M51 Supernova brightening. Supernova 2011dh, which was discovered in the Whirlpool Galaxy, M51, on May 31st, has been brightening ever since — though the brightening is now leveling off. As of June 16th the supernova was about V magnitude 12.6 and visible in a lot more amateur telescopes.

The M51 supernova is marked with the yellow tick. Lynn Hilborn of Grafton, Ontario, writes that she took this deep image of the galaxy on March 24th and added the supernova data from a second image taken June 7th. North is up. Wider view.

Lynn Hilborn

On the evening of the 16th S&T's Dennis di Cicco imaged the galaxy and supernova again with his 16-inch scope and was able to glimpse it visually with a 6-inch despite the moonlight. He writes, "With the Moon leaving the early-evening sky [as of about June 19th] and M51 seen best as soon as it gets dark, now is the time for people to have a look. With higher magnification and a moderately good sky, anyone with an 8-inch or larger scope should be able to spot the supernova. I can’t remember the last time we had one that was this easily visible."

Here's an up-to-date light curve from the American Association of Variable Star Observers. See our article. Plot an AAVSO comparison-star chart (enter the name SN 2011dh).

Friday, June 17

  • The Moon rises in the east-southeast in late evening, depending on where you are. Far to its upper left shines Altair. Farther on in the same direction are the other two stars of the Summer Triangle: Vega and lesser Deneb.

    Saturday, June 18

  • The two brightest stars of summer are Vega, high in the east these evenings, and Arcturus, even higher in the southwest. They're moderately near neighbors of ours as stars go: 25 and 37 light-years away, respectively. But that's only part of why they appear so bright. Vega is hotter, larger, and 50 times more luminous than the Sun, and Arcturus puts out 150 times the light of the Sun.

    The constellation Lyra

    The little constellation Lyra dangles to Vega's lower right these evenings. For most of the time, Beta Lyrae is almost exactly as bright as Gamma.

    Akira Fujii


    Sunday, June 19

  • The eclipsing binary star Beta Lyrae (near Vega) should be at minimum light all evening (centered on 0:00 June 20th UT) — magnitude 4.3 instead of its maximum of 3.3 or 3.4. That will make Beta obviously fainter than Gamma Lyrae next to it, which is magnitude 3.2. See the article in the June Sky & Telescope, page 60.

    Monday, June 20

  • Look low in the west-northwest for Pollux and Castor as twilight fades away. They're lined up not quite horizontally. These two "winter" stars have far outstayed their season. How much longer can you follow them down? Past the first day of summer tomorrow?

    Tuesday, June 21

  • The June solstice occurs at 1:16 p.m. EDT. This is the moment when the Sun is farthest north for the year and begins its six-month return southward. Summer begins in the Northern Hemisphere, where this is the year's longest day. In the Southern Hemisphere, winter begins.

    If you have a good view of the west-northwest horizon (from mid-northern latitudes), mark precisely where the Sun sets. In a few days you should be able to detect that it's again starting to set a little south of this point. Build your own Stonehenge?

    Wednesday, June 22

  • Now that the Moon is gone from the evening sky, try hunting out galaxies hear the head of Serpens using Sue French's "Deep-Sky Wonders" chart, photos, and article in the June Sky & Telescope, page 62. Find the Sombrero galaxy above Corvus right after dark using page 45. And check out "Galaxies near Bright Stars" on page 68.

    Thursday, June 23

  • Last-quarter Moon (exact at 7:48 a.m. EDT). The Moon rises very late tonight, around 1 a.m. EDT on the 24th depending on your location. Look above it for the Great Square of Pegasus.

    Friday, June 24

  • With summer here, look south-southeast after dark for the bright constellation Scorpius, "the Orion of summer," now reasonably high and standing upright. Like Orion, Scorpius is marked by several 2nd-magnitude blue-white stars and one of the two brightest red supergiants in the sky (Antares in Scorpius, Betelgeuse in Orion). However, Scorpius is some 30° farther south.

    Saturday, June 25

  • These evenings, look high in the east to spot bright Vega. The brightest star to its lower left, by two or three fist-widths at arm's length, is Deneb (the head of the Northern Cross). Farther to Vega's lower right is bright Altair. These three stars form the Summer Triangle. The summer Milky Way runs right through it, along the length of the Northern Cross, if you have a dark enough sky.

    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

    Jupiter on June 8, 2011

    Jupiter is coming into better view now low in the dawn, but it's still very far from its best. Christopher Go obtained this fine stacked-video image anyway 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


    Mercury is buried deep in the glow of sunset.

    Venus (magnitude –3.8) shines barely above the east-northeast horizon as dawn grows bright. Look for it 20 minutes before sunrise.

    Mars (dim at magnitude +1.4) is low in the dawn very far to the lower left of Jupiter, though not as far as Venus. Try with binoculars.

    Jupiter (magnitude –2.2, in southern Aries) shines in the east before and during dawn.

    Saturn (magnitude +0.8, in Virgo) is in good view in the southwest after dusk. Shining 15° left of it is Spica. And just 0.3° to Saturn's upper right is fainter Porrima (Gamma Virginis), turning Saturn into a naked-eye "double star."

    In a telescope Saturn's rings are 7.4° from edge on. The rings are casting a relatively wide, prominent black shadow southward onto the globe, and the globe's shadow on the rings is visible just off the globe's celestial east (following) side. The North Equatorial Belt is a dusky band. North of it, Saturn's seven-months-old white outbreak is still apparent in good images, as shown here; read more about this huge storm as studied from the Cassini Saturn orbiter and the Very Large Telescope in Chile.

    Saturn on May 30, 2011

    Saturn's white activity continues in the planet's northern hemisphere, as seen in this image taken by Christopher Go on May 30th. South is up. This image was created from stacked, selected video frames (taken with an 11-inch scope); don't expect to see this much detail visually!

    Christopher Go


    See how many of Saturn's satellites you can identify in your scope using our Saturn's Moons tracker.

    And don't skip over Porrima — it's a fine, close telescopic binary with equal components and a current separation of 1.7 arcseconds. Use high power and hope for good seeing. See the article in the April Sky & Telescope, page 56.

    Uranus (magnitude 5.9, in western Pisces) is low in the east-southeast before the first light of dawn.

    Neptune (magnitude 7.9, in Aquarius) is in the southeast before dawn.

    Pluto (magnitude 14.0, in Sagittarius) is highest in the south around 1 or 2 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:
    http://SkyandTelescope.com/observing/ataglance?1=1

    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.

    • About Alan MacRobert

    Alan M. MacRobert became an avid Sky & Telescope subscriber in 1966 at age 14, joined the editorial staff in 1982, and is now a senior contributing editor, semi-retired. He played a role in practically every part of the magazine and the company's other products for more than a generation, both on the amateur-observing side and the science-reporting side. In 1994 a book collection of his observing how-tos and telescopic sky tours was published as Star Hopping for Backyard Astronomers. He has produced This Week's Sky at a Glance online every week since 1989.

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