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Visual asteroids ID?

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#1 BSJ



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Posted 21 August 2012 - 01:59 PM

Has anyone ever noticed that asteroids appear “different” from stars? Last Saturday while I was at Stellafane we were observing Uranus in our various scopes. I noticed in Stellarium that Pallus was close by so I star-hopped to it, just to see if I could. It was exactly where it was supposed to be… But while observing it with my recently refigured and well collimated 10” Dob, it appeared “different” from the nearby stars. Slightly sharper, or more defined. Somewhat non-stellar, is the only way I can put it in words.

I asked my fellow observers if it was supposed to look different? No one had ever heard that it was possible to tell the difference. So another person took a look see. All he knew is that Pallus was within the field of view. He purposely didn’t look at Stellarium beforehand. Sure enough, he picked it out!

Is this a well know phenomena, or wishful thinking?

#2 James74


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Posted 28 October 2012 - 10:33 PM

I think you're probably right. I found 433 Eros visually before putting the camera on and I noticed that it looked a little different than the stars behind it. I felt like it was more of a color difference; 433 Eros was more orange than I expected most stars to be. I wonder if it was because of it's surface composition, or if it was the Sun's spectrum giving it that hue...

#3 jgraham



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Posted 29 October 2012 - 12:35 PM

Interesting. I've been observing asteroids visually for 40 years and I never noticed anything that stood out, but you are right, you can usually spot the asteroid in a field if you know one is there. I'm usually looking for the 'star' that doesn't belong. I wonder if they twinkle slightly differently and your eye picks up on that.

Neat stuff.

#4 *skyguy*



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Posted 29 October 2012 - 01:56 PM

Unlike stars, planets don't "twinkle" in the sky because they have resolvable disks. Perhaps asteroids, when viewed through a scope, don't "twinkle" as much as stars since they also have a very small, but resolvable disk. I don't know if this is true ... but, it's a thought. :)

#5 RedLionNJ


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Posted 22 November 2012 - 03:52 PM

That would appear to be correct - anything that subtends a "disk" does look different from a point source. I would think it only applies to objects greater than a certain apparent size, but I'd be hard-pressed to even begin to say what that size would be. Common sense says something in the order of maybe a quarter arcsec or so? Ceres looks non-stellar when near opposition, but it's HUGE compared to most minor planets. Vesta also looks remarkably non-stellar. But as I said, I'm not sure what the cut-off is, apparent size-wise.


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