This Week's Sky at a Glance
Some daily events in the changing sky for June 17 – 25
by Alan M. MacRobert
M51 Supernova brightening. Supernova 2011dh, which was discoveredin the Whirlpool Galaxy, M51, on May 31st, has been brightening eversince — though the brightening is now leveling off. As of June 16th thesupernova was about V magnitude 12.6 and visible in a lot more amateurtelescopes.
TheM51 supernova is marked with the yellow tick. Lynn Hilborn of Grafton,Ontario, writes that she took this deep image of the galaxy on March24th 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 Ciccoimaged the galaxy and supernova again with his 16-inch scope and wasable to glimpse it visually with a 6-inch despite the moonlight. Hewrites, "With the Moon leaving the early-evening sky [as of about June19th] and M51 seen best as soon as it gets dark, now is the time forpeople to have a look. With higher magnification and a moderately goodsky, anyone with an 8-inch or larger scope should be able to spot thesupernova. I can’t remember the last time we had one that was thiseasily 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 theeast-southeast in late evening, depending on where you are. Far to itsupper left shines Altair. Farther on in the same direction are the othertwo stars of the Summer Triangle: Vega and lesser Deneb.
Saturday, June 18
The two brightest starsof summer are Vega, high in the east these evenings, and Arcturus, evenhigher in the southwest. They're moderately near neighbors of ours asstars go: 25 and 37 light-years away, respectively. But that's only partof why they appear so bright. Vega is hotter, larger, and 50 times moreluminous than the Sun, and Arcturus puts out 150 times the light of theSun.
Thelittle 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 BetaLyrae (near Vega) should be at minimum light all evening (centered on0:00 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 thewest-northwest for Pollux and Castor as twilight fades away. They'relined up not quite horizontally. These two "winter" stars have faroutstayed their season. How much longer can you follow them down? Pastthe first day of summer tomorrow?
Tuesday, June 21
The June solstice occursat 1:16 p.m. EDT. This is the moment when the Sun is farthest north forthe year and begins its six-month return southward. Summer begins in theNorthern Hemisphere, where this is the year's longest day. In theSouthern Hemisphere, winter begins.
If you have a good view of the west-northwest horizon (from mid-northernlatitudes), mark precisely where the Sun sets. In a few days you shouldbe able to detect that it's again starting to set a little south ofthis point. Build your own Stonehenge?
Wednesday, June 22
Now that the Moon isgone from the evening sky, try hunting out galaxies hear the head ofSerpens using Sue French's "Deep-Sky Wonders" chart, photos, and articlein the June
Sky & Telescope,page 62. Find the Sombrero galaxy above Corvus right after dark usingpage 45. And check out "Galaxies near Bright Stars" on page 68.
Thursday, June 23
Last-quarter Moon (exactat 7:48 a.m. EDT). The Moon rises very late tonight, around 1 a.m. EDTon the 24th depending on your location. Look above it for the GreatSquare of Pegasus.
Friday, June 24
With summer here, looksouth-southeast after dark for the bright constellation Scorpius, "theOrion of summer," now reasonably high and standing upright. Like Orion,Scorpius is marked by several 2nd-magnitude blue-white stars and one ofthe 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 highin 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 theNorthern Cross). Farther to Vega's lower right is bright Altair. Thesethree stars form the Summer Triangle. The summer Milky Way runs rightthrough it, along the length of the Northern Cross, if you have a darkenough sky.
