Archive for June, 2012

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My moment of Zen

June 30, 2012

This month has been kind of a blitz, and this week has been a blitz within a blitz. My summer teaching started, I’m still organizing data from a research trip last week, and one of my best friends is moving away. I miss being outside, being alone, having time to think, and having time to not think.

After my evening responsibilities were over, I got out the little Mak and decided to get back to my in-town observing projects: the Astronomical League’s Urban Observing club and Double Star club. I am getting very close to finishing the observations for the Urban club, so that’s where I started tonight. I observed the globular cluster M62 in Scorpio, and the double star Graffias (Beta Scorpii). That only leaves two objects to go to finish the Urban club: the galaxy M77 and the variable star Algol (Beta Persei). Both are up in the early morning at this time of year, so my options are to get up before dawn some morning, or just wait a few months until they’re up earlier. I’ll probably make a Dawn Patrol run one of these mornings to knock them off; now that I am so close to having that list completed, I doubt if I’ll be able to wait very long.

Graffias is also on the observing list for the Double Star club, so it made a nice segue into double star observing, and that’s what I did for the rest of the session. Double stars are great because they don’t suffer much from light pollution. A gray sky background is not as pretty as a black one, but the stars themselves are easily visible, so I have something outside the solar system to observe on nights like tonight when the moon makes DSO hunting unrewarding at best.

It’s easy to get into a rhythm. I made an all-sky map showing the 100 double and multiple stars on the observing list, so I check that to see what’s well-placed in the sky and convenient. Then I pick up the Pocket Sky Atlas and figure out how to star hop to my target star. Once I’m on target, I swap eyepieces in and out until I find out which magnification yields the most pleasing view. Then I sketch the stars in my logbook and make a few notes. I logged nine doubles tonight in addition to Graffias, leaving 31 to go in that observing program.

Our cat, Moe, was outside with me, doing whatever it is he does after dark. At one point I looked up and saw him in the driveway, nosing at a slightly smaller animal. The second critter wasn’t yowling, hissing, or running away, so I figured it wasn’t one of the neighborhood cats. I shined my red flashlight in that direction and found myself staring into the glowing red eyes of an opossum. I like opossums. It’s cool that we have a native marsupial in North America, and it’s cool that opossums are still doing pretty much what their–and our–ancestors were doing under the feet of the dinosaurs. I went over to have a look at our nocturnal visitor, and after a minute he shuffled off to attend to his mysterious business. I went back to the sky.

I did take some time to look at the moon, and shared the view with Vicki and London before they turned in, and later on with our neighbor in the front house.

So, nothing spectacular. And that’s the point. I don’t write enough about the simple joys of stargazing. I spent two hours outside in the cool night air, saw some beautiful stars, got to chat for a few minutes with my neighbor, had a visit from a wild animal, and learned a little more of the sky. If I did this on a more regular basis, I’d probably be a happier, saner person.

I still haven’t blogged about the transit of Venus, which went swimmingly, or about the great observing run I had up Mount Baldy with Terry Nakazono a couple of weeks ago. I do intend to get to those things, as and when. In the meantime, I am going to get some sleep. Clear skies.

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Worth reading: Uncle Rod’s grab-n-go shootout

June 22, 2012

Hi folks,

I’ve been too busy to post lately, thanks to day-job work and a research trip to New York. But life continues apace elsewhere in the astroblogosphere, including at Uncle Rod’s Astro Blog, where astronomical observer, speaker, and writer Rod Mollise just posted an excellent head-to-head comparo between his Short Tube 80 refractor and StarBlast 4.5 reflector. Getting a handle on the performance of small telescopes is a topic near and dear to my heart, so get on over there for a well-written post packed with genuinely useful information.

Hopefully I’ll find time soon to get something up. In the meantime, clear skies!

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See the transit of Venus in Claremont

June 5, 2012

If no clouds come to spoil the fun, I will be in downtown Claremont this afternoon (Tuesday, June 5) with a scope set up for free public viewing of the transit of Venus. The transit starts at 3:06 PM, PDT, and will still be in progress when the sun sets at 7:59. I plan to be there for all of it. If all goes well, from about 2:50 onward I will be in the public square in front of the theater, on the northeast corner of First Street and Indian Hill Boulevard. Whenever the sun gets low enough to go behind the theater, I’ll head up to the top of the parking garage across the street, to watch the sun set with Venus still crossing the solar disk. You, whoever you are, are welcome to join me.

