Sky at a Glance | January 9th, 2009

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Jupiter is getting ever lower below Mercury. Can you still find it? Their brightnesses here are exaggerated. (The blue 10° scale is about the size of your fist held at arm's length.)
Alan MacRobert
Some daily events in the changing sky for January 9 – 17.

Friday, January 9

  • Look early and low enough in twilight with binoculars, and you still might detect Jupiter below Mercury, as shown at right. Both planets will rapidly drop lower in the coming days.
  • On the other side of the sky after dark, the bright frosty Moon shines in the feet of Gemini, just about halfway between Capella (high to the Moon's upper left in early evening) and Procyon (far to the Moon's lower right).

    Saturday, January 10

  • Full Moon (exact at 10:27 p.m. EST). The Moon is close to perigee, so this is the biggest and brightest full Moon of 2009 — a repeat of last month's extra-big full Moon.
  • The eclipsing variable star Algol (Beta Persei) should be at minimum light, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 1:07 a.m. Sunday morning EST; 10:07 p.m. Saturday evening PST. Algol takes several additional hours to fade and to rebrighten.

    Sunday, January 11

    The bright Moon passes Regulus, Saturn, and the rampant Lion in the east in late evening. (These scenes are drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way to the one for the previous date. In the Far East, move them halfway.)
    Alan MacRobert

  • Sirius, the Dog Star, the brightest star in the sky, now rises in the east-southeast as early as the end of twilight. Look for it below Orion and far to the right of the Moon. Between the Moon and Sirius (somewhat closer to the former) twinkles Procyon, the Little Dog Star.

    Monday, January 12

  • Look for Regulus, a star announcing the distant approach of spring, to the lower left of the Moon late this evening, as shown at right.

    Tuesday, January 13

  • Algol should be at minimum brightness for a couple hours centered on 9:56 p.m. EST.
  • On this date in 1610, Galileo discovered Jupiter's moon Ganymede.

    Wednesday, January 14

  • Venus is at greatest elongation, 47° east of the Sun in the evening sky.
  • Telescope users in the western halves of Russia and Asia can watch Venus passing just 1 arcminute south of the 4th-magnitude star Lambda Aquarii. They're closest around 14:47 Universal Time.
  • The waning gibbous Moon is about 6° to the right of Saturn after they rise late this evening (as seen from North America), as shown at right. The Moon is a similar distance below Saturn by Thursday dawn.

    Facing northwest just after dark
    Whenever Vega is preparing to set, the Northern Cross is turning to stand upright on the northwest horizon (as seen from mid-northern latitudes.)


    This scene, like the others, is drawn for our "standard latitude," 40° north. If you're farther north than that, Vega will be higher (maybe even circumpolar!). If you're farther south, Vega sets earlier in the evening and earlier in the season.

    Sky & Telescope diagram

    Thursday, January 15

  • Here we are halfway through January, and the "Summer Star" Vega is still hanging in view low in the northwest at nightfall, as shown at right.
  • International Year of Astronomy event: Live webcast of Harvard researcher Alyssa Goodman speaking on "The WorldWide Telescope: Astronomy of the Future". 7:30 p.m. Eastern Standard Time (0:30 Jan 16th Universal Time).

    Friday, January 16

  • Now that the moonlight is diminishing in the pre-dawn sky, take a look for this season's weird Comet Lulin. It's easily visible in a telescope now and should be a binocular comet in February.
  • Algol should be at minimum brightness for a couple hours centered on 6:46 p.m. EST.

    Saturday, January 17

  • Last-quarter Moon (exact at 9:46 p.m. EST).

    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 foldout 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 81,000 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 — 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 maps; 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 even more detailed 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? 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

    Mercury is dropping low after sunset and is also fading fast. Early in the week it's still fairly easy to spot at magnitude 0 just above the west-southwest horizon in mid-twilight, very far to the lower right of Venus. But by the end of the week it's lost from view.

    Venus (magnitude –4.5) is the dazzling "Evening Star" in the southwest during and after twilight. It doesn't set now until as late as about 9 p.m.

    In a telescope Venus is 24 arcseconds wide and near dichotomy: half-lit. Venus will be exactly 50% illuminated on the evening of January 16th. But because the sunlight illumination is dimmer at the terminator, in a telescope the waning Venus usually looks exactly half-lit 5 or 10 days earlier than when it really is. How well can you determine this date? Telescopically, Venus is best seen in bright twilight or even broad daylight. (It's less glary when seen against a bright sky, and it's also higher.)

    Mars remains hidden deep in the glow of sunrise.

    Jupiter (magnitude –1.9) is pretty completely lost deep in the glow of sunset now. It you want to try for it anyway, use binoculars to look below Mercury shortly after sunset early in the week, as shown at the top of this page.

    On Christmas night Richard Bosman in the Netherlands took this image of Saturn at its minimum ring tilt for this apparition, 0.8°. South is up. Bosman writes, "The northern part is still bluish. There were no storms or spots on display at this meridian. Remarkable is the beauty of the very narrow ring now at the minimum. The ring is not bright white but dull gray."


    The Cassini Division is visible near the rings' ansae (ends). The shadow of the globe is cast on the ring's western (left) side just off the globe's edge. Even a small scope will show the very prominent black shadow that the rings are casting on the globe. Bosman used an 11-inch Celestron Schmidt-Cassegrain telescope and an ATK-2HS camera at 5:02 UT Dec. 26, 2008.

    Richard Bosman

    Saturn (magnitude +1.0, near the Leo-Virgo border) rises around 9 or 10 p.m. It's highest in the south around 3 or 4 a.m. Don't confuse Saturn with similarly-bright Regulus 22° (about two fist-widths at arm's length) to its upper right after they rise, and more directly to its right in the early-morning hours.

    This week Saturn's rings are 0.9° to 1.0° from edge on. The rings will gradually open to 4° by late May, then will close to exactly edge-on early next September — when, unfortunately, Saturn will be out of sight in conjunction with the Sun. Saturn will again be poorly placed for our next ring-plane crossing 15 years hence. So now is the thinnest you can see Saturn's rings until 2038!

    Uranus (magnitude 5.9, in Aquarius) is upper left of Venus in the evening sky. Use binoculars with our article and finder chart.

    Neptune is getting lost in the sunset.

    Pluto is hidden in the glow of sunrise.

    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 Standard Time (EST) equals Universal Time (known as UT, UTC, or GMT) minus 5 hours.

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