The Moon and Planets
The moon is a shared global experience. Everyone on Earth sees the same phase of the moon. This week, the moon will pass from First Quarter to Second Quarter in its monthly trip around Earth. What’s Second Quarter, you ask? Why, it’s the Full Moon! Measuring from the New Moon phase, when the moon is hidden beside the sun in the daytime sky, the First Quarter Phase occurs about seven days later, at which time the moon passes a point in the sky that is 90° from the sun. (If you stretch one arm west towards the setting sun and the other south towards the first quarter moon, you’ll form that 90° angle.) A week later, the moon will appear opposite the sun in the sky and fully illuminated, rising just as the sun sets.
To be precise, First Quarter phase occurred last night (Saturday) at 9:12 pm EDT. So it will look slightly more than half full tonight (Sunday), and will be sitting just below the stars that form Leo (the Lion). For the rest of the week, the moon will wax fuller and rise later every evening. Remember that the waxing gibbous moon is still a terrific sight in binoculars and backyard telescopes!
On Wednesday evening, the moon will land among the stars of Virgo (the Maiden). Look for Virgo’s brightest star Spica sitting less than an outstretched fist’s diameter below the bright and nearly full moon. Your unaided eyes are unlikely to pick out the rest of Virgo’s dimmer stars — but binoculars will reveal them.
On Friday night, the very bright moon (only one day shy of full) will land between the two brightest stars of Libra (the Scales). The fairly bright star to the moon’s upper left is called Zubeneschamali “the Northern Claw”, while the star to the moon’s lower right is Zubenelgenubi “the Southern Claw”. Those two stars used to be considered part of Scorpius (the Scorpion). Alternate names for those two stars describe their roles forming the balance of the scales.
For the coming weekend, the moon will pass into Scorpius itself. The May full moon, known as the Full Milk Moon, Full Flower Moon, or Full Corn Planting Moon, will occur at 5:11 pm EDT on Saturday, so the moon will appear completely full all night long. Full moons always rise in the east as the sun sets, and set in the west at sunrise. Since no shadows are cast by the vertically impinging sunlight on a full moon, all of the brightness differences are generated by the reflectivity, or albedo, of the surface geology. Look for the bright rays of material arrayed around some of the younger craters. Tycho, the big, bright crater in the moon’s south-central region, has a huge set of them. Many more, smaller ray systems can be easily seen in binoculars.
Did you know that indigenous people in Canada and around the world have long understood that the tidal force generated by the moon’s gravity draws the water table higher and up into the trees? Their wood-workers know not to harvest wood around the full moon. The wood will be wetter, take longer to dry, and is prone to cracking. I suppose the same rule would apply to felling trees for firewood.
Reddish Mars is now truly beginning its “exit, stage West”. It will be visible for about an hour after dusk every evening, surrounded by evening twilight. Soon it will attain conjunction with the sun, followed by a re-appearance in the eastern pre-dawn sky in November.
The next available bright planet, mighty Jupiter, will rise in the east just before 11 pm local time this week. It’s gradually making its way into position for summer evening stargazing. For now, if you are walking through the house in your pj’s during the wee hours, Jupiter’s bright beacon might catch your eye through a southerly window. Jupiter will reach its highest point over the southern horizon at about 3:30 am local time and then descend towards the west as dawn arrives. If you’d like to see the famous Great Red Spot in your telescope, it will be on the side of Jupiter that faces Earth around midnight tonight (Sunday) and Wednesday. The rest of the time, you can look for the four bright Galilean moons arrayed to either side of Jupiter. Sometimes you’ll only see two or three of them if the rest are hidden by Jupiter itself.
Look for yellowish Saturn, which will be rising about 2 hours after Jupiter all summer, sitting about 2.5 outstretched fist diameters to the lower left (east) of Jupiter in the pre-dawn sky. Saturn will officially enter the evening sky in the last week of May. Dust off your telescope because even a small telescope will show its rings!
Distant and dim, blue Neptune is in the southeastern pre-dawn sky, among the stars of Aquarius (the Water-Bearer). The planet will rise a before 4 am local time. But I’ll wait for summer, when it will be available in the evening, to look for it.
Venus and Mercury are mostly invisible now, low in the eastern pre-sunrise sky. They’ll soon completely disappear in solar conjunction. Mercury will enter the western evening sky by May’s end, and Venus will appear there in September.
With the moon getting full this week, only the brighter stars will remain visible using unaided eyes. Here’s a rundown of the brightest ones. Facing west after sunset, look low in the sky for the bright yellowish Capella in Auriga (the Charioteer). A little higher, and to the east (left), is the matched pair of stars Castor (on the right) and Pollux (on the left) in Gemini (the Twins). Directly overhead, you can look for the seven bright stars of the Big Dipper.
Swinging around to the southeast, and looking well up the sky, you’ll find yellow-orange Arcturus, the brightest star in Boötes (the Herdsman). Finally, climbing the northeastern sky is Vega, in Lyra (the Harp). To Vega’s lower left is another bright star named Deneb. These two stars are the first corners of the Summer Triangle asterism to appear. And that tells us that summer will soon arrive in the Northern hemisphere!
Astronomy Skylights for the week of May 12th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!