by Geoff Chester, USNO Public Affairs | 24 October 2023 NGC 457, the "Owl Cluster" in Cassiopeia imaged 2019 September 27 at Blackwater Falls State Park, Davis, WV with a 10.2-cm (4-inch) f/6.5 Explore Scientific refractor and a Canon EOS Rebel SL2 DSLR The Moon climbs northward through the autumnal constellations this week, waxing to Full Moon on the 28th at 4:24 pm Eastern Daylight Time. You will find Luna to the east of yellow-hued Saturn on the evening of the 24th. On the 28th, the Moon’s full disc is just three degrees northwest of bright Jupiter. Luna ends the week among the rising stars of the winter constellations. October’s full Moon is widely known as the Hunter’s Moon, and it shares some of the same orbital geometry that produced last month’s Harvest Moon. Once again, the shallow angle of the Moon’s orbit with respect to the eastern horizon causes successive moonrises at the time of the full Moon to be closely spaced. Since the fields have already been harvested, there is little cover for game birds and animals, and hunters take advantage of the light of the rising Moon to pursue their quarry. The Hunter’s Moon will have another wrinkle this year for residents of most of Asia, Africa, and Europe. Viewers there will be treated to a partial, albeit small, partial lunar eclipse, where a small “bite” from the Earth’s umbral shadow will obscure about 12 percent of the Moon’s southern limb. October ends with the darkest of the traditional “cross-quarter” days, which we continue to observe as Halloween. These dates fall between the astronomical seasonal markers of equinoxes and solstices, and were widely observed in medieval times, especially in Celtic Europe. The Pagan feast of Samhain, which marked the end of the harvest and the coming of the long, dark nights of winter, became the Christian observance of All Hallow’s Eve, the prelude to All Saint’s Day on November 1st. Many of the traditions that we observe on Halloween were brought to America in the 19th Century by Irish and Scottish settlers, including dressing in costume and asking for “treats”. Interestingly, the popularity of Halloween has spread from America back to Europe, where the traditions are becoming re-established! This is one of my favorite times of the year for stargazing with my telescopes from the front yard. Despite the brightness of the full Moon and the pervasive street lights of my suburban location, the clarity of autumn air lets me track down dozens of double stars and star clusters that may be found in the brighter autumnal constellations. In the early evening it is still possible to see one of the most attractive double stars in the sky near the center of the retreating Summer Triangle. The star Albireo is one of the most colorful pairs in the sky, and the generous separation of its gold and blue components make it a splendid target for small telescopes. I actually prefer looking at it with smaller apertures; larger telescopes tend to wash out the delicate colors. By 10:00 pm the small, W-shaped constellation of Cassiopeia is climbing high in the northeastern sky. This distinctive group lies along the plane of the Milky Way, and it is chock full of star clusters to delight Earthbound observers. One of my favorites is located a few degrees south of the stars that form the left side of the “W”. Sweeping this area with a small telescope will reveal a scattering of stars with two brighter members off to one side. Place those stars near the top of your field of view and you will understand why this cluster, NGC 457, is widely known to amateur astronomers as the Owl Cluster! Saturn now crosses the meridian at around 9:00 pm local time. This is when the ringed planet reaches his highest point above the horizon, so take some time to train the telescope his way. Even a low magnification will reveal his mysterious rings, and as you increase the power more details will be revealed. A good three-inch telescope at 100X will show the hairline dark line near the rings’ outer edge that betrays the Cassini Division, a true gap in the ring system caused by gravitational resonance with the planet’s icy inner moons. Larger telescopes will bring out the subtle colors of the rings and some of the dusky cloud belts on the sphere of the planet itself. Jupiter is just over a week from opposition, and his bright glow dominates the eastern sky after around 8:00 pm. By 10:00 pm he’s well up in the east and beckons for a telescopic view. Old Jove is the best planet for small telescope owners. Not only is his disc nice and bright, his four large Galilean moons constantly change positions from night to night. You can even watch their orbital motion when they are near the planet’s limb. The pre-dawn sky is now dominated by the brilliant light of Venus, which is now at the peak of the current morning apparition. She is so bright that you can follow her westward progress on clear mornings until well after sunrise. It is therefore no wonder why the ancient Maya followed her motions as she moved from the morning to evening sky and vice versa. Their calendar, which is accurate over the span of some 2 million years, is based on their careful observations of the dazzling planet.