of Martian atmosphere in pockets of melted glass (Marti et al., 1995).

The specimens are embedded in a single block of acrylic that is 5 inches tall, 4 inches wide, and 1 inch thick. At $299 it’s not cheap, but it’s a pretty astounding collection of objects at any price. There is also a smaller, 10-specimen edition for $99. It doesn’t include Zagami or the Krayt Dragon, but it does have asteroid fragments, Stegosaurus plate, woolly mammoth meat, fulgurite, and the moon tree sample. These will sell out at some point, so if you’re interested in picking one up, don’t tarry.


Marti, K., Kim, J.S., Thakur, A.N., McCoy, T.J. and Keil, K., 1995. Signatures of the Martian atmopshere in glass of the Zagami meteorite. Science, 267(5206), p.1981.


Getting ready for Mercury

April 18, 2016


The planet Mercury will transit the sun on the morning of Monday, May 9. Mercury transits are not as rare as the more famous transits of Venus, but they still only come around once or twice a decade on average. The last Mercury transits before this one were in 2003 and 2006, and the next two after this year will be in 2019 and 2032. From southern California, the transit will already be underway when the sun rises at 5:57 AM, maximum transit (the point when Mercury is the furthest inside the sun’s disk as seen from Earth) will be at 7:58, and Mercury will exit the sun’s disk between 11:39 and 11:42 AM (all times in PDT).

For the transit of Venus in 2012, I used a simple homemade device called a “sun funnel” attached to a small reflecting telescope to project an image of the sun. You can read more about that here and here. The sun funnel worked well enough – I also used it for the annular eclipse in 2012 and the partial eclipse in 2014 – but the screen material degrades the resolution somewhat. Mercury is a lot smaller than Venus, and much closer to the sun, and both of those factors make it appear much smaller than Venus during a transit.


I want maximum resolution for observing and photographing the upcoming transit, so I finally sprung for a full-aperture solar film filter for my 80mm telescope, which you can see set up at the top of this post. I got it out the other day for a test drive and got some decent photos of the current large sunspot AR2529, shown above. I’m pretty happy with the results – now if we can just get clear skies on the morning of May 9. If you’re curious, the filter I got is the GoSky Optics full-aperture filter with Baader solar film. There are several sizes available to fit all kinds of telescopes, and the filter attaches securely to your telescope tube or dewshield with three nylon-tipped screws. I got the filter for telescopes 81-113mm in diameter (outside tube or dewshield diameter, not optical diameter!), which is currently a little under $50 on Amazon.

This is my second GoSky product, after the universal cell phone adapter I picked up last fall, and I’ve been impressed with the solid construction and good fit-and-finish of both products. Some of the weird large-scale blotchiness in sun photos is probably either distortion from the iPhone’s tiny field lens, or gunk on the surface, and the uneven margin of the solar disc is from atmospheric turbulence. But I think the graininess across the surface of the sun is actual solar granulation. I couldn’t see it on the iPhone – not enough image scale. If I had, I’d have thrown in a shorter focal length eyepiece and tried some higher-magnification shots. They might not have turned out well even if I had taken them – the seeing was pretty awful – but it would have been worth a shot. Something to try next time.

The diameter of the sun is 109 times that of Earth. Here's how Earth would compare to the current large sunspot if they were side-by-side.

The diameter of the sun is 109 times that of Earth. Here’s how Earth would compare to the current large sunspot if they were side-by-side.

Unfortunately, I won’t be here in California to share the transit with my local friends and fellow observers. I’ll be in Utah chasing dinosaurs from May 4 to May 14, so I’ll have to catch the transit from there. I’m driving up and bringing my 80mm scope to take advantage of dark Utah skies in the evenings. If you want to plan your own transit observation, or just want to investigate how the transit will appear from various points on Earth’s surface, this interactive map is excellent. And if you need safe, inexpensive ways to observe the sun, check out my page on safe solar observing. Clear skies!