Sky at a Glance | February 20th, 2009

Some daily events in the changing sky for February 20 – 28.

Comet Lulin on Feb. 20, 2009
"The Sword Comet — I have named it so!" writes Paolo Candy of the Cimini Astronomical Observatory and Planetarium in Italy. On the morning of February 20th, when Candy took this picture, the dust antitail (left) had grown in prominence to quite outdo the gas tail (right), which points away from the Sun. Candy used a 10-inch f/3 Baker-Schmidt Zen astrograph, and an SBIG STL 6303E camera, for L, R, G, and B exposures 3, 1, 1, and 2 minutes long, respectively. Click image for larger view.
Comet Lulin this week is at its brightest and closest to Earth — right when the sky is conveniently moonless. Use binoculars or a telescope to look for it once it's well up in late evening. The comet is glowing at about magnitude 5.6 as it moves rapidly westward across Virgo.

In recent days the comet's dust-spike antitail has grown longer and stronger, completely outclassing its "true" tail, which points properly away from the Sun like a comet's tail should.

On Monday night, February 23rd, the comet passes 2° south-southwest of Saturn.

Lulin’s closest approach to Earth, 0.41 a.u. (61 million km), occurs on February 24th.

On the night of February 25th the comet goes through opposition, nearly 180° from the Sun in our sky. Will there be an "opposition effect" brightening of its dusty coma and dust tail?

Full story and finder charts!


Friday, February 20

  • This is the time of year when Orion stands at his highest due south after dinnertime, around 7 or 8 p.m. So this is when your scope may do its best in revealing detail in the Great Orion Nebula — and in particular, if the seeing is very steady, the difficult fifth and sixth stars (stars "E" and "F") of the Trapezium multiple star in the nebula's heart. See photo and chart; scroll down.

    The waning crescent Moon joins the dawn challenge sightings on Saturday and Sunday mornings, Feb. 21 and 22. It will almost certainly be too low by the 23rd. (The Moon's positions are for North America.)
    Saturday, February 21

  • Get yourself up and out as dawn brightens early Sunday morning, look with binoculars low above the east-southeast horizon, and see if you can spot the lineup of the Moon, Mercury, Jupiter, and faint Mars as shown at right.

  • There's more. Can your telescope show Jupiter's moons through this much skyglow? It'll be a challenge. But if you can, writes David Likuski, "at approximately 6:30 a.m. Mountain Standard Time [the center of] Jupiter passes only half an arcminute from the star 19 Capricorni, magnitude 5.7." This means Jupiter's limb passes less than half a Jupiter-diameter from the star. "Also, about half an hour earlier, likely viewed most easily from locations in mid-western Mexico, the star forms an isosceles right triangle with two of Jupiter's moons: Io and Callisto, with the latter as the apex. Coincidentally, the triangle's [outer] corners are exactly the same magnitude!"

    Good luck on this one. To catch these events at their peaks you'll have to be located where Jupiter isn't too low but morning twilight isn't yet too bright. Elsewhere in the Americas, however, you can still try for them off-peak. The farther south you are the better.

    Sunday, February 22

  • As soon as the stars come out, look to the right of Venus for the Great Square of Pegasus. It's balanced on one corner. Depending on the latitude where you're observing from, the Great Square's left corner may be exactly horizontal with Venus.

    High above Venus is the little constellation Aries.

    Can you catch the Jupiter-Mercury conjunction before sunrise with your unaided eyes? In these diagrams, brightnesses are always exaggerated for objects when they're seen in bright twilight.
    Monday, February 23

  • Look low in the pre-sunrise glow on Tuesday morning for Jupiter and Mercury, which have now moved into conjunction, as shown at right. Tuesday is also the morning when they form their tightest trio with little Mars.

    Tuesday, February 24

  • New Moon (exact at 8:35 p.m. EST).

  • Quadruple transit of Saturn's Moons. "Titan, Mimas, Dione, and Enceladus will pass directly in front of Saturn and we'll see their silhouettes crossing Saturn's cloudtops — all four at the same time," says Keith Noll of the Space Telescope Science Institute in a NASA feature article. The Hubble Space Telescope will be watching this one — and some amateur astronomers will be able to watch too, though only big Titan and its shadow may be visible from the ground. The timing favors observers along the Pacific coast of North America, Alaska, Hawaii, Australia, and east Asia.

    Here's the NASA article, and here's its beautiful high-speed animation of the whole thing. (The animation gives times on the 24th in Universal Time.)

    Wednesday, February 25

  • The asteroid 1 Ceres is at its closest and best opposition of our lifetimes! All week it's an easy catch in binoculars at magnitude 6.9. See the article and finder chart in the March Sky & Telescope, page 60, or online.

