Sky at a Glance | April 15th, 2011

Alert: T Pyxidis has finally blown up! The recurrent nova T Pyxidis, which had its last outburst in December 1966 and has been very overdue for its next, has shot up from magnitude 15.4 to at least 8.5. In 1966–67 it reached 6.5. Read more about the ouburst of T Pyxidis.


Twilight view southeastward
As the Moon waxes to full, it teams up with Saturn in the evening sky.

Friday, April 15

  • Look high in the northeast after dark for the Big Dipper. It's tilting rightward on its handle. You probably know that the two stars forming the top end of the Dipper's bowl are the Pointers, pointing lower left toward Polaris. Less well known is that if you follow the Pointers backward in the opposite direction (by a greater distance), you land in Leo.

    Saturday, April 16

  • Upper left of the nearly full Moon this evening are Saturn and fainter Gamma Virginis (Porrima). They're currently only 2½° apart, and they'll close up further in the coming weeks. Also in the Moon's neighborhood are Spica and Corvus, as shown here.

    Sunday, April 17

  • Full Moon (exact at 10:44 p.m. EDT). Standing in a nearly vertical row above the Moon at dusk are Spica, Saturn, and Gamma Virginis, as shown here. As the night goes on, the whole arrangement rises higher and tips to the right.

    Monday, April 18

  • Vega, the "Summer Star," is now rising in the northeast right around the end of twilight (depending on your latitude). Later in the night as Vega rises higher, look for its dim little constellation Lyra dangling from it toward the lower right.

    Bright sky before sunrise
    Planets shortly before sunrise. Their visibility in bright dawn is exaggerated here.
  • A dawn challenge! On Tuesday morning, about 15 minutes before your local sunrise time, use binoculars or a wide-field telescope to look 15° lower left of Venus for faint Mars and even fainter Mercury in conjunction, as shown here. Not an easy sighting!

    Tuesday, April 19

  • Have you been keeping an eye on bright Sirius in the southwest, and Orion in the west, around the end of twilight? They're still in view but sinking lower daily. How much longer can you keep them in view?

    Wednesday, April 20

  • Sirius, the Dog Star, shines brightly low in the southwest right after dusk. High above it is Procyon, the Little Dog Star. Very far to Procyon's upper left is Regulus in Leo. Nearly halfway from Procyon to Regulus, look for a dim but distinctive asterism: the head of Hydra, the Sea Serpent. It's about the size of the end of your thumb at arm's length.

    Thursday, April 21

  • A small telescope will always show Titan, Saturn's largest moon. This evening Titan is four ring-lengths to Saturn's west. Look roughly one ring-length to Saturn's northwest for dimmer Rhea and Dione quite close together.

    Friday, April 22

  • The Lyrid meteor shower should peak late tonight, but it's usually quite weak. The best chance to see an occasional Lyrid will be around midnight daylight-saving time, when Lyra is up fairly high but the Moon hasn't yet risen.

  • Just south of Regulus is the dim but galaxy-ridden constellation Sextans, the Sextant. Dig up some of its far sights using Sue French's Deep-Sky Wonders column, chart, and images in the April Sky & Telescope, page 58.

    Saturday, April 23

  • Capella is the brightest star shining in the northwest right after dusk. Arcturus is the brightest shining in the east. Both are magnitude zero — and this week, both stand at exactly the same height above your horizon around nightfall (depending on your latitude). How accurately can you time this event for your location?



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    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 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 81,312 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

    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 sky 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

    Mercury, Mars, and Jupiter are buried deep in the glare of sunrise (well to the lower left of Venus).

    Venus (magnitude –3.9) is visible very low in bright dawn. Look for it above the eastern horizon about 30 minutes before your local sunrise time.

    Saturn at opposition on the night of April 3–4. The rings are especially bright compared to the globe due to the opposition effect (Seeliger effect). Christopher Go shot this image at
    Alan MacRobert

    Saturn (magnitude +0.4, in Virgo) is the only planet now in good view. After passing through opposition on April 3rd, it glows low in the east-southeast as the stars come out. Saturn rises higher in the southeast during evening and shines highest in the south around 11 or midnight. Look for twinkly Spica 12° below it or to its lower left. Don't confuse Saturn with brighter Arcturus 30° to its left or upper left.

    In a telescope, the rings have narrowed slightly in the last few months to 8° from edge on. See how many of Saturn's satellites you can identify in your scope using our Saturn's Moons tracker. Saturn's months-old northern-hemisphere white spot is now a much-faded double light band most of the way around the planet, as seen here.

    Uranus and Neptune are low in the glow of 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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