SJAA Ephemeris March 2003 | SJAA Home | Contents | Previous | Next

The shallow sky

Planets to in-Vesta-gate in March

Akkana Peck


Jupiter and Saturn continue to rule the night skies this month, up high in the sky where the seeing is good during evening hours. As I write this, we've seen some nice steady air in the early spring weather; perhaps this will be a good planet season.

Jupiter continues to fascinate with its ever-changing stormscape. First, we're going to have to stop making jokes about the "great spot formerly known as red" - this season the spot is distinctly pink, enough that several people who never saw color in it before have commented on it. Will it get redder over the next few years? Only time will tell.

Trailing the GRS in the southern equatorial band (SEB) is a long, long trail of white ovals. Those ovals (apparently formed by turbulence in the wake of the spot) just keep multiplying, and one observer recently commented, "I got tired sketching them all." In addition, there are some prominent dark spots (barges, or something else?) showing up in the NEB, as well as a big loopy festoon, and other observers have reported a linear dark feature (a festoon? or perhaps another split in the SEB?) immediately south of the GRS. By the time you read this, I guarantee things will have changed again. You won't run out of things to see looking at Jupiter this year!

Saturn, too, is presenting us with an unusually good face. The wide-open tilt of the rings is making features like the thin gaps in the A ring, and even the elusive "spokes," visible to visual observers in steady seeing. I've seen some spectacular sketches this year, showing spokes, the Encke minimum, and the Keeler Gap, all in one drawing. I haven't yet been blessed with seeing quite that steady myself, but here's hoping! Aperture will help when looking for this sort of feature - don't ignore the planets just because you're out with your big dob - but those with small optics won't be disappointed either. And as Saturn draws farther away from opposition, the shadows of the planet on the rings lengthen, increasing that wonderful three-dimensional effect that makes the ringed planet so beautiful.

This month is a good opportunity to try some asteroid watching. (4) Vesta, is at opposition on March 26. The brightest asteroid, Vesta will reach magnitude 5.9 at opposition, just barely bright enough to see with the naked eye, and almost exactly the same brightness as Uranus this month. More interesting, though, is its apparent size: at 0.58", a large telescope under very steady skies might be able to resolve Vesta as something other than a point of light. Look for Vesta in Virgo, just west of the halfway point between the stars delta and epsilon Vir.

While you strain to resolve that small disc, think about this interesting asteroid. Vesta is the only asteroid known to have distinctive light and dark areas, and the only one known to comprise layers of different types of rock, like the larger planets. A Hubble study in 1994 (when it was a bit farther from us than the 1.28 au we'll see at opposition) showed basaltic lava flows rather like the maria on our own moon, as well as craters and large impact basins similar to what we see on the moon, and a core of olivine, much like the earth's mantle. Where did the heat for lava flows come from, on such a small body (326 miles in diameter, or 525km)? Did it coalesce from radioactive material which provided heat for Vesta's core? That's one theory, but not the only possibility.

Mars is visible in morning twilight, slowly drawing nearer as we draw closer to its opposition this summer. It's still too small to see much detail, though.


Previous | Contents | Next