  • The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 10:16 p.m. EST. Algol takes several additional hours to fade and to rebrighten. Use our comparison-star chart.

    Don't miss the final Moon-Venus conjunction of this season's cycle. They'll be a real eye-catcher at dusk on Friday the 27th, at least if you're in the longitudes of the Americas.


    These scenes are always drawn for the roughly middle of North America (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 the Moons halfway. The blue 10° scale is about the size of your fist held at arm's length. For clarity, the Moon is shown three times actual size.

    Thursday, February 26

  • The thin crescent Moon hangs far below Venus at dusk, as shown at right. Get ready for tomorrow!

    Friday, February 27

  • Bright Venus and the crescent Moon pair up gorgeously in the western sky during and after twilight, as shown at right. Think photo opportunity! In various mythologies both are symbols of fertility and growth, so you can look upon their cozy pairing as a harbinger of next month's arrival of spring.

    Even in broad daylight this afternoon, the Moon provides an easy landmark for spotting Venus through the bright blue sky. They're only 2° apart in late afternoon as seen from North America, with Venus to the Moon's upper right; see the illustration in the February Sky & Telescope, page 47.

  • Uranus is at aphelion today, its farthest from the Sun in its 84-year orbit. For the rest of your life, Uranus will appear just a trace closer every year.

    Saturday, February 28

  • Now the waxing crescent Moon is high above Venus at dusk, leaving it behind as the Moon moves along its monthly orbit around the Earth.

  • Algol should be at minimum light for a couple hours centered on 7:05 p.m. EST.

  • Before sunrise Sunday and Monday mornings, Mercury has dropped to within 1° of faint Mars very low in the east-southeast.


    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).

    Pocket Sky Atlas
    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

    Jupiter, Mercury, and Mars (magnitudes –2.0, –0.1, and +1.2, respectively) remain very low in the glow of sunrise, where they're changing configuration daily. See the sky scenes above. Mars is very faint and may require binoculars.

    The thin waning crescent Moon joins them on Sunday morning the 22nd. Then on Tuesday morning the 24th, Jupiter and less-bright Mercury have a conjunction just 0.7° apart.

    Bring binoculars, and look just above the east-southeast horizon about 30 minutes before sunup. Find your local sunrise time by making sure you've put your location into our online almanac, and make sure the Daylight Saving Time box is unchecked.

    Venus (magnitude –4.8, in central Pisces) is the dazzling "Evening Star" high in the west during and after twilight. It's still at its peak brightness, nor does it set until about 9 p.m. In a telescope Venus is a rapidly waning crescent (about 24% sunlit) some 42 arcseconds from cusp to cusp. Telescopically, Venus is best seen in bright twilight or even broad daylight; it's less glary against a bright sky, and it's higher.

    Ceres resolved with an 11-inch scope!
    Ceres was 11 days from opposition, and 0.83 arcseconds wide, when John Sussenbach of Houten, Netherlands, resolved its disk by video imaging Feb. 14, 2009. At right is a star's diffraction pattern imaged for comparison. He used a Celestron 11-inch Schmidt-Cassegrain scope with a 3× Barlow, a DMK2AF4.AS video camera, and RGB filters. In each color he took 980 frames and used Registax 4.0 to select and stack the best 500 from each. Click image for more.
    Ceres (magnitude 6.9, in Leo), is having its best apparition of our lifetimes! This "dwarf planet," the largest of the main-belt asteroids, is at opposition on February 25th. See the article and finder chart in the March Sky & Telescope, page 60, or online.

    Ceres, with a diameter of 950 kilometers (590 miles), is estimated to contain a third of the mass of the asteroid belt — even though the main belt is believed to contain a million objects larger than 1 kilometer across.

    Saturn (magnitude +0.6, near the hind foot of Leo) rises in twilight, shines well up in the east by 9 or 10, and is highest in the south around midnight or 1 a.m. Don't confuse Saturn with similarly-bright Regulus 20° (two fist-widths at arm's length) to its upper right after they rise, and more directly to its right after midnight.

    Titan was leaving Saturn's face when Christopher Go in the Philippines took these images 10 and 12 minutes apart starting at 18:00 UT February 8th. As you can see, Titan's murky orange atmosphere is darker than Saturn's bright cloudtops. (The dark ring around Titan in the first frame is an image-processing artifact.) North is up. Click image to see an animation.


    P.S.: Here are the times and dates (in UT) of all of Titan's transits, and transits of its shadow, across Saturn in 2009.

    This week Saturn's rings are 2° from edge on. The rings will gradually 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.

    Uranus and Neptune are lost behind the glow of the Sun.

    Pluto is low 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 Standard Time (EST) equals Universal Time (known as UT, UTC, or GMT) minus 5 hours.


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