Arcturus, the bear guardian
As if returning from winter hibernation, the star Arcturus begins its seasonal procession across our night sky. Arcturus is alternately known as the ‘bear driver’ or ‘bear guardian’ star. Its path in the northern sky follows Ursa Major, the Great Bear, as it wheels around the polar axis. To locate this star, follow the curve of the Big Dipper’s handle and “arc to Arcturus”. If you find a dazzling yellow-white or topaz colored star – you got it!
Arcturus is the brightest of an otherwise dim grouping of stars that belong to the constellation Boötes, the herdsman. At a distance of approximately 37 light years, it has a luminance 100 times greater than our own sun. This combination of proximity and brilliance makes Arcturus the fourth brightest star in the night sky. The name Arcturus is derived from the ancient Greek word αρκτος or Arktos meaning bear.
To explore the connection between the Great Bear and Arcturus we must turn to Greek mythology. Zeus pursued and seduced Callisto, a nymph associated with Artemis the goddess of the hunt. Chastity was a virtue practiced by Artemis and her nymphs. Fiercely protective of her retinue, Artemis would block the advances of outsiders. But, by approaching her disguised as Artemis, Zeus was able to trick Callisto.
Callisto gave birth to a son she named Arcas. Fearing that his wife Hera would discover his infidelity, Zeus transformed Callisto into a bear and set her loose in the forest. Later, as a grown man Arcas encountered the bear, but did not recognize it as his mother. Delighted to see her son again after so many years, Callisto reared up and spread her arms wide to give him a hug. Interpreting the bear’s gesture as a sign of attack, Arcas drew his sword to defend himself. Zeus thwarted disaster by hurling them both into the northern sky. Callisto and Arcas then became the circumpolar constellations, Ursa Major and Ursa Minor.
Above mid-northern latitudes, the bears never set below the northern horizon. Myth attributes this limitation to Hera who, upon learning of Zeus’ antics, demanded that sea goddess Tethys forever prevent the bears from dipping into the waters along the horizon. To safeguard Callisto and Arcas from further trouble, Zeus placed the star Arcturus into the sky to keep watch over them.
Because bears are creatures of the boreal forests, it makes sense that we find these ursine constellations in the circumpolar part of the sky. Not only does the name Arcturus come from the word Arktos, but also the term used to describe the boundary of the northern polar region, the Arctic Circle.
According to Guy Ottewell, a very cool thing about Arcturus is that it’s not really a regular resident of the Milky Way: it’s zooming through the neighborhood as it passes through the plane of the galaxy! I can’t remember how long it would take to observe its movement, though….I wonder if it’s one of those galactic scale changes that someone can see in a lifetime? (as with precession, which as I recall is JUST visible over a couple generations, so a grandparent can point out the changes to a young observer)
Hi Jim,
Thanks for your comment. I am interested to know more about Arcturus and its alleged ‘transient’ nature. I know that AE Aurigae which illuminates the Flaming Star Nebula was ejected from the vicinity of Orion. So this kind of star movement is not uncommon.