by Geoff Chester, USNO Public Affairs | 25 April 2023 The Moon (with Earthshine) and Venus, imaged 2023 April 23 from Alexandria, Virginia with a Canon EOS Rebel SL2 DSLR. HDR composite of five subframes, 100mm efl, f/8 @ ISO 1600. The Moon climbs high into the evening sky this week, passing through the setting winter constellations before taking a southerly track along the ecliptic. First Quarter occurs on the 27th at 5:20 pm Eastern Daylight Time. Luna begins the week in the company of Mars and the Twin Stars of Gemini before moving into Leo and the rising stars of the springtime sky. Look for Luna three degrees to the north of Mars on the evening of the 24th. On the 27th, use binoculars to try to spot the “Beehive” star cluster a few degrees below Luna’s half-illuminated disc. The Moon then courses through the stars of Leo, ending the week among the stars of Virgo. May 1st is May Day, an occasion that was once observed throughout most of Medieval Europe, but is now largely forgotten but for a few locales. It is an ancient calendar marker called a “cross quarter” day that marked the mid-point of an astronomical season. These dates, along with the solstices and equinoxes, were traditional days when serfs paid their rent to their feudal masters, usually in the form of livestock or grain. Each season has a cross-quarter day, and although their observance has mostly been lost to history, we still celebrate several of them. The three that most of us are familiar with are Halloween, Groundhog Day, and May Day. Lammas, which falls on August 1st, is the least observed today. Cross quarter days are still preserved in some traditions around the globe, especially in Celtic cultures, as the beginnings of seasons. This is why you will find that many people refer to June 21st as “Midsummer’s Day”. International Astronomy Week continues, culminating in Astronomy Day on April 29th. Weather permitting, amateur astronomers will share their love of the night sky with friends and neighbors, either at scheduled “star parties” or right from their own front yards. Here in the Washington, DC area members of the Northern Virginia Astronomy Club will set up their telescopes at the Smithsonian’s Udvar-Hazy Center in Chantilly, Virginia on Saturday night. There are many other astronomy clubs, planetariums, and science centers between Baltimore and Richmond; here’s a link to many of them. The brightening light of the waxing Moon begins to take a toll on the constellations of spring, none of which have the “star power” of winter’s bevy of first-magnitude luminaries. By the end of evening twilight half of the bright stars of the Great Winter Circle have set, while the rest hover over the western horizon. To the east you will see the lonely beacon of Arcturus climbing into the sky, but other bright stars are relatively few and far between. At 10:00 pm local time you will see two of the season’s brighter constellations crossing the meridian in the form of Leo, the Lion, and the “Big Dipper” asterism of Ursa Major. This is the time of year when the Dipper reaches its highest point in the sky, seemingly emptying the contents of its “bowl” toward Polaris, the star that marks the north celestial pole. On the southern side of the zenith you’ll find Leo, led by the bright star Regulus. Leo’s “head” forms an asterism commonly called “The Sickle”, which is in turn followed by a right triangle that outlines the Lion’s haunches. Together, the two patterns resemble an Egyptian Sphinx, and it doesn’t take a huge stretch of the imagination to imagine a crouching feline in that part of the sky. Venus spends the week crossing the constellation of Taurus, the Bull. By the end of the week she slices between the stars that mark the tips of the Bull’s horns. The dazzling planet gains about a minute on the Sun each evening, but her progress will begin to slow as May begins. We will enjoy her company until July, when she starts her plunge toward Old Sol. Mars moves through the middle of the constellation of Gemini, the Twins, and by the week’s end forms a right triangle with the stars Castor and Pollux. The red planet has lost much of the luster that he sported at opposition last winter, and he now shines with the same brightness as the Twin Stars. Look for Mars just below the waxing crescent Moon on the evening of the 25th. Early risers can greet distant Saturn low in the southeastern sky at around 5:00 am local time. The ringed planet is located among the faint stars of Aquarius, the Water Bearer, so you should have no trouble spotting his pale yellow glow in the gathering twilight.