Sky at a Glance | April 2nd, 2010

Some daily events in the changing sky for April 2 – 10.

Bright Venus and lesser Mercury form an eye-catching pair low in the western twilight. You're free to copy and repost this image to do some astronomy outreach! Just be sure to include a link to SkyandTelescope.com.
Sky & Telescope magazine

Friday, April 2

  • Venus and Mercury shine together low in the west during twilight this week, as shown here. This unequal pair will be an eye-catcher, at least in the brief window of time after the sky grows fairly dark but before the planets sink too low. See article.

  • Mercury's closeness to Venus makes this a prime time to locate and observe it in broad daylight high in the sky. Late afternoon is best. See the April Sky & Telescope, page 53.

  • The waning gibbous Moon rises near Antares around midnight tonight daylight saving time. By early dawn Saturday morning they're even closer together together in the south, as shown below (for North America).

    Saturday, April 3

  • Venus and Mercury appear closest together this evening and tomorrow evening. They appear 3° apart, about the width of two fingers held together at arm's length. In reality they're not close at all; Venus is about 1½ times farther away. Mercury and Venus are 94 million and 146 million miles (8.4 and 13 light-minutes) from Earth this evening, respectively.

    Three reasons conspire to make Venus shine so brightly despite its greater distance right now. It’s about twice as big a planet as Mercury, it’s covered with brilliantly reflective white clouds compared to Mercury’s dark gray rocks and dust, and Venus is currently showing us more of its sunlit dayside.

    Dawn view
    In early dawn the waning Moon crosses Scorpius and Sagittarius. For clarity, the Moon is drawn three times actual size. It's positioned as seen at the time of dawn near the middle of North America (at latitude 40° north, longitude 90° west).

    Sunday, April 4

  • It's April, so this is the time of year when Orion is sinking in the southwest at dusk with his three-star belt horizontal. The belt points left to bright Sirius, and right more or less to orange Aldebaran and, farther on, the Pleiades.

    Monday, April 5

  • Asteroid to occult bright star for Los Angeles and points north. The easy naked-eye star Zeta Ophiuchi, magnitude 2.5, should be occulted for up to 8 seconds by the faint asteroid 824 Anastasia early on the morning of Tuesday, April 6th, along a narrow path running from Southern California through Idaho and then western Canada. The shadow path is predicted to run right across the Los Angeles basin, and across or near Calgary and Edmonton in Canada. The International Occultation Timing Association hopes to recruit many observers from the public, since anyone can see Zeta Oph blink out and reappear with nothing but their eyes! See article with maps and links.

    Tuesday, April 6

  • Last-quarter Moon (exact at 5:37 a.m. EDT).

    Wednesday, April 7

    Mercury is fading, but both planets are a little higher in the dusk than they were a week ago. As night falls, the Pleiades and Hyades come into view.


    You're welcome to copy and repost this image as long as a link to SkyandTelescope.com is included. A high-res print-media version is available from our press release.

  • Got a big telescope and looking for challenges? Try for the faint, swarming members of the NGC 3158 Galaxy Group, 300 million light-years away in Leo Minor, using Ken Hewitt-White's "Going Deep" article, chart, and photo in the March Sky & Telescope, page 66. Ken detected eight of the galaxies with a 12.5-inch scope and eleven with a 17.5-inch.

    Thursday, April 8

  • It's April, so this is the time of year when the bowl of the Little Dipper extends directly to the right from Polaris after dark. High above it is the Big Dipper, turned over to dump water into it.

    Friday, April 9

  • Mercury remains to the right of Venus at dusk, but see how it has faded! Mercury is swinging between between us and the Sun and, in a telescope, is becoming a thinner little crescent. See article.

    Saturday, April 10

  • At dawn Sunday morning, the waning crescent Moon is about 5° above Jupiter (dawn for North American time zones.)

  • A small telescope will always show Titan, Saturn's largest moon. Tonight and tomorrow Titan is 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 often visible in amateur scopes is in the April Sky & Telescope, page 47.


    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'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."


    This Week's Planet Roundup

    Mars was 9.0 arcseconds wide, and near the zenith, on the evening of April 2nd when S&T's Sean Walker took this image. The North Polar Cap (bottom) is diminishing in the northern-hemisphere spring. Walker writes, "The bright cloud on the edge of Mars was almost as bright visually as the polar cap!" He used a DMK camera on a Celestron 14-inch Schmidt-Cassegrain scope.
    S&T: Sean Walker

    Mercury and Venus are beautifully paired low in the west during twilight this week. Venus is by far the brighter of the two. Look for Mercury to its lower right. Venus is magnitude –3.9. Mercury is fading, from magnitude –0.8 on April 2nd to –0.5 on April 5th, +0.3 on the 10th, and +1.4 on the 15th. They appear closest together (3°) on April 3rd and 4th.

    This is as good an apparition as often-elusive Mercury ever puts on (for skywatchers at mid-northern latitudes). And with Venus lighting the way to it, you could hardly ask for Mercury to be any easier. Think photo opportunity. Use a fairly long lens to get a good image scale.

    Mars, dimming into the distance at magnitude +0.3, shines very high in the southwest during evening. It's in Cancer, left of Pollux and Castor and above Procyon. With binoculars, look for the Beehive Star Cluster to Mars's left.

    In a telescope Mars is gibbous and shrinking: from 9.0 to 8.4 arcseconds in diameter this week. Can you still see the north polar cap? Identify any other surface features you may see using the Mars map and observing guide in the December Sky & Telescope, page 57.

    Jupiter (magnitude –2.1) is emerging very low in the glow of dawn. Look for it just above the eastern horizon about 40 or 30 minutes before your local sunrise time.

    Saturn on April 3, 2010
    The low tilt of Saturn's rings this season is allowing a good look at both the southern and northern hemispheres of the planet. South is up in this image taken by S&T's Sean Walker on the night of April 3rd. Note the broad, bright Equatorial Zone, the reddish South Equatorial Belt, and the dark bluish North Polar Region.
    S&T: Sean Walker

    Saturn (magnitude +0.6, in the head of Virgo) is two weeks past opposition. Look for it in the east-southeast at dusk, higher in the southeast by late evening, and highest in the south by 11 or midnight. In a telescope Saturn's rings are tilted only 2.6° from edge-on. They'll narrow to 1.7° in May and early June, then begin widening again.

    Uranus and Neptune are hidden in the glow of sunrise.

    Pluto (magnitude 14, in northwestern Sagittarius) is well up in the south-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 Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.

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