Saturday, January 29, 2022

Arc to Arcturus




By Mike P. Usher


Extend the curve of the Big Dipper’s handle eastward and you will reach the bright star Arcturus. (You can always find it easily by remembering the mnemonic arc to Arcturus). The star itself is hard to miss; it’s the fourth brightest in the whole sky and the brightest star in the northern hemisphere – although Arcturus is close enough to the celestial equator to be easily visible over nearly the entire Earth. For the Hawaiian Islands this star appears directly overhead on summer evenings; ancient Polynesians could use this information to navigate to the southeastern shore of the Big Island. Arcturus is an orange giant star and it’s thought the Sun will look much like Arcturus in its old age.

Extend the curve of the Big Dipper’s handle past Arcturus and speed to Spica, the brightest star in the constellation Virgo. Rather dimmer than Arcturus, blue giant Spica is still the fifteenth brightest in the sky. The name Spica means “ear of grain”. Spica is only two degrees from the ecliptic – close enough that the Moon occasionally passes in front of it. This type of event is known as an occultation; important information about both the Moon and the star can be uncovered by careful studies of occultations.

The mythology of Virgo is a little confused, although nowadays the constellation is called “the Virgin”, since Babylonian times it has also been associated with fertility and the harvest. Possibly because in 2000 BC Virgo rose just before the Sun at harvest time and was a signal to reap the wheat. Alas, it is no longer the sign it once was; due to a phenomenon called precession of the equinoxes the Sun now is actually inside the constellation when it rises at harvest time and Virgo is invisible.

Virgo is the second largest constellation in the sky after Hydra. It takes the Sun about a month and a half to pass through it in the fall; a fact the horoscopes conveniently ignore.

On the other side of the sky Venus is putting on quite a show; the third brightest object in the sky after the Sun and Moon. Every night it will shine just a little brighter and rise a little higher until June 6; after that date it will still get brighter but begins to sink back towards the Sun.

See you next time!


Mr. Usher is a director of the Everglades Astronomical Society which meets the second Tuesday each month at 7:00PM in the Norris Center, Cambier Park, Naples.


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