Tuesday, February 25, 2014

A Spectacular Jupiter!

While Jupiter is the Solar System's largest planet, it doesn't get closer to the Earth than about 400 million miles, about 4.3 times the Sun-Earth distance.  As a result, it appears pretty small, about 1/40th the diameter of the Moon, not much larger than a medium-sized lunar crater.  It is just visible as a tiny disk in a pair of binoculars, and to see any details, you need a pretty decent telescope, at least a 2" or 3" with moderate magnification to see the cloud belts and perhaps spot the Great Red Spot (GRS) - a giant cyclone three times larger than the earth that has been observed for nearly 400 years!  But while it lacks details in small telescopes, it is my favorite planet, because in a really good telescope, you can achieve views that approach spacecraft quality, and with its 9.7 hour day, details on the rotating disk are readily seen, as well as the even tinier disks of the moons, moving around Jupiter like a tiny solar system.

A friend of ours, Tom Polakis, recently outdid himself on an image of Jupiter While no stranger to planetary imaging, his image from Sunday evening is shown here at left.  While admittedly it was a night of "decent" seeing (the wavering of the atmosphere usually limits resolution) I think this might be his finest Jupiter shot.  He was actually observing it because the little moon Europa was transiting the disk, and he observed its ingress before deciding to image.  While easily visible when he saw it enter the left edge of the "limb darkened" edge (the edge of Jupiter appears darker because of its dense atmosphere), as it moved into the disk, it was much harder to see against the same-brightness band it had entered.  The image at right shows Europa's location pointed out (still difficult to make out against belt detail), as well as the GRS.  The image is shown as it appears in the sky with North up and East to the left.

A few comments on how he gets these incredible images.  His workhorse telescope for these is a 10" Newtonian, of 55" focal length, using a 2.5X extender to enlarge the image a bit.  He uses what is called "webcam" techniques, where video frames are taken in quick succession.  While in the last decade and a half, amateurs have successfully used actual webcams for these images, newer cameras with rapid video frame rates are currently in vogue.  In this case, he uses a monochrome (B&W) camera, so to get a color image he needs to shoot image sequences through red, green and blue filters.  Because Jupiter rotates so quickly, this has to be done in less than a few minutes.  For these images, his usual routine is to take 1,000 images in each color, and uses a freeware program called Registax to discard the worst of the images, and slightly shift and align the remaining images (correcting for shifts caused by seeing)for a final high-resolution image for each color, then assemble the final color image.  He is currently about to upgrade to a new camera that has a bigger sensor, is more sensitive, takes data faster, and is less expensive than the camera he's used the last 7 years!  He must be doing something right - whenever you are getting details inside the GRS, you are doing pretty well!

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