You are here: Home USNO News, Tours & Events Sky This Week The Sky This Week, 2018 January 23 - 30
The USNO websites,,,,,, and are undergoing modernization efforts. The expected completion of the work and the estimated return of service is Fall 2020, subject to change due to potential impacts of COVID-19.

The Sky This Week, 2018 January 23 - 30

A Super-Bloody-Blue lunar eclipse?
Total Lunar Eclipse of 2014 October 8, 10:40 UT
imaged from Alexandria, Virginia with a Canon EOS Rebel T2i DSLR
and 250mm lens at f/8, 0.6 seconds, ISO 1600.

The Moon climbs high into the winter constellations as she waxes to Full Moon early next week.  This Full Moon will fall on the 31st at 8:27 am Eastern Standard Time.  This will be the second Full Moon for the month of January, which sets up an interesting scenario for the next two months.  Since February only has 28 days in 2018, there will be no Full Moon during that month.  Instead, March will also have two Full Moons.  This last occurred in 1999, and will next happen in 2037.  Note the 19-year differences in these dates; this was first described by the Greek astronomer Meton of Athens in 432 BCE.  The second Full Moon of a calendar month is often known as a “Blue Moon”, so this year you’ll have two chances to observe an event that occurs “once in a Blue Moon”!

The Full Moon that falls on the 31st has yet another special aspect to it: it will also pass through the shadow of the Earth, resulting in a total lunar eclipse.  Here in Washington we’ll get a brief glimpse of Luna as she begins to slip into the Earth’s umbral shadow shortly before moonset.  If you look to the west at around 6:15 am you may start to notice a subtle darkening of the Moon’s eastern limb as she moves through the penumbral shadow.  The umbral phase then begins at 6:48 am, but Luna will only be four degrees above the horizon.  She sets at 7:15 am, when she is about 25 percent obscured.  Folks who live further west will see more of the eclipse, and residents along the Pacific coast will see all of the total phase.  The best places in the U.S to see it from are Alaska and Hawai’i.  For what it’s worth, this eclipse occurs about a day after the second-closest lunar perigee of the year, which has led some people to refer to it as the “Super Blue Blood” Moon.  This is actually a fairly rare coincidence, happening only twice in the 500 years between 1800 and 2300.  The next such occurrence falls exactly one Metonic Cycle from now on January 31, 2037, so if you miss this one you still have another chance to experience it.  For those of you who just want to see the next total lunar eclipse visible from all of the U.S. you’ll only have to wait until January 21, 2019.

The waxing Moon washes out the fainter stars as the week progresses.  This shouldn’t be too discouraging to the casual skywatcher, though, since the bright stars of the Great Winter Circle shine through the light scattered by our atmosphere.  Most urban stargazers probably won’t notice much of a difference from their light-polluted yards and can still find plenty of interesting things to look at, especially with a small telescope.  One of my favorite activities during these winter Moon cycles is turning the telescope to the bright stars that dominate the winter sky.  Start high overhead with the star Capella, northernmost star in the Great Winter Circle.  This star shows a beautiful golden hue in small instruments.  Now proceed southwestward to Aldebaran, whose reddish tint marks the fiery eye of Taurus, the Bull.  Move on to the icy-blue glow of Rigel, then on to the dazzle of Sirius, brightest star in the sky.  Moving northward you’ll find Procyon, a star that always appears as a dazzling white luminary to my eyes.  North of Procyon you’ll find the Twin Stars of Gemini, Pollux and Castor.  Pollux has a faint yellowish hue that contrasts with the blue-white of Castor.  Castor itself is a close double star that should resolve in most small telescopes.  Finally, near the middle of the Circle is Betelgeuse, Orion’s ruddy “lead” star.  In my 3- and 4-inch telescopes it has a distinctive pink-orange tint, offering a striking contrast to Orion’s other bright star Rigel.  While all of these stars appear to be projected on a hemisphere over our heads, the variation in their distances is very large.  Sirius is bright because it is only 8.6 light-years from the Sun; Rigel is 100 times more distant!

Bright planets are hard to come by in the evening sky.  They are best seen before sunrise, but they are gradually becoming better-placed for casual observation.  Jupiter leads the way, hanging in the south among the dim stars of Libra.  Old Jove is hard to miss, but you’ll have to look a bit more carefully for nearby Mars.  The red planet moves into the “head” of the rising constellation Scorpius this week, and over the next few weeks he’ll drift north of the bright reddish star Antares, whose name literally means “Rival of Mars”.  If you have a clear view of the eastern horizon try to pick out Saturn in the twilight glow.

USNO Master Clock Time
Javascript must be Enabled