This Week's Sky at a Glance, April 11 – 20

FRIDAY, APRIL 11

■ The two Dog Stars stand vertically aligned around the end of twilight at this time of year. Look southwest. Brilliant Sirius in Canis Major is below, and Procyon in Canis Minor is about two fists above.

■ The Moon, one day short of full, shines above Spica this evening as shown below.

■ Then after the night is fully dark, look three fists left of the Moon for bright Arcturus. It's the narrow point of the Kite asterism of Boötes. The Kite is lying on its side, extending left from Arcturus. Its bottom edge, a straight row of three stars including Arcturus, points straight at the Moon tonight (for North America).

SATURDAY, APRIL 12

■ Full Moon (exact at 8:22 p.m. EDT). The full Moon of April always shines in the vicinity of Spica. This year they're especially close together, as indicated above. The Moon will occult Spica for most of South and Central America and the southernmost tip of South Africa; map and timetables.

And, this is a minimoon. The full Moon will be near the apogee of its orbit, so it will appear about 6% smaller than average. This is the smallest full Moon of 2025.

SUNDAY, APRIL 13

■ Vega, the bright "Summer Star," rises in the northeast these evenings. How early or late depends on your latitude and also on your longitude within your time zone.

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

MONDAY, APRIL 14

■ The Sickle of Leo stands vertically upright high in the south after dark. Its bottom star is Regulus, the brightest of Leo. Leo himself is walking horizontally westward. The Sickle forms his front leg, chest, mane, and part of his head. His tail tip is Denebola, about two and a half fists left of Regulus.

TUESDAY, APRIL 15

■ The waning gibbous Moon rises around 11 p.m. at the head of Scorpius. In the early-morning hours of Wednesday the 16th they stand higher in the southeast to south, with orange Antares shining to the Moon's lower left or left.

■ As it makes its way onto the head of Scorpius, the Moon will occult Pi Scorpii, magnitude 2.9, for observers in Canada, the contiguous U.S., and Central America. Map and timetables. The first two tables, with predictions for many cities, are long. The first table gives the times of the star's disappearance behind the Moon's bright limb, for which you'll need a telescope. The second gives the star's reappearance out from behind the Moon's dark limb; for this binoculars will do, but you'll have to be staring steadily at the right instant. Scroll to be sure you're using the correct table; watch for the new heading as you scroll down. The first two letters in each entry are the country abbreviation (CA is Canada, not California). The times are in UT (GMT) April 16th. UT is 4 hours ahead of Eastern Daylight Time, 5 hours ahead of CDT, 6 ahead of MDT, and 7 ahead of PDT.

For instance: Use the first table to see that for Chicago, Pi Sco will disappear on the Moon's bright limb at 3:36 a.m. CDT on the morning of the 16th, when the Moon will be 22° high in the south (at azimuth 186°). Chicagoans will see it reappear from behind the dark limb at 4:53 a.m. CDT, when the Moon will still be 18° high in the south-southwest (azimuth 204°).

WEDNESDAY, APRIL 16

■ Capella is the brightest star high in the west-northwest during and after dusk. Its pale-yellow color matches that of the Sun, meaning they're both about the same temperature. But otherwise Capella is very different. It consists of two yellow giant stars orbiting each other every 104 days.

That's common knowledge among starwatchers. But did you know that, for telescope users, Capella is accompanied by a distant, tight pair of red dwarfs? They're Capella H and L, magnitudes 10 and 13. Article and finder charts.

THURSDAY, APRIL 17

■ High above the Big Dipper late these evenings, nearly crossing the zenith, are three pairs of dim naked-eye stars, all 3rd or 4th magnitude, marking the Great Bear's feet. They're also known as the Three Springs (or Leaps) of the Gazelle, from early Arab lore. They form an east-west line that lies roughly midway between the Bowl of the Big Dipper and the Sickle of Leo. The line is 30° (three fists) long. See the evening constellation chart in the center of the April Sky & Telescope.

