Archive for July, 2012

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Guest post: A few thoughts about the Orion SkyScanner and other scopes, including the Bushnell Ares 5

July 8, 2012

Here’s the first guest post by frequent commenter and dedicated deep-sky observer Terry Nakazono. Actually “dedicated” is an appalling understatement, since Terry regularly challenges himself and his scopes by (1) observing faint deep-sky objects, mostly galaxies, (2) with small scopes he can carry on public transportation and by foot, (3) from light-polluted skies in and around Los Angeles. I’ve been looking forward to reading about Terry’s scopes and his observing techniques, so this guest post is most welcome–hopefully there will be more to follow.

I’ve been using the Orion SkyScanner the past 2 years for nearly all of my deep-sky observing needs because it’s so easy to transport and set up – crucial if you rely on public transport and your own two feet to get to darker sky sites. For a package weighing in at 6.2 lbs with scope and mount combined, 100mm of mirror is a lot of aperture.

Both scope and mount fits snugly in this Adidas Schmidt backpack. All that’s needed is a tripod to attach the mount to, and a solid Manfrotto weighing in at only 4.5 lbs. (but with a 15.5 lb. weight load capacity) provides a strong, stable support.

Factor in the eyepieces, star charts and other accessories, and you’re only transporting about 12-13 lbs. of equipment on your body. By comparison, the Orion StarBlast 4.5 weighs 13 lbs, while the Orion SkyQuest XT4.5 is 17.6 lbs. Both cost about twice as much ($199.99 and $239.99, respectively) as the SkyScanner ($109.99) and both add only 14mm of additional aperture to the mirror. As Joe Roberts says, you will not likely find a scope that will show more for the cost.

For deep-sky work, superb optics isn’t as critical compared to planetary and double star work, so a 100mm Newtonian reflector works well (for me). Despite not having a collimatable primary mirror, collimation can be achieved by center spotting the primary mirror and adjusting the tilt on the secondary with the help of a collimation cap, significantly improving the views of the planets and double stars as well as deep-sky objects.

Here, you can just see the notebook reinforcement ring I put on the center of the primary mirror; the secondary mirror is collimated by adjusting the three allen screws surrounding the main screw in the center of the secondary holder with an allen-head screwdriver.

Having said all that, I’m no longer wedded to the SkyScanner as my sole dark-sky instrument.

I now have an Orion shoulder bag that I can carry my Orion VersaGo II mount and Bushnell Ares 5 in.

I also have a Vixen Mini-Porta mount which will support my Celestron C90 Maksutov-Cassegrain (C90Mak, top) and Orion ShortTube 80-A (ST80A, bottom) telescopes. I just ordered a smaller Orion shoulder bag that will carry the aforementioned mount and one of these two scopes. These Orion bags are ergonomically well-designed and make it easy to carry both scope and mount over your shoulder without causing major strain.

I suspect that despite their better optics, both the C90Mak and the ST80A will not allow me to see “deeper” into space (i.e. detect fainter objects) than the SkyScanner. But I’ll need to perform a “shoot-out” between these scopes outside of light-polluted urban skies to confirm.

Right now, I see the collapsible tube Bushnell Ares 5 (BA5) as the scope that will eventually replace the SkyScanner as my deep-sky instrument once I’ve gone as far as I can with the latter. This is an F/5 130mm Newtonian which thanks to its unusual design, weighs only about 6.5 lbs. for the OTA. At only $164.99 (with no shipping or sales tax) from Optics Planet, this is probably the best scope deal in the country right now.

Here is the scope with the tube collapsed, mounted on an Orion VersaGo II (because of its bulkiness, I’ve discarded the 6.5 lb. tabletop mount that came with this scope).

And here is the scope with the tube extended all the way out.

I’ve created a light shroud made out of black felt to cover the open tube and protect it from the elements while observing.

In the limited amount of time I’ve used this scope in both light-polluted and semi-dark skies, I’ve had a tantalizing taste of what 130 mm. of light gathering power can show. In my light-polluted front driveway with direct vision, I was able to see the ring shape of M57 for the very first time, using only 65X magnification. With the 100mm SkyScanner, I can barely make out shading within the interior of the oval-shaped disk at 80X or more using averted vision in darker skies. Less than two months ago, I took my BA5 out to a semi-dark (orange-zone) site for the first time. M13 looked nothing like the views I saw through the SkyScanner – at 130X, this globular was just exploding with stars all over the place. Ditto for M5.

