This Week’s Sky at a Glance, June 20 – 29

FRIDAY, JUNE 20

■ It’s the longest day and the shortest night of the year for the Northern Hemisphere. Summer begins at the solstice, 10:42 p.m. EDT; 7:42 p.m. PDT; 2:42 June 21st Universal Time.

This is also when (in the north temperate latitudes) the midday Sun passes the closest it ever can to being straight overhead, and thus when your shadow becomes the shortest it can ever be where you live. This happens at your local apparent [i.e. solar] noon, which is probably rather far removed from noon in your civil (clock) time.

And if you have a good west-northwest horizon (in mid-northern latitudes), mark carefully where the Sun sets as seen from a particular spot to stand. In a few days you should be able to detect that the Sun is again starting to set a just little south (left) of that point, as it begins its six-month journey toward the winter solstice.

■ Watch Mars and Regulus draw farther apart this week as they sink in the west during and after late twilight. Tonight they’re 2° apart as shown below. In a week they’ll be 6° from each other and somewhat lower.

SATURDAY, JUNE 21

■ Look east-northeast at least 45 minutes before Sunday’s sunrise for the waning crescent Moon passing Venus, as shown below. This is a rather distant Moon-Venus passage; they’ll never be less than 6° apart.

SUNDAY, JUNE 22

■ Late these evenings, look south-southeast to south for orange Antares, the Betelgeuse of summer. Both are 1st-magnitude “red” supergiants, which are actually more like bright orange.

Around and upper right of Antares are the other, whiter stars of upper Scorpius forming their familiar, distinctive pattern. The rest of the Scorpion runs down from Antares, then left, then up to the stinging tail with its Cat’s Eyes pair. Left of there is the Teapot of Scorpius. The farther north you are, the lower they will appear.

MONDAY, JUNE 23

■ Right after dark, spot Arcturus way up high toward the southwest. Three fists below it is Spica. A fist and a half to Spica’s lower right is four-star Corvus, the springtime Crow, sliding down and away.

TUESDAY, JUNE 24

■ Comparing Hercules globular clusters. M13 in the edge of the Keystone of Hercules is famous as one of the best and brightest globular star clusters in the sky. It’s now high in the east after dark. But part of its fame is due to its easily findable location. Less known is its near-twin of a “great cluster in Hercules,” M92 off in the sparser wilderness 9½° to the northeast, as shown below. M92 is only slightly smaller that M13 and has a look of its own.

“To really appreciate the personalities of these two Hercules clusters, try rapidly going back and forth between them,” writes Matt Wedel in his Binocular Highlight column in the June Sky & Telescope. “Most of the visible differences are down to physical size, with M13 being almost twice as massive as M92. Regardless, each is worthy of the title ‘showpiece object.’ ”

WEDNESDAY, JUNE 25

■ This is the time of year when, at the end of twilight, the Little Dipper floats straight upward from Polaris — perhaps like a helium balloon escaped up into the night from some June evening party. Through light pollution or moonlight, however, all you may see of the Little Dipper are Polaris at its bottom and Kochab, the lip of the Little Dipper’s bowl, at the top. The rest of its stars are fairly dim at 3rd to 5th magnitude.

■ New Moon (exact at 6:32 a.m. on this date EDT). Lunation 1268 begins.

THURSDAY, JUNE 26

■ Say hi to Mercury left of the thin waxing crescent Moon low in the west-northwest after sundown, as shown below. Mercury will fade further for the rest of this rather poor apparition.

FRIDAY, JUNE 27

■ This is the time of year when the two brightest stars of summer, Arcturus and Vega, are equally high overhead shortly after dark: Arcturus toward the southwest, Vega toward the east.

Arcturus and Vega are 37 and 25 light-years away, respectively. They represent the two commonest types of naked-eye star: a yellow-orange K giant and a white main-sequence A star. They’re 150 and 50 times brighter than the Sun, respectively — which, combined with their nearness, is why they dominate the evening sky.

Vega’s white has just a touch of icy blue. Arcturus is pale yellow-orange: a summery ginger-ale color. Do their colors stand out a little better for you in the deep blue of late twilight than in full dark? They seem to for me. Binoculars, of course, always make star colors much more evident.

SATURDAY, JUNE 28

■ Dangling down from bright Vega are stars of the little constellation Lyra, forming a small triangle and parallelogram. Vega is the brightest star of the triangle, which is about the size of a thumbtip at arm’s length. The parallelogram hangs from the triangle’s lowest point.

The two stars forming the bottom of the parallelogram are Beta and Gamma Lyrae, Sheliak and Sulafat. They’re currently lined up almost vertically when you face them. Beta is the one on top.

Beta Lyrae is an eclipsing binary star. Compare it to Gamma whenever you look up at Lyra. For much of the time Beta is only a trace dimmer than Gamma. Eventually, however, you’ll catch Beta when it is quite obviously dimmer than usual.

