As Halloween approaches, try looking for the star Beta Persei, otherwise known as Algol in the constellation Perseus. This star’s proper name comes from the Arabic for head of the ghoul, or head of the demon. Click here for a more detailed chart of Perseus and Algol. Halloween derived from ancient Celtic cross-quarter day This star is known to vary in brightness over a regular time interval. The cycle lasts 2 days, 20 hours and 49 minutes. All the while, the star remains visible to the eye. Algol’s brightness variations are not due to some special quality of a single star. In fact, this is a multiple star system, where one star regularly passes in front of another as seen from our earthly perspective.
Every Halloween – and a few days before and after – the brilliant star Arcturus sets at the same time and on the same spot on the western horizon as the summer sun. What’s more, this star rises at the same time and at the same place on the eastern horizon as the sun does during the dog days of summer.
However, 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.
In the Northern Hemisphere – around Halloween – this brilliant pumpkin-colored star playacts as the ghost of the summer sun. At mid-northern latitudes, Arcturus now sets about 2 hours after sunset and rises about 2 hours before sunrise. By 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. You can verify that you’re looking at Arcturus once the Big Dipper comes out. Its handle always points to Arcturus. By the way, if you live as far north as Barrow, Alaska, the star Arcturus shines all night long, mimicking the midnight sun of summer.