Sky at a Glance | April 23rd, 2010

Some daily events in the changing sky for April 23 – May 1.

Venus and stars at dusk
Watch Venus pass between the Pleiades and the Hyades this week.

Friday, April 23

  • Low in the western sky at nightfall, look for the Pleiades to the upper right of bright Venus. They fit together in a 5° binocular field of view this evening through Sunday evening.

    Saturday, April 24

  • The "star" to the upper left of the Moon this evening is Saturn.

    Sunday, April 25

  • Saturn is above the Moon this evening.

    Monday, April 26

  • The star left of the Moon this evening is Spica. To the right of the Moon is the constellation Corvus. Above them is Saturn.

  • A small telescope will always show Titan, Saturn's largest moon. Tonight and tomorrow you'll find Titan four ring-lengths to Saturn's east.

    Tuesday, April 27

  • Full Moon tonight (exact at 8:18 a.m. EDT Wednesday morning).

    Wednesday, April 28

  • This week the Big Dipper floats upside down very high in the north after dark. Its Pointer stars, the two forming the end of the Dipper's bowl, point exactly straight down toward Polaris soon after nightfall.

    Thursday, April 29

  • The Moon is up in the southeast after 11 or so, depending on where you live in your time zone. Look lower left of the Moon for orange Antares on the rise. By dawn on the 30th they've moved over to the southwest, as shown below, with Antares now to the Moon's left.

    Moon crossing Scorpius as dawn begins
    If you're up when dawn is just beginning, the Moon lights the way to an early preview of the summer constellation Scorpius.

    Friday, April 30

  • The Moon is up above the southeast horizon by 11 or midnight tonight. Look for Antares and other stars of Scorpius to its upper right.

    Saturday, May 1

  • In late twilight, use binoculars to spot the 4th-magnitude star Kappa1 Tauri about ¼° lower left of dazzling Venus (at the time of twilight for North America). And look even closer to the lower left of Kappa1 for 5th-magnitude Kappa2.

  • Amateur observers usually assume that even the brightest galaxies of the Virgo Cluster are beyond the reach of binoculars. But are you sure? If you have a good dark sky and at least 50mm binos, pick a moonless night (like this evening) and give it a try using Gary Seronik's Binocular Highlight map and column in the May Sky & Telescope, page 45.

    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.

    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

    For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    Once you get a telescope, to put it to good use you must have a detailed, large-scale sky atlas (set of charts). The standards are the Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger and deeper Uranometria 2000.0 (stars to magnitude 9.75). And read how to use your charts effectively.

    You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner or the classic if dated Burnham's Celestial Handbook.

    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."

    This Week's Planet Roundup

    Mars on April 17, 2010
    Mars's north polar cap (bottom) is shrinking fast now in the late spring of the Martian northern hemisphere. Note the dark division that has appeared in the cap. Dark Syrtis Major is near the left limb, Sinus Sabaeus stretches above center, and three-pronged Sinus Meridiani is upper right of center.

    Gibbous Mars was only 8.0 arcseconds in diameter when Damian Peach in England took this extraordinary image on April 17th, using a 14-inch Schmidt-Cassegrain scope and a SKYnyx 2-0 video camera. Stacked-video images like this usually show much more detail than the eye can see even in the same telescope.

    Mercury is lost in the glare of the Sun.

    Venus (magnitude –3.9, in Taurus) shines brightly in the west-northwest during twilight. The Pleiades glimmer into view near it as the sky darkens. Venus is creeping a little higher each week; the Pleiades are sinking lower, passing to the planet's right. Also, look for orange Aldebaran to Venus's left or upper left.

    Mars, dimming farther into the distance at magnitude +0.6 now, is high in the southwest during evening. It's in Cancer east of the Beehive Star Cluster (use binoculars). In a telescope Mars is gibbous and shrinking: from 7.6 to 7.2 arcseconds in diameter this week. Can you still see its north polar cap? The cap is dwindling rapidly now in the late spring of Mars's northern hemisphere.

    One-belted Jupiter on April 12, 2010
    Jupiter's South Equatorial Belt had practically disappeared by the time Jupiter sank into the sunset last February, and it's still gone now that Jupiter is reappearing in the dawn. In a small telescope, Jupiter is one-belted! John Wesley in Australia took this image on April 12th at 19:50 UT, when the central-meridian longitude was 120° (System II). South is up.

    Jupiter (magnitude –2.1) is low in the dawn. Look for it above the eastern horizon about 60 to 45 minutes before your local sunrise time. Nothing else there is nearly so bright.

    Saturn (magnitude +0.7, in the head of Virgo) is high in the south during evening. In a telescope Saturn's rings are tilted only 2.1° from edge-on, practically at the minimum inclination of 1.7° that they'll display from mid-May through early June. Note the fine black shadow-line they cast on Saturn's disk. Now is also a fine time to try for the more difficult of Saturn's moons with your telescope; see the May Sky & Telescope, page 61.

    Uranus and Neptune are still in the glow of sunrise. Wait another few weeks.

    Neptune, however, is passing a historic milestone this month. For the first time since it was discovered in 1846, Neptune has completed a full circuit of the sky and has returned very close to the point (near the Aquarius-Capricornus border) where Johann Galle first spotted it from Berlin Observatory on September 23rd of that year — following a prediction by Urbain Le Verrier in France that a new planet should be there, based on gravitational perturbations of Uranus. See The Return of Neptune.

    The Saturn Electrostatic Disturbance (SED) white spot was visible when Christopher Go took this image on April 11th (at 13:50 UT; the spot is near System III longitude 15°), but by the 19th it had faded again. South is up. The satellite at right is Tethys.

    Note the dark reddish South Equatorial Belt, the bright Equatorial Zone, and the thin black line of the rings' shadow on the globe. The rings were tilted 2.5° to Earth's line of sight but 3.7° to the incoming sunlight. This disparity is what allows us to see the rings' shadow on the globe. This situation began in mid-March and will increase slightly in the next few weeks, making the shadow-line a little wider and more prominent.

    Pluto (magnitude 14, in northwestern Sagittarius) is highest in the south 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 (also known as UT, UTC, or GMT) minus 4 hours.

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