October 1, 2007
Ceres and Vesta
September 28, 2007
Pluto
This past week, Pluto passed very close to a brightish (mag. 8.70) star, SAO 160793 in Sagittarius. The actual moment of the close-pass happened while it was over central Asia (Mongolia, western China, maybe southern Siberia and northern India). Some predictions called for Pluto to pass on one side of the star, and its moon, Charon, to pass on the other. For individuals or observatories with photometry equipment, this near-occultation would provide a good means of checking to see if Pluto has a ring system, as has been speculated (so far, nobody is reporting any results of this event).
I figured I'd see if I could capture Pluto, since it was going to be close to a bright guidepost. With a near-full Moon in the sky, I could not see Pluto visually. But my first-generation Meade DSI color camera (an item now on closeout at $99) had no problem capturing Pluto, with only a 5 second exposure time. Three nights were easy; the fourth night, after the pass, I had to shoot through clouds. Even with thin hazy clouds obscuring dim Pluto (mag. 14.0), the camera had no problem capturing it.
Here's a time lapse of the four images.
To give some idea of how far we've come in 77 years, here's a link to Clyde Tombaugh's discovery images of Pluto, taken in January, 1930. The telescope he used, at Lowell Observatory in Flagstaff, AZ, still exists. It is a 13" three-element astrographic refractor — not much larger than my own Meade 12" LX200GPS. (The other significant piece of gear in the optical train included a Meade 0.33x focal reducer and a Lumicon UV/IR block filter). Back then, using glass photographic plates, Tombaugh was exposing these for one hour at a time (which was an improvement over the three hours that Percival Lowell had been spending). The glass plates were 14 x 17 inches, giving a field of 12 x 14 degrees — much larger than mine. His fields appear to reach about the same magnitude, but took more than 700 times as long to expose. I let the Meade software drive my scope to track the bright star while I had dinner.
Here is the story of Pluto's discovery, in Tombaugh's own words. And here's an American Heritage magazine article.
It's an interesting exercise to enter the date, January 23, 1930, into the free skymaping program Cartes du Ciel, set the time for midnight, have it center Pluto, and see the same field Tombaugh was dealing with. In the discovery photos, notice the galaxy he captured, at top center, NGC 2365; it's a star that doesn't look quite right.
September 18, 2007
Messier 16 and 20.
Images of Messier 16 and 20, shot with a Meade DSI Color on a Vixen ED80Sf, piggybacked on a Meade LX200GPS. Unguided 30 sec. exposures, luminance image processed using "Drizzle" method for higher resolution, combined with RGB images generated by DSI Envisage software.
M16:
M20:
September 14, 2007
Total Lunar Eclipse, August 28.
I finally got around to processing the images I shot of the total lunar eclipse last month. Here it is, in time lapse.
The camera used for this was my Kodak P850 on a tripod. These are all at maximum zoom (maximum optical + maximum digital zoom). This was a very dark eclipse, and I found that I had to switch from ISO 100 to ISO 400 sensitivity as it got darker, just to keep exposure times from getting out of hand and showing star (and Moon feature) trailing.
Toward the end of the sequence, the star TYC5807-00441-1, magnitude 7.31, can be seen to the right of the Moon, as the Moon passes it. This really shows how rapidly the moon moves in our sky; frames are nominally 5 minutes apart.
The sequence ends at some time past the deepest part of totality, when I ran out of battery. In all, I shot about 120 frames, at various exposure times, ISO sensitivity, and zoom factor.
The following wide-field image shot at 3:37 AM shows more field stars. 2 seconds at ISO 400, at maximum optical zoom, equivalent to 35mm 432mm focal length.
These may not all show up on your monitor but the stars are as follows: brightest star in the field, at upper left, is σ Aquarii, magnitude 4.82; to its left is 58 Aqr, mag 6.38 (in other words, barely visible with the unaided eye at a really dark location on a moonless night). Immediately to the left of the Moon, TYC5807-01695-1, mag. 7.01, only visible in binoculars; and the aforementioned TYC5807-00441-1 close to the upper right.
