May 1: The eight-day-old waxing gibbous moon is very close to Regulus, the bright star of Leo, early this evening. The moon will move slowly away from Regulus after dark.
May 3: The bright object to the east (left) of the moon tonight is Mars, with Saturn and Jupiter trailing in line to its left. The star close by below Saturn is Spica, in Virgo.
May 4: The moon is between (and above) Mars and Spica tonight.
May 4-5: The Eta Aquarid shower, about 20 shower meteors per hour at best, reaches maximum during the day on the 4th. Unfortunately, the gibbous moon will brighten the sky during after-midnight hours both mornings, so meteor watching will probably not be good.
May 5: The moon passes Saturn during the day, Spica during the early evening. After dark, they will both appear beneath the moon, Saturn higher and toward the right. The brighter Jupiter and Mars are left and right respectively.
May 7: Full moon, in Libra, to the right and above the bright stars of Scorpius' head.
May 8-9: The moon is to the right and above Antares (in Scorpius) on the 8th, to the left and above on the 9th, passing above the star during the day on the 9 th.
May 9: Mercury is at its greatest distance to the east (left) of the sun (greatest easterly elongation). The inclination of its orbit to the horizon is favorable, but the elongation distance is much less than maximum because of the orientation of the ellipse relative to earth. Observers with a clear horizon may be able to see the planet low in the western sky during late twilight for another week or so.
May 11: The waning gibbous moon is at apogee, farthest from earth. It is in Sagittarius tonight, above the ''Teapot,'' when it rises after 11 p.m.
May 13: Mars has completed its retrograde loop among the stars opposite the sun. Now, reflecting the motions of the earth and the planet relative to one another, it resumes its ''normal'' easterly motion. This will be very evident over the next several weeks in the decreasing distance between Mars and Saturn and Mars and Spica. Mars will catch and pass both Saturn and Spica in mid-July.
May 16: Last quarter moon.
May 19-20: The waning crescent moon passes Venus during the night on the 19 th. On the mornings of both dates, the moon and Venus will be an attractive pair in the east from about dawn till they fade in the brightening twilight. Watch the moon shift from west of Venus (to its right) on the morning of the 19th to its east (left) on the 20th.
May 21: Mercury begins its westerly (retrograde) motion as it approaches inferior conjunction in early June.
May 22-24: New moon occurs late in the day on the 22nd, perigee (nearest earth) less than 24 hours later. Expect exceptionally high tides on the 23rd and early on the 24th as the effect of perigee enhances the spring tide that comes with a new moon.
May 25-26: The young crescent moon may be visible during evening twilight on the 25th. It is in Gemini. You should certainly see it on the 26th, weather permitting, beneath and nearly in line with the twin stars Pollux and Castor.
May 28: The crescent moon, almost at first quarter, is near Regulus again, passing the star in the early evening. Even a half hour, if you look carefully, will show you the moon's easterly motion relative to Regulus, while both move to the right toward the horizon.
May 29: First quarter moon.
May 30-31: The gibbous moon passes Mars during the day on the 31st. It will be above the planet on both evenings, to Mars' west (right) on the 30th, east (left) of Mars on the 31st, with Saturn, Spica, and Jupiter further east.
All Month: All the planets were morning stars in March, just two months ago. Now, in May, all but two are evening stars when Uranus reaches opposition from the sun late in the month. Only Venus and Neptune stay in the morning sky.
Venus remains quite bright and is well separated to the sun's right, but its orbit is low relative to the eastern horizon as it rises. The planet doesn't rise until about dawn and stays low through twilight.
Mars, Jupiter and Saturn, all in Virgo, gathered near its bright star Spica, are now well up in the southeast at dusk. Jupiter, even though it is lowest of the group, will probably be the first one you see, since it is easily the brightest. Mars is still much brighter than Saturn and Spica, so it will become visible next, higher up the sky.
Then, in a while, Saturn and Spica will show up between Jupiter and Mars, both about equal in brightness, with Saturn the higher of the two. By about 11 p.m. they will all be in the south, stretched out in line from Jupiter on the left to Mars on the right. They set in the west about dawn or a bit earlier. From the 3rd through the 6th, and again at the end of the month, the waxing gibbous moon will be among them, bright enough to hide the other stars and make Mars, Saturn, Spica, and Jupiter stand out more easily.