January Rings and Rocks

We begin the new year with a lovely sky full of planets to look at: Venus, Saturn, and Jupiter will all be well placed this month.

Saturn rides high in the sky all night, hitting opposition on the first day of 2004. The ring tilt - we'll be looking at the southern face of Saturn's rings all year - is 25-26 degrees, plenty to show all the ring features we can see from earth (see last month's Ephemeris for details). Keep an eye on the ringed planet, as JPL's Cassini probe draws closer to its July rendezvous.

Jupiter rises in mid-evening to join Saturn in the January sky, gradually brightening as it approaches its March opposition. Don't wait for opposition, though - you can see Jupiter's cloud belts, storms, and red spot, and the Galilean moons and their shadows, whenever Jupiter is in the sky.

Venus dominates the evening twilight, setting around 8 p.m. At magnitude -4, it vastly outshines Mars, which sits some 6 degrees west of Venus as the month begins; the gap will widen throughout January, as Venus sinks lower into the twilight, its apparent size shrinks, and its crescent fattens.

Mars may still show a little detail, but its apparent size has shrunk to only five arcseconds (compared to 25 arcseconds at opposition). You'll see the polar cap and a few of the more prominent details, like dark Syrtis Major and light Hellas, but don't expect the rich detail we saw last summer.

Mercury is visible in the morning sky but by month's end will sink back into the twilight glow.

Uranus, Neptune, and Pluto are lost in twilight this month, though it might be fun to try searching for Uranus on the evening of the 15th, when Venus passes less than a degree north of it. Can you spot Uranus' faint green disc near bright Venus?

Ceres reaches opposition on the 9th, at magnitude 6.8 - within reach of binoculars and a fairly easy target for a telescope. Now is a good chance to see the brightest and first-discovered asteroid. It's 1.6 AU away, and at 1.4 arcseconds diameter, it might even be resolvable as something other than a point. Does it look different from a star? It might be interesting to try Ceres even on a night of poor seeing: does it twinkle less than nearby stars?