The Evening Moon Looks Lovely, Mercury Mounts, and Oh Look — it’s Ophiuchus!
The Moon and Planets
This is the best week of the month to view the moon. Tonight (Sunday) it will appear as a very slender crescent for a brief time low in the western sky after sunset. For the rest of the week, it waxes fuller and sets later. A denizen of the Earth-facing side of the moon would see the sun rising slowly in the east — taking all week for what we see it do in a few hours every morning. As the sun and moon geometry changes every day, the sun illuminates new segments of the moon, creating dramatically shadowed vistas in your binoculars or telescopes.
First Quarter, when the moon is half illuminated and sets about midnight, occurs on Friday evening. Meanwhile, on Tuesday evening, the crescent moon lands only a finger’s width to the lower left of Leo’s brightest star Regulus. On Friday and Saturday evening, look for the First Quarter moon to the west (right) and east (upper left) of Jupiter, with bright white star Spica below them. Also on Friday evening, from 10:40 to 11:48 pm, the moon will cross in front of (or occult) the medium bright double star Porrima in Virgo (the Maiden). Because the double star’s separation is one arc-second, telescope observers should see one star in the pair wink out seconds before the other one.
Mercury re-enters the western evening sky for a very good extended appearance for northern hemisphere observers this week. Early in the week, look very low in the west around 9:30 pm local time. By the end of the week, it climbs higher and sets just before 10 pm local time, giving you plenty of time to spot it. It’ll be quite bright. Next week will be even better!
Extremely bright Venus is rises in the eastern sky about 3 am local time and remains easily visible until dawn. Viewed in a telescope around now, the planet presents a more than half illuminated phase that is slowly waxing fuller and shrinking in diameter as it heads beyond the Sun. Nevertheless, it will be in the morning sky for a few more months while becoming easier and easier to view.
Saturn is the medium bright yellowish object visible low in the southeastern sky after the evening sky darkens. It crosses due south (at its highest elevation of 24°) at 12:30 am local time, and then sets in the west about dawn.
Jupiter is the extremely bright object in the southwestern evening sky this week. It sets about 1:30 am local time. The planet’s four large Galilean moons are easily visible in a small telescope. A larger telescope will also show the round black shadows they cast when they cross (or transit) the planet — and the Great Red Spot. 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 Monday, June 26 from 10:22 pm to 12:29 am, Io’s shadow will cross Jupiter. A short time later, on Tuesday, June 27 from 12:42 am until the planet sets, Europa’s shadow transits.
The Great Red Spot is visible on Jupiter for about three hours centred on Sunday, June 25 at 11:15 pm, Wednesday, June 28 at 12:54 am, Wednesday, June 28 at 8:46 pm (in twilight), and Friday, June 30 at 10:25 pm.
Finally, the icy giant planets Uranus and Neptune are well-placed for viewing in the pre-dawn sky. Uranus, in Pisces (the Fishes) rises about 2 am local time, and is 1.5 fist widths to the upper right of Venus. Neptune, rising about midnight local time, is in the southeastern sky about two finger widths to the lower left of the medium-bright star Hydor in Aquarius (the Water-Bearer).
Oh, Look — it’s Ophiuchus!
The twelve constellations of the Zodiac are only special because the great circle of the Ecliptic that the sun traces around the sky passes through each of them in turn. The Sun spends varying amounts of time in each one, and the dates repeat every year. For example, in the present era, the sun traverses the constellation of Gemini the Twins from June 21 to July 19 every year. Remember, the sun isn’t moving — it’s Earth’s motion around the Sun that makes it appear to change location compared to the fixed distant background stars.
If you’re an astrology enthusiast, you’ll be wondering by now why is the sun traversing Gemini in June and July when the Gemini “star sign” is for birthdays from May 22 to June 21? The simple reason is — those are the dates when the sun used to traverse Gemini, thousands of years ago when astrology was formulated by the Greeks and Babylonians — and it’s one of many reasons why most astronomers place no value in astrology whatsoever. By the way — if you have an astronomy app or program that allows the year to be changed, you can prove this for yourself by setting the app to noon, centring on the sun, and then changing the date to June 25th, 16 AD. The Sun hops into Cancer (the Crab), which sits east of Gemini!