September 10, 2007
And still more M27
I just can't leave this one alone. Last night I fitted an 0.63x focal reducer to the Meade 12" LX200 GPS, carefully focused the Meade DSI 1 Color camera (it can take 10 or 15 minutes to get a good focus), and let it rip while I passed out on the couch. The alarm clock rang to remind me to shut down the scope and button everything up.
I hand-selected about 100 of the best luminance images (those with the roundest stars), stacked and processed them, and used the R, G, and B layers generated automatically by the camera for the color info. The Luminance images were combined in Meade Envisage using Drizzle for higher spatial resolution; the four images (R, G, B, and L) were combined in Photoshop CS.
I do believe this is my best M27 yet.
September 2, 2007
Still trying to improve M27, Dumbbell Nebula
Last night I got what I thought were pretty good raw images for M27, the Dumbbbell Nebula. These were shot with a 12" Meade LX200 GPS, polar mounted, 0.33x focal reducer giving (nominally) f/3.3, (I haven't checked the actual plate scale; that comes from precise measurement of the reducer focal length, lens principal plane, and principal plane to imager spacing). The imager was a first-generation Meade DSI Color, a camera that's already obsolete (now on closeout at $99). Images were 15 second exposures, the scope was tracking but not actively guiding during exposures (although it would try to keep a stacking alignment star centered by guiding between exposures). Initially the software stacked 125 frames. For this multi-layer composite, I used the 125 frame color image generated by the software but used a Luminance layer with tightened quality criteria, so the L image has fewer staced frames. I used the "drizzle" feature of the DSI software, as described by Matt Taylor in his tutorial DVD.
A friend took that image and looked up the area in sky-map.org (more precisely, this link). It takes a while to load but eventually you can read off data on individual stars by mousing over them (a yellow data box pops up. If it didn't pop up on even the brightest stars, it's still loading, give it a few minutes).
It's easier to see faint detail in a negative view; here's the lower portion of the nebula and some faint stars with magnitudes marked. It seems I'm getting down to 18th magnitude -- from a well-lit suburban location, on a warm moonlit night with an uncooled $99 camera.
August 6, 2007
Mo' betta Jupiter
Tried a new (to me) technique of imaging a planet in color, and then in infrared, and using the IR image as a "luminance layer" in Photoshop. In other words, the color image tells us what color to make any given pixel, but the luminance image tells us how bright to make it. So the sharpness of the resulting image is defined by the sharpness of the infrared image, and infrared is slightly less susceptible to atmospheric "seeing" effects.
One little tweak is that chances are, you have to refocus for the two different wavelengths because the filters will change the optical path ever so slightly. This takes valuable time, and with Jupiter, you don't have much time; there's enough rotation in just a few minutes to show up in successive images. So I used a digital focus indicator based on the TeleVue TVFocus system. You find your focus positions beforehand, store those locations in memory, label them with descriptions if you like ("IR filter", "Visual filter"), and when you switch filters, quickly move to the predetermined position and immediately reset and start the camera again.
Here's the result. 12" Meade LX200GPS, TeleVue 2.5x Powermate, Atik manual filter wheel, Baader UV+IR block filter and Baader IR pass filter, Philips ToUcam 740K camera, my own custom 2" and T-thread to ToUcam lens mount. Exposure 220 sec. each, 5 frames per sec., about half (~550) of the resulting frames stacked. Captured with K3CCDTools 3, stacked in Registax 4, final processing in Photoshop CS.
And here's another. This was taken later, but I did not use the IR luminance layer technique. The difference between this color image and the previous: I used a shutter speed of 1/50 sec instead of 1/25 sec. This would tend to "freeze" atmospheric seeing rather than give it time to blur. Another run with 1/100 sec did not turn out as well. Somewhere there is a sweet spot between freezing seeing, and reducing your incoming light to the point where you have to increase amplifier gain and so you get more noise. Note also the amount of rotation (the Red Spot has moved). Time difference between these exposures is about 18 minutes. Compare sharpness of white spots in the "South-South Temperate Belt," below and left of Great Red Spot).
