Friday, November 05, 2010


Coming up in our night sky this weekend which, miraculously enough, is predicted to have clear nights skies.... With only a small low power telescope you'll be able to witness a rather unique event as all four of the Galilean moons of the planet Jupiter casts shadows that will be visible on the planet's surface. Jupiter can be easily spotted in the next few nights as it rises in the southeast and gradually makes its transit across the sky to the southwest as dawn approaches. It is quite bright ( -2.7 magnitude), and is in the constellation of Aquarius near to Pisces.

Tonight is also the peak night of the Taurid meteor shower, in Taurus of course. While not as spectacular as the Leonid meteor shower due to arrive later this month it has the advantage at least in Winnipeg of having good viewing conditions and relatively clement weather conditions.

Here's more on the upcoming "shadow transits" from the site.
Jupiter's Moons to Perform Weekend Show for Skywatchers
By Geoff Gaherty

This weekend, a remarkable series of events will take place on Jupiter: The planet's four big moons will cast shadows on the gas giant planet that can be seen from Earth using a small telescope.

The planetary shadow play, which begins Saturday night (Nov. 6) and runs through early Sunday, will be primarily visible from the western coast of the United States. [Illustration: Moon shadows on Jupiter]

The four bright moons of Jupiter are known as the Galilean moons after their discoverer Galileo Galilei. As they revolve around Jupiter, they sometimes pass across the face of the planet as seen from Earth, as well as behind the planet and in its shadow.

How to see Jupiter's moon shadows

First, a word of caution: The overnight between Saturday and Sunday is when we switch back from daylight saving time to standard time, so be careful you get the correct time for your location.

Because the complete sequence of events is only observable from the U.S. West Coast, we will use Pacific Time here to discuss the best viewing times. Observers further east will miss the later events, and should add the appropriate number of hours to the times depending on their location and time zone.

The show begins at 8:53 p.m. PDT (11:53 p.m. EDT) on Saturday (Nov. 6), when Jupiter's largest moon Ganymede begins to cross the planet's face.

Because Ganymede has a relatively dark surface, it appears bright against the limb of Jupiter — but quickly appears to change to a dark gray against the bright central parts of Jupiter's disk. This can be seen with telescopes that have as small as a 5-inch aperture.

At 9:47 p.m. PDT, a second moon — Europa — follows Ganymede across Jupiter's face.

Because Europa's surface is icy, it reflects a much more light than Ganymede, and closely matches Jupiter's cloud belts behind it. As a result, it vanishes in all but the largest telescopes, perfectly camouflaged.

At 10:24 p.m. PDT, yet another moon — the volcanic Io — begins to disappear behind the opposite side of Jupiter.

At 11:52 p.m. PDT, Europa's shadow starts to take a notch out of the western limb of Jupiter. This can be seen with telescopes that have as small as a 3-inch aperture. Two minutes later, Ganymede moves off the disk of Jupiter and is once again a bright spot in the sky.

But wait, there's more — the Jupiter moon show isn't over just yet. Here's a rundown of the movements of Jupiter's moons to watch for on Sunday:

At 12:31 a.m. PDT, Europa leaves the disk of Jupiter.
At 1:12 a.m. PDT, a second shadow, that of Europa, puts the bite on the west limb of Jupiter. We now have two shadows creeping across the face of Jupiter, while the moons casting them are off to the right, a wonderfully three-dimensional effect.
At 1:41 a.m. PDT, Io emerges from Jupiter's shadow, ending its eclipse.
At 2:00 a.m. PDT, Daylight saving time officially comes to an end, and you should move your clock back to 1 a.m.
Now, at 1:34 a.m., Pacific Standard Time, Europa's shadow moves off Jupiter's disk. Finally, at 3:08 a.m. PST, Ganymede's shadow also moves off the disk.
You may be puzzled by the fact that Ganymede leads Europa across Jupiter's disk, but Europa's shadow precedes Ganymede's all the way across.

That's because Europa orbits much closer to Jupiter than Ganymede, so that the angular distance between Ganymede and its shadow is much greater than the angular distance between Europa and its shadow.

Gallery: Photos of Jupiter and its Moons

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