Sky at a Glance | May 8th, 2009

Some daily events in the changing sky for May 8 – May 16.

Friday, May 8

  • Full Moon tonight (exact at 12:01 a.m. Saturday morning Eastern Daylight Time).

    Saturday, May 9

  • By 11 p.m. the Moon is well up in the southeast. Look to its lower left, by a bit less than a fist-width at arm's length, for reddish, summery Antares already on the rise. Scattered nearby are fainter stars of Scorpius. Tomorrow night, the Moon will shine on Antares's opposite side.

    Sunday, May 10

  • The asteroid 14 Irene (9th magnitude) is passing 0.2° north of 6th-magnitude 92 Virginis this evening for Europe and the Americas. See the chart in the May Sky & Telescope, page 46. Look early before the Moon rises.

  • 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 May Sky & Telescope, page 47.

    Monday, May 11

  • This is the time of year when the Gemini twins stand upright in the west as twilight fades. Their bright head stars, Pollux and Castor, are lined up nearly horizontally just 4½° apart, about the width of three fingers at arm's length.

    To the lower left of Pollux and Castor shines Procyon. Farther to their lower right shines Capella.

    Tuesday, May 12

  • Using binoculars in twilight, can you still pick up wintry Betelgeuse before it disappears below the western horizon? Every year, Betelgeuse is the last bright bit of Orion to go. Look for it below Gemini, and lower right of Procyon. How many more days can you continue to see it?

    Arcturus and aurora
    Arcturus, the brightest star just above the left trees, originated long ago and far away. Aurora photo by Paul Valleli.
    Paul Valleli
    Wednesday, May 13

  • Bright Arcturus dominates the eastern sky these evenings. It's such a familiar star, but it's actually an alien. It's only 37 light-years away, but its high velocity with respect to most stars in our vicinity means that it's just passing through our part of the galaxy. In fact, Arcturus seems to be part of sparse, high-velocity star stream that's the last identifiable remnant of a separate, ancient dwarf galaxy that fell into and merged with the Milky Way.

    Thursday, May 14

  • Vega, the summertime equal of Arcturus for brightness, is already making its way up in the northeast after dark. It's closer, 25 light-years distant. As night comes fully on, look lower left of Vega for Deneb.

    Friday, May 15

  • Face north at nightfall this week and look very high, almost overhead. There's the Big Dipper, floating upside down. The middle star of its bent handle is Mizar; can you see tiny Alcor hiding in its skirts? To find out on which side of Mizar to look for Alcor, notice that Vega is rising way off in the northeast. A line from Mizar through Alcor always points to Vega.

    Looking southeast in early dawn
    Early risers can watch the waning Moon pass Jupiter in Capricornus. (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.)
    Saturday, May 16

  • Jupiter is at western quadrature, 90° west of the Sun before and during dawn. In a telescope this month, do you notice that its western limb is slightly less illuminated than its eastern limb?

  • On Sunday morning the last-quarter Moon shines close to Jupiter. Also Sunday morning, Jupiter's own moons Io and Callisto both cast their tiny shadows onto Jupiter's face from 3:56 to 5:16 a.m. Eastern Daylight Time.


    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).

    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'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

    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. local time on 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
    Mercury is lost in the sunset.

    Venus (magnitude –4.7) shines brightly 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 now a thick crescent about 33% sunlit. The best telescopic views come in full early-morning daylight, when Venus is higher in steadier air.

    Mars (only magnitude +1.2) remains 6° lower left of Venus this week. Bring binoculars; Mars is about 200 times fainter than Venus!

    Jupiter (magnitude –2.3, in Capricornus) shines brightly in the southeast before and during dawn.

    Saturn (magnitude +0.8, in Leo) is highest in the south at dusk and moves to the southwest later. Regulus, not quite as bright, sparkles 15° to its right at dusk, and lower right later.

    Saturn on May 11, 2009
    Have you noticed how dim Saturn's rings are getting? It's because they've been turning more nearly edge-on to the Sun than to Earth. The black line across Saturn's globe is a combination of the dimly sunlit surface of the rings themselves and their darker shadow on Saturn's globe. The difference between the two dark lines is barely resolved in the top image here. Christopher Go took these images 15 minutes apart on the evening of May 11th in the Philippines. South is up; both the Sun and Earth see the rings' south face.
    Christopher Go
    In a telescope, Saturn's rings appear 4° from edge on, their widest this year. They'll close to exactly edge-on September 4th, when, unfortunately, Saturn will be out of sight practically in conjunction with the Sun.

    Uranus (6th magnitude) is low in the sunrise glow. It's to the upper right of Venus but 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 (also known as UT, UTC, or GMT) minus 4 hours.


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