Sky at a Glance | April 10th, 2009

Some daily events in the changing sky for April 10 – 18.

Forgotten but not gone? Comet Lulin remains within telescopic reach at 9th magnitude, in the feet of Gemini in the western sky just after dark. The window of moonless early evenings begins opening around Saturday April 11th. Use our chart. Good luck.

The Comet Yi-SWAN challenge. It isn't much at magnitude 8½, but this new comet is far north crossing the bright pattern of Cassiopeia this week. It's getting quite low in the northwest just after dusk — lower than it is in the northeast just before the first light of dawn. However, the Moon was full on Thursday the 9th, so the only moonless time to look for the comet this week will be right after dusk, starting about April 11th. Next week will be better, with the comet higher before dawn (but no brighter). See our AstroAlert with the comet's positions for plotting on your star atlas. Again, good luck.


Use binoculars to try for Mars.
By April 13th, Venus is getting to be distinctly higher than challenging little Mars deep in the dawn. (The scene is drawn for latitude 40° north. The brightnesses of objects are exaggerated in twilight this close to sunrise or sunset.)

Friday, April 10

  • When spring began, the Big Dipper stood upright high in the northeast after nightfall balancing on the end of its handle. Now it's April, so the Dipper is tipping leftward. Its top two stars, forming the front of its bowl, point lower left toward rather dim Polaris, the North Star, three fist-widths at arm's length away.

    Saturday, April 11

  • Sometime around 10 p.m. daylight saving time, bright Arcturus shines at exactly the same height in the east as bright Capella shines in the northwest. The time of this balancing act depends on your location, especially on how far east or west you are in your time zone. How accurately can you determine when it happens at your site?

    Sunday, April 12

  • Before dawn Monday morning, the waning gibbous Moon shines very close to Antares as seen from North America. The Moon occults (covers) Antares for Hawaii and some other Pacific islands; also parts of Mexico and New Mexico during daytime Monday morning. Timetable.

  • Saturn's big moon Titan casts its black shadow onto Saturn's globe from 7:22 to 11:51 Universal Time on the 13th; that's 12:22 to 4:51 a.m. tonight Pacific Daylight Time. Saturn will still be up in good view at the beginning of that time for western North America.

    For a list of all of Titan's eclipses, transits, and shadow-castings on Saturn for the next couple months, see the April Sky & Telescope, page 55, or the version online.

    Monday, April 13

  • As spring advances, Orion and its companions sink lower after dusk. Look for Orion in the southwest this week with his Belt almost horizontal. Left of Orion shines bright Sirius. A little farther to Orion's right is orange Aldebaran, with the Pleiades farther beyond.

    Tuesday, April 14

  • From winter to spring: As night falls, the winter star Sirius is lowering in the southwest while the spring star Arcturus is rising in the east. They'll be at the same altitude above your horizon around 8 or 9 p.m. daylight saving time, depending on where you live in your time zone.

    Wednesday, April 15

  • For most of our readers, Arcturus in the east shines higher at nightfall than Spica, which is off to its right in the southeast. However, if you live as far south as Miami (or Honolulu, Taipei, Calcutta, Doha, or Luxor), this isn't so; Arcturus and Spica are about equally high at nightfall.

    Thursday, April 16

  • Titan orbits Saturn every 16 days. So now, about four days after it passed nearly in front of Saturn and cast its shadow onto the planet, you'll find Titan is at its western elongation, about four ring-lengths to Saturn's west.

    Friday, April 17

  • Last-quarter Moon (exact at 9:36 a.m. Eastern Daylight Time).

  • Venus is passing 6° north (upper left) of Mars, low in the east before Saturday's sunrise.

    Saturday, April 18

  • During dawn Sunday morning, the waning crescent Moon hangs only 1° to 3° from Jupiter (at the time of dawn for North America).


    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

    Note the brand-new white outbreak, still pointlike, in Jupiter's dark North Equatorial Belt (NEB) just below center. South is up in this Christopher Go image taken on April 11th. The North Equatorial Belt remains dark reddish, but the outbreak is beginning to spread white material left and right along the belt's middle. South Equatorial Belt is wider and double, with busy turbulence all along its middle. The central-meridian longitude was 238° (System II) ,and the NEB outbreak had not quite reached the central meridian.
    Mercury (about magnitude –1) has its best evening apparition of the year this week and next. Look for it low in the west about 40 minutes after sunset. It gets higher later in the week.

    Venus (magnitude –4.5) is low in the dawn. Look for it above the eastern horizon about 60 to 30 minutes before sunrise. Don't confuse it with Jupiter, higher and far to the right in the southeast. (You can find your local sunrise time from our online almanac. If you're on daylight saving time like most of North America, make sure the Daylight Saving Time box is checked.)

    In a telescope, Venus is a thickening and shrinking crescent. The best telescopic views come in full morning daylight, with Venus higher in steadier air.

    Mars (magnitude +1.2) is very low in the sunrise glow, to the lower right of Venus. Use big binoculars. Good luck.

    Jupiter (magnitude –2.1, in Capricornus) shines in the southeast during early dawn.

    On March 25th, Christopher Go imaged Saturn and three of its moons during excellent seeing. Dione and Tethys are on the left, and fast-moving little Enceladus is just above the rings' tip on the right. North is up, and celestial east is left.


    Go writes, "The band details are again excellent in this image. The South Equatorial Belt is well resolved. The North Equatorial Belt is still rather dull. There is a lot of banding in the South Polar Region."

    Christopher Go
    Saturn (magnitude +0.6, near the hind foot of Leo) shines high in the southeast at dusk and highest in the south around 9 or 10 p.m. Regulus, a little less bright, sparkles 16° (roughly one and a half fist-widths at arm's length) to Saturn's upper right in early evening, and more directly to its right in late evening.

    In a telescope, Saturn's rings are 4° from edge on. They'll close to exactly edge-on next September 4th, when, unfortunately, Saturn will be out of sight practically in conjunction with the Sun.

    Uranus (6th magnitude) is hidden low in the sunrise glow, in the background of Venus and Mars.

    Neptune (8th magnitude) is also in the glow of dawn, in the background of Jupiter.

    Pluto (14th magnitude, in northwestern Sagittarius) is in the south-southeast before the first light of 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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