Skip to main content (Press Enter).
Official Website of the United States Navy
Mission & Vision
Naval Oceanographic Office
Fleet Numerical Meteorology & Oceanography Center
United States Naval Observatory
News from the Naval Observatory
Earth Orientation Department
USNO Earth Orientation Products
Contents of Bulletin A
USNO GPS Products
GPS User Information
USNO VLBI-based Products
VLBI Correlator Data
VLBI-based Earth Orientation Parameters (EOP)
Earth Orientation Information Center
General Information about Earth Orientation
Frequently Asked Questions About Earth Orientation
What Is Earth Orientation?
What Is Polar Motion?
What does the Earth rotation coordinate measure?
What is the Celestial Pole Offset?
What is a Leap Second?
How do we measure Earth Orientation?
What causes variations in the Earth's orientation?
Who uses Earth orientation information?
Publications About Earth Orientation Products
Earth Orientation Software
Precise Time Department
The USNO Master Clock
The USNO Master Clock
Time Dissemination at the USNO
USNO Alternate Master Clock (AMC)
Cesium Atomic Clocks
Hydrogen Masers at the USNO
Rubidium Fountain Clocks
USNO Time Scales
International Time Scales and the BIPM
Definitions of Systems of Time
Global Positioning System
Global Positioning System Overview
USNO GPS Data Categories Explanation
CGGTTS Data Format
USNO GPS Time Transfer
GPS Information: SA, DGPS, Leap Seconds, etc.
GPS Week Number Rollover
GPS Timing Data and Information
USNO Format Explanation
USNO Computer Display Clocks
Two-Way Satellite Time Transfer (TWSTT)
Network Time Protocol (NTP)
US Eastern Time Zone NTP Servers
US Mountain Time Zone Servers
DoD Customer Servers
Astronomical Applications Department
Celestial Reference Frame Department
Naval Oceanography Operations Command
Fleet Weather Center - Norfolk
Fleet Weather Center - San Diego
Joint Typhoon Warning Center
Public Use of Limitations
United States of America Department of the Navy Seal
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
, 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
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.
DoD Accessibility/Section 508
No Fear Act
Plain Writing Act
Veterans Crisis Line
DoD Safe Helpline
Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529
Official U.S. Navy Website