Sky at a Glance | March 12th, 2010

Some daily events in the changing sky for March 12 – 20.

Big Dipper
After dark in March, the Big Dipper stands upright high in the northeast.
Akira Fujii

Friday, March 12

  • The Big Dipper glitters high in the northeast these evenings, standing on its handle. You probably know already that the two stars forming the front end of the Dipper's bowl (currently the top two) are the Pointers; they point to Polaris, currently to their left.

    And you probably know that if you follow the curve of the Dipper's handle out and around by a little more than a Dipper length, you'll arc to Arcturus (now rising in the east).

    But did you know that if you follow the Pointers backward the opposite way, you'll land in Leo?

    Draw a line diagonally across the bowl from where the handle is attached, continue on, and you'll go to Gemini.

    And look at the two stars forming the open top of the Dipper's bowl. Follow this line past the bowl's lip far across the sky, and you crash into Capella.

    Saturday, March 13

  • With spring almost here, the bright "Spring Star" Arcturus rises above the east-northeast horizon just after dark. Two or three hours later (depending on your latitude), equally bright Vega rises in the northeast.

    Sunday, March 14

  • Daylight saving time begins at 2 a.m. Sunday morning for most of the U.S. and Canada. Clocks spring ahead. Then for six days we're on what I call winter saving time: we're using "summer time" while it's still winter.

    Bright-twilight view
    How soon after sunset will you first see Venus and this month's thin waxing crescent Moon? Their visibility in bright twilight is exaggerated here for clarity.

    Monday, March 15

  • New Moon (exact at 5:01 p.m. EDT).

    Tuesday, March 16

  • Look low in the west in bright twilight for Venus and, to its right, the thin crescent Moon, as shown at right. In the Eastern time zone of North America, the Moon is only 26 or 27 hours old (compare with the exact time of new Moon under Monday above). By the time twilight falls on the West Coast, the Moon is 29 or 30 hours old. Does this sighting set a young-Moon record for you?

    Wednesday, March 17

  • Venus shines below the smile-shaped crescent Moon low in the west after sunset. See the illustration at right.

  • A small telescope will always show Titan, Saturn's largest satellite. Tonight through Friday night, Titan is three or four ring-lengths to Saturn's west. 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 March Sky & Telescope, page 47.

    Looking west after dark
    Mark your calendar for the Moon-Pleiades conjunction on Saturday March 20th. These Moons here are drawn three times their actual apparent size for clarity, and they are always positioned as seen from about the middle of North America (from latitude 40° north, longitude 90° west).

    Thursday, March 18

  • Look for the stars of Aries to the right of the Moon at nightfall, as shown at right.

    Friday, March 19

  • This is the time of year when Orion declines in the southwest after dark, with his Belt roughly horizontal. But when does Orion's Belt appear exactly horizontal? That depends on where you're located east-west in your time zone, and on your latitude.

    For instance, in Boston this evening, the Belt should be perfectly horizontal around 8:20 p.m. How accurately can you time this event at your location? Orion's Belt is slightly curved, so judge by the two stars on its ends. Can you rig up a sighting reference to make your measurement more precise, and track the time's day-to-day change? Welcome to pre-telescopic astronomy.

    Saturday, March 20

  • The crescent Moon shines right next to the Pleiades in late twilight — a beautiful sight, especially in binoculars! The Moon occults (covers) some of the bright Pleiads as seen from parts of Central and South America (timetables), and some of the cluster's faint, outlying stars for the U.S. and Canada (graze maps; look for the March 20 and 21 events; occultations happen south of the graze lines).

    David Dunham of the International Occultation Timing Association writes:

    "Our last Pleiades passage in the USA until 2023 will occur Saturday evening, with the crescent Moon, about 25% sunlit, moving over the southern and eastern part of the cluster but missing all of the bright stars (except for Merope in the Corpus Christi, Texas area). But several 8th to 6th magnitude stars will be occulted, and one 5th-mag. star. Predictions of these (and of other total lunar occultations for all of 2010 for stars to mag. 6.0) for 40 of the larger North American cities can be downloaded in .zip files from Bob Sandy's website. There are some regional sites with predictions of fainter stars, for example for stars to 8th mag. in the Mid-Atlantic region (computed for near Washington, DC) at the bottom of my Mid-Atlantic occultation and expedition page."

  • The equinox occurs at 1:32 p.m. Eastern Daylight Time, when the Sun crosses the equator heading north for the year. Spring begins in the Northern Hemisphere, fall in the Southern Hemisphere.


    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.

    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

    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 on March 13, 2010
    Mars was only 10.8 arcseconds wide on the evening of March 16th when S&T's Sean Walker took this image at 7:41 p.m. EDT. The North Polar Cap (bottom) seems to be diminishing. Note the cloud in Hellas (at the 11 o'clock position on the limb) and the apparent blue cloud over Syrtis Major (left limb). Walker used a DMK camera on a Celestron 14-inch Schmidt-Cassegrain scope. He writes, "One hour later, the seeing was so bad I couldn’t be sure there was a polar cap on Mars!"
    S&T: Sean Walker

    Mercury is hidden in the glare of the Sun.

    Venus (magnitude –3.9) is slowly emerging from the sunset. Look for it very low due west about 40 minutes after sundown.

    Mars, now faded to magnitude –0.2, shines very high in the southeast at dusk and toward the south by 8 or 9 p.m. It's in Cancer, below Pollux and Castor at nightfall and left of them later in the evening.

    In a telescope Mars is gibbous and shrinking: from 10.9 to 10.3 arcseconds in diameter this week. The north polar cap remains its most visible marking. Identify other surface features using the Mars map and observing guide in the December Sky & Telescope, page 57.

    Jupiter is hidden deep in the glow of sunrise.

    Saturn (magnitude +0.5, in western Virgo) is nearly at opposition, which comes on the night of March 21st. Saturn glows low in the east at nightfall, higher in the southeast late in the evening, and highest in the south around 1 or 2 a.m. daylight saving time. In a telescope, Saturn's rings are tilted only 3.4° from edge-on. They'll narrow further to 1.7° in May.

    Saturn on March 13, 2010, with SED
    South Equatorial Belt is very prominent, while the North Equatorial Belt looks faint. There are a lot of band details, especially in the northern hemisphere."

    Little Dione is in the background below the right end of the rings. South is up. Click image for a .wmv movie of eight images (with north up)." credits="Christopher Go" width="" height="" align="right"]
    Uranus and Neptune are hidden in the glare of the Sun.

    Pluto (magnitude 14, in northwestern Sagittarius) is up in the 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 Standard Time (EST) equals Universal Time (also known as UT, UTC, or GMT) minus 5 hours.


    "Science is built up of facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house."
    — Henri Poincaré (1854–1912)


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