Every Halloween – and a few days before and after – the brilliant star Arcturus, brightest star in Bootes the Herdsman, sets at the same time and on the same spot on the west-northwest horizon as the summer sun. This star rises at the same time and at the same place on the east-northeast horizon as the summer sun. That’s why – every year at this time – you can consider Arcturus as a ghost of the summer sun.
At mid-northern latitudes, Arcturus now sets about two hours after sunset and rises about two hours before sunrise.
If you live as far north as Barrow, Alaska, the star Arcturus shines all night long now, mimicking the midnight sun of summer.
If you live in the Southern Hemisphere, you can’t see Arcturus right now. South of the equator, Arcturus sets at the same time and on the same place on the horizon as the winter sun. In other words, Arcturus sets before the sun and rises after the sun at southerly latitudes at this time of year.
If you are in the Northern Hemisphere, try watching this star in the October evening chill. You can envision the absent summer sun radiating its extra hours of sunlight. Not till after dark does this star set, an echo of long summer afternoons. Similarly, Arcturus rises in the east before dawn, a phantom reminder of early morning daybreaks.
Halloween – also known as All Hallows’ Eve or All Saints’ Eve – is observed in various countries on October 31, especially in the United States. It’s a big deal for America children, who roam from house to house trick or treating, hoping for candy and other treats.
This modern holiday is based on a much older tradition, that of cross-quarter days.
Bottom line: At mid-northern latitudes, Arcturus sets about two hours after sunset around Halloween, at the same point on the horizon as the summer sun. It’s a Halloween ghost of the summer sun and an echo of long summer afternoons.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.