Monday, January 27, 2014

Jupiter, Io and a shadow transit

Arriving home from work tonight under partly cloudy skies, I did not even bother to open the observatory roof.  This turned out to provide good karma as my poor planning led to skies that were crystal clear at 9 PM.  While the transparency (clarity of the atmosphere) was reasonable for observing Jupiter, the seeing (atmospheric stability) went from average to poor rather quickly between 9 and 10 PM.  This was unfortunate as tonight was a transit of the Galilean moon Io and its shadow.  Regardless of sky conditions, being the faithful amateur astronomer that I am, I took several videos through my 11-inch Celestron Edge HD SCT and my ASI120MC camera in order to stack the frames and create an image of the event.

First up, is a stack of 2 images, each of which itself represented a stack of approximately the best 450 frames out of a 60 second video.  That is Io's shadow cruising through the south equatorial band.  Just think, if you were on Jupiter standing in the shadow you would be seeing a solar eclipse!
Seeing had deteriorated significantly by the midpoint of the transit, and the image below is a stack of three images, each of which was a stack of only 90-120 frames each from a 30 second video.  Compared to the above image the details are far less clear.  Io's shadow is nearly on the center of the disc, and the Great Red Spot has come around onto the face.
Next up is the image I was after.  You can see that the Great Red Spot has rotated onto the face (less than an hour after the previous image), Io's shadow has moved further along, and on the limb of Jupiter the moon itself is now visible!  Despite the obviously poorer seeing conditions, I ended up with a salvageable picture, and the process gives me confidence that with better conditions I may be able to capture some nice transit images.

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