Sky at a Glance | August 16th, 2013

Nova Delphini 2013 on the discovery evening
A closeup of Nova Delphini 2013, at center, taken on the evening of August 14th (Eastern Daylight Time). It's brightened a lot since then. Click for larger view 10° wide with Sagitta on the right. S&T's Dennis di Cicco used a 180-mm f/2.8 lens at f/8 on a Nikon D700 DSLR, set at ISO 400, for this 5-minute tracked exposure.
S&T: Dennis di Cicco

Bright nova in Delphinus. The nova discovered in Delphinus last Wednesday brightened to magnitude 4.4 in the next 48 hours. Delphinus is conveniently high in the evening sky. The nova is easy to see in binoculars, and it's visible to the naked eye if you have a dark sky. See Bright Nova in Delphinus, with a finder chart and a link to a continuously updated light curve.


Supernova in M74. Meanwhile, the supernova in the galaxy M74 remains about magnitude 12.6 three weeks after it erupted. See Supernova Still Bright in M74.


Friday, August 16

  • By about 10 p.m. (depending on where you live), W-shaped Cassiopeia is now as high in the northeast as the Big Dipper is in the northwest. Cassiopeia will grow ever more ascendant over the Dipper for the next several months as the seasons turn.

    Moon over Sagittarius
    The bright Moon shines over the Teapot of Sagittarius Friday and Saturday evenings (the 16th and 17th). The Cat's Eyes shine at a tilt low in the tail of Scorpius.

    Saturday, August 17

  • The waxing gibbous Moon shines in the south after nightfall. Below it is the Sagittarius Teapot, as shown at right.

  • Look high to the Moon's upper left for bright Altair. Just above Altair is 3rd-magnitude Tarazed, an orange-red giant star (can you see its tint?) 20 times farther away.

    Sunday, August 18

  • The two brightest stars of summer are Vega, passing overhead soon after dark, and Arcturus shining in the west. Vega is a white-hot type-A star 25 light-years away. Arcturus is an orange-yellow-hot type-K giant 37 light-years distant. Both are much brighter than the Sun. Their color difference is pretty clear to the unaided eye.

    Monday, August 19

  • Look east in early dawn for the next few mornings and spot bright Jupiter. Look lower left of Jupiter for faint Mars. Mars forms the bottom end of a curving line with similarly bright Pollux and Castor (to its upper left). Watch this line straighten out day by day as Mars speeds eastward. It becomes exactly straight on Sunday morning the 25th.

    Tuesday, August 20

  • Full Moon (exact at 9:45 p.m. Eastern Daylight Time). The Moon rises around sunset and shines in dim Aquarius after dark.

    Wednesday, August 21

  • This is the time of year when the Big Dipper scoops down during evening, as if to pick up the water that it will dump from high overhead early next spring. Look northwest.

    Thursday, August 22

  • After dark, spot Vega overhead and Arcturus in the west. A third of the way down from Vega toward Arcturus is the dim Keystone of Hercules. Two thirds of the way is the dim semicircle of Corona Borealis, the Northern Crown. Corona has only one modestly bright star, Alphecca.

    Friday, August 23

  • The Great Square of Pegasus, tipped up on one corner, hangs above the waning gibbous Moon after the Moon rises in mid-evening.

    Saturday, August 24

  • The asteroid 7 Iris (the 7th discovered) is just past opposition in Aquarius. Find it at magnitude 8.0 this week with a small telescope and the finder chart in the September Sky & Telescope, page 52.


    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.

    This is an outdoor nature hobby. 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).

    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 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, which means heavy and expensive). 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 hidden deep in the glow of sunrise.

    Venus (magnitude –4.0) shines brightly low in the west in evening twilight, far below Arcturus. Look to its left and somewhat higher for much fainter Spica, and further on, Saturn. In a telescope Venus is still small (14 arcseconds) and gibbous (78% sunlit).

    Mars and Jupiter shine in the east before and during dawn. Jupiter is the highest and brightest (magnitude –2.0). Look for faint Mars (magnitude +1.6) increasingly far to Jupiter's lower left. Both are in Gemini; Pollux and Castor twinkle to Mars's upper left.

    Saturn (magnitude +0.7, on the border between Virgo and Libra) glows in the southwest as twilight fades, with Spica 12° to its lower right and Venus much farther lower right.

    Uranus (magnitude 5.8, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are both in view toward the southeast by 11 or midnight. Finder charts for Uranus and Neptune.


    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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