Sky at a Glance | April 12th, 2013

Evening twilight view
Day by day this weekend, the waxing crescent Moon marches up past stars and bright Jupiter. (The Moon is shown positioned for the middle of North America. For Europe, move each Moon symbol a quarter of the way toward the one for the previous date.)

Friday, April 12

  • As twilight fades in the west this evening, look far to the lower left of Jupiter for the crescent Moon. Less far above the Moon, you can see the Pleiades emerging into view — as shown at right.

    Saturday, April 13

  • The thin crescent Moon floats between Aldebaran and the Pleiades in the west as twilight fades, with Jupiter above it, as shown at right.

    Sunday, April 14

  • The Moon and Jupiter shine side by side high in the west after dusk, 3° or 4° apart, with Aldebaran below them. Although they look close together, the Moon is 1.3 light-seconds from Earth, Jupiter is currently 47 light-minutes distant, and Aldebaran is 65 light-years in the background.

    Monday, April 15

  • The Moon right after dark is in the top of Orion's very dim Club. That's not far from the center of the huge Winter Hexagon: Sirius, Procyon, the Pollux-and-Castor pair, Capella, Aldebaran (under Jupiter), Rigel, and back to Sirius.

    Tuesday, April 16

  • Look left of the Moon after dark for Procyon. High above the Moon is Pollux, with Castor at its right. Equally far below the Moon is Betelgeuse, the top corner of Orion.

    Wednesday, April 17

  • The Moon this evening is passing almost midway between Procyon to its lower left and Pollux to its upper right. Castor, slightly dimmer, shines to the right of Pollux.

    Thursday, April 18

  • The Moon is exactly first quarter at 8:31 a.m. EDT this morning, which means it looks equally "first quarter" on the evenings of the 17th and 18th from North America's eastern time zones. The Moon this evening is in dim Cancer, inside the big, long triangle of Procyon, Pollux, and Regulus.


    Friday, April 19

  • Look for Regulus and the Sickle of Leo to the left of the Moon this evening, as shown here.

    Saturday, April 20

  • The Moon now shines under Regulus after dark.


    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 the center of each issue of Sky & Telescope, the essential guide to 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).

    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 81,312 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 — to hunt among the stars.
    Sky & Telescope
    The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

    You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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

    Mercury is buried deep in the glow of dawn.

    Venus and Mars remain hidden behind the glare of the Sun.

    Jupiter (magnitude –2.1, in Taurus) is the first "star" to come out in the west after sunset. It descends through the evening and sets around 11 or midnight. Below Jupiter is orange Aldebaran. Farther to Jupiter's lower right are the Pleiades. In a telescope, Jupiter has shrunk to just 35 arcseconds wide.

    Saturn on April 15, 2013
    Saturn on April 15th, imaged by Christopher Go in the Philippines using a Celestron 14 scope and a Point Grey Research monochrome Flea3 (ICX618) camera with Chroma Technology LRGB color filters. South is up. "The polar hexagon is prominent on this image," he writes. "Note the white spots on the North North Temperate Zone."
    Christopher Go

    Saturn (magnitude +0.2, in Libra) glows low in the east-southeast by the end of twilight. Look for it well to the lower left of Spica, and farther lower right of brighter Arcturus. Saturn rises higher all evening. It shines highest in the south around 1 or 2 a.m. daylight saving time — more or less between Spica to its right, and Delta Scorpii (and then Antares) farther to its lower left. Saturn will reach opposition on the night of April 27th.

    Uranus is out of sight behind the Sun.

    Neptune (magnitude 7.9, in Aquarius) is very low in the east-southeast just before dawn.


    All descriptions that relate to your horizon — 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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