The Sky This Week
U.S. Naval Observatory's Weekly Blog

Late Dusks and Early Dawns

by Geoff Chester, USNO Public Affairs
21 June 2022

Messier 5, globular star cluster in Serpens, imaged 2022 June 20 from Alexandria, VA, USA
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor, iOptron AZ Mount Pro, and a ZWO ASI183MC CMOS imager.
"Live Stack" of 31 10-second exposures captured with an ASIAir Pro digital telescope/camera controller.

The Moon graces the early morning sky this week, passing through the rising autumnal constellations as she wanes toward New Moon, which will occur on the 28th at 10:52 pm Eastern Daylight Time.  Luna begins the week between the planets Jupiter and Mars before setting her sights on the bright glow of Venus.  She flirts with the dazzling planet on the mornings of the 24th and 25th.

The first full day of summer heralds the shortest night of the year.  From a dark sky site there are just over five hours of total darkness between the end and beginning of astronomical twilight.  Those of us who thrive on gazing at “faint fuzzies” through our telescopes thus have precious little time to enjoy our passion.  To add just a bit more irony, the year’s latest sunset occurs on the 28th.  In Washington that means that Old Sol goes below the horizon at 8:38 pm EDT, with astronomical twilight ending two hours later.  For astronomers, though, the passing of the solstice means that the nights will slowly get longer, and we’ll once again have darker skies at reasonable hours.

Late night darkness notwithstanding, the June campaign for the Globe at Night citizen-science observing program runs through the week until the evening of the 29th.  The target constellation this month is Hercules, the Strong Man, which occupies much of the space between the bright star Arcturus near the meridian and Vega, rising in the northeast.  Hercules has few bright stars; none are brighter than second-magnitude.  He does have a distinctive asterism, though, made up of four third-magnitude stars and known as “The Keystone” due to its resemblance to the top stone in a Roman arch.  The Keystone is difficult to see from urban and suburban skies, but its distinctive shape and position between the two bright stars make it fairly easy to spot in darker locales.  The Globe at Night website should help you locate Hercules in your sky, and the site’s web app will give you simple instructions to record your observations.  So far this year over 11,000 people have recorded sky brightness estimates for the project, more than halfway to their annual goal of 20,000.

The approaching weekend heralds one of the biggest “star parties” in the country.  The annual Astronomy Festival on the National Mall will take place on the 25th in Washington, DC from 6:00 to 11:00 pm EDT.  In the past this event has attracted thousands of participants and dozens of telescopes provided by amateur astronomer as well as demonstrations and exhibits sponsored by many different space-themed entities.  This is a great opportunity to explore the world of amateur astronomy with dozens of other like-minded people and to look through a wide variety of telescopes at many of the splendors that the summer sky has to offer.  We will have instruments to safely observe the Sun, and as darkness falls we will move to observing bright double stars and star clusters.  The event will take place between 3rd and 4th Streets near the U.S. Capitol grounds, and best of all it’s free!

The summer sky brings the densest parts of our Milky Way galaxy into view, and with those massive star clouds we also see a special kind of star cluster.  Known as globular clusters, these objects hover around the great halo of older stars that surrounds the Galaxy’s center.  They all have a distinctive round shape and in small telescopes look like a puff of smoke.  Larger aperture telescopes begin to resolve them into their component stars, which can number in the hundreds of thousands in larger instruments.  Most of these objects are located tens of thousands of light years away from us and hold some of the oldest stars known in the universe.

The parade of planets in the morning sky is gradually stretching into the late night hours.  Saturn now rises before midnight in the southeastern sky and is followed by Jupiter, Mars, and Venus before morning twilight begins to brighten the eastern horizon.  The elusive planet Mercury rises in the brightening twilight and may be found in binoculars about halfway between Venus and the horizon about 20 minutes before sunrise.  This is one of those rare opportunities to see all of the planets known to the ancients in the sky at the same time.

 
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