by Geoff Chester, USNO Public Affairs | 28 March 2023 The Moon, imaged 2022 May 12, 01:50 UT from Alexandria, Virginia with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor, 1.6X Barlow lens, and a ZWO ASI183MC CMOS imager. Click in the image for the full resolution version. The Moon moves away from the winter constellations and moves southward along the ecliptic to meet up with the rising springtime stars. Full Moon occurs on April 6th at 12:34 am Eastern Daylight Time. Luna begins the week just to the northeast of the ruddy glow of Mars. On the following evening she cozies up to the star Pollux, forming a triangle with that star and its twin, Castor. She ends the week by closing in on the bright star Spica in the southeastern sky. April’s Full Moon goes by a variety of names in the skylore of different cultures. It is most commonly known as the Pink Moon since it coincides with the blooming of spring wildflowers. It is also known as the Breaking Ice Moon, Budding Moon, Seed Moon, and Egg Moon. This year, though, it is referred to as the Paschal Moon, since it is the ecclesiastical Full Moon that is used to calculate the date of Easter. The name derives from the Aramaic “Pascha”, the Jewish celebration of Passover. Most people think of Easter as falling on the first Sunday following the Full Moon that occurs after the vernal equinox. However, the date is actually determined by a set of rules known as the Computus. The origins of the Computus date back to the Council of Nicaea, convened in the year 325 CE. It was at this conclave that the “ecclesiastical equinox” was defined as occurring on March 21 and the concept of a Paschal Moon, as defined by the 19-year Metonic Cycle, would fix the Easter celebration. The Paschal Moon would thus fall on the same day every 19 years, so a simple table would allow parish priests to compute the dates of Easter for decades into the future. Easter thus fell on the Sunday following the Paschal Moon, which was the tabular Moon that fell after March 21. The waxing Moon dominates the evening sky this week, standing near the zenith as the week opens. She remains quite high in our sky through the week, and her phase reveals more of her battered surface features with each passing night. Her features can be discerned quite easily in a steadily held pair of binoculars, and more detail is revealed if you have a good spotting scope. However, the small- to moderate-aperture telescope is far and away the best way to enjoy our nearest neighbor in space. Luna’s terminator line slowly reveals new features with each passing night. One of her most prominent features is well-placed on the evening of the 31st. Just north of the center of the terminator is a very prominent crater named for the astronomer Nicolas Copernicus. Its steep, terraced walls and prominent bright “rays” give it a very fresh appearance, but it formed somewhere around a billion years ago! While comparatively small compared to the vast Mare Imbrium basin, it is still 93 kilometers (56 miles) from rim to rim. Winter’s bright stars hang on to make a final stand in the western sky. At the end of evening twilight you will find Orion in the southwest, surrounded by the bright stars of the Great Winter Circle. The first of these bright stars to set is Rigel in Orion, which goes below the horizon at around 11:30 pm. By midnight bids his farewell. The most prominent constellations at the midnight hour are Leo, the Lion, and the Big Dipper asterism of Ursa Major. You may have seen headlines of late that tout the visibility of five planets in the evening sky. What they didn’t tell you is that two of these worlds are very hard to see without a telescope, and another is a bit of a challenge to find. The early evening sky hosts the elusive planet Mercury. Half an hour after sunset, look for the fleet planet just above the western horizon. As the week opens he’s only five degrees above the treeline and should be visible in binoculars. Just below Mercury is Jupiter, which should also be visible in binoculars, but not for long. Jupiter is headed for solar conjunction, but Mercury will continue to climb a bit higher each night. He will be at his greatest elongation from the Sun next week. Venus remains a steady bright beacon in the west, staying visible well into the late evening. On the evening of the 30th use your binoculars to track down distant Uranus, which will be just over a degree to the left of Venus. Uranus will look like a grey-greenish star in binoculars. A good 4-inch telescope will resolve his tiny disc. The last of the five evening planets is Mars, is now drifting through the “feet” of Gemini, the Twins. On the first few nights of the week the red planet is located near the galactic star cluster Messier 35, which will look like a fuzzy patch of light in binoculars from a dark sky site. His ruddy glow continues to fade; he’s now dimmer than his other red-tinted companions, the stars Betelgeuse and Aldebaran.