Double spots on Jupiter, and Last Quarter Moon makes Darker Evenings!

Star Walk
5 min readMay 15, 2017


Binocular Comet Update

The comets I’ve been mentioning recently are still observable in binoculars and low power telescopes, and the waning moon will make that easier this week. Expect the comets to appear as faint greenish blobs (quite different from a star). If a comet develops a tail, it will point roughly away from the Sun. If you find one in a telescope, watch for 15 minutes or so — you’ll see it moving with respect to the stars nearby.

Comet 41P/Tuttle-Giacobini-Kresak is an all-night comet visible as soon as it’s fully dark, but highest in the sky before dawn. It is slowly dropping in brightness, but is still visible in binoculars. This week, look for the comet in the eastern evening sky to the lower right of the very bright star Vega. It’s dropping lower and westward, increasing the distance from Vega from 10° to 16° over the course of the week.

Comet 41P/Tuttle-Giacobini-Kresak in Star Walk 2 app.

Comet C/2015 ER61 (PANSTARRS) is a pre-dawn comet in the eastern sky that is moving eastward (towards the left) along the stars that form the western fish in Pisces (the Fishes). It’s in the region of sky about 10° to the upper right of Venus. It rises about 3:20 am local time. It is slowly dropping in brightness, but is still visible in binoculars.

Comet C/2015 V2 (Johnson) is an all-night binocular comet that is still brightening, and visible as soon as it’s fully dark. This week, it is moving through the constellation of Bootes (the Herdsman) in a direction towards that constellation’s brightest star, Arcturus. In the evening, this part of the sky is high above the eastern horizon, about a palm’s width from the circle of stars forming Corona Borealis (Northern Crown).

I posted finder charts for the comets’ paths during May here.

The Moon and Planets

This week, the moon is west of the Sun, when it rises after midnight and lingers into the morning daytime sky. The Last Quarter phase, when it is illuminated on its sunward half, occurs Thursday evening. On the weekend, the moon will appear as an attractive waning crescent in the eastern pre-dawn sky — landing to the upper right of Venus, and then moving closer to our bright sister planet every morning through next Monday.

The Last Quarter Moon in Solar Walk 2 app.

Sitting at a similar angle with respect to the sun, Venus viewed in a small telescope will also show a crescent phase. Right now Venus’ orbit is carrying it in the opposite direction that the moon is travelling, so the planet is waxing instead of waning. Venus rises about 4 am local time and is the easily brightest celestial body in the sky, after the sun and moon.

On Thursday of this week Mercury reaches its farthest position west of the sun for this morning appearance. It has been shifting farther west, away from the Sun (but moving southward in the sky) while the spring Ecliptic tilts higher — both effects combining to make Mercury rise earlier than the Sun and easier to see. The best time to hunt for it this week is just after 5:15 am local time. Search about 25° (2.5 fist diameters) south of the where the Sun will rise. From Thursday onwards, the planet swings slowly back towards the sun, but remains nicely in view for another couple of weeks.

Mercury in Solar Walk 2 app.

Yellowish Saturn is now a middle-of-the-night object. It rises about 11 pm local time this week, and remains visible until dawn, when it’s two fist diameters above the southern horizon. We’re only a few weeks from opposition, when the ringed planet will be closest and brightest for this year.

Extremely bright, white Jupiter is now an outstretched fist diameter to the upper right of Virgo’s (the Maiden) brightest star Spica. This week, the planet shines halfway up the southeastern evening sky after dusk, reaches its highest point over the southern horizon about 10:30 pm, and sets in the west at 4:30 am local time.

Jupiter in Star Walk 2 app

Jupiter and its four large Galilean moons are easily visible in a small telescope. A slightly larger telescope will also show the Great Red Spot and the round black shadows cast by Jupiter’s moons when they cross (or transit) the planet. Here are the best events in Eastern Daylight Savings Time. (Simply add or subtract the appropriate hours to convert them to your time zone.)

On Thursday, May 18, from 11:51 to 12:42 am, the shadows of Io and Europa will cross Jupiter simultaneously. Europa’s shadow will lead the way starting at 10:17 pm. At 11:53 pm Io’s shadow joins in for 49 minutes, with the two shadows near the opposite sides of the planet. After Europa’s shadow departs at 12:40 am, Io’s continues alone until about 12:42 am.

The Great Red Spot is visible on Jupiter for about three hours centred on Tuesday, May 16 at 12:15 am, on Thursday, May 18 at both 1:53 am and 9:45 pm (in twilight), and on Saturday, May 20 at 11:23 pm.Dim, reddish Mars is now sinking into the evening twilight, setting about 10:30 pm local time this week. It will soon be lost from view while it passes the sun. It late summer it will re-appear in the morning sky — on the way to a terrific viewing opportunity next summer.

Stargazing News for this week (from May 14th) by Chris Vaughan.



Star Walk

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