Uranus and moons; Ariel, Titania, Umbriel and Oberon

[Dennis]

Hello,

Here is an image of Uranus and the brighter moons Ariel, Titania, Umbriel and Oberon as captured from Brisbane on 11th September 2008. The seeing was around 5/10 so the 12 and 7 sec exposures resulted in the significant “smearing” of Uranus’ disc.

I was imaging with the Mewlon 180 F12, a TeleVue x4 PowerMate and the SBIG ST7E at an efl of 8640mm, F48. I took 20x12 sec sub frames for L and 10x7 secs for the RGB channels. The composite image with the SkyTools chart shows the benefits of image stacking to increase the signal to noise ratio, even for these relatively short exposures.

Just to illustrate how dim the moons appeared, I have included a single 5 sec raw exposure (to prevent Uranus’ disc from swamping the closer moons) from the same evening, along with some measurements using Maxim DL, an image processing and camera control application. The average background signal was 104 with Ariel reading approx 127 and Titania approx 139; their peaks some 23 and 35 photons above background respectively.

Cheers

Dennis

PS - When I later tried the DMK21AF04.AS, all I could see with a 15 sec exposure was the bloated disc of Uranus – no moons. I need more aperture, not to mention steadier seeing!:lol:

[h0ughy]

the King of the far flung planets has done it again!! Dennis you are a modern marvel!

[AlexN]

Geez... for a second there I thought your Mewlon was able to cut through storm clouds... :D

Another very good image of something so small and dim. Did you check the angular separation of Uranus and Titania on a pixel level to check the arc/sec:pixel ?

Now that I've got some aperture to back me up I'm going to have a go at this! :D

[Dennis]

Hi Alex

I used Ron Wodaski’s killer app, CCD Calculator, and just plugged in the Mewlon 180 F12, x4 PowerMate and ST7E and it spits out the answer.

Your 11” should eat this, although I would try it with your most sensitive camera – probably the QHY8?

Cheers

Dennis

[AlexN]

yeah.. QHY8 binned 2x2 or 4x4 will pull it out in pretty quick exposures I guess.. I'll need a 2x or 4x powermate... as I dont have a 2" barlow any more.... 4x will give me something like 11200mm.. might be a bit much for brisbanes "seeing" or not-seeing as I call it..

[iceman]

Very cool Dennis, excellent imaging.

[Dennis]

Thanks Mike

It’s been a bit of an imaging drought up here recently due to the poor conditions.

Cheers

Dennis

[Dennis]

Hi Alex

When the moons of Uranus are well separated from the planet’s disc, a modest scope (e.g. ED80) should be able to record them as pin pricks of light very close to the disc?

I’d try at the C11 at the 2800mm prime focus first, but make sure that the moons are far enough away from Uranus along their orbits. The attached file shows 3 of the moons within 3 or 4 arcsecs of the disc, a less favourable positioning.

Cheers

Dennis

[AlexN]

Will give that a go Dennis, Thanks.

[RB]

Beautiful shot Dennis.

[Ric]

Lovely capture Dennis, good to see the outer planets getting a showing.

Cheers

[Matty P]

Amazing capture of Uranus Dennis.

Very well done. :)

[Lester]

Good capture Dennis.

[Dennis]

Thanks Andrew, Ric, Matt & Lester.

Uranus is approx 3.7 arc secs in diameter and unfortunately, the 12 sec Luminance exposure has blown the disc out so we’re seeing a blob of around 7 or 8 arc secs, not the real disc of the planet.

One day, when the seeing gets good and my technique improves! LOL!

Cheers

Dennis