Jupiter at Peak Planet, a Late-night Lunar X, and Mars and Mercury Hang Out in the West!
The Moon and Planets
Both the moon and Jupiter will be dominating our night skies this week, worldwide. Here are the Skylights!
The moon will tempt you to view it throughout this week. Sunday evening will feature the nearly half-illuminated moon tucked a palm’s width below the stars that form the eastern, back half of Leo (the Lion). Hours later, at 2 am Eastern Time on Monday morning, the moon will officially reach its First Quarter phase. At that time, it will be positioned 90 degrees away from the sun.
The term expresses that the moon has completed the first quarter of its orbit around Earth since the previous New Moon. The relative positions of the Earth, sun, and moon cause us to see the moon half-illuminated — on its eastern side. At first quarter, the moon always rises around noon and sets near midnight, so it is also visible in the afternoon daytime sky, too. The evenings around first quarter are the best times to see the lunar terrain while it is dramatically lit by low-angled sunlight.
At this first quarter, a feature called the Lunar X will be visible in strong binoculars and small telescopes. For a few hours, the illuminated rims of the craters Parbach, la Caille, and Blanchinus will form a small, but very obvious X-shape located at moon coordinates 2° East and 24° South. That point is on the terminator (the pole-to-pole line that divides the lit and dark hemispheres) and about one third of the way up from the southern pole of the moon. The “X” should start to develop around midnight on Sunday.
From Monday through Thursday, the moon will pass head-to-foot through the large constellation of Virgo (the Maiden). Every night, our natural satellite will fill up with light and set later as it swings wider from the sun. On Thursday and Friday, the nearly full moon will cross Libra (the Scales).
On the weekend, the moon will hop past Jupiter, landing on Jupiter’s upper right on Saturday and then dropping to Jupiter’s lower left on Sunday. On both nights, notice the relative positions of the two objects while they are over the eastern horizon, and compare that to the way they look hours later. Earth’s rotation causes constellations and planets to flip by 180 degrees as they cross the sky from east to west. The June full moon will occur in the wee hours of next Monday, so the moon will look full on Sunday evening, too.
This is a big week for Jupiter — literally! On Monday, June 10, Earth’s faster orbit will pass Jupiter on the inside track, causing Jupiter to be positioned exactly opposite the sun in our sky, worldwide. Planets at opposition always rise at sunset, and remain visible all night long. On Monday, Jupiter will also be closer to Earth than on any other date this year — only 640.9 million km, or 4.284 Astronomical Units from us. (1 A.U. is the average sun-Earth separation.) The planet’s light will be taking 36 light-minutes to reach us — meaning that we are seeing Jupiter more than half an hour in the past!
Jupiter will also shine at its brightest (visual magnitude -2.6) for 2019, and its apparent disk diameter will max-out at 46 arc-seconds. (That’s 2.5% of the full moon’s diameter.) Don’t worry if your skies are cloudy on June 10. Jupiter will be about as good for a week surrounding that date, and then it will slowly start to shrink in size and brightness. We’ll be enjoying Jupiter through our telescopes all summer long!
Around opposition, Jupiter’ moons are more visible, too. From time to time, the small, round black shadows cast by Jupiter’s four Galilean moons become visible in amateur telescopes as they cross (or transit) Jupiter’s disk. Starting late on Tuesday evening, observers in the Americas can see two of those shadows on Jupiter at the same time! At 11:29 pm EDT, Ganymede’s shadow will join Io’s shadow already in transit. The two shadows will cross Jupiter for 64 minutes until Io’s shadow moves off the planet at 12:33 am. Ganymede’s shadow will continue to transit the northern polar region of Jupiter until 1:50 am EDT.
Due to Jupiter’s rapid 10-hour rotation period, the Great Red Spot (or GRS) is only observable from Earth every 2nd or 3rd night, and only during a predictable three-hour window. The GRS will be easiest to see using a medium-sized, or larger, aperture telescope on an evening of good seeing (steady air). If you’d like to see the Great Red Spot in your telescope, it will be crossing the planet after midnight tonight (Sunday). More GRS viewing opportunities occur in the hours surrounding 9:45 pm EDT on Monday evening, 11:15 pm EDT on Wednesday, and 1 am EDT on Saturday.
Yellowish Saturn will be rising in the east-southeast a little before 11 pm local time this week. Its position in the sky is just to the left (east) of the stars that form the teapot-shaped constellation of Sagittarius (the Archer). Saturn is quite a bit dimmer than Jupiter. To find it, look about 2.5 fist diameters to the lower left (east) of Jupiter. Dust off your telescope — because even a small one will show its rings and several of its brighter moons!
Distant and dim, blue Neptune is in the southeastern pre-dawn sky, among the stars of Aquarius (the Water-Bearer). The planet will rise before 2 am local time. After mid-June, Neptune will become part of the evening sky. Brighter, blue-green Uranus is rising at about 3 am local time, and is sitting among the stars of Aries (the Ram).
Last to rise is our bright, next-door neighbour Venus. She is sitting low in the east-northeastern pre-dawn sky this week, creeping ever-closer to the rising sun. Venus will shine with a steady, unmoving light — unlike airplanes.
Mars and Mercury are hanging out just above the northwestern horizon after sunset this week. Mercury will become easier to spot every night because it is climbing away from the sun and brightening. The best time to look for it falls between 9:45 and 10:15 pm local time. Mercury is heading directly towards dimmer Mars. Tonight, Mars will be about a palm’s width to the upper left of Mercury. By Sunday, that will reduce to a finger’s width! And next week, those two planets will “kiss”!
Astronomy Skylights for the week of June 9th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!