[image: ildefonso-castor-pollux-heads-only.jpg]
*Castor and Pollux: * Brotherly Love
Castor and Pollux, or Polyduces, were both twin brothers and half brothers:
a most unusual combination. Making twin half brothers requires two
fathers and one rather efficient mother. (The proper term for this
conception is "Heteropaternal superfecundation.") Their mother was the
Ateolian princess Leda who became the Spartan queen when she married
Tyndareus, who was Castor's father. Zeus, however, sired Pollux when
she seduced Leda while assuming the form of a swan. As a result of both
couplings, Leda produced two eggs. One of them contained Castor and his
sister Clytmenstra. (We met her on May 11th.) Out of the other egg
hatched the famous Helen and her brother Pollux. While Helen and her
sister were often estranged, Castor and Pollux were the best of friends
almost from birth and remained devoted to one another throughout. They
matured into fine horsemen and warriors. In fact, the named
Polyduces means "Boxer." These two formidable fighters embarked on many
adventures together, notably the Calydonian boar hunt in which Atalanta -we
met her on May 7th- figured prominently. They joined Jason and the
other Argonauts in their pursuit of the Golden Fleece. They also angrily
pursued Theseus when he kidnapped the young Helen. The fame-seeking
Theseus had heard the prophecy that Helen's abduction would precipitate the
greatest war the world had ever known. Theseus had hoped to bring that
conflict about and then serve heroically in it. Alas, all he managed to
do was incur the wrath of her brothers. They found Helen at the home
of Aethra, Theseus' mother. Theseus decided to keep her there while he and
Pirithous ventured down into the underworld to kidnap Hades' wife
Persephone. We might recall that Hades welcomed them both to his house and
had them sit on chairs of forgetfulness. The god knew full well their
intentions and it amused him to keep them in states of utter bewilderment.
This situation proved to be a blessing for Theseus, for he was not
present when Castor and Pollux arrived to collect Helen. He might have
been a match for one of the Gemini twins, but not both of them. It was
one of the mythological realm's greatest ironies: Theseus' life was spared
by having been imprisoned in the land of the dead*. One day, as Castor
and Pollux were engaged in a battle within Sparta, Castor was slain by
Argive King Lynceus, whom Pollux then promptly killed. As he embraced
his brother's corpse, Pollux, who was immortal by virtue of his parentage,
pleaded with Zeus to kill him, instead, and bestow immortality on his
brother. Although Zeus refused to fulfill this request, he did allow
Pollux to ascend into Olympus with his brother's shade. They were both
then placed in the sky as the Gemini twins, a constellation prominent in
the winter and spring evening sky. Unlike many of the other disagreeable
characters adorning the firmament, the Gemini twins exemplify the finest
human traits: bravery, filial devotion and selflessness. Resembling
conjoined stick figures, the Gemini twins represent the everlasting love of
brothers.
*Recall that Hercules rescued Theseus when the former descended into the
underworld to abduct Cerberus, his twelfth and last labor.
THE SOUTHWORTH PLANETARIUM
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2020-2021: III
THE DAILY ASTRONOMER
Wednesday, September 2, 2020
Remote Planetarium 81: Galactic Survey I
Today and tomorrow we're going to conduct a thorough survey of our Milky
Way Galaxy. We can pretend that we've been granted a 100 million year life
span and have to figure out ways to spend all that time by composing a
galactic travel itinerary. What to see. What to avoid. What to
admire from a great distance. In a sense we will be roaming through the
Milky Way Galaxy over the next few courses. What will we encounter?
*The Supermassive Black Hole in the nucleus:*
[image: unnamed.jpg]
A very good object to avoid! Tucked away in the galactic nucleus is a
supermassive black hole about four million times more massive than our Sun.
While not visible optically owing to the intervening gas and dust clouds
within the 26,000 light years of space separating it from us, the central
black hole is detectable as a powerful radio source dubbed Sagittarius A*.
Astronomers have determined its diameter to be about equal to 60
million kilometers. Scientists were able to estimate its mass by
measuring the velocities of stars within its vicinity. As we learned
yesterday in our dark matter discussion, stellar velocities are determined
by the mass of the material surrounding the stars. While life tends to
be placid out here on our spur, the region surrounding this black hole is a
sight of furious activity. It is likely every elliptical and spiral
galaxy contains such a supermassive black hole at their cores. We
would be well advised to avoid them, as well.
*Major Spiral Arms:*
[image: spitzer20150603main.jpg]
The Milky Way Galaxy is a barred spiral, meaning that its center consists
of a bar from which protrudes a series of curling spiral arms. The four
major arms are:
- Norma
- Sagittarius
- Scutum-Centaurus
- Perseus
Yes, that is correct. Each arm is named for a different constellation that
defines the region these arms seem to occupy. Our Sun is actually
located on a minor arm, the Orion-Cygnus. More specifically, the Sun is
located within the Orion spur, an offshoot arm of stars approximately 2/3
out from the nucleus. Spiral arms contain the densest collections of
stars, gas and dust. Here one will encounter most of the star formation
as gaseous nebulae condense to create new stars from the galactic material.
Astronomers estimate that 5 - 8 stars are formed each year within
the Milky Way.
*Galactic Halo:*
[image: Post - May 2013 (14) - 1.jpg]
We recognize three main parts of the galactic halo, the spherical region
surrounding the nucleus:
- *Stellar Halo *the halo containing the "metal poor" stars within
the globular clusters. These globe-shaped clusters -hence the name-
contain some of the oldest stars that are deficient in heavier elements as
they formed from material that wasn't as chemically enriched as the matter
from which the Sun was made. Up to one percent of the galaxy's mass is
contained within his halo, which extends up to 100 kiloparsecs (100,000
parsecs) from the nucleus. According to the most recent census, the halo
contains about 150 - 200 globular clusters
- *Galactic corona *a region of hot ionized gases within the galactic
halo. This rarefied region is likely replenished by cataclysmic
events such as supernovae in and around the galactic nucleus. These
"bubbles" travel up as though a chimney in this corona before being
disseminated through the disc region.
- *Dark matter halo *a vast region that might encompass the entire
galaxy. This DMH is hypothetical as dark matter has not yet been
observed. However, as we discussed yesterday, the surprisingly rapid
stellar motions within the galaxy's outer regions might be explicable by
the presence of such a halo.
We conclude our survey tomorrow...
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