update: This post was intended to be a "quickie" demonstration of the need for proper video lengths when imaging Jupiter, which could be of use to beginning planetary imagers. Thanks to a post by @Niall MacNeill I realized that I should've explained this more clearly. I invite those who are interested to read his post below for a really good technical discussion of the science of selecting lengths for Jupiter imaging videos to be used for lucky capture. I should have also have pointed out the movement of Jovian cloud features over time is not the same as the movement of Io's shadow owing to the movement of Io in its orbit at a rate that is not synchronous with the spin rate of Jupiter's cloud features and the parallax effects caused by Io lying at a different distance from the sun than Jupiter. Thus the motion of Io in the blink comparisons does not indicate anything with regard to the proper lengths of lucky capture videos for Jupiter. Indeed, showing a moon's shadow in a de-rotated Jupiter image compiled from several videos requires software correction to recreate the shadow at the selected moment of the final de-rotated image. Accordingly, the thing to look for in the blink animations posted here is to select a clear feature near the equator (where the motion is most apparent) and see if it jumps back and forth to a noticeable extent. Such movement clearly visible in the longest video, but difficult to see in the shorter videos.In correspondence with my imaging colleagues, the issue came up about the length of videos for lucky captures involving Jupiter. Experienced Jovian imagers know that planetary rotation begins to smear features out after about 3 minutes (a limit I've seen stated in many places and determined by the available angular resolution vs the amount of angular smearing caused by rotation for a given set of typical conditions). Of course, this limit is dependent on the seeing-limited angular resolution; in extraordinary seeing the videos might need to be significantly shorter. In the most recent image of Jupiter I posted, I used 15s videos, not because the seeing was extraordinary, which it never is at my site, but because my ancient and cranky roll-out mount is really hard to align and its tracking capability is less than good. Image drift during longer videos moves the planetary disk so far that problems with stacking might arise. A 15s limit keeps things much more centered.
All of that said, the close temporal spacing of my videos sparked an idea for demonstrating the rotation of Jupiter over time, not as a frame-to-frame animation on this occasion, but as a blink comparison of mid-exposure time to mid-exposure time for different spans. I thought the blink approach might be interesting to see and hope you find it useful! I may be decently able to do astrophysical calculations. but I am terrible at posting more than one image together. To clarify the labels:
original/final = 1 minute 6 seconds
revision C = 3 minutes 23 seconds
revision D = 5 minutes 59 seconds
Comments