This Week's Sky at a Glance, April 19 – 28

Periodic Comet Pons-Brooks is sinking down and away during evening twilight for observers at mid-northern latitudes, though it should still be near its peak magnitude of about 4.2. Southern Hemisphere observers can catch it low at nightfall.

Supernova in NGC 3621 in Hydra. Discovered on the rise April 11th, SN 2024ggi was about magnitude 12.0 as of April 18th and had been holding there for five days. It's rather far south at declination –33°. For info and finder charts see Bob King's Jupiter meets Uranus in twilight; Supernova erupts in nearby galaxy. Here's the AAVSO's table of recent observations.

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FRIDAY, APRIL 19

■ Bright Arcturus is climbing high in the east these evenings. Equally bright Capella is descending high in the northwest. They stand at exactly the same height above your horizon some time right around the end of twilight, depending on your latitude.

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

■ Uranus is in close conjunction with Jupiter for the next few days. Use optical aid to try catching them very low near the end of twilight; see Uranus in This Week's Planet Roundup below.

SATURDAY, APRIL 20

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

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

SUNDAY, APRIL 21

■ As night descends, look high in the west for Pollux and Castor lined up almost horizontally (depending on your latitude). These two stars, the heads of the Gemini twins, form the top of the enormous Arch of Spring. To their lower left is Procyon, the left end of the Arch. Farther to their lower right is the other end, formed by 2nd-magnitude Menkalinan (Beta Aurigae) and then brilliant Capella.

The whole thing sinks in the west through the evening. It's the last part of the even larger Winter Hexagon to depart.

MONDAY, APRIL 22

■ This evening the Moon, just a day from full, passes 1° or less from Spica for North American skywatchers. Cover the Moon with your fingertip to block its glare. The time of their closest approach, and their separation then, will depend on your location.

TUESDAY, APRIL 23

■ Full Moon (exact at 7:49 p.m. EDT). Now it shines about 12° below Spica as shown above. Three times as far upper left of the Moon is brighter Arcturus.

WEDNESDAY, APRIL 24

■ The brightest star sparkling low in the southwest as twilight fades is Sirius, the Dog Star. Two fists above it is Procyon, the Little Dog Star. To their right is orange Betelgeuse, the uppermost shoulder of sinking Orion. The three form the equilateral Winter Triangle.

A little less far to the lower right of Betelgeuse, look for orange Aldebaran, the lurking eye of sinking Taurus.

THURSDAY, APRIL 25

■ Right after dark, the Sickle of Leo stands upright high in the south. Its bottom star is Regulus, the brightest of Leo. Leo himself is walking 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.

FRIDAY, APRIL 26

■ Face north just after nightfall, look very high, and you'll find the Pointers, the end stars of the Big Dipper's bowl, on the meridian pointing toward Polaris straight down below. From the Pointers to Polaris is about three fists at arm's length.

SATURDAY, APRIL 27

■ Vega, the Summer Star, the zero-magnitude equal of Arcturus, now twinkles 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.

SUNDAY, APRIL 28

■ These spring evenings, the long, dim sea serpent Hydra snakes almost level far across the southern sky. Find his head, a rather dim asterism about the width of your thumb at arm's length, in the southwest. It's almost halfway from Procyon to Regulus. Left or lower left of Hydra's head, by about a fist and a half, is orange, 2nd-magnitude Alphard, Hydra's lonely heart.

Hydra's dim, irregular body and tail stretch all the way to Libra just risen in the southeast. He carries Crater and Corvus on his back.

Hydra's star pattern, from forehead to tail-tip, is 95° long. That's more than a quarter of the way around the celestial sphere. No other constellation does that. Even the star pattern of the river Eridanus is only 66° from end to end.

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This Week's Planet Roundup

Mercury, Venus, and Neptune are hidden in the glare of sunrise.

Mars and Saturn, both about magnitude +1.2, rise around the beginning of dawn. Look for them low above the east-southeast horizon about 45 minutes before sunrise, as shown near the top of this page. Saturn is the easier one, on the upper right. They widen from 6½° apart on the morning of April 20th to 11° on the 27th.

Jupiter, magnitude –2.1 in Aries, is the bright "star" sinking low in the west-southwest in twilight. It sets before twilight ends.

Uranus, magnitude 5.8, hides close to Jupiter. Low altitude and twilight make it a hard catch! It passes through conjunction with Jupiter, ½° to Jupiter's upper right or right, on the 19th through 21st. For easy finder charts relative to Jupiter through the 21st, see Bob King's Jupiter meets Uranus in twilight; Supernova erupts in nearby galaxy.

In a telescope, Uranus's usual giveaway is that it's slightly nonstellar at high power (it's 3.4 arcseconds wide). But the atmospheric seeing at such a low altitude will be awful. Faint stars will appear nearly that big.

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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. UT is also known as 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 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.

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), which shows all 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 mag 9.75). 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.

Can computerized telescopes replace charts? Not for beginners I don't think, especially not 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 the sky. 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."

If you do get a computerized scope, make sure the 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. Learn the tricks at How to Use a Star Chart with a Telescope. 

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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 naked-eye 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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