If by some freak chance it is cloudy this afternoon, I’m going to throw my gear in the car and run up to Big Bear, which gets more sunny days than almost anywhere else in SoCal (that’s why the solar observatory is there). In which case, you’re still welcome to join me, if you can find me. Try the Discovery Center on the north shore, if it’s sunny…or the nearest pub if it’s not.

Fingers firmly crossed for clear, sunny skies!

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More low-cost solar observing

June 4, 2012

In preparation for the transit of Venus tomorrow, I did a little hacking and tinkering late this afternoon. Although the sun funnel worked well enough for watching the eclipse, as we’ll see below it is not perfect for photographing the sun in any detail. My full-aperture solar filter still hasn’t arrived, but I got to thinking about how to make a safe direct viewing setup.

I recently acquired a Celestron Travel Scope 70, a little 70mm (2.75 inch) f/5.7 achromatic refractor. Like a lot of small refractors, the dust cap for the objective lens has a smaller removable cap in the middle, in case you want to stop down the scope for more pleasant viewing of bright targets like the full moon. The diameter of the small hole in the middle of the big cap is 40mm, so with big cap on but the small cap off, the scope functions as a 40mm f/10.

I don’t have any loose solar film to make a 70mm solar filter or even a 40mm solar filter. But I do have a stack of eclipse glasses, each of which has two 1×1.5 inch eye holes covered with solar film. So I cut one of the eclipse glasses in half, made a round 25mm aperture in a square piece of cardboard, and mounted the eclipse glasses ‘lens’ (solar film still surrounded by two sheets of thin cardboard) and the 25mm aperture stop on the back side of the big dust cap. I didn’t think to take any pictures of the inside of the dust cap to show how it all goes together, but hopefully the general idea is clear enough. With the big dust cap on and the small dust cap off, the scope admits a 25mm beam of fully solar-filtered light to the objective, turning the scope into a 25mm f/16 solar refractor. And because the solar filter is on the inside of the big dust cap and protected by the small dust cap (in front) and the second piece of cardboard with the 25mm aperture stop (behind), I can leave it in all the time. Take the big dust cap off, the scope functions normally. Take only the small one off, I’ve got a 1-inch solar scope.

Two other design decisions to note. First, the finder–and I use the term advisedly–that came with this scope is without doubt the worst finder I have ever seen on a commercial scope from a brand name manufacturer. It looks like a 5×20 straight-through magnifying finder. However, right behind the (single, plastic) objective lens is an aperture stop with only a 1-cm hole in the middle. So in fact it’s a 5×10 finder with a plastic singlet objective. The immense irony is that the scope doesn’t need a finder at all; throw in a 32mm Plossl and you get 12.5x and 4-degree true field of view, so the scope effectively functions as its own superfinder. So I unscrewed both ends of the finder and dumped out all the plastic optics, turning it into a hollow sight tube. Why is this important right now? Because it’s really dumb to leave a magnifying finder on a telescope being used for solar observing; it’s too easy to forget what you’re doing and accidentally looking through the unfiltered finder and cause serious eye damage or blindness. There’s a good reason that every commercial telescope comes with a “don’t point the scope at the sun, dummy” tag or sticker or both. This is not something to mess around with. If you’re going to observe the sun with a telescope, cultivate the same habits of awareness and deliberate action that you would use around loaded firearms and power saws.

Oh, the included 45-degree prism diagonal is also rubbish and the light tripod looks pretty dodgy. Today I used my standard small-scope setup–an AstroTech 90-degree dielectric star diagonal and a Universal Astronomics DwarfStar alt-az head on a Bogen/Manfrotto tripod–and I’ll doubtless do the same in the future.

The other design thing was the sun shield. At first I tried going without but look into a dark eyepiece to catch a filtered (= comparatively dim) view of the filtered sun while unfiltered sunlight was hitting the top of my head and my upper eyelid had me squinting and developing a minor headache almost immediately. The plastic dewshield on this scope pulls right off, so I got a handy piece of cardboard (part of the packaging of a picture frame), cut a hole just big enough to admit the front end of the scope without the dewshield, slid the cardboard sunshield on and used the plastic dew shield (and dust cap with solar filter) to hold it in place. I also cut a second, smaller hole to let light in to my sight tube sun finder.

