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ASTRO: Phil Plait -- the asteroid
The same night I tried to image Lulin though snowy skies and clouds I
also gave this asteroid a shot as it was sitting right beside the comet. Looking at the subs as they came down I figured I didn't have a chance but with nothing but more clouds and snow since and several dozen Arp galaxies I should be processing I decided to give it a try. I was surprised that I was able to get it at a predicted magnitude 19.1. This is 80 minutes of snow in the 14" LX200R. Nearby were (167642) 2004 DK50 at magnitude 20.7 to the north west (up and to the right) and 2004 FJ28 at magnitude 20.0 to the north east. I did selectively brighten 2004 DK50 as at magnitude 20.7 it was really faint compared to the other two when I set the background to be dark enough to hide all the crap from the bright skies. Only 2004 DK50 was separately enhanced. The other two were untouched from the combine. To combine the images and still see the asteroids a standard average or add combine wouldn't work as they'd be in only one frame while the stars were in all 8 making them artificially dim. So I used two combines. One for the star field done normally using a sigma reject combine. This removed the asteroids. Then I did it again with a lighten combine. This uses the brightest pixel in each frame thus picking up the asteroids at full brightness but results in harsh stars and maximum background noise. So I then selected the asteroids and dimmed everything but the asteroids so the stars and noise were now faint but the asteroids their real brightness. This image was then combined with the star field image again using a lighten combine so the stars and asteroids were now at their correct relative brightness. This left 2004 DK50 still very faint and hard to find so I cheated and brightened it some. It's interesting how the clouds altered each differently. PhilPlait seems rather even in brightness except for the 5th 10 minute frame while the other two had a very different light curve during this 80 minutes of exposure time. Odd how the clouds and snow were different over such a small distance. This frame is only about a half degree wide. 1.5" per pixel to be exact. PhilPlait was moving at a rate of 4.5" of arc during each 10 minute frame so only covered 3 pixels each frame. That made it nearly round. The other asteroids were moving slightly slower. In a separate post I'll try and post a movie made from these 8 frames of just PhilPlait to hold down the band width. Still it is over 1.2 meg in size and might not make it to all servers. I've found SpaceBanter usually doesn't pick up animated gif files but Usenet Replayer sometimes does but it often takes 36 or more hours to appear their. So if you don't see the movie post on your news server try http://www.usenet-replayer.com/webrings/astro.html after a day or two. Rick -- Correct domain name is arvig and it is net not com. Prefix is correct. Third character is a zero rather than a capital "Oh". |
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