Mercury - Mercury's best evening apparition of the year begins this month. It may be visible again very low in the west-northwest as early as May 11 after undergoing inferior conjunction on May 3. The speedy planet lies 7 degrees north of Aldebaran on May 16 and 2.5 degrees south of the Moon the next evening. On May 23, Mercury is positioned halfway between third magnitude Zeta Tauri and second magnitude Beta Tauri as it shines at -0.3 magnitude some 7 degrees above the horizon in the west-northwest. Mercury's disk increases in size but decreases in illumination as the month progresses and by May 27 only half of the planet is sunlit. The planet's brightness drops by almost two full magnitudes during the course of the month.

Venus - visible in the evening sky. Look for it about 30 to 35 degrees up in the west just after sunset. Venus shrinks in illumination but increases in apparent size. By the end of May, it is 5" larger but is only 55% illuminated.

Mars - Mars reaches first magnitude status this month but at 6" in apparent size is still too small for fruitful observation. It is situated low in the east-southeast at dawn. The Red Planet begins the month in Aquarius. On May 9, it heads into Pisces and then enters Cetus on May 24. By May 29, Mars is back once again in Pisces.

Jupiter - will be in Ophiuchus about 10° below Antares, as seen in the late evening. In addition the asteroid (4) Vesta will be just under 10° from Jupiter and to its left. As Vesta approaches opposition on May 31 it will brighten to magnitude 5.4. Unfortunately the full Moon will then be a little above Antares, making viewing the asteroid with the unaided eye impossible. A chance to do so should arise a few days later in early June.

For detailed postions of Jupiter's Moons try this interactive javascript utility.

Saturn - Saturn reaches eastern quadrature during the second week of May. As a result, Saturn's shadow falls on its rings, giving the planet an enhanced three-dimensional appearance. The rings have an angular extent of 41" by 11" and the disk 18" this month. On the night of May 22, Titan (magnitude 8.8) is due east of Saturn. Rhea, Dione, and Tethys all shine at around tenth magnitude while the planet hugging Enceladus is a difficult target at nearly twelfth magnitude. Bizarre Iapetus is west of Saturn in early May and then swings to the east of the planet, decreasing in brightness from eleventh to twelfth magnitude as it does so. Titan and Iapetus are less than 1' apart on May 7. The position of Iapetus in relation to Saturn is as follows: May 2 (5" west), May 4 (1" east), May 8 (12" east), May 12 (22" east), May 18 (33" east), May 24 (37" east), and May 30 (34" east).

The Cassini spacecraft continues its observation of Saturn and its many moons and rings. For the latest images from Cassini, see:

http://saturn.jpl.nasa.gov/home/index.cfm

For detailed postions of Saturn's Moons try this interactive javascript utility.

Uranus - 1.7 degrees northwest of Mars and is less than 30' to the southwest of the fourth magnitude star Phi Aquarii on May 1.

A finder chart for Uranus can be found on page 66 of the May issue of Sky & Telescope.

Neptune - is too close to the Sun to be readily observed.

A finder chart for Neptune can be found on page 66 of the May issue of Sky & Telescope.

Pluto - is located in northwestern Sagittarius near the border with Serpens Cauda. On May 1, Pluto is 2.7 degrees north of the open cluster M23 and 6 degrees west of the bright emission nebula M17 (the Checkmark, Horseshoe, Lobster, Omega, or Swan Nebula).

Eris (pronounced "EE-ris") - formerly known as Xena, 2003 UB313, and "the tenth planet"  is magnitude 19 in central Cetus, high in the south during evening.

For detailed information please visit Astronomical Delights

Eta Aquarids Meteor Shower -The May 5th peak of the Eta Aquarids, a minor meteor shower produced by debris from the famous periodic comet 1P/Halley, is compromised by a waning gibbous Moon. The Eta Aquarid meteor shower favors observers in the southern hemisphere but the Orionids, another shower that is caused by Comet Halley, favors the northern hemisphere in October.

Asteroid 4 Vesta -reaches opposition on May 30, seventeen dayperihelion. This makes the minor solar system body almost a full magnitude brighter than normal and a fairly easy naked-eye target from a dark site until the end of June. Vesta is located to the northwest of Eta Ophiuchi and to the southeast of Zeta Ophiuchi on May 1. It passes westward through Ophiuchus during May and is situated less than two degrees south of the eighth magnitude globular cluster M107 on May 30.

For a finder chart, see: http://skytonight.com/observing/home/Vesta