The Shallow Sky

Akkana Peck

The big news this month is the Mercury transit on the afternoon of November 15. This is a fairly rare event - once a decade or so -so break out your solar filter and take a look! (Of course, the usual warnings about solar viewing apply - don't look at this without a safe front-aperture solar filter or a projection setup.)

Mercury will be very close to the sun's northern limb, and because of limb darkening (the tendency for spherical objects to appear darker at the edges), some observers predict that it may be somewhat difficult to see the silhouette of the small planet (only 9.9 arcseconds) against the sun's limb, so seeking out clear skies and good seeing may be worthwhile. Use a relatively high magnification, rather than the low power full-sun view many people prefer for sunspot and general solar viewing.

Viewed from San Jose, the planet should first hit the sun's northeast limb at about 1:11pm PST, and end its transit almost exactly an hour later. Some observers of past transits have reported seeing Mercury slightly before first contact, silhouetted against the inner corona.

What do you do at night while you're waiting for the 15th? Well, look at Jupiter and Saturn, of course! The biggest planets are both high in the sky, visible all night, and perfectly placed for observing this month. Jupiter just passed opposition on October 23rd - as close as it will be to us for the next decade - while Saturn's opposition, a nice one with its rings tilted a generous 20 degrees to us, will occur on November 5th.

On Jupiter, the Great Red Spot (more like light pink) and the white ovals following it are interesting targets, as are the festoons (long pink streamers running from the bands into the equatorial zone) and transits of its moons and their shadows. You can get transit times for Jupiter's moons and for the GRS in magazines like Sky & Telescope, or use my Java applet:

On Saturn, look for Cassini's division, a narrow gap between the two main (A and B) rings, and for the semi-transparent C or "Crepe" ring inside the main rings. In steadier seeing, try for the much more difficult gaps in the outer A ring.

Mars is low in the western sky, and isn't well placed for observing surface details, but a telescope will show it as a red, gibbous disk, perhaps with a few smudges of lighter and darker color. Neptune and Uranus follow a bit behind Mars, while the shrimps of the solar system (hey, I resemble that remark!), Pluto and Mercury, are both lost in the sun's glare. Venus shines high in the morning sky, showing exactly half phase as November opens.

Akkana Peck; last updated: October 03, 2007 Prev Next