Winter’s immortalized pair.

Gemini … and You

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Gemini …

From Mythology

Twins? Castor and Pollux had the same mother and they were "born" at the same time. The rest of the myth involves complications of paternity, divinity, allegory, heroism, and fortune – you know, myth-type stuff.

Their mother was Leda the Swan whose husband was Tyndarius. It is said that mighty Zeus put on his swan suit to pay a visit to her. She presented two eggs which issued forth four children Helen (yes, that Helen), Clytemnestra, and this month’s co-stars, Castor and Pollux. Twins in many ancient cultures could be regarded as either good or bad omens. Many stories around twins create marked differences between them. It seems the Gemini story was settled in arbitration with that in mind.

You see, Pollux and Helen popped out of one egg, while Castor and Clytemnestra issued from the other. Divinity was bestowed on the first pair owing to Zeus’s participation, and mortality was assigned the other two; nevertheless, Castor and Pollux were lifelong friends sharing many exploits. They were handsome, wealthy, and associated with hospitality and the protection of sailors. They were on that famous cruise with Jason and many other heroes who sailed the Argo in pursuit of the Golden Fleece. During one violent storm, after many desperate prayers, balls of fire appeared over the Twins, and the storm abated, earning the Twins special reverence among the crew.

The devotion of Castor and Pollux toward one another extended beyond death. In one fierce battle, Castor was slain. and Pollux grieved over the loss of his brother and over his own immortality – he would not be able to join his brother in the afterlife. Zeus was taken with this fealty and he bestowed immortality on them both – some say by putting them up in the heavens.

Constellation Gemini

Credit: Roberto Mura, public domain

It seems that Zeus assigned marked differences to Castor and Pollux, the alpha and beta stars of the constellation shown above on the left. Pollux has a distinct orange tinge while Castor is pure white. Castor is a system of at least six stars. Pollux travels alone. Pollux is the visually brighter star, while Castor photographs brighter due to its bluer spectrum. Moderately powerful telescopes will separate Castor’s A and B components [see projects].

The chart above shows Gemini rising in the east. A vivid imagination like yours can make out the two stick figures threatening to stomp on Orion's sore shoulder, Betelgeuse. Later in the evening, or later in spring, Orion will tip forward and the Twins will set standing upright in the west.

Interactive Sky Chart

Messier 35, at Castor's westerly foot [above] is an open cluster available to small scopes, but a keen eye or a larger aperture will distinguish a second smaller cluster NGC 2158 just off to the side. It’s a twofer both shown below.

Credit: N.A.Sharp/NOAO/AURA/NSF

NASA reports: Open clusters of stars can be near or far, young or old, and diffuse or compact. Found near the plane of our Milky Way galaxy, they contain from 100 to 10,000 stars, all of which formed at nearly the same time. Bright blue stars frequently distinguish younger open clusters. M35, on the upper left, is relatively nearby at 2800 light years distant, relatively young at 150 million years old, and relatively diffuse, with about 2500 stars spread out over a volume 30 light years across. An older and more compact cluster, NGC 2158, is at the lower right. NGC 2158 is four times more distant than M35, over 10 times older, and much more compact with many more stars in roughly the same volume of space. NGC 2158's bright blue stars have self-destructed, leaving cluster light to be dominated by older and yellower stars.

Sources New Larousse Encyclopedia of Mythology Burnham's Celestial Handbook Audubon Field Guide to the Night Sky

… and You

1. Find the separation and orbital period of Castor A and B.

2. The cluster in the view with M35 is said to be compact. Is NGC 2158 an open or a globular cluster? How do astronomers make this distinction? 3. Find the period and change in amplitude of variable star Zeta Gemini.

4. The star U Geminorum exhibits several strange behaviors, such as ...