As Matt has shown us through his reports on using “Stubby Fats” in the desert, you can do some serious deep-sky observing with a 130 mm F/5 Newtonian in semi-dark or dark skies.

But the BA5 has to wait until I’ve exhausted all the possibilities of the 100mm F/4 SkyScanner.

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Mission 21: Nova in Sagittarius

July 7, 2012

Mission Objective: Nova

Equipment: Binoculars, Magnifying Finder, Telescope

Required Time: 10 minutes

Related Missions: Not Everyone’s Pot of Tea

Just got this via email from Sky & Telescope:

A fairly bright nova has been discovered in Japan by Koichi Nishiyama (from Kurame) and Fujio Kabashima (Miyaki). They made their find on July 7, 2012, using a 105-mm f/4 camera lens and CCD, describing the nova as magnitude 7.8. It is located in Sagittarius roughly between the “lid” and “spout” of the Teapot stars, at right ascension 18h 20.5m, declination -27° 44′ (equinox 2000.0). A number of other observers in Japan have made confirming sightings.

The discovery was announced on CBET 3166, issued July 7th by the Central Bureau for Astronomical Telegrams in Cambridge, Massachusetts. This circular assigns the star the official designations Nova Sagittarii 2012 No. 4 and also PNV J18202726-2744263.

The American Association of Variable Star Observers (AAVSO) is requesting observations of this nova. The AAVSO collects magnitude determinations by skilled observers to aid in the study of novae and other variable stars, and their site offers guidance on the techniques involved.

Whether or not you go as far as submitting observations to the AAVSO, the nova should be fun to track down and a relatively easy catch. And, hey, since you’ll be in Sagittarius anyway, you’ll have plenty of other pretty things to look at after you find the nova.

Here’s a widefield finder chart I knocked up in GIMP, using this photo from Wikipedia. The green lines mark out the “teapot” asterism in Sagittarius–if you don’t know how to find this, check here. The box is the field shown in the closeup finder chart below. The nova is indicated by the white cross. The red arrow is not the nova, it’s a magnitude 4.7 field star that will help you orient the closeup finder chart.

And here’s the closeup finder chart, courtesy of the AAVSO’s free oonline chart generator. I added the arrow to indicate the same field star as shown in the above image (the arrow points the same way, too). This is rotated 180 degrees from the sky (for Northern Hemisphere observers looking south) and from the widefield finder chart above, so you can use it as-is in a Newtonian reflector or straight-through finderscope, or flip it around for binoculars or a right-angle correct-image (RACI) finder. If you have a refractor or Cassegrain scope and you’re using a star diagonal, you can use the AAVSO plotter to make a rightside-up but reversed chart to match what you’ll see at the eyepiece. Copy and paste the nova’s designation into the box and select the options you want: PNV J18202726-2744263.

And now I’m going to post this and go look for the nova myself. Happy hunting!

Update the next day (July 8): I found it. I had to do a lot of flipping back and forth between chart and telescope to make sure I had the right object–it looks just like another 7th magnitude star in the eyepiece. And actually I used the finder rather than the scope. A 10×50 finder (or just about any pair of binoculars) collects enough light to show the nova easily, and gives a wide enough field to make it easy to find. I was using the SkyWatcher 90mm Mak, which has a maximum true field of about 1.5 degrees–too narrow to show most of the surrounding stars I needed to use to orient myself (imagine plotting a cross-country trip on Google Maps if you couldn’t zoom out and only saw a 10-mile stretch at a time).

Anyway, in all of the back-and-forthing I figured out a couple of geometric relationships that helped me figure out which 7th magnitude star was the nova. The next two charts are modifications of the AAVSO chart that show these relationships. I stripped out all the stars fainter than 8th magnitude, and all of the clutter of magnitude numbers, and rotated the charts 180 degrees to match the view in binoculars or a RACI finder (from the Northern Hemisphere).

First, the 4th magnitude star (red arrow) that I use as my “anchor” in this stretch of Sagittarius sits at the top of a north-south chain of 6th and 7th magnitude stars, and makes a diagonal with the second-brightest star in the field. The nova is about midway along that diagonal line, just above and to the left.

That helped, but as usual I was nervous about whether the star I thought was the nova actually was, so I used another relationship to double check.

The “anchor” star forms a right triangle with the two closest semi-bright (~6th-7th magnitude) stars, and the nova is almost straight down from the left-hand (eastern) point of the triangle.

