Heads Up! – Triple Shadow Dance on Jupiter


Triple Shadow Transit2

Something very special is going to happen on Jupiter this Friday night.

If you have a telescope be sure to train it on Jupiter Friday evening or into Saturday morning for a rare sight. For 24 minutes we will see three of Jupiter’s moons casting their shadows onto Jupiter’s cloud tops at once.

We will not see this sight again until March 20, 2032. 

The shadows of the Jovian moons Io, Europa and Callisto will be on the disk of Jupiter from:

• 1:28 a.m. until 1:52 a.m. EST, after midnight on January 27 for those in eastern North America.

For those in western North America the times are:

• 11:28 p.m. until 11:52 p.m. MST, or 10:28 p.m. to 10:52 p.m. PST, before midnight on January 26.

Callisto’s shadow enters the disk earlier in the evening for North America, at 10:11 p.m. EST. A double shadow transit begins when the small but intense shadow of Io enters the disk at 11:35 p.m. EST. Double shadow transits are fairly common.

The rare sight begins just under two hours later, at 1:28 a.m. EST or 11:28 p.m. MST when Europa’s shadow also enters the disk.

It is short-lived, however. The fast-moving shadow of Io leaves the disk 24 minutes later, at 1:52 a.m. EST, or 11:52 p.m. MST, leaving only the shadows of Callisto and Europa on the disk. (The graphic illustrates the triple transit halfway through the 24-minute-long window.)

You’ll need a telescope to witness this rare dance of shadows. An 80mm refractor or 100mm reflector should suffice. Use high power. The shadows will appear as dark spots of varying size and intensity. Io’s will be darkest, Callisto’s will be largest but less intense. Europa’s shadow will look the smallest.

The disks of Io and Callisto will also be on the disk but will appear as bright dots, making them harder to pick out against the bright cloud bands.

Jupiter is the brightest object in the eastern sky in the late evening. You can’t miss it!

For more details see Sky and Telescope’s webpage.

— Alan, January 21, 2015 / © 2015 Alan Dyer / www.amazingsky.com

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