APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Comments and questions about the APOD on the main view screen.
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DavidLeodis
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by DavidLeodis » Thu Apr 10, 2014 12:07 pm

When I click on the 'Lucie Maquet' link in the credit I keep getting the webpage cannot be found message. It may just be a temporary problem but in case not does anyone know of another link to information on Lucie Maquet. Thanks.

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geckzilla
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by geckzilla » Thu Apr 10, 2014 12:36 pm

She doesn't actually have one. That link was supposed to be an email address written in English but the mailto: was left off the front so it is treated as a local site URL.
Just call me "geck" because "zilla" is like a last name.

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DavidLeodis
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by DavidLeodis » Thu Apr 10, 2014 1:25 pm

geckzilla wrote:She doesn't actually have one. That link was supposed to be an email address written in English but the mailto: was left off the front so it is treated as a local site URL.
Thanks geckzilla for that clarification. :)

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Anthony Barreiro
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by Anthony Barreiro » Thu Apr 10, 2014 1:53 pm

Chris Peterson wrote:
Anthony Barreiro wrote:
Chris Peterson wrote: ... (and at 18 magnitude, the object is very bright, easily captured by small amateur telescopes, though not resolved by them) ... .
Chris, your ideas of "very bright" and "small amateur telescopes" are very different from mine! Or maybe everything is different at 3000 meters elevation. Maybe a 200 mm aperture dobsonian telescope shipped from sea level will swell to 1000 mm aperture in the lower air pressure.
When I say "captured" it means I'm talking about imaging. If I meant visually, I'd say "see" or something along those lines. Imaging a mag 18 point source is quite trivial with a small telescope and an electronic camera. At any elevation, and even under less than perfectly dark conditions.
Thanks for the clarification. I still would not call an 18th magnitude object very bright. I don't take pictures, but I can't imagine that imaging an asteroid 50 times fainter than Pluto would be a trivial undertaking. Charilko is currently in Scorpio, transiting during astronomical dawn. Could you snap us a picture tomorrow morning?
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by geckzilla » Thu Apr 10, 2014 2:27 pm

Anthony Barreiro wrote:Thanks for the clarification. I still would not call an 18th magnitude object very bright. I don't take pictures, but I can't imagine that imaging an asteroid 50 times fainter than Pluto would be a trivial undertaking. Charilko is currently in Scorpio, transiting during astronomical dawn. Could you snap us a picture tomorrow morning?
Andre van der Hoeven recently created a deep image of M81 and M82 which captured objects to almost magnitude 24.
https://www.flickr.com/photos/avdhoeven/13589009855/
Andre is pretty great, so maybe it is not trivial to him but not terribly difficult, either. 18 is bright compared to 24.
Just call me "geck" because "zilla" is like a last name.

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Chris Peterson
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by Chris Peterson » Thu Apr 10, 2014 2:28 pm

Anthony Barreiro wrote:Thanks for the clarification. I still would not call an 18th magnitude object very bright. I don't take pictures, but I can't imagine that imaging an asteroid 50 times fainter than Pluto would be a trivial undertaking. Charilko is currently in Scorpio, transiting during astronomical dawn. Could you snap us a picture tomorrow morning?
That's Scorpius. And I don't casually do imaging early in the morning! However, it might be a fun thing to go for this summer, when Scorpius is better placed.

For reference, I was imaging a Pluto occultation a few years ago and needed very short exposures to preserve the timing. The image below is an unprocessed, single 5-second frame from the sequence (I just converted the FITS to a JPEG and added the annotation). The S/N for Pluto is 40 (with 3 the usual standard for detection). A mere 30-minute exposure of Pluto would saturate my camera. Chariklo at mag 18 is only 16 times fainter than Pluto at mag 15, suggesting I should be able to capture an image with similar S/N in an exposure of about 90 seconds. I do call that a bright object.
pluto-043-anot.jpg
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Anthony Barreiro
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by Anthony Barreiro » Thu Apr 10, 2014 4:33 pm

Chris Peterson wrote:
Anthony Barreiro wrote:Thanks for the clarification. I still would not call an 18th magnitude object very bright. I don't take pictures, but I can't imagine that imaging an asteroid 50 times fainter than Pluto would be a trivial undertaking. Charilko is currently in Scorpio, transiting during astronomical dawn. Could you snap us a picture tomorrow morning?
That's Scorpius. And I don't casually do imaging early in the morning! However, it might be a fun thing to go for this summer, when Scorpius is better placed.

For reference, I was imaging a Pluto occultation a few years ago and needed very short exposures to preserve the timing. The image below is an unprocessed, single 5-second frame from the sequence (I just converted the FITS to a JPEG and added the annotation). The S/N for Pluto is 40 (with 3 the usual standard for detection). A mere 30-minute exposure of Pluto would saturate my camera. Chariklo at mag 18 is only 16 times fainter than Pluto at mag 15, suggesting I should be able to capture an image with similar S/N in an exposure of about 90 seconds. I do call that a bright object.
pluto-043-anot.jpg
Thanks for the lesson about imaging what I still think of as faint solar system objects. If you do take a picture of Chariklo at some time, I would be grateful to see it. And I'll content myself with the fact that in the context of astrophotography Chariklo has been downgraded from "very bright" to merely "bright."

By the way, according to my planetarium software Pluto is currently visual magnitude 14.2 and Chariklo magnitude 18.6. 2.512^4.4 = 58, right? So isn't Pluto now 58 times as bright as Chariklo? Am I doing the math wrong?

Oh, and P.S. -- I'll start calling that constellation Scorpius if you promise to start using proper Latin genitives. In the mean time, I know what you mean by "Alpha Centaurus" and you know what I mean by "Scorpio."
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Chris Peterson
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Re: APOD: Two Rings for Asteroid Chariklo (2014 Apr 09)

Post by Chris Peterson » Thu Apr 10, 2014 4:55 pm

Anthony Barreiro wrote:By the way, according to my planetarium software Pluto is currently visual magnitude 14.2 and Chariklo magnitude 18.6. 2.512^4.4 = 58, right? So isn't Pluto now 58 times as bright as Chariklo? Am I doing the math wrong?
Nothing wrong with your math. When I made that image of Pluto in 2008 I measured it at mv = 15.0. And I think the most recently published magnitude for Chariklo is mv = 18.3. If so, there's a factor of 20 brightness difference between the two. In any case, these magnitude values can be pretty variable, as our distances shift and the orientation with respect to the Sun changes. Whatever numbers we use, the difference is still relatively small in terms of imaging parameters. Even at a factor of 50, the exposure time is still quite short.
Oh, and P.S. -- I'll start calling that constellation Scorpius if you promise to start using proper Latin genitives. In the mean time, I know what you mean by "Alpha Centaurus" and you know what I mean by "Scorpio."
No, I'm going to keep pushing to eliminate the Latin genitive form in English. I only point out "Scorpio" because that term has already been co-opted by astrologers. Knock yourself out if you want to use it... we'll all know what you mean, of course.
Chris

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