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The Sky This Week, 2015 June 9 - 16

Our shortest nights are upon us.
Cass_to_Sag_140524_01small.jpg
The summer Milky Way from Cassiopeia to Sagittarius
imaged from Morattico, Virginia

The Moon wanes through her crescent phases in the pre-dawn hours this week, passing through autumn’s sparse star-fields as she skirts the southeastern horizon. New Moon occurs on the 16th at 10:05 am Eastern Daylight Time. Luna has very few bright companions to call on this week, the exception being a one-degree encounter with a fourth-magnitude star with the tongue-twisting name of Torcularis Septentrionalis, the name bestowed on the star Omicron Piscium in a 1515 edition of Ptolemy’s “Almagest”.

By the end of the week we begin to enter the two-week series of events tied to the Summer Solstice. Due to the small but measurable eccentricity of the earth’s orbit the dates of earliest sunrise and latest sunset occur about a week before and a week after the solstice respectively. Here in the Washington, DC area Old Sol will rise at his earliest time for the year, 5:42 am EDT, on the morning of the 14th. By the time we see our latest sunset on the 28th sunrise will be about three minutes earlier.

The nights around the summer solstice are the shortest we’ll experience for the year, just over five hours long between the end of evening twilight and the beginning of morning twilight. This leaves us with little time to enjoy the sights of a moonless dark sky, but if you’re up late in the evening you can help chart the brightness of your local sky by participating in the citizen-science “Globe at Night” program. This month’s campaign uses the stars of the constellation Boötes, the Herdsman. While the ancients would like you to imagine the figure of a man leaning on a staff holding two dogs on leashes herding Ursa Major (the Great Bear) around the pole, I find it far easier to imagine an ice-cream cone with the bright star Arcturus marking the cone’s pointed tip. Most of the constellation’s other stars are much fainter second- and third-magnitude stars. From my suburban lawn I can spot only three other stars besides Arcturus, but in darker skies you should be able to pick out up to a dozen more.

By midnight the sky begins to undergo a significant change. Rising in the east are the bright stars associated with the midsummer sky, dominated by the trio of first-magnitude stars known as the Summer Triangle, Vega, Deneb, and Altair. Running from north to south through the triangle are the bright star clouds of the Milky Way, which reach down to the southern horizon to the east of the bright reddish star Antares, brightest star in the constellation of Scorpius, the Scorpion. These star clouds will be wonderful targets for binoculars and small telescopes as the summer progresses. Chock full of star clusters and glowing nebulae, these areas of the sky offer a welcome sight after evenings spent hunting down faint galaxies in the dark spaces between the spring’s few bright stars.

Bright Venus closes to within 10 degrees of slightly dimmer Jupiter during the course of the week. The two planets will converge over the course of the next few weeks, then spend a week less than a degree apart from each other after a spectacular close conjunction on June 30th.

Jupiter is becoming increasingly difficult to observe in a telescope as he steadily loses ground to the advancing Sun. Strong summer sun heats up rooftops and tree canopies which then radiate that heat back into the sky after sunset. By the time the air stabilizes Old Jove is not very far from the western horizon. You can still track the comings and goings of his four bright moons, but searching for fine detail in his cloud tops is now a very difficult task.

Saturn crosses the meridian at midnight, so the hours between twilights are the best times to view him. Despite his southerly declination the ringed planet shows off his signature rings to owners of small telescopes. They are tilted about 25 degrees to our line of sight, giving the planet a unique aspect among all of the sights in the night sky.

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