Jupiter’s moons dominate the night sky in January

On the night of Jan. 23 three moons and their shadows cross the disk of Jupiter

Jupiter’s moons are putting on an amazing show this month. The orbital path of the moons is tilting edge-on to the Earth and the sun.

This lineup makes it possible to watch the moons pass in front of each other (an occultation), or pass through another moons’ shadow (an eclipse), and even cast tiny black shadows onto Jupiter. You must find  your old binoculars to see this amazing event.

Jupiter rises by 10:30 p.m. at the beginning of the month, and by 8:30 p.m. at the end of the month.

Have you noticed that the moon rises in the east and sets in the west, just like the sun. Well you might be surprised to learn that every planet also rises in the east and sets in the west.

So Jupiter will be seen rising in the east above Mount Baker.

Even through the smallest telescope or binoculars you should be able to see the two prominent belts on each side of Jupiter’s equator, and the four Galilean moons: Io, Europa, Ganymede and Callisto.

Jupiter’s Great Red Spot is challenging to see now, and it has actually shrunk to less than half the size of historical observations  (25,500 miles) in the late 1800s. The Voyager spacecraft measured it to be 14,500 miles across in 1979. Recent Hubble telescope observations confirm it to be 10,250 miles across. And it is shrinking by 580 miles per year.

On the night of Jan. 23  three moons and their shadows cross the disk of Jupiter.

If you want to try  to see their shadows, you’ll want to start looking through telescopes at 7 p.m. At 7:11 p.m. the first shadow – of Callisto – appears, followed by Io’s shadow at 8:35 p.m. and Europa’s at 10:27 p.m.

Then for 25 minutes  – until 10:52 p.m. – the three black shadows will appear on the planet’s disk at the same time. This triple shadow transit won’t happen again until 2032.

There’s one more treat in store for Jupiter observers this same evening. Io is eclipsed by Calisto’s shadow, beginning at 9:41 p.m.  Eagle-eyed observers will see Io dim in brightness about 10 minutes later, then resume its brightness in another 10 minutes.

Dark skies to all friends of Cattle Point Star Park.

Summary is from the transcript of “What’s Up In January 2015” by NASA announcer and astronomer Jane Houston Jones with specific permission for localization to Cattle Point Urban Star Park and the Oak Bay News.

Bill Smith is a volunteer at Cattle Point Dark Sky Urban Star Park.


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