Jupiter

Red Spot!

More than a year has gone by since my last attempt to image Jupiter. It was time to try again in nearly perfect conditions on the evening of May 15th. The sky was completely clear with very little wind and low humidity as the temperature dropped from pleasant middle 60's to slightly chilly low 50's during my time outside.

I lost some telescope operating efficiency while my Stellarvue 130mm refractor sat idle for so many months. Consequently, I made several blunders during set up. The most serious mistake was forgetting to sufficiently tighten screws holding the telescope in the mount. When the mount performed its initial homing slew the telescope began sliding down out of the mount and was well on its way to crashing into the concrete observing pad below. Fortunately, I happened to be standing next to the mount and desperately caught the sliding telescope in my arms at the last minute before any damage was done. Yikes! How could I be so dumb?

I also used a new laptop for this imaging session, so there were several delays getting software to communicate with the mount and the camera. Finally, since I stupidly forgot to line up the finder scope with the main telescope, it took way too long to get Jupiter centered in the eyepiece after the mount initially failed to place Jupiter in the field of view. In spite of these problems Jupiter eventually appeared on my laptop screen and I began recording images. The initial view looked like the first image below, recorded at 10:23 pm EDT with a 3X Barlow lens.

Three Galilean moons are visible to the right of Jupiter. They are, from left to right, Io, Europa, and Ganymede. The fourth moon, Callisto, was out of the field of view far off to the right. At first I didn't realize that Jupiter's Red Spot was located on the lower left edge of Jupiter, ready to rotate into view over the next hour. Can you see the hint of the Red Spot on the left edge of the lowest white band?

Just 29 minutes later, at 10:52 pm EDT, the Red Spot had become more visible as you can see in the next image.

The moons hardly changed position during the 29 minutes between the first two images. The Red Spot, however, was coming into better view. The next image was captured at 11:18 pm EDT, 26 minutes after the previous image.

I switched to a 5X Barlow for the next image, captured 17 minutes after the previous image at 11:35 pm EDT. The 5X Barlow gives too much magnification for my telescope/camera combination, so I have to reduce the image size by half to display a pleasing amount of detail.

Finally, I switched to a 2X Barlow lens and took this last image after midnight at 12:08 am EDT on May 16th. Another 33 minutes had passed since the previous image.

While I captured the images above over a span of one hour and 45 minutes the Red Spot rotated from the edge of Jupiter around to nearly the central meridian. From the image sequence you can see it would take more than two hours for the Red Spot to rotate halfway across the face of Jupiter. The exact time is 2 hours and 29 minutes, making the Red Spot's transit time across Jupiter's face 4 hours and 58 minutes. (The sidereal rotation period of Jupiter is about 9 hours 55 minutes. Half this period is 4 hours 58 minutes.) 

Because the Red Spot isn't obviously visible near the very edges of Jupiter, visual observers have less than four hours to see it cross the Earth-facing disc of Jupiter. During these four hours good observing conditions are required. Jupiter needs to be above the horizon on a clear night. No wonder I've rarely seen the Red Spot.