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The Sky This Week, 2011 June 14 - 21

A long time ago in a galaxy not so far away ...

Supernova SN 2011dh in Messier 51, discovered 2011 May 31
Imaged with the USNO Flagstaff Station's 1.3-meter reflector, 2011 June 7 UT
U.S. Naval Observatory image courtesy of Dr. Marc Murison

The Moon emerges from Earth’s shadow shortly before rising on the evening of the 15th. Most of the rest of the world will have witnessed a total lunar eclipse by that time. In fact, this eclipse has the longest duration of totality since the eclipse of July 16, 2000. Our next opportunity to see a near-central lunar eclipse here in Washington will come in June of 2028, so mark your calendars! Luna spends the week skulking among the constellations of late summer and early autumn, climbing from the southerly reaches of the ecliptic as she wends her way toward Last Quarter, which occurs on the 23rd at 7:48 am Eastern Daylight Time. Look for the Moon in the vicinity of the "Teapot" asterism of Sagittarius on the evenings of the 16th and 17th. From there she moves into the sparsely populated fall constellations.

The summer solstice occurs on the 21st at 1:16 pm EDT. At that instant the center of the Sun’s disc stands directly above the Tropic of Cancer at a point along the north coast of Cuba. This also marks the year’s longest day, with a sunlight duration of 14 hours 55 minutes here in Washington. Careful skywatchers may notice, however, that the latest sunset for the year won’t occur until the 28th.

Some 27 million years ago a massive star in an outer spiral arm of a galaxy known as Messier 51 reached the end of its life. Within a matter of minutes the star’s core collapsed onto itself, then rebounded in a cataclysmic explosion known as a supernova. The "flash" of visible light from the dying star, billions of times brighter than the star’s normal light output, enabled Earth-based astronomers to detect the event on May 31, 2011. Supernovae are extremely rare events that occur infrequently in most galaxies. No supernova has been observed within our Milky Way galaxy since the one discovered by Johannes Kepler in 1604. While supernovae are discovered almost daily in very remote galaxies, the opportunity to study one in a nearby galaxy such as M51 comes along only a few times in a decade. Messier 51 is a favorite target of astronomers and may be seen with binoculars or small telescopes from dark locations on a Moonless night. It was nicknamed "The Whirlpool Nebula" by William Parsons, Third Earl of Rosse, who first detected the galaxy’s spiral structure with his 72-inch aperture reflecting telescope at Birr Castle in Ireland in 1845. Even at an estimated distance of between 23 million to 27 million light-years from Earth, M51 is one of the closer galaxies to the Earth and has therefore been studied extensively with state-of-the-art Earth- and space-based telescopes. Recent reports indicate that the supernova is now bright enough to be seen in 12-inch or larger backyard telescopes under dark skies!

Saturn remains as the only planet visible in the evening sky. The ringed planet is now well past the meridian as twilight fades, but he forms the westernmost apex of a large triangle with the bright stars Arcturus and Spica, and so should be easy to pick out. Saturn grudgingly resumes his eastward trek around the Zodiac on the 14. In the meantime he remains tightly wedged close to the third-magnitude star Porrima, one of the best-known double stars in the sky.

Pre-dawn observers can note the steady progress that bright Jupiter is making as he rises earlier each morning. Old Jove rises at around 3:00 am EDT now and is well up in the east as twilight begins to brighten the horizon. Half an hour before sunrise you can still catch the bright glimmer of Venus just above the horizon, but you need a very open view to the east to do so. Between these two is ruddy Mars, but it will probably be several more weeks before you can spot the red planet in the gathering twilight glow.

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