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The Sky In May

Natural History, May, 2001 by Joe Rao

Mercury is just above the west-northwestern horizon at midtwilight, climbing higher night after night. For observers at temperate northern latitudes, mid-May offers the year's best chance to see Mercury. It's at greatest eastern elongation from the Sun (22.5 [degrees]) on the evening of the 22nd, rendering the "elusive planet" not so elusive at all. The only trick to seeing it is knowing when to look. Mercury will be positioned above and to the right of Saturn on the evening of May 6 and will appear nearly one full magnitude brighter. During the evenings of May 13-17, it rapidly tracks past the brighter Jupiter. A two-day-old crescent Moon sits off to the left of Mercury on the evening of the 24th. Thereafter, the planet dives back down to the horizon, fading rapidly into the sunset.

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Venus is a dazzling diamond low in the east at early dawn's light. Technically it reaches its greatest brilliance on May 4 (magnitude -4.5) but will look about the same all month. Venus gains only a little altitude in May, continuing to rise at about the break of dawn. Seen through a telescope, the planet is dwindling in size. At the same time, because of its position vis-a-vis Earth and the Sun, its crescent is thickening. A waning crescent Moon slips well below and to the right of Venus on the morning of the 19th.

Mars, in the constellation Sagittarius, rises at about 11:30 P.M. local daylight time on the 1st but about two hours earlier by month's end, dominating the south-southeastern sky the rest of the night. Mars becomes everyone's object of fascination this month as its golden-orange glow brightens from magnitude -1.1 on May 1 to a dazzling -2.0 by the 31st. From May 13 through August 2, it will in fact surpass Sirius (the brightest of all stars) in brilliance. On May 11 the planet begins retrograde (westward) motion against the backdrop of stars. For observers with telescopes, the brightening Mars is a thrilling, though still challenging, planetary target. The Martian north pole is tilted well toward us this spring as the planet's northern-hemisphere summer draws to an end. Look for the shrinking northern polar ice cap as well as increasingly prominent surface features.

Jupiter is low in the west-northwest during twilight. It is still the brightest "star" at dusk in early May, despite being dimmed by its low altitude and its great distance from Earth (on the opposite side of the solar system). Jupiter has had a brilliant yearlong apparition, but sky watchers are running out of time to view it. The giant planet sets only about fifty minutes after the end of twilight on May 1, and two weeks later it sets with the fading twilight. By the 24th, Jupiter is gone completely, hidden behind the glare of the Sun.

Saturn might be glimpsed very low near the west-northwestern horizon about an hour after sundown during the first week of May. Use the brighter Mercury to guide you to Saturn on the evening of the 6th. For the rest of the month, Saturn lies too close to the Sun to be visible. Saturn's solar conjunction occurs on May 25.

The Moon is full on May 7 at 9:52 A.M. Last quarter comes on May 15 at 6:11 A.M., and the new Moon falls on May 22 at 10:46 P.M. First quarter is on May 29 at 6:09 P.M.

Unless otherwise noted, all times are given in Eastern Daylight Time.

Richard Panek is the author of Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Heavens (Penguin, 1999).

The Sky In May

Natural History, May, 2001 by Joe Rao

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