According to the ancient Arabian story, the gazelle was drinking at a pond — the big, dim Coma Berenices star cluster — and bounded away when startled by a flick of Leo's nearby tail, Denebola. Leo, however, seems quite unaware of all this, facing the other way.

Another version of the story sees Coma Berenices as Leo's extended tailtip and the pond as formed by stars in Ursa Major.

FRIDAY, APRIL 18

■ Right after dark, Orion is still in the southwest in his spring orientation: striding down to the right, with his belt horizontal. The belt points left toward Sirius and right toward Aldebaran and, farther on, the Pleiades. Above Aldebaran shines bright Jupiter as shown below.

SATURDAY, APRIL 19

■ Right after dark, the Sickle of Leo stands vertical high in the south. Its bottom star is Regulus, the brightest of Leo. Leo himself is walking horizontally westward. The Sickle forms his front leg, chest, mane, and part of his head. Off to the left, a long right triangle forms his hind end and long tail.

SUNDAY, APRIL 20

■ Find Procyon high above brilliant Sirius in the southwest right after dark. Look upper left of Procyon by 15° (about a fist and a half at arm's length) for the dim head of Hydra, the enormous Sea Serpent. His head is a group of 3rd- and 4th- magnitude stars about the size of your thumb at arm's length.

About a fist and a half lower left of Hydra's head shines Alphard, his 2nd-magnitude orange heart. The rest of Hydra zigzags (faintly) from Alphard all the way down to the southeast horizon. For more on Hydra and his hellish lore, see Stephen James O'Meara's "Alphard and the Golden Bough" in the April Sky & Telescope, page 45.

■ Last-quarter Moon tonight (exact at 9:36 p.m. EDT). The half-lit "backward" Moon doesn't rise until around 3 a.m. daylight-saving time. By the very beginning of dawn, roughly an hour and a half later, it's still low in the southeast: in dim Capricornus and about two fists lower left of the Sagittarius Teapot.

This Week's Planet Roundup

Mercury and Saturn are barely detectable very deep in the glow of sunrise. But they hide under a bright marker, Venus. On the morning April 12th they're 6½° under Venus as shown below. That morning Mercury and Saturn are a mere magnitude +1.0 and +1.2, respectively. Maybe try for them with a telescope if you have a very flat east horizon.

By the 19th Venus is a little higher. Saturn by then is 5½° below or lower right of it and still mag +1.2. Mercury by then has brightened to mag +0.5 but is no higher over the dawn horizon than it was a week before, which means it's now 9° under or lower left of Venus. Use the scenes below. Good luck.

Venus, magnitude –4.6. rises due east at the very beginning of dawn. For skywatchers at mid-northern latitudes, Venus will continue to rise right at the start of dawn for all the rest of April and May.

In a telescope as dawn grows bright, Venus is a shrinking but thickening crescent. It will fill out to become half lit around the end of May. How far into broad daylight can you follow Venus with your scope?

Mars (magnitude +0.7, at the Gemini-Cancer border) glows high in the southwest right after dark. It's still nearly in line with Pollux and Castor to its right, which are magnitudes +1.1 and +1.6, respectively. Mars draws a little farther away from them every day.

For telescope users Mars has shrunk to only 7 arcseconds in diameter. Good luck making out any surface markings aside from (maybe) the North Polar Cap. At least you can see that Mars is definitely gibbous, 90% sunlit. This is as gibbous as it's going to get this season.

Jupiter (magnitude –2.1, in Taurus) shines bright white in the west in early evening, 41° lower right of Mars along the ecliptic. Jupiter continues to form a nearly equilateral triangle with Taurus's two horntip stars, Beta and Zeta Tauri, above it.

Farther below Jupiter shines orange Aldebaran. Farther to Jupiter's lower right are the Pleiades. Jupiter sets in the west-northwest around midnight.

In a telescope Jupiter has shrunk to only 35 or 34 arcseconds wide, just about as small as it gets. For the daily doings of its Galilean moons see the April Sky & Telescope, page 51.

Uranus, magnitude 5.8, is sinking away in the western twilight.

Neptune is hidden in the glare of dawn behind Mercury and Saturn.

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 new 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 finicky 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