Last night (10th July) I was investigating/eliminating some of the potential causes of flexure in my side-by-side system and as part of the investigation, captured a series of 5 minute exposures of Pluto and the surrounding star field.
I am pleased to report that I made considerable progress in resolving some of the problems that were causing elongated stars, as well as managing to record the movement of Pluto against the background of fixed stars.
The animation is made up of 2 frames; Frame 1 recorded at 10:59pm and Frame 2 recorded at 11:54pm, so there is almost 1 hours worth of orbital movement in the animation. (In-line gif at 86KB)
Tak Mewlon 180 F12 (2160mm fl) with ST7 at prime focus.
The animation is a 600x400 crop from the 765x510 original.
FOV is approx. 8.5x5.6 arcmin at 0.86 arcsec/pixel.
Thanks for looking!
Cheers
Dennis
PS - some details about Pluto
Pluto is now a Dwarf Planet, Magnitude: 13.94.
Earth Distance: 30.7 AU
Sun Distance: 31.7 AU
Diameter: 2302.0 km
Hi Dennis,
Wow, that's amazing.
Is that Pluto's movement around the Sun that we can see?
I didn't know it would be noticable in such a short time span.
Ta for that.
Molly.
Ironically, Pluto's nodding like one of those toy dogs you put on the back dash of your car.
Excellent capture Dennis. My boys just loved the animation.
Is that Pluto's movement around the Sun that we can see?
I didn't know it would be noticable in such a short time span.
Most of the apparent movement in Dennis' shots is a parallax effect of Earth's orbital movement I think. If Pluto had a circular orbit (which it doesn't) it's movement viewed from the Sun (and Earth is close enough to that relative to Pluto's extreme distance) would be around 0.6 arcseconds per hour based on a period of nearly 250 years, or less than a pixel in Dennis' shots. Of course with its elliptical orbit its orbital speed varies, but not enough to account for the movement shown in the shots.
Is that Pluto's movement around the Sun that we can see?
Molly.
Hi Molly
Thanks and what a good question! I had assumed that the movement had 2 components; both the Earth’s movement in its orbit and Pluto’s movement along its orbital path. However, I hadn’t realized how small Pluto’s contribution was until Rob very nicely explained the difference in his post!
Quote:
Originally Posted by Rob_K
Most of the apparent movement in Dennis' shots is a parallax effect of Earth's orbital movement I think.
Cheers -
Rob
Hi Rob
Thanks for your comments and the excellent explanation to Molly’s question. I appreciate you doing the maths and clarifying the nature of the movement. Another lesson learned today at the Ice In Space School!
They also show a decent size disc as well and not just a wee little dot.
Good work.
Hi Geoff
Thanks! The apparent size of Pluto is around 0.1” and I think the Mewlon can resolve around 0.6” (Dawes limit) so what we are seeing is not the disc of Pluto, but the effects of smearing due to the Earth’s atmosphere along with errors in tracking.
I think this is why the stars, which are effectively pin points of light, also appear as discs?
Wow Dennis, I honestly thought you would need more hours
if not even days to get movement like that.
Probably nothing but is that another moving object lurking
at the bottom of the frame...When I look at your
animation at the spot arrowed I see something moving?
Thanks for your comments and observations. I think that the “moving” stuff is likely to be caused by imaging artifacts between the 2 frames. The seeing was quite poor on the night and some of the stars are slightly elongated so the animation appears to show this as movement.
I performed an image link in CCDSoft which links to The Sky Pro 6 and could not find any asteroids.
Ironically, Pluto's nodding like one of those toy dogs you put on the back dash of your car. 
