This Week’s Sky at a Glance

Some daily events in the changing sky for March 13 – 21.

Comet Lulin is fading this week; it should dim from about magnitude 6 to 7. But now it's free from moonlight again, and it's conveniently highest in early evening, in Gemini. See our article and finder chart.

Sirius is far and away the brightest star of Canis Major, the Big Dog, which fills the frame from top to bottom here.
Photo by Akira Fujii

Friday, March 13

  • This is the time of year when Sirius, the brightest star after the Sun, stands highest due south right at nightfall. Sirius forms the bottom corner of the big, equilateral Winter Triangle. The triangle's other two corners (far outside the photo here) are Betelgeuse to the upper right and Procyon to the upper left.

    Sirius is not only the brightest star after the Sun, but at a distance of 8.6 light-years, it's also the nearest star that's visible to the naked eye from mid-northern latitudes. Alpha Centauri is nearer, but you can't see it from these latitudes. A handful of red-dwarf stars are also nearer, but they're so dim you can't see them without optical aid.

  • Only 1 in 16 Friday-the-13ths follow right after a Friday-the-13th the previous month. O lucky day.

    Saturday, March 14

  • The early-evening sky is free of bright moonlight for the next two weeks — so this is a fine time to look for the zodiacal light as twilight fades away. You'll need a clean, unpolluted sky. The zodiacal light is a huge, narrow, pyramid of pearly glow extending up from the western horizon and tilting left, running along the constellations of the zodiac. What you're seeing is interplanetary dust in the plane of the solar system, lit by sunlight. At this time of year, the western-sky ecliptic after dusk — and therefore the zodiacal light — is tilted highest with respect to the horizon, for skywatchers in the northern latitudes.

    Sunday, March 15

  • Right as the stars come out at this time of year, the Big Dipper stands at the same height in the northeast as Cassiopeia does in the northwest. Both are standing on end.

    Monday, March 16

  • Comet Lulin, now faded to around 7th magnitude but in a moonless sky, is about 1° from Delta Geminorum this evening. See our article and finder chart.

    Tuesday, March 17

  • While you're tracking Comet Lulin near Delta Geminorum, use your scope to look in on the Eskimo Nebula and double stars (including Delta itself) right nearby! See Ken Hewitt-White's "Suburban Star-Hop" in the March Sky & Telescope, page 47.

  • The bright eclipsing variable star Algol, now sinking northwestward in the evening, should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 10:01 p.m. Pacific Daylight Time. Algol takes several additional hours to fade and to rebrighten. Use our comparison-star chart.

    Wednesday, March 18

  • Last-quarter Moon (exact at 1:47 p.m. EDT).

    Thursday, March 19

  • If you've got at least a 10-inch scope and a really dark sky, have you ever looked for the faint galaxies that are visible right through the Beehive Star Cluster in Cancer? See Sue French's "Deep-Sky Wonders" column in the March Sky & Telescope, page 63.

    As winter turns to spring, Orion's Belt turns horizontal as Orion sinks lower in the southwestern evening sky. S&T's Tony Flanders took this 15-second exposure with a Canon A80 point-and-shoot digital camera on March 21st two years ago.
    Tony Flanders

    Friday, March 20

  • At last! The equinox occurs at 7:44 a.m. EDT, marking the start of spring in the Northern Hemisphere (fall in the Southern Hemisphere). This is when the Sun crosses the equator heading north for the year. The Sun rises and sets nearly due east and west, and day and night are nearly equal in length.

    And no, eggs do not balance on end any more easily than at any other time (try it). Why should they? When will this goofy urban legend finally die?

  • Algol should be at minimum light for a couple hours centered on 9:50 p.m. EDT.

    Saturday, March 21

  • With the coming of spring, the winter constellation Orion is tilting over in the southwest on the way to its seasonal departure. Accordingly, Orion's Belt is tilting around to become more horizontal, as in the photo at right.


    Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,000 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — among the stars.
    Sky & Telescope
    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts; the standards are Sky Atlas 2000.0 or the smaller Pocket Sky Atlas) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the even more detailed Night Sky Observer's Guide by Kepple and Sanner, or the classic Burnham's Celestial Handbook). Read how to use them effectively.