If you do something similar, make sure that the sun shield can’t get blown off and take the solar filter with it. In my case, the dewshield slides on a long way and grips both the sun shield and telescope tube firmly; a strong enough breeze might upend the whole setup, but it couldn’t blow off just the shield and filter. Again, eye safety is paramount; don’t take any chances.

Okay, so how did it work in practice? Pretty darned well. I had already aligned the sight tube with the telescope, so all I had to do was rotate the sun shield a bit to make sure the second, smaller hole lined up with the sight tube. Then I could point the scope roughly at the sun and pan around until a perfectly round beam of sunlight (projected on my hand) emerged from the sight tube. That always put the sun in the field of view of a 25mm Plossl (16x, 3 degree true field of view). The view of the sun at the eyepiece was reasonably bright–for an astronomical object, not compared to the unfiltered sunlight streaming down all around–and razor-sharp. The sunspots with their umbrae (dark centers) and penumbrae (lighter borders) were striking, like they’d been etched on stained glass.

Happily, the filtered scope yielded nice, even light all over the surface of the sun, no matter where it roamed in the field of the view. My one beef with the sun funnel is that it can be hard to get really good photos because of the inherent granularity of the screen material. Inevitably some part of the projected sun is brighter than another, and if you manage to get the light perfectly centered, it can easily wipe out the sunspots. The best way I’ve found to avoid this flashlight-beam effect is to photograph the sun from a bit to the side, out of the direct path of the projected light (that’s how I got this very sharp photo), but then the sun is out of round–not ideal if you’re hoping to combine images into a composite or movie, or even get a nice, square-on shot of a circular sun.

For example, in the photo above the sunspots on the left are sharp enough–the big one even shows the umbra and penumbra clearly–but the dimmer two on the right are lost in the flashlight glow of the sun lighting up the screen material from behind. And in this view the sun is already way out of round.

Also note that this image is flipped horizontally compared with the image from the refractor. In fact, this image is correctly oriented. Normally Newtonian reflectors show things rotated by 180 degrees, but projecting the image on the screen undoes that and gets everything back to normal. The solar filter on the refractor just cuts down the intensity of the light, it does nothing to reorient the image, so the image at the eyepiece is right side up but, because of the 90-degree mirror, flipped left-to-right.

I didn’t go to all of this trouble just for the transit of Venus. I mean, I happily would have, had the transit been the only game in town. But it’s not–the Astronomical League has a Sunspotters observing program, and now that I have the gear for solar observing, I might as well start logging. I’ll keep you posted on that.

Now, I should point out that the flashlight-beam effect washing out the sunspots in the sun funnel is mostly a photographic concern. For visual appreciation, even solo, I think the sun funnel still wins. A 4-inch image scale and the ability to put your head and eyes wherever you want–and even wear polarized sunglasses to observe–can’t be beat. But for photography, I prefer the filtered direct view–even in a one-inch scope.

Fortunately I’ll be rolling with both tomorrow. Now if the weather just cooperates…

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Guest post: Four-way diagonal comparison!

June 2, 2012

I’m happy to host another guest post (here’s his last one) by frequent commenter and indefatigable scope hacker David DeLano. In this one David compares four 90-degree diagonals: a high-end prism and mirror, and a low-end prism and mirror.

The Test Scope and Target

Here are pictures of the setup I used to test the diagonals.  But first, here’s the dovetail on spare ring that I made for my RDF.

Here is a picture of the target I shot.  It’s the AC unit in the middle of the picture.  This picture is taken at the same zoom level as I used for the pictures taken through the scope.

Here is the scope setup.

The Contenders

Here are the StellarVue prism diagonal on the left and the Astro-Tech mirror diagonal on the right.

Here are the generic diagonals, prism on the left (with SV helical focuser) and mirror on the right.

Here is a shot of the SV diag to show that it’s stopped down.  The generic has similar baffling.

The Camera Mount

Here are the parts to the camera setup, the part that fits onto the camera mount hole to give a T-thread, the barrel that holds the EP and provides a T-thread, and both together.

