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

The Shallow Sky

A Christmas Eclipse

Akkana Peck


The biggest news in the December shallow sky is the solar eclipse on Christmas morning. Beginning at 7:33 a.m. and lasting until 9:13 a.m., the eclipse will only obscure 18.5% of the solar disk at the maximum eclipse time of 8:21, with the sun only 9 degrees above the horizon. Residents of eastern North America (or anyone taking the excuse to visit them for the holidays) will see a much more pronounced eclipse, up to 55.9% in New York and 61.4% in Montreal.

This eclipse isn't total (or even annular) from anywhere on earth, so the sun won't be significantly less bright than it usually is, nor any less dangerous to the eye: a safe solar filter will be required to observe it directly. You can get extensive information about solar filters from ALPO Solar Coordinator Jeff Medkeff's Solar Observing FAQ, linked off my shallowsky.com web site. Projection (pointing the eyepiece end of the telescope at a piece of paper or a white wall) can also work fine, especially if you want to take the opportunity to show the eclipse to family or neighbors (since many people can look at a projected image at once). Use a cheap eyepiece for this, and the smallest telescope you have (or an aperture mask): there's always the chance that the intense heat can damage an eyepiece, and this is particularly true with modern, multi-element eyepiece designs. And be sure to cover your finder and keep kids (and adults) away from the "business end" of the telescope whenever it is pointed at the sun.

Projection via the pinhole technique also works: any small opening will act like a "pinhole camera," projecting a tiny image of the eclipsed sun onto whatever is beyond it. Try lacing your fingers together and observing the shadow, with tiny eclipses at each of the bright spots.

Solar activity is still very high, so there's a good chance of a nice sunspot display during the eclipse.

What to do for the rest of December while you're waiting for the eclipse to happen? Why, look at Jupiter and Saturn, of course! The planets are both high in the sky now, just past opposition and perfectly placed for observing, making a lovely pattern with the star clusters of Taurus. Last month, we talked about Jupiter's belt structure, features such as the GRS (great red spot) and the SEB (south equatorial band) that surrounds it. If you haven't looked closely at the giant planet, try looking at the color of the red spot - quite noticeable now compared to its pale appearance over the last several years - and the split in the SEB preceding and following the GRS. And, of course, the ballet of Jupiter's four Galilean moons, and the transits of the moons and their shadows over their parent planet, is always wonderful to watch. Don't be fooled by all the "extra moons" Jupiter seems to have picked up this year as it passes through the bright local star cluster the Hyades. In fact, this is a wonderful opportunity to observe how different the Galilean moons look from stars, distinguished by their tiny disks (which look steadier, especially in unsteady seeing, than the point-source appearance of stars) and their off-white color.

Saturn is lovely as always, with the rings tilted well up, showing us the best view we're likely to get for many years of their structure. The big gap between the outer A ring and the inner B ring is called the Cassini division, and should be visible in any telescope on all but the worst nights. The faint, translucent C ring (also called the "Crepe Ring", inside the B ring, is harder to see, but should be visible on most nights. Sometimes, the B ring appears to shade from brightest at the Cassini division to dimmer at the inside where the C ring begins. On extremely steady nights, with good optics, you may be able to see more details in the B ring, such as spokes (radial darkenings, most visible at the "ansae", the points where the rings are farthest from the planet from our point of view) or other bands of light or dark, seen by spacecraft but only by a few earthbound observers. In the A ring, look for a darkening near the outer edge. The narrow gap popularly known as the Encke gap will probably not be visible - in fact, Encke didn't see it, either. Instead, what he saw was a gradual darkening, informally known among Saturn observers as the "Encke Minimum"; the actual Encke gap is a very thin line, very difficult to spot under most circumstances. I have more information on the gaps in Saturn's A ring, and links to other pages discussing the history of their observation, at shallowsky.com.

Venus rides high in the sky at sunset, outshining even Jupiter at magnitude -4.2, and remaining in the sky by nearly four hours after sunset. Its phase, viewed through a telescope, is waning gibbous, but its apparent size grows from 16.3" at the start of the month to 20.5" by month's end.

Sharing Capricornus with Venus are distant Uranus and Neptune, with Uranus less than two degrees away from Venus. This month is the last good chance to observe them this winter before they dip into twilight and reappear in the morning sky. The same constellation also holds the brightest asteroid 4 Vesta, the same brightness as Neptune at 8th magnitude.

Pluto and Mercury are lost in the Sun's glare all month.


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

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