7 replies to this topic

[555aaa]

I'm curious to know if any amateurs have imaged Charon, Pluto's moon, and if not, I throw this down as a challenge, and here's the scoop on how I think one can go about it.

 

Pluto is about 15th magnitude, and Charon is about 16.5 or so, and they only get 0.9 arc seconds apart, with a six day orbital period. It should be detectable as an oblong composite image using lucky imaging. I think you should be able to detect a round blob, then an elongated blob, and then another round blob.  Our friends down south have the best shot at this as Pluto is high in the sky for them, as it is at -22 declination. It is possible with amateur equipment to get star FWHMs down around one arc second, so I'm pretty confident it's possible.

[Mike Phillips]

I've seen some results that looked promising, but can't recall where.

[james7ca]

I've clearly imaged double stars that were about 0.9 arc seconds apart using a 5" refractor, so I don't think the separation is a factor. It's probably the faintness of Charon that's going to require a fairly long exposure and it's exceedingly rare to get diffraction limited results with that kind of exposure time.

 

That said, I know that there is a faint (magnitude 17 to 18) and closely separated multiple star that is near to the Ring Nebula and that object has been resolved by CN user exaxe as shown here:

 

  https://www.cloudyni.../#entry10429275

 

The separation of that fifth component (in what otherwise is an optical double double star) must be well under one arc second (exaxe reported it to be 0.5 arc seconds). This particular object is also shown in a Hubble image from the following thread that discusses the double (or multiple) star system HL 9001.

 

  https://www.cloudyni.../#entry10302605

 

But, Charon is also moving in relation to Pluto which limits how long you can expose on that particular object. It might require some special alignment techniques as was used to detect Jupiter's moon Thebe (shown __HERE__ and __HERE__ with this latter only a suspected detection).

Edited by james7ca, 06 September 2021 - 12:14 AM.

[RedLionNJ]

This comes up from time to time in this forum, the most recent I could find being in 2018:

 

https://www.cloudyni...resolved-in-20/

 

Bart DeClerq clearly resolved Ceres and it was discussed how resolving Charon as a 'bump' on Pluto would take a reasonable-sized scope with good seeing in the southern hemisphere. It's just unlikely we northerners would get good enough seeing at declination around -23 degrees.

 

Sky & Telescope (or was it their short-lived "CCD Imaging"?) put out this challenge many years ago and as far as I know, it was never met.

[KpS]

Pluto is very low for northerners. However, I think there is a way to detect Charon. Measure its FWHM (x, y) for a sufficiently long time while focusing on the position angle. Charon now orbits Pluto almost in a circle as seen from Earth. A few measurements mean nothing. It would be necessary to statistically process dozens and possibly hundreds of measurements and look for a correlation with Charon's orbital period.

Edited by KpS, 06 September 2021 - 06:58 AM.

[John Boudreau]

Some years ago (2008) Daniele Gasparri posted here on Cloudy Nights what I thought was a well researched attempt with a Meade 14" SCT.  There wasn't a clean split, but an obvious elongation that was spot-on to the correct position angle. As I recall there was a minor drive error that had to be accounted for, but that was occurring along a different line from the Charon elongation from Pluto. I couldn't find any CN search references, but did find these links via Google:

 

https://www.discover...-jupiter-charon

 

https://www.universe...ur-astronomers/

 

Perhaps this was what Mike Phillips was recalling.

[555aaa]

Pluto is very low for northerners. However, I think there is a way to detect Charon. Measure its FWHM (x, y) for a sufficiently long time while focusing on the position angle. Charon now orbits Pluto almost in a circle as seen from Earth. A few measurements mean nothing. It would be necessary to statistically process dozens and possibly hundreds of measurements and look for a correlation with Charon's orbital period.

I agree, a program like Astrometrica can measure positions down to 0.1 arc second easily. If you did that over a couple cycles it should be easy to see a cyclical motion. I read a paper using this method but I think the direct method using one second exposures and stacking is the best. Pluto moves so slowly that there is no issue with it’s motion relative to field stars. The trick is to have a good metric for discarding blurred images which means either Pluto or a nearby field star has to have a high enough SNR to be selectable as good or bad.

[555aaa]

Some years ago (2008) Daniele Gasparri posted here on Cloudy Nights what I thought was a well researched attempt with a Meade 14" SCT. There wasn't a clean split, but an obvious elongation that was spot-on to the correct position angle. As I recall there was a minor drive error that had to be accounted for, but that was occurring along a different line from the Charon elongation from Pluto. I couldn't find any CN search references, but did find these links via Google:

https://www.discover...-jupiter-charon

https://www.universe...ur-astronomers/

Perhaps this was what Mike Phillips was recalling.

Thanks, looks like it’s been done. Using a filter is beneficial also.