Outer solar system satellites

[xilman]

The latest in the series is Caliban, aka Uranus XVI. Like Sycorax it was discovered by the Hale 5m back in 1997.

This was really challenging because it shines at magnitude 22.2. A three hour exposure produced a barely visible image of the satellite. The signal to noise ratio is about 3 and extreme contrast stretching was needed to make the satellite visible. The included image is the best I have managed to produce. More details are available at http://www.astropalma.com/Projects/S...s/caliban.html

[Spherical Cow]

Wow- Congratulations on that one- Mag 22.2. Incredible.

Norm

[Dr Sardonicus]

Originally Posted by xilman

This was really challenging because it shines at magnitude 22.2.

I would say so! Good grief. At magnitude 22.2, "shines" just doesn't sound right.

Let's see here. Mr. Sun is magnitude -26.7. So halfway between that and Caliban's 22.2 is magnitude -2.3. That's brighter than the night time stars, but not a whole lot, so -- what? Jupiter or Saturn, maybe? So this object is about as many times dimmer than Jupiter or Saturn, as they are dimmer than the sun.

It reminds me of a light bulb in the movie Mr. Hobbs Takes a Vacation, of which the title character says something like, "if you turn it on, the whole room goes black."

[xilman]

Originally Posted by xilman

Here's an image of Sycorax, aka, Uranus XVII, a 160km satellite of Uranus.

Two years later I had another go at Sycorax. Same telescope, different camera and a longer exposure.

Sycorax is much easier to see this time. The star marked with an asterisk is mag. 19.03. A number of background galaxies are in the frame but I have not yet identified them. My guess is that they are mag 18.5 -- 21.5. Sycorax itself is magnitude 20.7.

[Uncwilly]

That is an impressive magnitude. HST is often quoted as getting to 29 or so.

[xilman]

Originally Posted by Uncwilly

That is an impressive magnitude. HST is often quoted as getting to 29 or so.

HST has several advantages

• It has an aperture six times that of mine, which corresponds to 36 times the light grasp, so there's 4 magnitudes for a start
• It has a dark sky: no light pollution, no airglow from molecular recombination reactions
• It has diffraction limited optics which put all the light from a star into a disc 50mas across; mine is seeing limited and rarely does better than 2000mas. An area difference of 1600 times makes a big difference to the contrast!
• The extreme deep field has an exposure time of 23 days; I have yet to reach 3 hours, about 200 times shorter. The Hubble image reaches mag 31.2 for a 5-sigma detection.

My current limit for 5-sigma is probably about 22.5 from a single night's data.

[xilman]

Here is the third largest and brightest satellite of Neptune. It was the second discovered, after Triton, and the second easiest to image from these parts. Proteus is in second place in the first two categories but orbits so close to Neptune that it is extremely hard to see with earthbound telescopes.

The prominent asteroid trail is of (16095) Lorenball which happened to be in the district at the time --- 2020-09-14 02:00.

2200 second exposure made from 38 subs.