Tuesday, April 13, 2021

The Chained Princess



By Mike P. Usher

Tonight we look at the sky in the same place as we did last time; being two weeks later, the sky has obligingly rotated westward about 15 degrees bringing new stars into view.

Nearly centered in the chart is Andromeda, the chained princess. Her mother, the nearby Cassiopeia, had a disagreement with the gods, ultimately resulting in Andromeda’s confinement to a rocky beach. She was rescued by her future husband Perseus just before being devoured by a sea monster (the nearby constellation of Cetus).

Andromeda the constellation is rather unusual in that it shares one star, Alpheratz, with the adjoining Pegasus. Andromeda is also unusual in hosting the only galaxy plainly visible to the naked eye in the northern hemisphere. Listed on the chart by its historical name, the Great Nebula in Andromeda, it stretches across the apparent width of three full Moons! The full extent can not be seen with the naked eye or even binoculars, but the nucleus is not difficult to spot with your eyes and dead easy with binoculars.

Not far away is the Triangulum galaxy, the closest face on spiral galaxy to Earth. At 5.7 magnitude it would be visible to the naked eye if the light was not so spread out – a phenomena known as low surface brightness. Despite this, you should still be able to glimpse it with binoculars. By the way, the Triangulum galaxy may be a satellite of the much larger Andromeda galaxy.

In the constellation Perseus, Algol is a tiny bit brighter than Almaak in the constellation Andromeda – usually. Once every two days, 20 hours and 49 minutes Algol’s brightness dims and becomes no brighter than the nearby stars in Triangulum! Algol belongs to that class of stars known as eclipsing binaries; a dim star is closely orbiting the larger Algol and periodically passes in front of the brighter star, blocking its light.

See you next time!


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

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