Sky at a Glance | April 24th, 2009

Some daily events in the changing sky for April 24 – May 2.

Comet Yi-SWAN isn't much at magnitude 8½, but it's nearly circumpolar — crossing northern Perseus. It's low in the northwest right after dark, and low in the northeast right before the first light of dawn. See our AstroAlert with the comet's positions for plotting on your star atlas.


Venus is only about 5° from faint Mars low in the eastern dawn. (The visibility of Mars in bright twilight is exaggerated here.)
Friday, April 24

  • As spring advances, bright Sirius is getting lower in the southwest at dusk. How late in the season can you keep it in sight? In other words, what will be Sirius's date of heliacal setting at your latitude? Start keeping watch now!

  • New Moon (exact at 11:23 p.m. EDT).

    Saturday, April 25

  • After sunset, an elusive, extremely thin young crescent Moon displays its early-springtime upright Cheshire Cat smile (as seen from mid-northern latitudes). Look for it just above the west-northwest horizon, to the lower right of Mercury. Bring binoculars.

    Will this sighting set your personal young-Moon record? The crescent will be only about 21 hours from new at viewing time from the East Coast of North America, and 24 hours from new as seen from the West Coast. Have you ever seen a crescent this young? (Calculate from the exact time of new Moon under Friday above.)

    Sunday, April 26

  • As twilight fades, look for the Pleiades glimmering between Mercury and the waxing crescent Moon, as shown at right. Think photo opportunity! The Moon has just finished occulting the Pleiades for skywatchers on the Atlantic Ocean.

    Monday, April 27

  • The red long-period variable stars T Hydrae and R Ophiuchi should be at their brightest (8th magnitude) around now.

    Tuesday, April 28

  • Mercury is less than 2° from the center of the Pleiades at dusk from this evening through Friday evening.

  • Saturn's big moon Titan casts its shadow onto Saturn's face tonight, starting at 11:22 p.m. Pacific Daylight Time, 12:22 a.m. Mountain Daylight Time, and 1:22 a.m. Central Daylight Time — when Saturn is still in good view for telescope users in those time zones (especially in the far west). The shadow transit lasts nearly 5 hours. See the article on these events in the April Sky & Telescope, page 55, or online.

    Venus on April 26, 2009
    Have you tried looking for Venus with your scope in broad daylight after sunrise? Sean Walker shot this stacked-video image of Venus at 10:04 a.m. Eastern Daylight Time on Sunday, April 26th. He used a 12.5-inch reflector, a DMK21AU04.AS camera, and a Baader 300–400nm ultraviolet filter. Venus's crescent was 21% illuminated at the time.
    S&T: Sean Walker
    Wednesday, April 29

  • The Moon shines in the middle of Gemini this evening: below Pollux and Castor, which are lined up almost horizontally.

    Thursday, April 30

  • Irene and Flora, two springtime asteroids, are just past opposition now. At 9th and 10th magnitude they await your telescope, and your chart-using skills, as they drift about 4° apart between the legs of Virgo. See the article and the 10th-magnitude chart in the May Sky & Telescope, page 46.

    Friday, May 1

  • First-quarter Moon (exact at 4:44 p.m. EDT).

  • Mayday is also known as Beltane, for the ancient Gaelic festival that gave rise to some of our May Day traditions. Beltane is one of the four cross-quarter days about midway between the equinoxes and solstices. In other words, this is the midpoint of spring (Northern Hemisphere spring).

    More or less. The actual midpoint between this year's March equinox and June solstice comes on May 5th, at 4:45 p.m. Eastern Daylight Time.

    The Moon shines under Regulus on May 2nd and Saturn on May 3rd. (These scenes are 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. For clarity, the Moon is shown three times actual size.)
    Saturday, May 2

  • The Moon shines about 3° below Regulus during evening for North America, as shown at right.

  • Venus in the morning sky is at its greatest illuminated extent: when its sunlit area appears to be largest as seen in a telescope (when it shows the most illuminated square arcseconds). This is about when Venus is at its greatest brilliancy.


    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).

    Sky Atlas 2000.0 (the color Deluxe Edition is shown here) plots 81,312 stars to magnitude 8.5. That includes most of the stars that you can see in a good finderscope, and typically one or two stars that will fall within a 50× telescope's field of view wherever you point. About 2,700 deep-sky objects to hunt are plotted among the stars.
    Alan MacRobert
    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 more detailed and descriptive 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? I don't think so — not for beginners, anyway, and especially not on mounts that are less than top-quality mechanically. 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

    Facing west-northwest 60 minutes after sunset
    By May 1st and 2nd, the Pleiades slide down to pose directly to Mercury's right. Don't confuse Mercury with Aldebaran, a little higher.
    Mercury, low in evening twilight, fades rapidly from about magnitude 0 to +1.5 this week. Look for it low in the west-northwest about an hour after sunset. As the sky gets darker, the Pleiades glimmer into view very near it. The Pleiades are above Mercury early in the week, and to the right of it by May 1st and 2nd, as shown here.

    Venus (magnitude –4.7) shines low in the east during dawn. Don't confuse it with Jupiter, higher and far to the right in the southeast. In a telescope, Venus is a thickening, shrinking crescent. The best telescopic views come in full early-morning daylight, when Venus is higher in steadier air.

    Mars (only magnitude +1.2) remains about 5° from Venus all week. It's below Venus early in the week, and lower left of it toward the week's end. Bring binoculars.

    Mars is beginning a long, slow apparition that will find it at opposition on January 29, 2010.

    Jupiter (magnitude –2.2, in Capricornus) shines in the southeast before and during dawn.

    Saturn (magnitude +0.7, in Leo) is high in the south during evening. Regulus, not quite as bright, sparkles 16° (roughly one and a half fist-widths at arm's length) more or less to Saturn's right.

    In a telescope, Saturn's rings appear 4° from edge on, their widest for the year.

    Uranus (6th magnitude) is hidden low in the sunrise glow, in the background of Venus — and 17,000 times fainter.

    Neptune (8th magnitude) is the background of Jupiter — and 11,000 times fainter.

    Pluto (14th magnitude, in northwestern Sagittarius) is highest in the south before the first light of dawn. It's 250 times fainter than Neptune.

    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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