by Geoff Chester, USNO Public Affairs | 21 March 2023 The Crescent Moon and Venus, imaged 2020 May 23 from Mollusk, Virginia with a Canon EOS Rebel SL2 DSLR. HDR composite of 5 frames. The Moon returns to the evening sky this week, and for many people it is one of the most important lunations of the year. More on that shortly. First Quarter occurs on the 28th at 10:32 pm Eastern Daylight Time. Look for the Moon near the bright glimmer of Venus on the evenings of the 23rd and 24th. On the evening of the 25th you will find Luna just two degrees south of the Pleaides star cluster, offering a fine deep twilight photo opportunity. The Moon ends the week bracketing the ruddy glow of Mars, high on the northern reaches of the ecliptic. As I mentioned above, this lunation is one of the most significant of the year for the followers of the Abrahamic religions of Christianity, Islam, and Judaism. For the followers of Islam, the holy month of reflection and fasting, Ramadan, begins with the first sighting of the thin crescent Moon in the evening sky. This will likely occur on March 22nd in the Gregorian Calendar. The Islamic Calendar is a strictly lunar calendar, with each month beginning with the sighting of the first crescent. The year consists of twelve months of either 29 or 30 days, depending on when the Moon is first sighted. Thus the year is either 354 or 355 days long, which is why Ramadan falls on different dates of each year in the Gregorian Calendar. Ramadan ends with the sighting of the next crescent Moon, which will end the fasting period on April 21, beginning the Islamic month of Shawwal with the Eid al-Fitr celebration. In the Hebrew Calendar, March 22nd marks 1 Nisan, the first day of the first month of spring. The celebration of Passover occurs on 15 Nisan, which corresponds to the Full Moon that falls on April 6. The Hebrew Calendar is a “Luni-Solar” calendar, with months dictated by the New Moon, with intercalary months introduced to keep the calendar in synch with the 19-year Metonic Cycle to make up the difference between the lunar months and the solar year. In Christianity, the date of Easter, the most important of the “moveable feast” days, is dictated by the Moon and the vernal equinox. Using an ancient formula known as the Computus, Easter (with very rare exceptions), falls on the first Sunday following the first Full Moon to occur after the “ecclesiastical equinox”, which always occurs on March 21st, no matter what the sky says. While Easter and Passover generally occur close to each other each year, this is one of those rare years when all three major observances occur at the same time. As we transition from the winter sky to that of spring, we bid farewell to the bright winter stars and welcome a single beacon that is now rising in the east. Rose-tinted Arcturus has always been my celestial sign of spring. It is the third-brightest star in the entire sky, and brightest in the northern celestial hemisphere. Its return brings warmer days and a fundamental change in what we view in the sky. Where the region around Orion is dominated by star clusters and bright glowing nebulae, Arcturus marks an area of the sky where we look out of the plane of the Milky Way toward the depths of intergalactic space. For sports fans it may be the time of March Madness, but for amateur astronomers it’s Galaxy Season! The early evening sky is the domain of bright Venus, who continues her climb above the western horizon each passing night. Venus generally appears in the evening sky five times in an eight year cycle, and the current apparition is the best for Northern Hemisphere viewers for this series. Venus was revered by the ancient Maya, and many of their ceremonial centers were built to mark the movements of the dazzling planet. Ruddy Mars keeps pace with the advancing Sun as he moves into Gemini. The red planet is moving eastward along the ecliptic at a pretty fast pace, and by the end of the week he lies in the same low-power telescope field as Messier 35, a bright star cluster at the “foot” of the twin Castor. He still maintains a colorful triangle shape with the red stars Aldebaran in Taurus and Betelgeuse in Orin.