Sky at a Glance | April 3rd, 2009

Some daily events in the changing sky for April 3 – 11.

Comet Yi-SWAN may not be much at magnitude 8½, but it's far north crossing the bright pattern of Cassiopeia this week. For now it's about equally high in the northwest just after dusk and in the northeast just before the first light of dawn. Choose your time to avoid moonlight if possible. (Full Moon is April 9th.) See our AstroAlert with positions for plotting on your star atlas.


James White/signalnoise.com / IAU / IYA

Friday, April 3

  • We're now in the worldwide 100 Hours of Astronomy, part of the UN's International Year of Astronomy 2009. Public star parties, lectures, webcasts, observatory tours, chances to run a telescope on the far side of the Earth from your computer — take a look around the website, and see the April Sky & Telescope, page 72.

  • Arcturus, the "Spring Star," sparkles brightly in the eastern sky these evenings. After about 9 or 10 p.m. look for Vega, the "Summer Star," rising low in the northeast. They're equal in brightness — but Vega, being lower, will be dimmed more by atmospheric extinction.

    Saturday, April 4

  • As part of the 100 Hours of Astronomy, Saturday evening brings the 24-hour Global Star Party as twilight sweeps around the world. At more than 1,000 public gatherings, people are invited to view the Moon, Saturn and its own moons, and other sights with a variety of telescopes. Use this Google map of events to zoom in and find the ones near you.

    The Moon is waxing gibbous as it passes Regulus and Saturn. The view is drawn for the middle of North America. 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.
    Sky & Telescope
  • The Moon after dusk forms a straight, diagonal line with Regulus and Saturn at its lower left, as shown at right.

    Sunday, April 5

  • Solar observing? Today is Sun Day in the 100 Hours of Astronomy. Here's a list of Sun Day events (choose your country from the drop-down list).

  • After the Sun goes down, Regulus sparkles above the Moon, as shown at right.

    Monday, April 6

  • The waxing gibbous Moon is 5° to 7° to the lower right of Saturn around dusk for North America, as shown here. It appears below Saturn later.

    Tuesday, April 7

  • Using binoculars, do you know where to spot the lonely star cluster M48 at the Monoceros-Hydra border? The two stars of Canis Minor point the way, and the odd little lineup of 1, C, and 2 Hydrae helps. See Gary Seronik's "Binocular Highlight" in the April Sky & Telescope, page 45.

    Wednesday, April 8

  • A small telescope will nearly always show Titan, Saturn's largest moon. Tonight and tomorrow Titan is about four ring-lengths to Saturn's east. A 6-inch telescope will begin to show the orange color of its smoggy atmosphere. A guide to identifying other Saturnian satellites that are sometimes visible in amateur scopes is in the April Sky & Telescope, page 56.

    Thursday, April 9

  • Full Moon (exact at 10:56 a.m. EDT). Above it shines Spica, almost lost in the lunar glare.

    Friday, April 10

  • When spring began, the Big Dipper stood upright high in the northeast balancing on the end of its handle after nightfall. 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?


    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 on March 16, 2009
    is visible [indistinctly] on the upper left. But its color is a paler than last year. Will it turn white this year? Who knows. . . ."

    South is up. "The [double] South Equatorial Belt and the North Equatorial Belt are the same dark red color. The mid-SEB section is very busy. The Equatorial Zone looks quiet with little festoon activity. The NEB is also devoid of activity. It is just dark red. The North Temperate Belt is distinct. The polar regions are dark."" credits="Christopher Go" width="" height="" align="right"]Mercury is emerging from the glow of sunset. By late this week, you should be able to spot it glimmering (at about magnitude –1.5) low above the western horizon 30 or 40 minutes after sunset.

    Venus (magnitude –4.2) is low in the dawn. Look for it above the eastern horizon about 20 or 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 slim crescent.

    Mars (magnitude +1.2) is both dim and very low in the sunrise glow. Using big binoculars, you can try looking for it well to the right of Venus about 30 minutes before sunrise. Good luck.

    Jupiter (magnitude –2.1, in Capricornus) shines low 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 in the southeast at dusk. It's highest in the south around 10 or 11 p.m. Look for Regulus 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 later at night.

    In a telescope, Saturn's rings are 3½° from edge on. The rings will open to a maximum of 4° in 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 (6th magnitude) is hidden low in the sunrise glow, in the background of Venus and Mars.

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

    Pluto (14th magnitude, in northwestern Sagittarius) is located in the 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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