SJAA Ephemeris November 2000 | SJAA Home | Contents | Previous | Next

The Shallow Sky

Give Thanks for the Great Gas Giants

Akkana Peck


This November is a month for planetary observers to be thankful. On a Fremont Peak night last month, I observed Mercury, Venus, Earth, the asteroid Juno, Jupiter, Saturn, Uranus, and Neptune - all the major planets except Mars, which is still in the morning sky, and Pluto, which is hidden in the Sun's glare this month. This bountiful planetary cornucopia will carry us through Thanksgiving and into early December, so give thanks and get out there with your telescope (or if you don't have one, borrow one of the club loaners).

This month marks the opposition of the two great gas giants, Jupiter (November 28) and Saturn (on the 19th). They rise in the early evening and are visible all night, Saturn preceding Jupiter by about ten degrees, and the two of them making a lovely pattern with the Seven Sisters and the bull's eye Aldebaran.

Saturn's ring tilt is now at maximum, and this makes it much easier than usual to pick out ring detail. Cassini's division should be easy in any telescope; I've seen hints of the much fainter "Encke minimum", a dimming in brightness in the middle of the A (outer) ring, in telescopes as small as 4". Can it be seen in an 80mm or smaller? This is the year to find out; try it and let me know.

Jupiter's opposition is an unusually close one - the planet will be about as big and bright as we're likely to see it. Look for transits of its satellites and their shadows, and see how many features you can pick out in its stormy, multi-hued atmospheric bands. See the accompanying article on observing Jupiter and its features.

Near opposition, one interesting challenge on Jupiter is to watch for its moons eclipsing their own shadows. Normally, due to the angles between the sun, earth, and Jupiter, a Jovian moon and its shadow transit Jupiter's disk at different times: the shadow preceding the moon before opposition, following the moon after opposition. Within a few days of opposition, they transit at almost exactly the same time, and if the seeing is good (alas, often difficult in winter months), you can sometimes see a crescent-shaped shadow as the rest of the shadow is blocked by the moon.

Try for this with Io's shadow:

With Ganymede's shadow, try

For Europa, try

Neptune and Uranus are in Capricornus, visible most of the night as small greenish or blue-green disks. It's easy to see, after viewing these far-off planets in a small telescope, why early observers called nebulae like the Cat's-eye or the Ghost of Jupiter, which look so similar in a small instrument, "planetary nebulae". Modern observers who have access to Hubble photos might find this less easy to understand.

Mars rises about 3 a.m. in Virgo, moving eastward toward Spica as the month progresses. Its tiny reddish disk whets our appetite for the upcoming opposition this winter. More on that in future columns.


Mail to: Akkana Peck
Copyright © 2000 San Jose Astronomical Association
Last updated: July 19, 2007

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