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A different conjunction: Jupiter and Uranus


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nrothschild Neil is an expert in several areas, including camera support Registered since 25th Jul 2004
Tue 21-May-13 12:53 PM | edited Tue 21-May-13 02:21 PM by nrothschild

Once every 13 years and 4 months, Jupiter passes by Uranus. Jupiter's "year" is 11.9 Earth years, where Uranus' year is 84 Earth years. This is one of those celestial events that we only see a handful of times in our lifetime.

The closest approach of the last conjunction occurred on January 4, 2011. I was fortunate to be blessed with good weather that night, capturing that "moment" of closest approach. The separation was about 31' (arc-minutes), exactly the typical diameter of our Moon.

I used a D300 and 500 f/4 AFS, TC17E-II and TC14E-II. I used two exposures for this final image...

A short exposure of 1/50s f/11 ISO 200 with the TC17 imaged Jupiter, properly exposing it for best reproduction of the equatorial bands.

A longer exposure of 13s f/8 ISO 400 to record Jupiter's 3 visible moons, Uranus, and the few background stars. Those stars appear to be as faint as magnitude 11.

And truth be told, I shot the background with both the TC14 at 13s and the TC17 at 10s, and I am not 100% sure which image made it into the Photoshop composite. But I am fairly certain it was the 700mm 13s exposure. I need to study the images to clarify that.

When doing these composites I try to remember to rename the layer to the original image name used in the respective layer. I did not do that here .

I did several composite versions of these shots. I suspect that in this version Jupiter is a bit larger than reality but in the proper proportion I find it difficult to see detail. I just preferred this version even if I used a bit of artistic license on it (rare for my astro images).

The camera was mounted on a Questar 7 fork mount in order to make the 10s to 13s long exposures while avoiding star trailing. The shorter exposure could have been done from a fixed tripod and I have done that from time to time when imaging Jupiter and Saturn.

Speaking of Saturn, now is a very good time to try to image the rings. I have not shot it for a couple of years and may try to do so myself in the near future. I know they will image as a recognizable ring structure at 500mm, and possibly 400mm, especially on the newer 24mpx DX cameras.

(click this image to see the full size image)

Click on image to view larger version

Uranus shines at about Magnitude 6. That is, technically, visible with the naked eye at a very dark site that has a limiting (sky glow) magnitude of mag 6 or better. Those places are few and far between, especially in the continental USA.

In a visual telescope, Uranus can be just barely resolved into a non-stellar disk, larger than stellar diffraction disks. And given enough time and money thrown at the problem, it can be photographed as a somewhat non-stellar disk and has a fairly unique blue-green color.

You could image Uranus as a stellar object in just about any lens because capturing Mag 6 - Mag 8 stars is not terribly difficult. At wider focal lengths you might not even need a tracking mount. That would be an interesting project.

For that matter, Neptune is about Mag 8, and while more challenging than Uranus I do not believe it would be terribly difficult either in a wide-ish fast lens, somewhere around 50-100mm FX . But in reviewing my images I see I have never done it. Another project, to complete my planetary collection

Fortunately Pluto was de-listed as a planet. It is now relegated with the status of a large snowball, or something to that effect. That is a good thing because, at mag 14, that is a very seriously challenging project and generally you have to throw a large sum of money at that problem, as well as time and knowledge.


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