movie

Io Transit of Jupiter on 29 Dec 00

Jupiter has four moons that are easily seen using small telescopes or binoculars. They are named Io, Europa, Ganymede and Callisto. Io is the closest to Jupiter and makes one circuit around Jupiter every 1.8 days. When a moon passes in front of Jupiter as viewed from earth, it is called a transit. Transits of Io occur every 1.8 days so this is not a rare event. Still, one must plan to view a transit since the time at which it occurs may make it visible in Europe but not in the USA for example. I use the Redshift 3 program to determine when the transits will occur. I saw that a transit would occur on 29 Dec 00 from approximately 11:00 PM to 01:11 AM local time with Io's shadow continuing until about 01:27 AM.

So I set up the telescope in the back yard, started my ImCap program and focussed the camera. A blue filter, No. 80A, was used. I set my new ImCap controls to autocenter and autosave the images in Flexible Image Transport System or "FITS" (.fit) file format (AIP4WIN cannot read BMP files.) I then put ImCap into "autoshoot" mode. Over 900 images were taken during the transit. I then used AIP4WIN to automatically apply simple unsharp masking to all 900+ images. I then modified ImCap to provide methods to do wholesale conversions between Windows bitmap images (.bmp) and FTS file format (.fit) images. I then used ImCap to convert all of the FITS files to BMP files so that I could read them with Paint Shop Pro's Animation Shop 3. I selected every tenth image in order to create the GIF movie which you see below.

Io transit
Please wait for all 483K to load to see entire movie.

The movie reruns continuously. The beginning displays the word "START". Then look for Io. It is a small white dot at the lower right of Jupiter's image. It is on top of the lower dark cloud band. As the movie runs, Io becomes nearly lost from view in the glare of Jupiter's cloud bands. The sun is shining on Jupiter a little to the left of its center so the right edge of Jupiter is dimmer than the left edge. Io thus shows up a little better when it is near the right edge where Jupiter is slightly darker.

As Io becomes lost in glare, Io's shadow appears. It's shadow trails along behind. The shadow, according to RedShift, was visible from 11:18 PM local to o1:27 AM local. It is easily seen in the above movie moving from right to left across the lower cloud band.

Io eventually emerges at the left edge of Jupiter near the end of the sequence. Shortly after it emerges into the darkness, it disappears from view. (Probably because the number of photons from Io are not alone sufficient to be seen by the CCD camera? The number of photons from Jupiter's dark limbs add to Io's to provide a sufficiently strong image?)

Note that Jupiter rotates in 9 hours and 55 minutes. During the two hour span of the movie (you are seeing the movie in compressed time...), Jupiter rotates about one quarter turn. If you watch the details in the upper dark cloud band, you will see that Jupiter is clearly rotating.

This movie replaces an earlier one I made of a similar event on 29 Dec.

Occasional dust dots and dust circles appear on some of the frames above. They wander around because I was using ImCap's LX-200 telescope controls to try to avoid them but wasn't always successful right away. Atmospheric conditions could have been better. Some high thin clouds were encountered at one point which blurred some of the frames. I will continue working on this until I get it right...