You are here: Home USNO News, Tours & Events Sky This Week The Sky This Week, 2020 January 28 - February 4
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, 2020 January 28 - February 4

Lunacy and groundhogs
The Moon near First Quarter phase, 2016 November 7, imaged at the U.S. Naval Observatory
The Moon near First Quarter phase, 2016 November 7, 22:42 UT
Imaged with a Canon EOS Rebel T2i DSLR and USNO's 30.5-cm (12-inch)
Clark/Saegmüller refractor.

The Moon waxes from crescent to First Quarter this week, ending the week among the bright stars of the Great Winter Circle.  First Quarter occurs on February 1st at 8:42 pm Eastern Standard Time.  Look for Luna passing between the bright star Aldebaran and the Pleiades star cluster on the evening of the 3rd. 

This is a good week to dust off the telescope and explore our only natural satellite.  As the Moon waxes she climbs higher along the ecliptic, placing her well above the horizon for telescopic perusal. A higher altitude means that there’s less of our own atmosphere to look through, and typically this allows for sharper rendering of the Moon’s finer details.  Don’t expect to see any of the flags left at any of the Apollo landing sites, though.  Under the best of circumstances a telescope such as our venerable 12-inch refractor won’t show features much smaller than a kilometer or so.  That said, there’s a great deal of detail that can be glimpsed on Luna’s desolate surface from your own yard with a modest instrument.  I particularly like the days just before and after First Quarter when the slow-moving terminator line reveals the battered southern “highland” area.  Here you will find mute testimony to the violent formation of the solar system, with impact craters packed one on top of another.  This surface is one of the oldest we see in the solar system and reflects an age of intense bombardment of newly-formed planets by thousands of “planetessimals”.  This period has largely been wiped from Earth’s geological record by plate tectonics and erosion, but on the airless Moon it is a “window” on conditions that existed over four billion years ago.

February 2 is a date that is widely celebrated as “Groundhog Day” where, according to legend, we rely on the prognostication power of a large indigenous rodent of the marmot family to tell us how long winter will last.  According to the legend, if the groundhog sees its shadow on that fateful morning, winter will last for another six weeks.  Statistically the groundhog has nearly a 100 percent chance of being correct, since the vernal equinox falls just over six weeks from the 2nd.  However, astronomical seasons don’t necessarily correspond to meteorological ones, so the groundhog’s “guess” is about as good as anybody else’s this far in advance.  While we may think of Groundhog Day as a quaint observance by a group of dapper-dressed folks in a small Pennsylvania town, it is actually a traditional astronomical observance whose roots date back over a thousand years.  As it turns out, Groundhog Day is what was once known as a “cross-quarter” day, one of eight traditional days when feudal serfs paid their land-owner masters.  These dates were determined by the astronomical seasons as defined by the equinoxes and solstices.  These annual markers divided the year into quarters, and the dates halfway between these markers further divided the year into eighths.  We are all familiar with the quarter days, but the cross-quarter days have become a bit more obscure.  However, three of these dates still linger in our modern culture, so if you observe Groundhog Day, May Day, and Halloween, you are unwittingly carrying on the tradition.  The fourth cross-quarter day, Lammas, which falls on August 1st, seems to have vanished in American folklore, but in many European cultures it is the day to start one’s traditional summer vacation.

Venus keeps an eye on the waxing Moon as the latter pulls away in the evening sky.  The pair are close together at dusk on the 28th, then Venus resumes her lonely vigil in the sparse constellations of the autumn sky.  The dazzling planet continues to pull away from the approaching Sun as she moves northeastward along the ecliptic, and she now sets almost two hours after the end of evening astronomical twilight.  You should have no trouble spotting her in the west shortly after sunset.

Mars now rises at around 4:00 am local time, and as morning twilight gathers you can find the red planet low in the southeastern sky.  Mars is steadily moving eastward along the southernmost part of the ecliptic, passing through constellations that we associate with the summer sky.  If you’re up at around 6:30 am and have a clear view to the southeast start looking for the bright glimmer of Jupiter.  Mars is drawing a bead on the giant planet, and early risers in mid-March will get a great view as Mars passes his distant companion.

USNO Master Clock Time
Javascript must be Enabled