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
Senior Enlisted Advisor
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
Reflections on a distant journey, and clusters in the summer sky
by Geoff Chester, USNO Public Affairs
13 July 2021
Crescent Moon with Venus & Mars, imaged 2021 July 12 from Alexandria, Virginia
with a Canon EOS Rebel SL2 DSLR. HDR composite of four exposures.
The Moon waxes as she dives southward along the ecliptic this week. First Quarter occurs on the 17th at 6:11 am Eastern Daylight Time. On the evening of the 16th you’ll find Luna to the northwest of the bright star Spica. By the end of the week the Moon will pass north of the star Antares in the constellation of Scorpius.
Each year in mid-July I take the time to reflect on an event that was a pivotal one in my experience. Fifty-two years ago I, along with millions of other people around the globe, spent the better part of a week glued to our television sets as the Apollo 11 flight to the Moon played out. From the liftoff of the massive Saturn-V rocket on the morning of July 16th to the splashdown of the tiny Command Module “Columbia” eight days later, I followed the flight almost minute-by-minute. One of the memories that stands out is watching Neil Armstrong take the first steps by a human on the surface of another world while simultaneously looking at the Moon through my 3.5-inch telescope. Outwardly the Moon looked the same as it had countless times before, but somehow on that night it was very different. There were three fellow humans up there, two on the surface and one in orbit, and although I couldn’t see them, I sensed their presence in the eyepiece. Since that time I have never looked at the Moon without knowing that we went there, if only for few fleeting moments. Each year I set the telescope up in my yard when the Moon is close to the same phase that it had on July 20th, 1969. This year that evening will be the 15th. The view never gets old.
The hazy nights of midsummer often mask the splendors of the season’s skies, but with a little patience you can find plenty of interesting sights to see despite the less-than-ideal conditions. Summer is the season for globular star clusters, which are spherical swarms of tens of thousands of stars that orbit the galactic center. About 150 of these clusters are known in the Milky Way’s environs, and the vast majority of them are visible during the summer and autumn months. Small telescopes show these clusters as spherical puffs of amorphous light, while a four-inch instrument will begin to resolve the brighter ones. My 8-inch reflector betrays the stellar nature of all but the most distant ones. Two of these clusters lie very close to bright stars in the summer sky and are quite easy to locate. The first is Messier 4, which lies just over a degree west of the star Antares inn Scorpius. This cluster should easily resolve in 4- to 6-inch telescopes, especially if you move Antares out of the field of view. Under dark skies the smaller, more distant cluster NGC 6144 may be glimpsed just a degree northeast of M4. One of my favorite globulars, Messier 22, may be found in the adjacent constellation of Sagittarius. This constellation contains an asterism formed by its brightest stars known as “The Teapot”, and the cluster lies just over two degrees northeast of the star Kaus Borealis, the star that marks the Teapot’s “top”. This is a bright, well-resolved cluster that is ideal for the small telescope. Once again, there are other more distant clusters near the reference star. Messier 28 lies just one degree west of Kaus Borealis, while the far-flung cluster NGC 6638 is located just half a degree to the east.
Early evening is now dominated by the bright glimmer of the planet Venus. The dazzling planet begins the week fresh from a close conjunction with the more distant Mars, but she quickly leaves her companion world in her wake as she presses eastward through the setting springtime stars. If you have binoculars look for the bright star Regulus to the east of Venus. By the end of the week the bright planet will close ranks with the star, which she will pass early next week.
Mars now lags behind his brighter rival and will continue to lose ground to Venus as he gradually sinks into the twilight haze. You will probably need binoculars to glimpse him as he also pursues the star Regulus.
The gas giants Saturn and Jupiter can now be seen in the late evening sky, glowing brightly in the southeast. Saturn rises at around 9:30 pm local time while Jupiter follows about an hour later. After the Moon, these two distant worlds are the night’s best targets for small telescopes. Jupiter sports his four bright Galilean moons and delicate streaks in his atmosphere, while Saturn displays his incomparable rings. They are well worth staying up late for.
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