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EI2GYB > ASTRO 01.03.23 09:36l 128 Lines 9044 Bytes #999 (0) @ WW
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Subj: This Week's Sky at a Glance, February 24 - March 5
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This Week's Sky at a Glance, February 24 - March 5
By: Alan MacRobert February 24, 2023
FRIDAY, FEBRUARY 24
Ý After dinnertime at this time of year, five carnivore constellations rise upright in a row from the northeast to south, as if out of hibernation. They're all seen in profile with their noses pointed up and their feet (if any) to the right. They are Ursa Major the Big Bear in the northeast (with the Big Dipper as its brightest part), Leo the Lion in the east, dim Hydra the Sea Serpent in the southeast, Canis Minor the Little Dog higher in the south-southeast, and bright Canis Major the Big Dog in the south.
SATURDAY, FEBRUARY 25
Ý It's not spring for another 3« weeks, but the Spring Star Arcturus seems eager to thrust itself into view. It rises above the east-northeast horizon around 9 or 10 p.m. now depending on your location.
To see where to watch for it to rise, find the Big Dipper as soon as the stars come out; it's high in the northeast. Follow the curve of its handle down and around to the lower right by a little more than a Dipper-length. That's the spot on the horizon to watch.
Atmospheric extinction keeps Arcturus rather dim when it rises. But soon it dominates the low eastern sky.
SUNDAY, FEBRUARY 26
Ý First-quarter Moon (exactly first quarter at 3:06 a.m. tonight EST). This evening the Moon shines between Aldebaran and the Pleiades, as shown below. Mars is off to the Moon's left.
MONDAY, FEBRUARY 27
Ý The Moon shines just a degree or two from Mars tonight, as shown above. Watch their separation change hour by hour. The Moon occults Mars for parts of the Arctic.
Ý Spot the big, bright, equilateral Winter Triangle in the south-southeast. Sirius is its brightest and lowest star. Betelgeuse is above Sirius by about two fists at arm's length. Left of them shines Procyon.
TUESDAY, FEBRUARY 28
Ý February has been Orion's month to stand at his highest in the south in early evening. Now the approach of March pushes Orion westward and brings his dog, Canis Major sporting Sirius on his chest, onto the meridian.
Sirius is not only the brightest star in our sky after the Sun, it's also the closest naked-eye star after the sun, at 8.6 light-years, for those of us at mid-northern latitudes. That makes Sirius the closest naked-eye object for us after Saturn (or yes, maybe Uranus if your sky is very dark).
Alpha Centauri is the actual closest star at 4.3 light-years, but you have to be farther south to see it. And in the northern sky three dim red dwarfs are closer than Sirius, but these require binoculars or a telescope.
Ý Want to try for Sirius B, the famous white dwarf? This year Sirius A and B are at their widest apparent separation in their 50-year orbit: 11.3 arcseconds apart. They will remain at essentially this separation for the next few years before they start closing up again. You'll want at least an 8- to 12-inch scope, a night of really, really excellent seeing (keep checking night after night), Sirius standing at its very highest near the meridian (in early evening now), and the Sirius-B hunting tips in Bob King's article Sirius B - A New Pup in My Life.
The Pup is east-northeast of the Dog Star and 10 magnitudes fainter: one ten-thousandth as bright. As Bob recommends, put a homemade occulting bar across your eyepiece's field stop: a tiny strip of aluminum foil held with a bit of tape, with one edge at the center of the field. Nudge the edge of the strip into sharp focus with a pencil point as you hold the eyepiece up to a light and look through it. In the telescope, rotate the eyepiece to hide blinding Sirius A just behind the strip's east-northeastern edge.
Even with an occulting bar, Sirius B has been undetectable in my 12.5-inch f/6 reflector on all but the very, very steadiest nights.
And the farther south you are the better, because Sirius will be higher when it's crossing the meridian. I'm in Massachusetts at 42ø north latitude, so. . . yeah.
Don't worry about moonlight; the glare of Sirius A is much more the problem.
WEDNESDAY, MARCH 1
Ý Venus and Jupiter reach conjunction. They shine in the west during and just after dusk, as shown below. Try taking pictures! Rest your camera on something solid to keep it still during time exposures.
Although they certainly look close together, Venus tonight is 11 light-minutes from Earth while Jupiter is 48 light-minutes away, more than four times farther.
HURSDAY, MARCH 2
Ý Now Jupiter and Venus have separated to shine 1ø apart at dusk.
Ý Then as night deepens, the Moon shines a couple degrees from Pollux. Castor looks on from nearby.
FRIDAY, MARCH 3
Ý Venus is above Jupiter at dusk, more or less as shown below. They're now 2ø apart.
SATURDAY, MARCH 4
Ý Looking on the other side of the sky to the east, the bright waxing gibbous Moon forms a tall isosceles triangle with Regulus and orange Gamma Leonis (Algieba), as shown below.
SUNDAY, MARCH 5
Ý Now the Moon, only a day and a half from full, shines between Regulus and Gamma Leonis. Moonlight too bright for them? Binoculars do the trick. The stars are about 4ø and 4«ø from the center of the Moon, respectively, less than the width of a typical binocular's field of view.
This Week's Planet Roundup
Mercury is hidden deep in the sunrise.
Venus and Jupiter, the two brightest planets, shine close together in the west-southwest at dusk, changing orientation every day. They're magnitudes -3.9 and -2.1, respectively, a five-times difference in brightness.
Jupiter starts the week on top. They pass each other at conjunction on March 1st, when they'll appear just half a degree apart (during twilight for the time zones in the Americas). Thereafter, Venus is the higher one.
Telescopically Venus is a shimmering little gibbous ball, 12 arcseconds in diameter and 86% sunlit. Jupiter is 34 arcseconds wide. That's small for Jupiter; it's nearly on the other side of the solar system from us.
In a telescope Jupiter displays a strikingly dimmer surface brightness than Venus - something you wouldn't guess looking with the unaided eye. It's because Jupiter is nearly 7 times farther from the illuminating Sun than Venus is. Jupiter partly makes up for this deficit by its disk currently showing us 5 times as much apparent surface area (number of square arcseconds) as Venus.
Mars, near the horns of Taurus, shines very high toward the southwest in late dusk, almost overhead. It moves lower toward the west as evening grows late. Mars continues to fade, from magnitude +0.3 to +0.4 this week, and it's now only 8 arcseconds wide. That's too small to show visual details in most telescopes most nights, aside from its gibbous shape (90% sunlit, see below) and maybe signs of the North Polar Cap.
Aldebaran shines some 12ø below Mars. At magnitude +0.8 it looks more like Mars all the time. They'll match brightnesses right at the turn of spring in about three weeks.
Saturn is buried deep in the sunrise.
Uranus, magnitude 5.8 in Aries, is still observable in the west right after dark. It displays a tiny, very slightly blue-greenish gray disk 3.6 arcseconds wide. It a telescope at high power it's definitely non-stellar. See the Uranus finder charts in the November Sky & Telescope, page 49.
Neptune is lost in the sunset.
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 Standard Time (EST) is Universal Time minus 5 hours. Universal Time is also called UT, UTC, GMT or Z time.
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