This Week's Sky at a Glance, April 21 – 30

FRIDAY, APRIL 21

■ In twilight this evening, look for the thin crescent Moon far to the lower right of Venus as shown below. As the sky gets darker watch for Aldebaran to appear, and then, much fainter, the Pleiades.

SATURDAY, APRIL 22

■ Venus, the crescent Moon, and Aldebaran form a nearly isosceles triangle in the west as darkness falls, as shown above. The long sides of the triangle are both 8° long (for much of the Americas).

SUNDAY, APRIL 23

■ Now the thickening Moon shines over Venus during and after dusk, as shown above.

■ These spring evenings, the long, dim sea serpent Hydra snakes far across the southern sky. Find Hydra's head, a rather dim asterism about the width of your thumb at arm's length, high in the southwest. It's lower right of Regulus by about two fists at arm's length. Also, a line from Castor through Pollux points to it about 2½ fists away.

Hydra's tail stretches all the way to Libra, now rising low in the southeast. Hydra's star pattern, from forehead to tail-tip, is 95° long. Hydra is by far the longest constellation and is also the largest in area.

MONDAY, APRIL 24

■ After dark, look high in the west for Pollux and Castor lined up almost horizontally (depending on your latitude). Mars, looking similar, is a third dot down below them.

Pollux and Castor 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 Menkalinan (Beta Aurigae) and then brilliant Capella. Venus shines under its Arch's right side. The whole thing sinks in the west through the evening.

TUESDAY, APRIL 25

■ The thick waxing crescent Moon pairs with Mars in the center of Gemini this evening, as shown below.

WEDNESDAY, APRIL 26

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

Arcturus forms the pointy end of a long, narrow kite-skaped asterism formed by the brightest stars of Boötes, 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 fist-widths at arm's length.

■ Now turn northwest. The brightest star there is Capella, essentially the equal of Arcturus in brightness. They stand at exactly the same height above your horizon in late twilight, depending on your latitude.

■ And Vega, the Summer Star, the other zero-magnitude equal of Arcturus and Capella, 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.

THURSDAY, APRIL 27

■ First-quarter Moon (exact at 5:20 p.m. EDT), in dim Cancer. As the stars come out this evening, look for Regulus about two fists at arm's length to the Moon's left, and Pollux and Castor not quite as far to the Moon's right.

As the night grows later, this straight line of three tilts clockwise.

FRIDAY, APRIL 28

■ The Moon, a day past first quarter, shines high toward the south-southwest after dark. It's hanging off the crook of the Leo Sickle, which is nearly upright.

SATURDAY, APRIL 29

■ Now the Moon shines just behind (left of) the Sickle's handle. The Moon is roughly equidistant from Regulus and Algieba, the Sickle's two brightest stars.

SUNDAY, APRIL 30

■ 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.

 

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This Week's Planet Roundup

Mercury is lost in the sunset.

Venus (magnitude –4.1, in eastern Taurus) is the brilliant "Evening Star" in the west during and after dusk. It doesn't set until two hours after full dark. Night by night, watch as the horntip stars of Taurus slide down toward it. Venus will pass between them on Monday May 1st.

In a telescope Venus is a dazzling little gibbous globe (69% sunlit) 16 or 17 arcseconds in diameter. It's gradually enlarging while waning in phase. It'll be 50% lit by late May, and will be a bigger, dramatic crescent from mid-June through mid-July.

BTW, forget the Face on Mars. Now there's the Monkey on Venus. With 85,000 volcanos newly mapped on Venus, it had to happen. Wave hi to the monkey up there beyond the twilight.¹

Mars is crossing central Gemini this week. Look for it high in the west in early evening, lower later. It's upper left of Venus by about three fists at arm's length, and it's below Pollux and Castor.

Mars has faded to magnitude +1.3, the barest trace fainter than Pollux. Mars shows a slightly deeper orange tint. Mars is drawing closer to Pollux and Castor and will line up with them, to their left, on the evening of May 16th.

Because Mars is nearly on the far side of its orbit from us, in a telescope it's a tiny blob just 5½ arcseconds wide.

Jupiter is out of sight, very deep in the glow of sunrise.

Saturn (magnitude +1.0, in dim Aquarius) is low in the east-southeast in early dawn.

Faint Uranus and Neptune are out of sight, very low in the evening and morning twilight respectively.

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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 sometimes called 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 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. 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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1. Of course there's no monkey up there to say hi to, so don't write me about it! The Venus volcano photo is an example of pareidolia: the overinterpretation of a sensory input to create the actual experience of seeing, for instance, grotesque faces, figures, and animals in clouds or tree trunks. Or stick-figure people and animals in the stars. Although these things are not actually real, the experiences of them are entirely real. Endless confusion in the world arises from people not grasping how fully both types of experience, the factual and the creative, arise from our same neural process of reality-determination and consciousness formation. See the beholder's share in art theory (especially for how impressionism works). For the currently favored neural mechanism responsible for the formation of all conscious perceptions and ideas, real or hallucinated, see Bayesian brain. Recent developments; see the second section.

End of Philosophy 101. Go skywatch, and say hi to your pareidoliated monkey who isn't there but is.

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