You are here: Home USNO News, Tours & Events Sky This Week The Sky This Week, 2016 May 31 - June 7
The USNO websites,,,,, and are undergoing modernization efforts. The expected completion of the work and return of service is estimated as 30 April 2020. Please submit a requirements form to the USNOPAO if the information you are seeking is not accessible via other means.

The Sky This Week, 2016 May 31 - June 7

Saturn reaches opposition.
Mars, Saturn, Scorpius, and the rising summer Milky Way,
imaged from near Belle Isle State Park, Morattico, Virginia
on 2016 May 29

The Moon spends the better part of the week as a slender crescent, visible just before sunrise until New Moon, which occurs on the 4th at 11:00 pm Eastern Daylight Time. By the week’s end she may be spotted during evening twilight, wending her way between the last of winter’s stars.

We are now well into the season of the shortest nights of the year, so you only have about five and a half hours to explore the sky under maximum darkness from the vicinity of Washington. With such a short time available it is more important than ever to understand the impact of artificial night lighting by helping scientists map the distribution of light pollution. This sets the stage for the June campaign of the Globe at Night citizen-science program. This month’s featured constellation is Boötes, the Herdsman. The main star in Boötes is easy to find since it is the brightest star in the northern sky, Arcturus. Arcturus is high in the eastern sky at 10:00 pm, which makes it almost impossible to miss. The rest of the constellation consists of second-magnitude and fainter stars that take the shape of a kite, with Arcturus marking the kite’s tail. From my suburban location I can only spot three of the constellation’s stars, but observers in darker sites should be able to make out the kite’s complete shape. For the Globe at Night project you can report the number of stars that you can see from your chosen site. I was fortunate to be at Belle Isle State Park in Virginia’s Northern Neck over the recent holiday weekend; from this location stars down to sixth magnitude were visible along with the rising star-clouds of the summer Milky Way.

High overhead at the end of evening twilight you’ll find the distinctive asterism that we call the Big Dipper. It’s a great place to start your late spring evening’s sky tours. Test your eyesight by looking at the star Mizar, which forms the "bend" in the Dipper’s "handle". With the unaided eye you should be able to spot a faint star tucked nearby. This star is known as Alcor, and it has been used as a vision test for thousands of years. Fortunately my eyeglasses allow me to see it! But point a small telescope at these two stars and you’ll find a nice surprise: Mizar itself is a true double star, with its two components orbiting each other over the course of a millennium. Modern spectroscopy indicates that each of the components of Mizar are very close binary systems themselves, making Mizar a true "four star" attraction. The Big Dipper also boasts a number of deep-sky objects including the bright galaxies M51, M81, M82, and M101.

Jupiter is now well west of the meridian by the end of evening twilight, but he still provides a good view through the telescope. You can start observing him as soon as he becomes visible after sunset. Keep an eye out for Jupiter’s famed Great Red Spot, which will rotate across the planet’s disc on the evenings of the 2nd and the 4th.

Mars has just passed his closest point to the Earth for the current apparition, sporting a disc that is about half the apparent size of Jupiter’s. Unfortunately his southerly declination means that he never gets higher than 30 degrees above the southern horizon when he transits at around local midnight. However, on nights with steady air you should be able to see some of his surface features. By the week’s end a feature known as Solis Lacus should be in view, looking somewhat like a dark greenish eye on the planet’s rusty face.

Saturn reaches opposition in the wee hours of June 3rd, rising at sunset and setting at sunrise. He crosses the meridian at around 1:00 am at this time. During the days leading up to and just after opposition you may notice a curious lighting effect. During this time the planet’s rings become much brighter than the planet’s disc in much the same way that the Moon’s surface becomes much brighter around the time of Full Moon. Known as the "Seeliger Effect", it is only visible when Saturn is close to opposition.

USNO Master Clock Time
Javascript must be Enabled