M51 Supernova update. The supernova in the Whirlpool Galaxy (M51) peaked at magnitude 12.6 and is now dimming. It was magnitude 13.0 as of June 28th. That still makes it detectable in a lot of amateur telescopes, what with the sky being moonless early in the week, but don't delay; this is probably your last chance.

Here's an up-to-date light curve from the AAVSO. See our original article and finder photo. Plot an AAVSO comparison-star chart (enter the name SN 2011dh).

Friday, July 1

  • A small telescope shows Saturn's largest moon, Titan, about four ring-lengths east of the planet this evening and tomorrow evening. They're a little less than 3 arcminutes apart. Porrima is about 30 arcminutes to Saturn's northwest. And a little closer to Saturn's northeast is a 6th-magnitude yellow star.
  • New Moon (exact at 4:54 a.m. EDT). A slight partial eclipse of the Sun is theoretically visible just above the horizon for a small section of the stormy winter ocean off Antarctica. This is an eclipse that not a single human is likely to see, and probably not even penguins or albatrosses.

    Saturday, July 2

  • Mercury is becoming better placed for observers at mid-northern latitudes; look low above the west to west-northwest horizon as the glow of sunset fades, as shown below. This evening, can you spot the thin crescent Moon below Mercury about a half hour after sunset? Bring binoculars.

    Dusk view

    Watch the waxing crescent Moon thicken and advance eastward from day to day as July gets going.

    Sky & Telescope diagram

    Sunday, July 3

  • In twilight, look well to the right of the crescent Moon for Mercury, as shown above.
  • Saturn is at quadrature, 90° east of the Sun.
  • If you have a dark enough sky, the Milky Way now forms a magnificent arch high across the whole eastern sky after nightfall is complete. It runs all the way from below Cassiopeia in the north-northeast, up and across Cygnus and the Summer Triangle in the east, and down past the spout of the Sagittarius Teapot in the south.

    Monday, July 4

  • Regulus is upper right of the Moon in twilight, as shown above.
  • Watching fireworks this evening? While you're waiting for them to start, point out some sky sights to family and friends. In addition to the Moon and Regulus (see previous item), Saturn and Spica shine higher in the southwest, far to the Moon's upper left; Saturn is the one on the right. Very high above them is brighter Arcturus. Bright Vega is very high in the east. And the fire-colored supergiant Antares is the brightest star lower in the south.
  • Earth is at aphelion, its farthest from the Sun for the year — just one part in 30 farther than at perihelion in January.

    Tuesday, July 5

  • Now's the time of year to work through the rich but low tail of Scorpius with your telescope. Explore a whole nest of star clusters near M6 there with Sue French's Deep-Sky Wonders article and chart in the July Sky & Telescope, page 66.

    Wednesday, July 6

  • Have you learned, really learned, the star pattern of little Lyra around bright Vega? Look very high in the east after dusk. The main part of Lyra dangles to Vega's lower right. Get out your sky atlas: Epsilon (ε), Zeta (ζ), and Delta (δ) Lyrae are fine binocular or telescopic double stars, Beta (β) Lyrae is an eclipsing variable, the Ring Nebula is located between Beta and Gamma (γ), and faint T Lyrae, a carbon star near Vega, is one of the reddest stars in the sky.

    Look just after dark

    The waxing Moon this month again passes under Virgo with Saturn and Spica.

    Sky & Telescope diagram

    Thursday, July 7

  • The first-quarter Moon forms a nice triangle with Spica and Saturn above it this evening, as shown above.

    Friday, July 8

  • Spica shines to the Moon's upper right during and after dusk, as shown above.

    Saturday, July 9

  • Arcturus is the brightest star very high in the southwest or west after dark. Vega is the brightest very high in the east. A third of the way from Arcturus to Vega, look for the mostly dim semicircle of Corona Borealis, the Northern Crown. Two-thirds of the way, look for the Keystone of Hercules.

    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).

    Sky Atlas 2000.0 (the color Deluxe Edition is shown here) plots 81,312 stars to magnitude 8.5. That includes most of the stars that you can see in a good finderscope, and typically one or two stars that will fall within a 50× telescope's field of view wherever you point. About 2,700 deep-sky objects to hunt are plotted among the stars.

    Alan MacRobert

    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 (about magnitude –0.3) can be spotted very low in the west-northwest in twilight. Don't confuse it with Regulus far to its upper left.

    Venus (magnitude –3.9) shines barely above the east-northeast horizon as dawn grows bright. Look for it about 15 or 20 minutes before sunrise if the air is very clear.

    Mars (magnitude +1.4, in Taurus) is low in east-northeast in early dawn. Look for it very far lower left of Jupiter. Below or lower right of Mars is Aldebaran, similar in brightness and color.

    Jupiter on June 8, 2011

    Jupiter is coming into better view now in the dawn, but it's still very far from its best. Christopher Go obtained this fine stacked-video image on June 8th. Jupiter's dark South Equatorial Belt (above center) has fully returned and is very wide. The narrower North Equatorial Belt remains darker red-brown, with even darker barges. At the time of the photo the Great Red Spot had just barely passed the planet's central meridian (where the System II longitude was 163°). The SEB practically encompasses the Red Spot, and the Red Spot Hollow around the spot has changed from white to dark. South is up.

    Christopher Go

    Jupiter (magnitude –2.3, in southern Aries) rises around 2 a.m. and shines prominently in the east by dawn.

    Saturn (magnitude +0.9, in Virgo) is southwest after dusk and getting lower. Shining 14° left of it is similar Spica. And 2/3° to Saturn's right is fainter Porrima (Gamma Virginis).

    In a telescope, Saturn's rings are 7.6° from edge on. The rings are casting a their shadow southward onto the globe as a thin black line. The globe's shadow on the rings is just off the globe's celestial east (following) side. The North Equatorial Belt is a dusky band. North of it, signs of Saturn's seven-months-old white outbreak are still apparent in good images.

    Uranus (magnitude 5.9, in western Pisces) and Neptune (magnitude 7.9, in Aquarius) are about equally high now before the very first light of dawn, in the southeast and south, respectively.

    Pluto (magnitude 14.0, in Sagittarius) is highest in the south around midnight or 1 a.m. A big finder chart for it is in the July Sky & Telescope, page 64.

    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.

    To be sure to get the current Sky at a Glance, bookmark this URL:

    If pictures fail to load, refresh the page. If they still fail to load, change the 1 at the end of the URL to any other character and try again.

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