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

A Mid-Summer Celebration?

by Geoff Chester, USNO Public Affairs
26 July 2022

The Milky Way, Scorpius, and Sagittarius, 2020 July 26
Imaged from Mollusk, Virginia with a Canon EOS Rebel SL2 DSLR and an Omegon LX2 mechanical star tracker

The Moon returns to the evening sky this week, appearing as a slender crescent after New Moon, which occurs on the 28th at 1:55 pm Eastern Daylight Time.  If it’s clear on the 29th, and if you have a flat western horizon, look for the day-old lunar crescent half an hour after sunset.  She will be just a few degrees above the horizon, but should be easy to spot, especially with binoculars.  Two degrees below Luna’s sliver, look for the glow of Mercury in the twilight.  By the end of the week the Moon’s growing crescent will be closing in on the bright star Spica.

As July transitions to August, we have a somewhat obscure astronomical event to observe.  It occurs on August 1st, when we pass a date in ancient traditional calendars.  As you know, the astronomical seasons are defined by clearly-defined dates, the solstices and equinoxes.  We know that these seasonal markers were important events in early civil and religious calendars since we find evidence of structures used to determine them from multiple bygone cultures around the globe.  Examples such as the complex of constructions surrounding Stonehenge, megalithic structures that abound throughout northern Europe, and ancient Egyptian temples have been found to align with the movements of the Sun to define calendars and time-scales for human activities.  In the Americas we also find such cultural relics among the ruins of Inca, Maya, and Aztec cities as well as their more ancient predecessors, and in the U.S. there are dozens of sites that mark these critical dates.  Less well-known are the dates that fall between the seasons, the so-called “cross-quarter” days.  Most widely observed among Pagan cultures in Europe, these dates marked the mid-point between each astronomical season.  Traditionally these were the dates when serfs payed rent to their landlords.  Some of these dates have survived to be celebrated in modern times, and we still observe Halloween, Groundhog Day, and May Day.  Less well known is Lammas, the fourth cross-quarter day that falls on August 1st.  This day derives from the Celtic observance of “Lughasadh” that was marked by athletic contests and the celebration of the first fruits of the year’s new harvest.  As with the other cross-quarter days, the pagan rituals were adapted to Christian feasts and festivals.  The name “Lammas” derives from “Loaf-mass”, when the bread used in the rite of Communion was made with the first new grain of the year.

The August sky is characterized by the splendor of the summer Milky Way and its attendant bright stars and constellations.  As evening twilight ends the colorful constellation of Scorpius sails across the meridian to the south.  The Scorpion’s ruddy heart, marked by the bright star Antares, contrasts with the bluer members that make up much of the creature’s head and body, with the pair of stars that marks its “stinger” embedded in one of the Milky Way’s densest star clouds.  Just east of Scorpius is the constellation of Sagittarius, the Archer, whose distinctive shape looks more like a teapot than a centaur.  Just above the teapot’s “spout” the Milky Way rises like a cloud of steam to the northeast, where it pierces the center of the Summer Triangle, an asterism composed of the bright stars Vega, Deneb, and Altair.  This is an area of the sky that is wonderful to explore with binoculars.  The amorphous glow of the Milky Way begins to resolve into clouds of countless stars interspersed with bright knots of light that reveal star clusters and glowing gas clouds in small to modest telescopes.  It’s a great way to enjoy a pleasant summer evening.

As mentioned earlier, you have a chance to glimpse the elusive planet Mercury near the hairline crescent Moon on the evening of the 29th.  Once you’ve found him you should be able to re-locate him over the next several nights.  This isn’t a very favorable evening apparition for the fleet planet, so finding him at all is a small victory.

By midnight two bright planets are in view.  The first is Saturn, which is high in the southeast at that time, while Jupiter shines brightly in the southeast.  As the morning hours tick by the two gas giants climb higher and are joined by the ruddy glow of Mars, which rises just before 1:00 am in the east.  As morning twilight begins to brighten the eastern horizon look for dazzling Venus to complete the planet parade.
 
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