The sky in May

Natural History, May, 2004 by Joe Rao

Mercury reaches its greatest western elongation, 26 degrees from the Sun, on May 14. The planet nonetheless presents a crummy apparition this month for viewers at mid-northern latitudes, because it rises less than an hour before the Sun. The farther south you are, the better your chances of seeing Mercury.

Venus is the first "star" to appear at dusk, and by late twilight it is truly dazzling. On the 2nd Venus reaches its greatest brilliancy for this apparition: magnitude -4.5. The planet is so bright it can easily be seen with the naked eye in a deep-blue, haze-free afternoon sky. After nightfall at a very dark site, the planet's light can cast Venus-shadows. Venus begins the month more than 35 degrees above the western horizon at sunset and doesn't set for another three hours; by month's end, though, it plummets to a sunset altitude of less than 10 degrees and sets only an hour later. This month is an exciting time to follow Venus with a telescope; it's a beautiful crescent that grows bigger and (somewhat counterintuitively) thinner week after week.

Dim Mars is low in the west-northwestern sky at dusk and sets in the northwest between 11 P.M. and 11:30 P.M. local daylight time.

After Venus, Jupiter is the brightest starlike object in the sky, shining this month high in the south-southwest at dusk. It overpowers the first-magnitude star Regulus, 9 or 10 degrees to the planet's west. Examine the two after it gets dark enough to compare their colors: Regulus shines with a bluish hue, whereas Jupiter appears silvery white. The Moon can be found to the right of Jupiter on the 26th, and above and to the left of the planet the following night.

Saturn, in the constellation Gemini, starts the month well up in the northwestern sky at dusk, and sets just after midnight. By month's end, however, it sets by around 10:30 P.M. local daylight time. Mars, much dimmer than the ringed planet, passes less than 2 degrees north of Saturn on the evening of the 24th.

The Moon waxes full on the 4th at 4:33 P.M. There is a total lunar eclipse that day, not visible from North America, though part or all of the eclipse can be seen in Africa, Antarctica, most of Asia (including the Middle East), Europe, and South America. Our satellite wanes to last quarter on the 11th at 7:04 A.M. It becomes new on the 19th at 12:52 A.M. and waxes to first quarter on the 27th at 3:57 A.M.

In the first week of May, early risers might get a glimpse of Comet C/2002 T7 (LINEAR) just above the eastern horizon, about an hour before sunrise. Thereafter, the comet moves too far south for observers to see it from the northern hemisphere.

On the 5th, about an hour after sunset, Comet C/2001 Q4 (NEAT) should be hovering about 10 degrees to the left of Sirius, in the constellation Canis Major. (Your clenched fist, held at arm's length, spans roughly 10 degrees.) Look low in the southwest for blue white Sirius, the dog star; it's the brightest star in the night sky. On the following nights the comet climbs progressively higher in the southwestern sky and becomes correspondingly easier to see.

Both comets could reach first magnitude or brighter. But both also seem to be making their first approach to the vicinity of the Sun, and past experience has shown that "first timers" usually fall far short of brightness expectations.

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