    Can a computerized telescope take their place? 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, they note, "the sky never becomes a friendly place."

    More beginners' tips: "How to Start Right in Astronomy".


    This Week's Planet Roundup

    Mercury is disappearing into the sunrise.

    S&T Illustration

    Venus (magnitude –4.5, in Pisces) is still shines brilliantly in the west during evening twilight, but it's getting lower every day. And it's changing rapidly as it swings toward inferior conjunction between Earth and Sun. In a telescope Venus is an eerily thin crescent, waning from 7% sunlit on March 14th to just 3% on the 20th. And it's big: nearly an arcminute from cusp to cusp.

    There have been reports over the years of people with exceptionally sharp vision resolving the thin crescent of Venus with the naked eye. If you want to try, look right after sunset in a bright sky before the planet's glare becomes a problem. To reduce the effects of your eye's optical aberrations, try looking through a small, round hole 1 or 2 mm wide in a piece of aluminum foil or cardboard. Of course, this also reduces your eye's aperture and theoretical resolving power, so experiment with different-sized holes. Send me your results! Email amacrobert(AT) skyandtelescope(DOT)com, and put Venus Crescent in the subject line.

    Telescopically, Venus is best seen in the afternoon daylight; it's less glary against a bright sky, and it's higher in steadier air. Just don't let your telescope accidentally point at the Sun! Safest is to observe in the shade of a building located to your west.

    For more on Venus's especially favorable conjunction phenomena this year, see the March Sky & Telescope, page 58, or online.

    Daylight saving time makes it easier to get up in time to see dawn sky sights. On Sunday morning March 22nd, Jupiter shines left of the waning Moon. Although they look close together, Jupiter is actually 2,200 times farther away just now. And it's 40 times bigger!

    These scenes are always drawn for the middle of North America (to be exact, latitude 40° north, longitude 90° west). European observers: Move each Moon symbol a quarter of the way toward the one for the previous date. In the Far East, move it halfway.

    Alan MacRobert

    Mars (magnitude +1.2) is very low in the sunrise glow. Using binoculars, look for it just above the east-southeast horizon, well to the lower left of much brighter Jupiter, about 30 minutes before sunrise. Good luck.

    Ceres, the largest asteroid, is now magnitude 7.3 above the back of Leo. Spot it with binoculars using the article and finder chart in the March Sky & Telescope, page 60, or online.

    Jupiter (magnitude –2.0, in Capricornus this year) is getting a little higher in the dawn each week. Look for it very low in the east-southeast about an hour before sunrise.

    Saturn (magnitude +0.5, near the hind foot of Leo) is just past opposition. It glows low in the east at dusk, well up in the southeast by midevening, and highest in the south around midnight daylight saving time. Don't confuse Saturn with slightly fainter Regulus 18° (nearly two fist-widths at arm's length) to its upper right in early evening, and more directly to Saturn's right late at night.

    Saturn two days before opposition, imaged by Christopher Go of Cebu, Philippines, on March 6th. The images were taken 13 minutes apart; note the motions of Saturn's moons Dione (left) and Tethys (just below ring) during this time.

    Saturn's rings are 3½° from edge on. The rings will open to 4° by late May, then will close to exactly edge-on next September 4th — when, unfortunately, Saturn will be out of sight practically in conjunction with the Sun.

    P.S.: Remember the quadruple transit of Saturnian moons across the planet's face that made news on February 24th? Hubble was looking, and the Hubble Heritage Project has just released the images. Wow. These are not science-fiction space art, they are actual photographs.

    Here's a timetable (in Universal Time) of all of transits by Titan and/or its shadow for the rest of 2009.

    Uranus is hidden behind the glare of the Sun.

    Neptune is hidden deep in the glow of sunrise, far in the background of Jupiter and Mars.

    Pluto (in northwestern Sagittarius) is in the southeast before dawn.

    All descriptions that relate to your horizon or zenith — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (known as UT, UTC, or GMT) minus 4 hours.


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