This Week’s Sky at a Glance, April 12 – 20

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Moon and stars, April 10-12, 2019

The Moon crosses Gemini as it reaches first quarter. . .

Moon under Leo, April 14-15, 2019

. . .and then it crosses Leo while waxing gibbous.

Friday, April 12

• First-quarter Moon (exactly so at 3:06 p.m. EDT). Early this evening, the Moon shines high in the southwest with Pollux and Castor to its upper right and brighter Procyon lower left of it, as shown here.

Saturday, April 13

• At this time of year, the two Dog Stars stand vertically aligned around the end of twilight. Look southwest. Far under the Moon this evening is Procyon in Canis Minor. Brilliant Sirius, in Canis Major, is a similar distance below Procyon.

Later in the evening the arrangement moves lower and rotates a bit clockwise, as seen here. The Dog Stars are following Orion down toward making their seasonal exits in the southwest.

• Use binoculars tonight to look for M44, the scattery Beehive Star Cluster in Cancer, roughly 3° to the right of the glary Moon (as seen from the longitudes of North America).

Sunday, April 14

• The gibbous Moon shines upper right of Regulus this evening.

• The huge, bright Winter Hexagon still fills the sky to the southwest and west at the end of twilight. Start with brilliant Sirius in the southwest, the Hexagon’s lower left corner. High above Sirius is Procyon. From there look even higher for Pollux and Castor, rightward from Castor to Menkalinan and bright Capella, lower left from there to Aldebaran, lower left to Rigel way down at the bottom of Orion, and back to Sirius.

Monday, April 15

• Arcturus shines brightly in the east these evenings. The Big Dipper, very high in the northeast, points its curving handle lower-right toward it.

Arcturus forms the pointy end of a long, narrow kite asterism formed by the brightest stars of Bootes, the Cowherd. The kite is currently lying on its side to Arcturus’s left. The head of the kite, at the far left, is bent slightly upward. The kite is 23° long, about two fists at arm’s length.

Tuesday, April 16

• As Arcturus climbs the eastern sky these evenings, equally bright Capella is descending high in the northwest. They stand at exactly the same height above your horizon at some moment between about 9 and 10 p.m. daylight-saving time, depending mostly on how far east or west you live in your time zone.

How accurately can you time this event for your location? Like everything constellation-related, it happens 4 minutes earlier each night.

Wednesday, April 17

• Vega, the bright “Summer Star,” rises in the northeast right around the end of twilight depending on your latitude.

Exactly where should you watch for it to come up? Spot the Big Dipper almost overhead in the northeast. Look at Mizar at the bend of its handle. If you can see Mizar’s tiny, close companion Alcor (binoculars make it easy), follow a line from Mizar through Alcor all the way down to the horizon. That’s where Vega makes its appearance.

Thursday, April 18

• The Moon this evening, nearly full, shines between Spica to its lower right and brighter Arcturus about four times farther to the Moon’s upper left (for North America).

Friday, April 19

• Full Moon (exact at 7:12 a.m. Eastern Daylight Time). This evening look for Spica about a fist and a half to the Moon’s upper right, and brighter Arcturus about twice as far to the Moon’s upper left.

Saturday, April 20

• About an hour after dark now, the Pointer stars forming the end of the Big Dipper’s bowl point straight down toward Polaris, three fists at arm’s length below them. Face north and look way up.


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 an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Jumbo Pocket Sky Atlas cover

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Sample chart.

Once you get a telescope, to put it to good use you’ll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) and Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You’ll also want a good deep-sky guidebook, such as Sue French’s Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer’s Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don’t think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And 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.”

Jupiter, Ganymede, Europa and double shadows, March 25, 2019

Europa and Ganymede, the smallest and largest of Jupiter’s four classic Galilean moons, were both casting their shadows onto the planet when Damian Peach used the 1-meter Chilescope to take this image on March 25th at 9:31 UT. South is up. The extremely high resolution here reveals many surface markings on Ganymede. Click and open in a new tab for full-size view.

Venus-Mercury challenge continues. Venus (magnitude –3.9) and much fainter Mercury (about magnitude +0.2) are both very low in the brightening dawn. Pick up Venus near the east horizon about 20 or 25 minutes before sunrise. Then use binoculars or a wide-field telescope to look for little Mercury 4½° down to its lower left.

Mars (magnitude +1.5, in Taurus) glows in the west after dusk. Start with Orion in the west-southwest, and look to the right from there for the orange pair of Aldebaran and Mars. Mars, slightly dimmer, is the one on the right or, later in the week, upper right. They remain about 7° apart.

Compare the colors of these two similar-looking, but utterly different objects. To me Mars looks very slightly redder.

And remember — nowhere in human experience but astronomy are things so different than they appear.

Jupiter (magnitude –2.3, at the feet of Ophiuchus) rises in the southeast around midnight or 1 a.m. daylight-saving time. It shines fairly high in the south before the beginning of dawn, so that’s the best time to observe it telescopically. Set up your scope about two hours before your local sunrise time.

At that time you’ll find Antares to Jupiter’s lower right, and the dimmer Sagittarius Teapot a similar distance to Jupiter’s lower left. The Teapot is about the size of your fist at arm’s length.

In addition, Saturn (magnitude +0.6, in Sagittarius) will be glowing pale yellow-white about 25° to Jupiter’s left or lower left.

Uranus and Neptune are out of sight in the glare of the Sun.


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 that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.


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


“I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.”
— Isaac Newton, 1642–1727



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