Archive for November 6th, 2009


Galileo Club, Part 2: Jupiter’s Moons in Eclipse

November 6, 2009


Task #4 for the Astronomical League’s Galileo Club:

4. 1612 – Jupiter’s moons in eclipse: The objective is to show that in addition to the moons being occulted by Jupiter, they also travel through Jupiter’s shadow and are eclipsed. Observe and sketch, noting the timing, one of Jupiter’s moons during an ingress or egress with Jupiter’s shadow. Callisto or Ganymede is the most dramatic. Two observations should be done.  One should be close to when Jupiter is at opposition. The second should be done when Jupiter is at quadrature (90 degrees from the sun). Note how close to the planet the moon is when the event occurred. (Editor’s note: At least two observations and timings are required.)

This is one of the ones that needs to be done Real Soon Now, because the eastern quadrature of Jupiter is this coming Tuesday, November 11. After this Jupiter is going to keep heading west and then disappear into the sun’s glare for a while. Western quadrature won’t be for another six months, and then you’ll have to either get up real early or stay up real late to catch it; western quadrature is equivalent in terms of sky position to last quarter moon.

Unless you want to spend all night watching, waiting, and hoping, you’ll want some idea of when to observe to see the entry or exit of a moon from Jupiter’s shadow. So here’s a list of ingressions and egressions for the next week, taken from Sky & Telescope’s Jupiter moon calculator. Sometimes there is an exit with no entrance, because the moon in question went directly behind the planet as seen from Earth; that’s an occultation rather than an eclipse. Everything is listed both by Universal Time (UT), equivalent to Greenwich Mean Time or London time, and Pacific Standard Time (PST). If you live somewhere else, you can look up your offset from UT at this helpful site.

I’ve never watched one of these events so I don’t know how long they take. Probably worthwhile to start observing 15-30 minutes ahead of the stated time and keep watching until you know it’s over. That blows my titular goal of providing things you can do in 10 minutes, but…whatcha gonna do? Feel free to leave a comment if you make a successful observation. Photo borrowed from here.


Saturday, November 7, 2009
18:18 UT (10:18 AM PST), Io exits eclipse by Jupiter’s shadow. Daytime for US.

Sunday, November 8, 2009
02:22 UT (6:22 PM PST), Europa exits eclipse by Jupiter’s shadow.

Monday, November 9, 2009
04:50 UT (8:50 PM PST), Callisto enters eclipse by Jupiter’s shadow. Sunday night in the US!
09:30 UT (1:30 AM PST), Callisto exits eclipse by Jupiter’s shadow.
12:48 UT (4:48 AM PST), Io exits eclipse by Jupiter’s shadow.

Tuesday, November 10, 2009
08:52 UT (12:52 AM PST), Ganymede enters eclipse by Jupiter’s shadow.
12:32 UT (4:32 AM PST), Ganymede exits eclipse by Jupiter’s shadow.

Wednesday, November 11, 2009
07:16 UT (11:16 PM PST), Io exits eclipse by Jupiter’s shadow. Tuesday night in US!
15:40 UT (7:40 AM PST), Europa exits eclipse by Jupiter’s shadow. Daytime for US.

Friday, November 13, 2009
01:46 UT (5:46 PM PST), Io exits eclipse by Jupiter’s shadow. Thursday evening for US, probably too early for PST.


Get your Mars on

November 6, 2009

Victoria crater small

The Boston Globe’s The Big Picture feature covers Mars today, thanks to the HiRISE camera on board the Mars Reconnaissance Orbiter. See craters, dunes, water-eroded gullies, dust devils, and the tracks of our rovers, courtesy of what is still the coolest non-Hubble camera in existence.