Northern Hemisphere gazer's guide
May 1-5: Learn to pick up Jupiter, Mars, and Regulus as soon as you can this month, so that you can follow their movements relative to one another. The two planets are huddled quite close to Regulus, the bright star in Leo, but Mars is moving swiftly to the left (east) of the star, Jupiter more slowly. On the night of May 1, Mars is still to the right of Jupiter, between the planet and Regulus. By the evening of the 4th, Mars passes Jupiter and moves to its left (east). On the 5th, Jupiter is clearly between Regulus (to its right) and Mars (to its left), and on successive nights Mars moves quickly away to the left. It is easy to distinguish among the three, Jupiter by far the brightest, Mars second brightest and orange- yellow in color, and Regulus the dimmest.Continue watching them in the weeks ahead to see Jupiter move slowly east (left) from Regulus, Mars move rapidly east (left) of both and dim rapidly till it is only barely brighter than Regulus.
May 4: The Eta Aquarid meteor shower, reaching maximum early this morning, is not among the more productive (about 20 shower meteors per hour at maximum), but its meteoroids are swift and the resulting meteor displays often bright. Look this morning after 1 o'clock.
May 8: Venus reaches its greatest brilliancy in the evening sky. The planet has been producing one of its more spectacular displays as an evening star this winter and spring, but it has only a few more weeks of glory left. The very factors that have made it so dramatic now begin to turn against it. It has been growing brighter in our sky because it is moving swiftly closer to earth. But in moving closer, it swings in between earth and sun (inferior conjunction), causing it to turn its bright (sunlit) face away from us. This factor dominates after today, and the planet will be dimming rapidly in the weeks ahead. By early June, it will no longer be noticeable. In partial compensation between now and then, however, the crescent shape of Venus -- one of the most startling and significant discoveries made by Galileo centuries ago -- is now very easy to see with binoculars. From now till the end of May, it looks like a very tiny crescent moon!
May 12: The moon is at perigee, nearest earth.
May 13: Mercury is in superior conjunction (in line with but beyond the sun) and enters the evening sky.
May 14: Uranus, at opposition, becomes an evening star.
May 15: The occultation of Aldebaran by the moon this morning (about 9 a.m., eastern standard time) occurs above the horizon in North America, but in daylight and very close to the sun.
May 16: The young crescent moon is near Venus tonight.
May 20-23 The waxing gibbous moon offers an exceptional opportunity to meet Regulus Jupiter, Mars, and Saturn (all in Leo) on these nights, marching slowly past them so closely that it occults (covers) each in turn, though none of the occulations occur in the North American sky. On the evening of the 20th, the moon is to the right of all four bright objects. Early at night on the 21st, Jupiter (the brighter) and Regulus are to the moon's right, Mars and Saturn to its left, but the moon is moving slowly away from Jupiter and toward Mars. If you watch during the night, you will easily see the moon pass Mars about 1 a.m., e.s.t. At dusk on the 22nd, the moon is between Mars (to its right) and Saturn (to its left), moving toward Saturn, which it passes about 5 a.m., e.s.t. On the 23rd, Saturn, Mars, Jupiter, and Regulus (in that order) are all to the moon's right.
May 23: Saturn completes its retrograde (westerly) motion through the stars. It now begins to move east again, taking away from Regulus and toward Spica (in Virgo).
May 24: The moon is at apogee, farthest from earth.
May 24: Venus becomes stationary among the stars, and begins to shift westerly (retrograde). The apparent "backwards" movement of Venus occurs because the planet is moving in between earth and sun, traveling in its orbit more rapidly than earth. This also rapidly decreases the distance between the planet and the sun, causing Venus to disappear from the evening sky within the next week or so.
All month: The bright planets continue to dominate the evening sky during May: Venus in the west; Jupiter, Mars, and Saturn (and the nearby bright star Regulus) in the east. But an experienced observer will see signs that they are past their prime.
Venus is high and bright at sundown, brighter than it has been all winter and spring. But it will be noticeably lower when it appears on successive nights, and it will set noticeably earlier each night after mid- month. By the last week of the month, it will begin to fade in brightness. Jupiter, Mars, and Saturn are conspicuous in Leo, along with its brightest star, Regulus. They will be well up in the south at dusk, moving into the southwest in the early evening, setting a few hours past midnight. Jupiter and Mars are very close to Regulus in early May, and Mars is still quite bright, presenting a very impressive gathering of bright objects.