Monthly Archives: February 2013

Horizontal vs Celestial Coordinates, Polaris

I’m trying to understand the relationship of horizontal coordinates (altitude, azimuth) and the celestial coordinate system. One thing I’d not appreciated is the altitude of Polaris, the north star, is pretty much always at a fixed elevation. Its Declination is 89° 15′ 50.8″, or about 90° (at the celestial north pole). And at my house at 39.2°N it’s pretty much always at altitude 39.2° above the horizon. I guess that sort of makes sense, it’s the only way it makes sense as a North Star, but I’d never really noticed it before and naively thought Polaris’ elevation would change with the seasons.  Maybe because its at the tip of the little Dipper which does rotate with the seasons, and when the bowl is higher in the sky it feels like Polaris is too.

This makes determining your latitude in the northern hemisphere pretty easy; just site the north star and measure its angle from the horizon. Preferably in calm seas with clear skies.

Advertisements

Stack fail

I took a stab at stacking images of Jupiter using a Microsoft LifeCam Cinema I had lying around. Total failure; partly because Mac software is so limited, partly because of the optical difficulty.

Mac software.. So the only webcam capture app I can even find is fucking Photo Booth. And it’s limited to 480p; the camera is 720p, maybe 1080p. And it has zero controls for exposure, etc. The $8 Webcam Settings program did give me control over camera exposure and focus, but no digital zoom to fake out the Photo Booth limitations. So my pictures of Jupiter ended up being like 20×20 pixels and still overexposed, no detail to recover.

The optics are hard. I started with the 25mm Plossl, then put a 2x Barlow on it, all too tiny. Then I tried the 7.5mm Plossl but the barrel on that eyepiece is so short the little clamp thingy I have doesn’t really work. I tried just handholding and got some pictures but again, all still awful.

The gear I’m using is just not good enough. I really wish I had a tracking mount to do any photography at all. And some way to do proper afocal imaging without an eyepiece in the way.

 

Good clear night

Nice night for looking at stars; even before the sky was fully dark after sunset I got great views of the Orion Nebula. And lots of other stuff.

  • Mercury. It’s near its highest now, about 15° off the sun, so I caught it about 5° off the horizon after the Sun had set far enough I could see it. So bright! -1 apparent. And Mars just below it by 1°; I missed the closest approach yesterday. It’s the first time I’m aware of really seeing Mercury and I’m surprised at how bright it was. But in the 48x scope I couldn’t see any sign of its phase, just a bright dot. I tried the 160x magnifier but the chromatic aberration was so awful I just saw a rainbow, no shape. Not sure why it’s more severe for Mercury; close to the horizon? Mars was also uninteresting in the scope, need more magnification I guess. Nice color though.
  • M1 – Crab Nebula. Yay! This object is fascinating because it’s the cloud remnant of a supernova from 1054, a historoical event well recorded (magnitude -7!). I wonder if there was a continuous historical record of this object? Probably not, it was apparently only visible for a couple of years, so it would have taken telescopes to find it and make the connection. According to Wikipedia that connection was only made in 1939.
  • Caldwell 41 – Hyades star cluster. Not very interesting to look at, honestly, mostly I put it on my list because I’m fascinated by the naked eye V shape that Aldeberan is on the tip of. In general I don’t find loose clusters like this interesting.
  • Messier 37, another open cluster. Only this one is so tight! Very pretty.

I’d intended to pick up M36 and M38 tonight too, but I couldn’t find them. In general I’m doing better finding objects, even without a proper finderscope. I’ve learned to take advantage of the way my FOV is about 1° with the 48x eyepiece to make rough measurements when hopping around. But I was having a hard time with M36 and M38 tonight, oh well.e

Fun night, at least for about 45 minutes until I started getting cold and frustrated. I’m learning not to stay out once it stops being fun.

Drawing the ecliptic

I’m still plugging away at my map to the stars in D3. It’s fun. I finally managed to get the ecliptic drawn on it.

