This Week's Sky at a Glance, March 25 – April 2

FRIDAY, MARCH 25

■ The Big Dipper glitters softly high in the northeast these evenings, standing on its handle. You probably know that the two stars forming the front of the Dipper's bowl (currently on top) are the Pointers; they point to Polaris, which is currently to their left or lower left.

And, you may know that if you follow the curve of the Dipper's handle out and around by a little more than a Dipper length, you'll arc to Arcturus, now rising in the east.

But did you know that if you follow the Pointers backward the opposite way, you'll land in Leo?

Draw a line diagonally across the Dipper's bowl from where the handle is attached, continue far on, and you go to Gemini.

And look at the two stars forming the open top of the Dipper's bowl. Follow this line past the bowl's lip far across the sky, and you come to Capella.

SATURDAY, MARCH 26

■ Castor and Pollux in Gemini are still very high overhead these evenings, though trending toward the southwest. They're 4½° apart, roughly three finger-widths at arm's length.

Now that there's no moonlight, have you ever looked in on the Clown-Face Nebula, NGC 2392, in Gemini not very far from Castor and Pollux? It's a little disk of a planetary nebula, 9th magnitude and just 1 arcminute wide, which means it has enough surface brightness to show through light pollution better than most nebulae. It's pretty easy if you star-hop to exactly the right place. (Here's how, step by step.) The nebula's central star, magnitude 10.5, shows distinctly at high power. It's the clown's nose.

Read lots more, including other sights along the way and how to piece out more of the face, with Ken Hewitt-White's Suburban Stargazer column in the March Sky & Telescope, page 54.

■ In early dawn Sunday morning, the waning Moon shines in the southeast. Look left of it for the evolving triangle of Venus and fainter Saturn and Mars, as shown below.

SUNDAY, MARCH 27

■ Low in Monday's dawn the waning crescent Moon is below Venus, Mars, and Saturn, which now form an isosceles (two sides equal) triangle as shown above.

MONDAY, MARCH 28

■ This is the time of year when Orion declines in the southwest after dark, with his Belt roughly horizontal. But when does Orion's Belt appear exactly horizontal? That depends on where you're located. Seen from most mid-northern latitudes it should be close to the end of twilight.

TUESDAY, MARCH 29

■ After dark, Sirius shines brilliantly in the south-southwest. Lower left of Sirius, by about one fist, is the triangle of (from right to left) Adhara, Wezen, and Aludra. They form Canis Major's hind foot, rear end, and tail, respectively. Or, alternatively, the lower end and handle of the Meat Cleaver.

A few degrees upper left of this triangle are the three uppermost stars of the constellation Puppis, 3rd and 4th magnitude. They form a gently curving arc 7° long, from lower right to upper left. "Puppis" is not a puppy as some guess, although it follows right behind the Big Dog across the sky. It's the Poop Deck (stern) of the giant ancient constellation Argo Navis, the ship of Jason and the Argonauts. These three stars are the only pieces of Argo that are readily visible naked-eye to mid-northern skywatchers.

Just 1.5° upper right of the middle star of the three, binoculars on a dark night will show the 6th-magnitude open cluster M93. It's quite small and elongated northeast-southwest.

■ Algol, heading down toward the northwest these evenings, should be at its mid-eclipse brightness (magnitude 3.4 instead of its usual 2.1) for a couple hours centered on 8:41 p.m. EDT: best for the Eastern time zone. Any random time you glance up at Algol, you have a 1 in 30 chance of catching it at least a magnitude fainter than normal.

WEDNESDAY, MARCH 30

■ The signature fall-and-winter constellation Cassiopeia retreats down after dark. Look for it in the north-northwest. It's standing roughly on end.

But for skywatchers at mid-northern latitudes Cassiopeia is circumpolar, never going away completely. By 1 or 2 a.m. daylight-saving time it's at its lowest due north, lying not quite horizontally.

■ Low in Thursday's dawn, Venus, Mars and Saturn form yet another nearly isosceles triangle, their third in just a week! This time the triangle is very flat, with Venus as its left corner.

THURSDAY, MARCH 31

■ The huge, bright Winter Hexagon is still in view early after dark, filling the sky to the southwest and west. It's the biggest well-known asterism in the sky.

Start with brilliant Sirius in the southwest, the Hexagon's lower left corner. High above Sirius is Procyon. From there look higher upper right for Pollux and Castor (lined up nearly horizontal), lower right from Castor to Menkalinan and then bright Capella, lower left from there to Aldebaran, lower left from there to Rigel at the bottom of Orion, and back to Sirius.

The Hexagon is somewhat distended. But if you draw a line through its middle from Sirius to Capella, the "Hexagon" is fairly symmetric with respect to that long axis.

FRIDAY, APRIL 1

■ This is the time of year when the dim Little Dipper juts to the right from Polaris (the Little Dipper's handle-end) during late evening. The much brighter Big Dipper curls over high above it, "dumping water" into it. They do the reverse water dump in the fall.

■ New Moon (exact at 2:24 a.m. EDT on this date).

SATURDAY, APRIL 2

■ Castor and Pollux shine together very high to the southwest after dark, far above Orion. Pollux is slightly the brighter of these "twins."

Draw a line from Castor through Pollux, follow it farther out by a big 26° (about 2½ fist-widths at arm's length), and you're at the dim head of Hydra, the Sea Serpent. In a dark sky it's a subtle but distinctive star grouping, about the width of your thumb at arm's length. Binoculars show it easily through light pollution or moonlight, though it slightly overspills some binoculars' field of view.

Continue the line farther by about a fist and a half and you hit Alphard, Hydra's 2nd-magnitude orange heart.

Another way to find the head of Hydra: It's almost midway from Procyon to Regulus.

 

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This Week's Planet Roundup

Mercury, Jupiter, and Neptune remain out of sight in the glare of the Sun.

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

Mars, vastly fainter at magnitude +1.1, glimmers 5° to 7° to Venus's right.

Saturn, Marslike at magnitude +0.9, glows below Venus early in the week, and right of it by week's end.

These three planets form three different isosceles triangles (triangles with two equal sides) in the span of just a week: On the mornings of March 24th, 28th, and 31st.

In a telescope, Venus appears just about at dichotomy: half-lit. The March Sky & Telescope, page 50, discusses the non-obvious conundrum of Venus's slightly mistimed dichotomies, which puzzled astronomers starting in 1793. You'll have your crispest telescopic views of Venus when it's high in thinner air: in a blue daylight sky even long after sunrise.

Mars in a telescope is a hopeless little fuzzdot 5 arcseconds across. But expect a good Mars opposition next December — when it will be 17 arcseconds wide very high in the midnight sky, not far from overhead.

Saturn too is badly blurred by the poor seeing so low. But look forward to its opposition time in August and September. Saturn is entering the season in its 30-year "year" when massive white spots — gigantic, continent-size thunderhead clouds — sometimes well upward into view from the deeper, hidden atmospheric layers below. See Bob King's Will Saturn Sprout Spots This Observing Season?

Uranus (magnitude 5.8, in Aries) is very low in the west right after dark.

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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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