If you haven’t yet mastered star-hopping, that’s basically all there is to it–working from the chart to the finder and eyepiece, you notice little geometric patterns and work from big, bright anchors to fainter, dimmer targets. After a while, it gets to be reflexive. You learn to build in double-checks to keep from wasting your time on chance alignments of stars that are close to–but not exactly–what you’re looking. Your internal monologue might run like so:

Looking at chart: Okay, there should be an arc of four stars like an eyebrow about two degrees left of [bright star].

Looking through finder: Got it.

Back to chart: Hmm, if I follow that arc to right, I should find a triangle of faint stars that points to [target].

Looking through finder: Sweeping right…hmm. There’s a triangle of faint stars, but is it the right one? I should find [target] right over here, but…nothing there.

Back to chart: Okay, now I see that the triangle of faint stars I want is not just right of the “eyebrow”, but right and a bit down, and it has a pair of stars like eyes just to the south.

Looking through finder: Here’s the triangle I thought was the right one, but–nope, no pair of stars like eyes. Let me back up to the “eyebrow” and try again. Now this time I go right and a bit down…yep, all right, there’s another triangle of stars, there’s the pair of stars like eyes. Hmm. Still don’t see the target, but it’s a small galaxy, so maybe it’s just not showing up in the finder. It should be right about…here. [put finder cross-hairs where target should be]

Looking through eyepiece: Well, hello beautiful!

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Observing report: the transit of Venus in Claremont

July 4, 2012

Here, just one day shy of being one month overdue, is my post on the transit of Venus on June 5. As promised, I took scopes downtown and did some sidewalk astronomy, and eventually some rooftop astronomy. As with the solar eclipse on May 20, the primary instrument was my son’s Astroscan with a homemade sun funnel, and once again it performed beautifully.

My partner in this enterprise was fellow Claremont paleontologist Matt Benoit. He was there for the whole thing, and helped keep scopes on target and help people understand what they were seeing. We hit a grocery store beforehand for soda and snacks and basically made an extended party out of the event.

I wanted to see the transit, period, but I was especially keen to watch the entry of Venus onto the solar disk to see if I could spot the “black drop effect” that bedeviled transit-timers in previous centuries. Sure enough, as Venus started to pull away from the limb of the sun there was a persistent dark blob or zone that seemed to connect the planet to the black space beyond, like surface tension keeping a drop of water from falling off the faucet. The black drop effect was once thought to be an effect of the atmosphere of Venus, but it’s not, because airless Mercury shows the same effect during its transits (the next of which is coming up in 2016, by the way). It’s nothing to do with our visual perception, either, since it’s easily recorded photographically, as you can see above. It’s now understood to be an effect of diffraction when a vanishingly thin line of light separates two darker spaces or silhouettes. You can see it by holding your finger and thumb up to the light and bringing them together–just before they touch, the black drop effect will seem to bridge them.

Along with the Astroscan and sun funnel, we had along the Celestron Travel Scope 70 with the aperture mask and solar filter described in this post, for direct viewing. Here’s my friend Marcy, who was there with friends for about half of the transit, getting her first look.

Although we both put in time on both scopes, for the most part I drove the Astroscan while Matt minded the Travel Scope. He also helped people get some photos through the eyepiece, as he did here with Marcy’s DSLR.

The view through the filtered scope was not as detailed as in the sun funnel, but the warm yellow color was more aesthetically pleasing, and many of our visitors appreciated both views.

Like the eclipse, the whole effect of the transit was a little unreal. In addition to the scopes, we also had eclipse glasses and a piece of welder’s glass. Every few minutes we would look up with our naked eyes and see a little black dot on the sun, and know that it was a whole world. And not just a world, but a twin of Earth. Someone on Mars watching a transit of Earth would see something very similar–our whole planet, all our evolutionary and human history, everything we’ve done or built (except for the handful of tiny things we’ve sent away)–all shrunk to a point, no larger, to the naked eye, than the period at the end of this sentence.

We had a steady stream of visitors downtown until a little after 6:00, when the theater blocked the view of the sun from the public square. So we decamped to the top of the parking garage across the street. Some people followed us over from downtown, and some found us up there on their own. One guy said that he found us because he had Googled for Venus transit events in Claremont and found my morning-of invitation post, which is nice, because that’s exactly why I put it up. In all, about 85 people saw at least some part of the transit through one of our scopes.

My son, London, watching the very tail end of the transit with the welder’s glass.

Venus was still crossing the face of the sun when they set together. As with the eclipse, I managed to get a shot right when the world crossing the sun touched Earth’s horizon. A moment later, it was gone, and the last transit of Venus until 2117 was over. I’m glad I got to see it, and to share it. I hope you had the opportunity to do the same.