Wednesday evening, during a rare clear night in May, I was able to capture this sequence of events happening on Jupiter. At the very start you can see Jupiter’s moon Ganymede over to the left and its shadow on the face of the planet. Almost immediately you will see the shadow of another moon, Io, appear on the right and start chasing the shadow of Ganymede. Each frame represents 2 minutes of real time and the entire sequence is an hour and 40 minutes long. As you watch, you will also notice the Great Red Spot moving along with the shadows and if you look closely you might notice Io itself transiting the disk of Jupiter but it is not nearly as obvious as the shadow. You might also notice the difference in the size of the shadows. Ganymede is the most massive moon in the solar system while Io is quite a bit smaller. Eventually Io leaves the disk and becomes visible against the black background. Finally at the end the two shadows merge as Ganymede eclipses Io. Jupiter was dropping into the trees as this happened so I was not able to capture the end of the eclipse when the two shadows separated. I want to thank my friend Carl Freyaldenhoven for bringing this event to my attention. The images were taken from my backyard in West Little Rock.
In the latest episode of Extreme Makeover: Telescope Edition, Jim makes more rings, a box, and something to put in the box. First, I made two plywood rings that will be the basis of the secondary cage which holds the secondary mirror, the focuser, a finder, and maybe a soda. Next I worked on the mirror box and primary mirror cell which I started on yesterday. You can see the cell sitting in the open box, the back side of the cell with its collimation screws salvaged from the original tube, and finally the cell back in the box with the upper surface of the box.
Next up, not necessarily in this order will be to finish the cell and mae it with the primary mirror, construct the secondary cage, build the truss arms, assemble, determine the balance point so that I will know where the previously covered altitude bearing will be attached then build the rocker box, sand, paint, get the soda from its place in the secondary cage and enjoy.
You may remember the MDF round I cut last weekend. Today I made two more cuts. First about 2.5″ inside to give me an 18″ OD ring that I will cut in half to make the altitude bearings of the scope and another to make the cell that will hold the mirror. In hindsight the cell doesn’t need to be as precise as the bearings and cutting it with a jigsaw would have been way easier. Also in hindsight I used MDF because I had it lying around and it was a test cut that turned out well but plywood is easier on the router. The ring on the right will be tossed.