    

The Comparison

I used my 80AR on my AZ mount for this test.  I had to extend the legs all the way to get a decent target in sight, and then had to pull out my step stool to be able to see into the camera.  I used the bracket I have that puts a T-thread on my Sony P71.  I put a SkyWatcher 10mm Super Plossl into the barrel I have, and attached it to the T-thread.  I’m just not steady enough to shoot freehand like Matt does.  I picked an AC unit about a block away, and was shooting at 91x.  I could see heat waves, so took a couple pictures with each diagonal.  I had the camera set to macro, so the telescope was doing all the focusing.  I still found it very difficult to get a decent focus on my LCD screen, and it shows in the pictures.  I shot the pictures to get email versions, but have the full versions for closer examination.  I tried to use the same zoom for each picture, though one set is one setting wider.  I used the timer on my camera so that I wasn’t touching anything when the picture was taken.

The prisms are on top, the mirrors on the bottom, the generic versions on the right, and a diagonal-less shot at the end.  It was a lot more difficult to get the straight shot, believe it or not, and I didn’t realize that it had drooped on me as much as it did.  The collage is from the full sized pictures, reduced by 50%. I can zoom in and inspect specific data on the originals, but it really only tells me that there was a light breeze blowing.  I took at least two pictures from each setup and took the best picture.

I still have the same conclusions.  The generic prism is the worst, but probably not as bad as the one Matt has.  Definitely good enough for a finder or lower power viewing.  The A-T is slightly brighter, but note that it’s a little less bright than straight through.  The generic mirror holds its own, and I don’t think anyone would be disappointed using it.  That is the main message here for the posters that didn’t want to buy the A-T but wondered if a generic mirror was good enough – it is.

I think this convinces me that I’m not losing much with my SV prism, but it also shows me that I should give the A-T a decent shot in the 80AR.  Zooming in on the pictures, I can almost read some of the tags in the A-T shot (though the text is backwards), but I can also see purple edges with the A-T that aren’t there with the SV.  People disagree with Vic [Maris, of StellarVue] that their prism takes out some CA, but these pictures would say that he’s right (and I’ve not heard an explanation as to why it reduces CA).

An interesting note…..there is a seam on the electrical box going down the middle of the edge.  On all these shots, I used that to focus on, to be as consistent as possible.  It was definitely there in the camera LCD.  You can’t see it very much at all in any of the pictures.

Conclusions

Well, this isn’t quite what I expected.  I’m guessing my ability to focus is a variable that needs to be removed.  But, I’d be happy with any of these, with the generic prism coming in last.  If your prism is of worse quality, I can see you not wanting to use it.  But the SV appears to hold its own, and knocks down some of the CA (which it is rumored to do – I won’t say advertised).  The A-T is definitely a brighter view, and I look forward to getting it out under the stars to see how it does.  For those worried about a generic mirror, it holds its own.  My guess is that I spent $15-20 for this one and it’s the one I started with several years ago.

BTW, I have a third prism that I didn’t test.  I have an Orion brand in the GS.  It too is stopped down more than a mirror.  I’m guessing that stopping down an underperforming prism would help with the reflections.

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Transit of Venus comic book!

June 1, 2012

This is awesome: the National Centre for Radio Astrophysics in India has produced a freely-available 16-page comic book on the transit of Venus, and it’s already available 11 languages and will soon be translated into at least 10 more. (I know, they call it a graphic novel, and that’s fine, but my inner fanboy rebels at calling any single-issue comic of less than, say, 50 pages a ‘graphic novel’. Also note that the June 6 date listed on the cover is for the transit as seen from India–as noted inside, in the Western Hemisphere the transit will be visible on June 5.)

I just finished reading the fine nonfiction book The Transits of Venusby William Sheehan and John Westfall, which covers all of the observed Venus transits in exhaustive detail and includes data for the unobserved (so far as we know) ones in antiquity. With most of that information still in my memory, I was impressed at how much the author and illustrator–Niruj Mohan Ramanujam and Reshma Barve–of the comic were able to cram into 16 pages (actually more like 12 if you don’t count the cover, license page, and a couple of blank pages). The book explains what transits are, why they were important historically, why they’re still important, and how, when, and where to observe the upcoming one safely. It’s free and cool, go check it out.