The Moon and Planets
Tonight, Sunday evening, the very bright waxing gibbous (nearly full) moon will start a tour of the major planets — landing less than a palm’s width to the left of Jupiter and accompanying it as it crosses the sky all night. Look for the pair of objects in the southeastern sky after dusk.
On Monday evening, the moon will hop east to appear a fist’s width above the bright orange-red star Antares, “the Rival of Mars” in Scorpius (the Scorpion). The moon never ventures too far from the zodiac constellations because its orbit is tilted only 5° from the ecliptic, the imaginary circle that defines the 13 zodiac constellations. Yes! I said 13. Annually during the first half of December, the sun passes across the foot of Ophiuchus (the Serpent-Bearer). Maybe he’s trying to trip Ole Sol!
(Above: The sun’s path along the ecliptic, as indicated by the green line, carries it through the 13th zodiac constellation, Ophiuchus, in December every year. This week, the moon will hop over Ophiuchus’ foot, as shown here for 10:45 pm local time on Monday, May 28.)
On Tuesday morning at 10:20 am EDT, the moon will reach a point opposite the sun in the sky, triggering its full moon phase. The full moon of May, known as the Full Milk Moon, Full Flower Moon, or Full Corn Planting Moon, always shines in or near the stars of Libra (the Scales). To unaided eyes, the moon will look full on Monday night, and still look full when it rises on Tuesday at sunset. But binoculars or a telescope will reveal shadows in craters along only its left edge on Monday and along its right edge on Tuesday.
Look for a medium-bright star sitting a few finger widths to the upper left of the full moon in the southeastern sky during late evening on Tuesday. That star, named Sabik, marks the knee of our friend Ophiuchus! On Wednesday evening, the moon will hop over Ophiuchus’ leg, putting Sabik about a fist’s diameter to the moon’s upper right.
(Above: This week, the moon’s eastward orbital motion along the ecliptic, as shown here at 11:45 pm local time on Wednesday, May 30, carries it past Saturn and Mars.)
Also overnight on Wednesday, the moon will be situated a fist’s diameter to the upper right of yellowish Saturn. Then on Thursday evening at about 10:45 pm local time, the now waning gibbous moon will rise in the east with Saturn. The moon will sit only two finger widths to the left of the ringed planet and both objects will fit easily within the field of view of binoculars.
Saturn is sitting near three deep sky Messier objects this week. (If you wait a few days for the moon to pass out of the sky, you’ll have better luck seeing them.) Messier 25, an open star cluster 2,000 light-years away and nearly as broad as the full moon, will be sitting a few finger widths to the upper left of Saturn. Messier 22, a globular star cluster nearly ten thousand light-years away, will be two finger widths below Saturn. And Messier 28, another globular star cluster that is almost 18,000 light-years distant, will be three finger widths to the right, and below, Saturn. You should be able to see Saturn itself until almost 5:30 am local time, when it will sit about 1.5 fist widths above the southwestern horizon.
Wrapping up the moon’s tour, low in the southeastern sky between 1 am local time and dawn on the morning of Sunday, June 3, the waning gibbous moon will sit a few finger widths above bright reddish Mars. Both objects will fit into the field of view of binoculars. Mars, now noticeably brighter than Saturn, continues to steadily brighten and increase in size as the Earth’s faster orbit brings us closer to the red planet this summer. (We will pass it on the “inside track” in late July.)
Venus continues to gleam in the western evening sky this week as it climbs away from the sun. The planet sets at about 11:30 pm local time. Tonight (Sunday), our sister planet will end up extremely close to a yellow, modestly-bright star named Mebsuta which marks the waist of Castor, the westerly twin. Both objects will fit into the field of view of a small telescope. You can observe Venus drawing away from Mebsuta on each subsequent evening.
Jupiter is still visible all night long this week. Look for it as a very bright object in the southeastern sky after dusk. It will reach its highest elevation (about three fist diameters) above the southern horizon around midnight local time, and then descend into the southwestern horizon before the sun rises. The bright star sitting just to the right of Jupiter is Libra’s (the Scales) brightest star, Zubenelgenubi. In binoculars or a small telescope, it splits into a closely spaced pair of stars.
On Wednesday, May 30 between 11:07 pm and 1:17 am, the black shadow of Jupiter’s moon Io and its little round black shadow will cross (or transit) Jupiter’s disk. A reasonable backyard telescope will show the black shadows, but a very good telescope is needed to see the moons themselves.
The Great Red Spot takes about three hours to cross Jupiter’s disk. But the planet’s 10-hour rotation period (i.e., its day) means that the spot is only observable from Earth every 2–3 nights. If you’d like to see the GRS, use a medium-sized telescope (or larger). You’ll have your best luck on evenings with steady air — when the stars are not twinkling too much. The best times to try this week are: Sunday, May 27 at 10:10 pm, Tuesday, May 29 at 11:49 pm, Friday, June 1 at 9:19 pm, and Sunday, June 3 at 10:57 pm. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone. Try to look within an hour before or after the times I’ve given.
Distant blue Neptune, still among the modest stars of Aquarius (the Water-bearer), has become observable in telescopes in the pre-dawn eastern sky after it rises about 2:15 am local time. I’ll post sky charts for the observable planets here.
Astronomy Skylights for this week (from May 27th, 2018) by Chris Vaughan.
Keep looking up to enjoy the sky!