This Week's Sky at a Glance, April 15 – 23

FRIDAY, APRIL 15

■ This evening the Moon is not quite full, a mere 2/3 of a day short of full (for evening in North America). It will be exactly full at 2:55 tomorrow afternoon EDT.

Look below the Moon after dark for Spica glimmering through its glare. Much farther to the Moon's left shines brighter Arcturus.

■ During dawn tomorrow morning the 16th, spot Venus shining in the east as shown below. Upper right of it are Mars and then Saturn, much fainter; binoculars help as dawn grows bright. Lower left of Venus by 12°, Jupiter is coming into view.

SATURDAY, APRIL 16

■ Full Moon (exactly full at 2:55 p.m. EDT). At nightfall, the Moon is in the dim feet of Virgo. Spica shines about 9° to its upper right (nearly a fist at arm's length), perhaps struggling to be seen through the moonlight. Brighter Arcturus is some 30° to the Moon's upper left.

SUNDAY, APRIL 17

■ Look west-southwest as the stars come out to catch Orion tilting down and away in his spring orientation, with his belt horizontal. The belt points left toward Sirius and right toward Aldebaran and, farther on, the Pleiades.

■ Look very high above Orion for Pollux and Castor, lined up roughly horizontally. They form the top of the huge Arch of Spring.

Lower left of Pollux and Castor, Procyon forms the Arch's left end. Look farther to the lower right from Pollux and Castor for 2nd-magnitude Menkalinan and then brilliant Capella, the Arch's right end. The Arch is part of the even larger Winter Hexagon, the rest of which is getting very low or setting.

Modern skywatchers are not alone in seeing the Arch of Spring as one big asterism. Extend it down past Procyon to add Sirius, and you've got the Hawai‘ian Canoe-Bailer of Makali‘i.

MONDAY, APRIL 18

■ Leo walks horizontally across the meridian these evenings. The Sickle of Leo (the Lion's head, front, and forefoot Regulus), stands upright, with its open side to the right: a backward question mark. Its brightest stars are Regulus, the bottom of the Sickle's handle, and Gamma Leonis (Algieba), above Regulus in the Sickle's crook.

About two and a half fists left of Regulus is Denebola, Leo's tail-tip.

■ Stay up till about 1 a.m., look southeast, and you'll find the waning gibbous Moon among the stars of the head of Scorpius. The brightest is Antares, a little to the Moon's lower left. The Moon is very close to Delta Scorpii, the middle of the row of three head stars.

And if you're in the northeastern US or eastern Canada, the Moon occults Delta Sco very late tonight. You'll need to use a scope at fairly high power to watch, because the star disappears in the Moon's dazzling bright limb. Map and timetables for this event. (The first two letters in the Location column are the country abbreviation. The table has two parts: the long list of disappearance times and circumstances, then the same for the star's reappearance.)

TUESDAY, APRIL 19

■ In mid-April, the two Dog Stars stand vertically aligned in mid-twilight. Look southwest. Brilliant Sirius in Canis Major is below. Procyon in Canis Minor stands above it by 25°, two or three fists at arm's length.

WEDNESDAY, APRIL 20

■ Arcturus is climbing high in the east, brilliant at magnitude zero and pale yellow-orange. Turn around to the northwest. Descending there is equally bright Capella. They stand at exactly the same height above your horizon at some moment between about 8:30 and 10:00 p.m. daylight-saving time, depending on both your latitude and longitude.

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

■ Before the first light of dawn on Wednesday the 20th, the waning gibbous Moon shines between the Sagittarius Teapot to its left and the stars of upper Scorpius to its right: a preview of summer evenings.

THURSDAY, APRIL 21

■ Capella, high in the northwest during and after dusk, has a pale yellow color matching the Sun's, which means they're about the same temperature. But otherwise Capella is very different. It consists of two yellow giant stars orbiting each other every 104 days.

Moreover, for telescope users, it's accompanied by a distant, tight pair of red dwarfs: Capella H and L, magnitudes 10 and 13. That's about 10,000 and 160,000 times fainter than Capella itself! Article and finder charts. Can you make out at least H with your scope, now that the Moon is out of the evening sky?

■ The Lyrid meteor shower should be active late tonight and late tomorrow might, though the shower's timing is less than ideal for North America. Best times to try watching are from about 11 p.m. until moonrise both nights, writes Bob King in Celebrate Spring with the Lyrids. The shower is usually weak; under good observing conditions you might see a Lyrid every 5 minutes or so of steady watching on average.

FRIDAY, APRIL 22

■ Arcturus is the brightest star high in the east these evenings, pale yellow-orange. Spica, paler blue-white, shines lower right of Arcturus by about three fists at arm's length.

To the right of Spica by half that distance is the distinctive four-star constellation of Corvus, the springtime Crow.

■ The last-quarter Moon rises as late as 3 a.m. daylight-saving time Saturday morning, in Capricornus far to the lower right of Altair. It's exactly last-quarter at 7:56 a.m. Saturday morning EDT.

SATURDAY, APRIL 23

■ Vega, the Summer Star, the zero-magnitude equal of Arcturus, is now twinkling low in the northeast after nightfall. . . depending on your latitude. The farther north you are the higher it will be. If you're in the latitudes of the southern US, you'll have to wait until a bit later after dark for it to appear.

 

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This Week's Planet Roundup

Mercury, after last week's conjunction with the Sun, creeps up into the low afterglow of sunset late this week. By about Thursday the 14th, look for it low above the west-northwest horizon 30 or 40 minutes after sunset. At least it's bright, magnitude –1.2 that evening. Binoculars will help, and with binoculars you may start to pick it up a few days earlier.

Venus, magnitude –4.4, is the bright "Morning Star" shining low in the southeast during dawn.

Mars and Saturn glimmer to Venus's upper right, in that order. They're vastly fainter: almost identical at magnitudes +1.1 and +0.9. Mars, however, is more orange than pale yellow Saturn. Each morning they're a little farther from Venus and from each other.

Jupiter emerges into dawn view this week, well to the lower left of Venus. On the morning of April 9th, it's 19° from Venus. By April 16th they close to within 13° of each other. Look for Jupiter about 45 to 30 minutes before sunrise.

Uranus is lost in the sunset.

Neptune remains invisible in the sunrise glow, close to Jupiter but only magnitude 7.9.

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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. (Universal Time is also called UT, UTC, GMT or Z time.)

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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 magazine of astronomy.

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) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to 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.

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."

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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.

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"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."
            — John Adams, 1770

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