The orbital period of this interacting binary is just 1.4 hours short of exactly 13 days. So expect its behavior to nearly repeat every two-weeks-minus-one-day throughout a given year’s observing season. Beta Lyrae’s exact brightness varies continuously, as shown in this light curve (V magnitude) courtesy of the AAVSO:

SUNDAY, JUNE 29

■ Vega is also the top star of the enormous Summer Triangle holding sway over the eastern sky after dark. Lower left of Vega by about two fists at arm’s length is Deneb. Three fists lower right of Vega is the third star of the Summer Triangle, Altair.

With the Moon now gone, perhaps you can see the Milky Way (if you’re not too light-polluted) running grandly just inside the Triangle’s bottom edge. This stretch of the Milky Way includes the Cygnus Star Cloud, one of one of its richest regions. That’s because when we look toward Cygnus, we’re looking downstream through the local arm of our galaxy.

That’s the direction we’re flying at 220 kilometers per second in the Sun’s orbital motion around the Milky Way.

■ As evening grows late and even Altair rises high, look left of Altair, by hardly more than a fist, for the compact little constellation Delphinus, the Dolphin.

Did you get it? Then try for even fainter, smaller Sagitta, the Arrow. It’s to Altair’s upper left just a little closer. The Arrow points lower leftward, past the head of Delphinus. Binoculars will reveal them even through a mediocre sky.

This Week’s Planet Roundup

Mercury remains very low in the afterglow of sunset. About 40 to 60 minutes after sundown, look for it a little above your west-northwest horizon. It’s slowly fading there: from magnitude –0.2 on June 20th to +0.2 by the 27th.

Venus, brilliant at magnitude –4.3, rises above the east-northeast horizon about a half hour before the beginning of dawn — a weird UFO if you’re not expecting it. Its background constellation is Aries. Venus climbs higher until the dawn sky grows too bright for it. In a telescope Venus’s shrinking globe (now about 19 arcseconds pole to pole) appears slightly gibbous, 60% sunlit.

Mars is drawing farther away from Regulus in the west after dark. They’re still 2° apart on Friday June 20th but widen to 6° apart by Friday the 27th, with Regulus moving farther to Mars’s lower right.

Is Mars starting to look just a little fainter than Regulus to you by the end of the week?

In a telescope, Mars is just a tiny blob 5 arcseconds wide and is in the increasingly poor seeing toward the horizon.

Jupiter is out of sight in conjunction with the Sun.

Saturn (magnitude +1.0, at the border of Aquarius and Pisces) rises around 1 a.m. daylight-saving time. Just before and during early dawn, find it about four or five fists to the upper right of Venus.

The best time to try a telescope on Saturn is just as dawn is beginning, when Saturn has had time to get about 30° high out of the worst seeing but still stands out against a reasonably dark sky. You may be surprised by Saturn’s appearance; its rings are nearly edge-on to us this year.

Uranus is out of sight low in the dawn.

Neptune, a telescopic “star” at magnitude 7.9, lurks in Saturn’s background about 1° from it. Catch this outermost major planet before dawn begins by using the finder chart for Neptune with respect to Saturn in the June Sky & Telescope, page 51. With a pencil, put a dot on the path of each planet for your date. Get everything all planned out and ready to go the evening before, so that dawn doesn’t overtake you.

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world’s mid-northern latitudes. Descriptions and graphics that also depend on longitude (mainly Moon positions) are for North America.Eastern Daylight Time (EDT) is Universal Time minus 4 hours. UT is also known as UTC, GMT, or Z time.

Want to become a better astronomer? Learn your way around the constellations. They’re the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For a more detailed constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

For the attitude every amateur astronomer needs, read Jennifer Willis’s Modest Expectations Give Rise to Delight.

Once you get a telescope, to put it to good use you’ll need a much more detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas, in either the original or Jumbo Edition. Both show all 30,000 stars to magnitude 7.6, and 1,500 deep-sky targets — star clusters, nebulae, and galaxies — to search out among them.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many, as well as many more deep-sky objects. It’s currently out of print, but maybe you can find one used.

The next up, once you know your way around well, are the even larger Interstellarum atlas (with 201,000+ stars to magnitude 9.5 and 14,000 deep-sky objects selected to be detectable by eye in large amateur telescopes), and Uranometria 2000.0 (332,000 stars to mag 9.75, and 10,300 deep-sky objects). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.

You’ll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham’s Celestial Handbook. An impressive more modern one is the big Night Sky Observer’s Guide set (2+ volumes) by Kepple and Sanner. The pinnacle for total astro-geeks is the new Annals of the Deep Sky series, currently at 11 volumes as it works its way forward through the constellations alphabetically. So far it’s up to H.

Can computerized telescopes replace charts? Not for beginners I don’t think, and not for scopes on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting technology to work rather than learning how to explore the sky. As Terence Dickinson and Alan Dyer say in their Backyard Astronomer’s Guide, “A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand and a curious mind.” Without these, “the sky never becomes a friendly place.”

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn’t simple either. Do learn the essential tricks at How to Use a Star Chart with a Telescope.

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty’s monthly
podcast tour of the naked-eye heavens above. It’s free.

“The dangers of not thinking clearly are much greater now than ever before. It’s not that there’s something new in our way of thinking, it’s that credulous and confused thinking can be much more lethal in ways it was never before.”
            — Carl Sagan, 1996

“Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence.”
            — John Adams, 1770