I’m doing everything in the equatorial coordinate system, that’s the one all the astronomy books use with objects located in Right Ascension and Declination. It took me a long time to understand this system; it’s basically spherical polar coordinates of where a star is relative to the center of the earth. Only RA is measured in 24 hours instead of 360 degrees. And the earth’s rotation is normalized out so that a star’s RA/dec coordinates don’t change with the seasons (thank goodness!). The stars’ RA/Dec do move around at various larger time scales; the Earth’s 26,000 year precession, its nutation (18.6 year is the dominant cycle), and the relative motions of the stars themselves. I’m ignoring all those niceties although where I can I’m taking data normalized to the J2000.0 epoch.

I’m so bad at spatial geometry, it took me a long time to decide the ecliptic didn’t move with the seasons in this coordinate system, either. But duh, in retrospect, of course. The ecliptic is just one of those things I didn’t ever understand until recently. Anyway, the very definition of the equitorial coordinate system is that RA=0h00, Dec=0° is the place where the sun crosses the equator at the vernal equinox. (Well and that the plane Dec=0° is the plane of the earth’s rotation, and a right handed convention). And because the earth is tilted at an angle of 23.44°, it naturally follows that at the summer solstice the sun is at RA=6h00, Dec=23.44°. Those two points are enough to define the great circle which is the ecliptic, which is how I’m drawing this in my code. Of course the ecliptic goes back around to 12h00,0° and then 18h00,-23.44°.

I feel dumb that it takes me minutes (hours?) to figure this stuff out! To sanity check what I’m doing, I’m comparing my drawings to a chart that Sky & Telescope publishes. There’s also a helpful  chart in the Wikipedia article for Declination. Just for fun all three images have different projections. I’m using Mollweide.

My map

My map

Sky & Telescope

Sky & Telescope

800px-Stars_and_dec

 

 

Saturn

Finally woke up early enough to see Saturn. It was pretty. At first the shadow of the planet across the rings looked backwards to me, isn’t the sun to the left of Saturn? Duh, the scope reverses the view, amazing I’m still having a hard time with that. Anyway it looked great, particularly at 160x with the 7.5mm eyepiece. I tried doubling that with the Barlow but too fuzzy. Also saw Titan. Very small and faint, but visible. Didn’t particularly try to see the Cassini division but I don’t think I could have.

Unrelated, but my left eye seems to see better than my right eye. It’s also my dominant eye. But I reflexively squint my left eye closed and look through the right eye, it’s what I’ve always done. I can’t even really squint just the right eye closed reliably. But when I think to switch to my left eye suddenly I can see everything better, it’s kind of nice.

 

Stuff what I saw

Tonight I saw NGC 457 (Owl Cluster) and NGC 884 / NGC 869 (Double Cluster). Not very effectively; my original plan was to learn the shape of Perseus and use that to find nearby stuff. But it was right overhead, an awkward angle from the chair or with binoculars. So I ended up scanning up from Cassiopeia in the telescope and happened to stumble into the Double Cluster out of sheer luck. Owl Cluster was even luckier, just kind of scanning around for interesting stuff.

I’m a bit disenchanted with the backyard astronomy at the moment. I need some structure, or maybe a social setting, or some reason to hunt these things down other than “they’re there.”

Stacked photos of Jupiter

I tried an experiment stacking multiple S100 photographs to make one high quality image. Unfortunately the software that everyone recommends for this, Registax, is Windows only. So I used Lynkeos instead. The docs are good but it’s a bit fiddly. Basically you load a lot of images, identify the chunk of all the images that might possibly contain your object, then do align / analyze / stack. Then fiddle with the processing parameters to get a clearer image. I found the most valuable things to muck with were overall gamma and the Wavelets (particularly #2 and #3).

The result is not awesome. I think part of my problem is I’m working with only about 8 images, still photos from the S100 with interval photography taken every 2 seconds or so. This stacking technique is mostly applied to webcam images with 30+fps and I think is intended for hundreds of photos. The S100 can shoot movies too but I can’t figure out how to change the exposure, the automatic program is way overexposed. Anyway the final images are better than any individual but still pretty crappy. Too bad.