Most of the Zodiac constellations are inconspicuous — if not nearly invisible. Aries (the Ram) has two decently bright stars that form a little stick, while Cancer, Pisces (the Fishes), Aquarius (the Water Bearer), and Capricornus (the Goat) are seriously tough to make out — unless you travel to dark skies. A few of them, Gemini (the Twins), Taurus (the Bull), Scorpius (the Scorpion), and Leo (the Lion), have very bright stars that form easily recognizable shapes, and the rest fall in the medium bright range.
All of the major objects in our Solar System always travel near the Ecliptic/Zodiac. This year, Saturn is sitting in the “thirteenth zodiac constellation”, and July is a prime month to observe it. Ophiuchus (“Oh-phee-YOU-cuss”) the Serpent Bearer is a huge constellation (11th largest by area) that sits above and between the Teapot of Sagittarius (the Archer) and Scorpius, and below Lyra (the Lyre) and Hercules. The Ecliptic crosses the southernmost (lower) stars of Ophiuchus, but it has never been considered part of the zodiac because that would exceed the special system of 12 sky divisions important to astrologers.
In China, Ophiuchus is considered part of 天市左垣(Tiān Shì Zuǒ Yuán), Left Wall of Heavenly Market Enclosure. Ophiuchus’ stars are only moderate in brightness, so it’s another constellation that benefits from a dark sky. The shape is roughly a large upright box (26° tall and 16° wide) with a pointed triangle on the upper edge. (Think of a Dalek from Doctor Who, but without the plunger.) The brightest star, Rasalhague “the head of the serpent charmer”, marks the peak of the triangle. It sits about midway between very bright star Vega (above) and Antares, the reddish star that’s well to the west of Saturn this summer.
Just to the east and to the west of the main body are the two long sections of the divided constellation, Serpens (the Serpent), which Ophiuchus carries. The western (right) half is called Serpens Caput (the Head), and the eastern (left) portion is Serpens Cauda (the Tail).
From east to west (left to right in the Northern Hemisphere), the stars forming the bottom of the box are: medium bright Sabik “the preceding one”, dimmer Zeta Ophiuchi, and two dimmer stars a finger width apart named Yed Prior “leading hand” and Yed Posterior “trailing hand” which mark the western hand. About a palm’s diameter to the upper left of the Yeds is Marfik “the elbow”. Like Polaris for Earth, Sabik is the Pole Star for Uranus!
You’ll need an astronomy app and a small telescope to see it, but Ophiuchus is home to Barnard’s Star — a red dwarf six light-years away. It is the fourth closest known star, and the closest observable from the northern hemisphere. The star sits 3.5° to the east (left) of Celebrai, Ophiuchus’ eastern shoulder star. Being so close, we can actually watch Barnard’s Star travel through the galaxy, a process known as proper motion. It moves about half the Moon’s diameter in a human lifetime.
Because Ophiuchus sits just above the plane of the Milky Way, it is chock full of Globular Clusters — spherical concentrated balls of stars that orbit our galaxy tens of thousands of light-years from us. A large, reasonably bright one, Messier 10, sits just about where his belt buckle would be. I’ll post a star chart that shows where the better ones are here. You can see them in binoculars and a small telescope, especially from a dark sky site.
The bottom of the constellation dips into the Milky Way. In late evening, the centre of Ophiuchus is due south, about halfway up the sky, and shifting westward. Let me know if you check it out!
Binocular Comet Update
The early-setting moon this week helps when looking for comets. I’ll post finder charts for the paths of two visible ones during June/July here. In binoculars and low power telescopes, 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 C/2015 ER61 (PANSTARRS) is a pre-dawn binocular comet that has recently passed peak brightness. It rises about 2 am local time, and is travelling parallel to Aries (the Ram), about a palm’s width below the line of stars. It’s slowly moving in the direction of the Sun while staying above Venus.
Comet C/2015 V2 (Johnson) is a binocular comet that is still brightening. It’s visible in the evening southeastern sky as soon as it’s fully dark, and sets before 3 am local time. This week, it moves downward through the legs of Virgo while veering eastwards (to the left) of Spica (which is near Jupiter).
Stargazing News for this week (from June 25th) by Chris Vaughan.