*[image: vedder_crop_light.jpg]*
*The Pleiades: Seven Sisters*
Though he is principally known today for balancing the heavens upon his
shoulders, Atlas wasn't always the sky holder. Initially, he was one of
the strongest Titans, a child of Iapetus and the Oceanid Clymene. By
virtue of his formidability, Atlas was chosen to command the other Titans
in their ill-fated conflict with the gods, a ten-year struggle now known as
the "Titanomachy." Led by Zeus, the gods prevailed and most of the
vanquished Titans suffered ineluctable torments after the Titanomachy
ended. Atlas was made to hoist the sky upon his shoulders for all
eternity, the most wearisome of labors that the vindictive Zeus deemed
condign punishment for Atlas' contributions to the Titanic struggle.
However, long before he was condemned to this endless toil, Atlas lived a
most active life. For instance, he engaged in two illicit affairs. With
the Oceanid Aethra he sired the Hyades and the Hesperides. The Pleiades
were born out of his affair with the Oceanid Pleione. The Pleiades
numbered seven - hence the alternate name "The Seven Sisters." They were
Alcyone, Celaeno, Electra, Maia, Merope, Sterope and Taygete. These
beautiful young women were destined to be loved by either gods or
disreputable men: you can decide which fate is less appealing.
To cite some examples: By the ocean god Poseidon, Alcyone
conceived Aethusa, Hyrieus, Hyperernor, Hyperes, and Anthas. Aethusa
and Apollo eventually conceived Eleuther, founder of Eleutherae. Hyrieus
became King of Hyria and began the royal line that included Zethus and
Amphion, the pair who constructed Thebes. Hyperes and Anthas constructed
the cities of Hypereia and Antheia, respectively. These cities merged to
become Troezen. Consequently, Alcyone became known as the "Grandsire of
Empires." Electra was captured by Zeus and carried to Olympus to become
his lover. By this god, Electra gave birth to Dardanus, founder of
Dardania, the city that would eventually become known as "Troy." Maia,
the eldest of the Pleiades, was also seduced by Zeus who often visited her
while she slept. By these relations they conceived Hermes, the winged
messenger. One could say that Merope's lover, Sisyphus, was the worst
of them all. (We met him on April 28th.) Knowing that he was to soon
die, he persuaded his love Merope to leave him unburied. Thus, when he
did die, Sisyphus was able to persuade Persphone, wife of Hades, to release
him back to the upper world until he could coax Merope to inter him with
all due ceremony. When Sisyphus returned to the world, he instead fled at
once to hide from Death.
[image: pleiades-seven-sisters-nov2019-e1572962425736.jpg]
Collectively, the Pleiades were also known to have been coveted by the
great hunter Orion. He was said to have been wandering through a forest
when he spied the seven sisters gathering by a waterfall, Having
efficiently fallen in love with all of them at once, Orion pursued the
Pleiades with alacrity. The sisters, having been afflicted with high
standards and a keen sense of aesthetic judgement, fled in terror when
Orion appeared. Realizing that they weren't as fast as their lustful
pursuer, they pleaded to the gods for help. Zeus transformed the Pleiades
into doves and hoisted them into the sky. This transformation and
subsequent elevation protected the sisters initially. However, after his
death Orion ascended into the heavens close to the Pleiades and resumed his
pursuit. Though he persists in his infatuation, Orion is condemned to
remain forever frustrated as he cannot diminish the distance separating him
from the seven sisters by even an inch.
After midnight one can observe the Pleiades poised on the back
of Taurus the Bull. Soon after their emergence, Orion will ascend into
the eastern sky as he trails behind the seven beautiful young women he will
never be able to reach.
THE SOUTHWORTH PLANETARIUM
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Julian Date: 24591136.16
2020-2021: XXIX
THE DAILY ASTRONOMER
Tuesday, October 13, 2020
Remote Planetarium 107: General Relativity III - Proving the Curvature
Humanity's perception of the cosmos changed forever when Albert Einstein
published his two relativity theories: The Special Theory (1905) and the
General Theory (1916). Until the publication of these two theories, our
view of the Universe was rigidly Newtonian. Space and time were disparate
aspects of physical reality. Spatial motions did not affect temporal
progression and vice versa. Or, at least that is how the clockwork
cosmos appeared to operate according to our intuition. Einstein's
Relativity so shifted this paradigm that we now know that space and time
are conjoined and malleable. Space-time changes in different regions and
in certain situations.
In his General Theory of Relativity, Einstein explained that the
force we perceive as gravity is not a mysterious force exerted between
massive objects. Instead, "gravitational attraction" results from
space-time curvature. For instance, Earth isn't "holding you down."
You are trapped within the planet's gravity well.
[image: c0026862-800px-wm.jpg]
Earth, being a massive object, distorts its local space-time geometry so
that any object within its vicinity will be ensnared by it. That
statement summarizes the Einsteinian view of Earth's gravity.
How is it possible to measure such space-time distortions?
How can Einstein's space-time curvature be proven? Or, more correctly,
how can scientists accumulate evidence supporting this notion? The
evidence involved the observation of starlight. General Relativity
predicts that a light beam's path is distorted by the presence of a highly
massive object. The most highly massive object within our vicinity is
the Sun. The positions of stars around the Sun should appear slightly
altered as a consequence of the Sun's space-time indentation.
[image: Star-Positions.jpg]
The problem, of course, involves observing these stars. Stars are not
visible around the Sun because of our parent star's blinding light.
However, if that light could be shut off, astronomers would be able to
measure the star positions around it. That light is shut off during every
total solar eclipse.
In 1919, Sir Arthur Eddington (1882-1944) led an expedition to observe a
total solar eclipse on May 29, 1919. While he was stationed on
Principe, an island off the African coast, another team observed the
eclipse from Sobral in Brazil.
[image: Arthur_Stanley_Eddington.jpg]
*Sir Arthur Eddington *
The British astrophysicist who was believed to have been second only to
Einstein in the depth of his knowledge of the General Theory of
Relativity. He was the CS Lewis to Einstein's Tolkien.
Einstein's GR predicted that the positions of the stars around the Sun
during this eclipse would be about 1.75 arcseconds away from their usual
locations.* Eddington's team managed to photograph the sky around the
solar eclipse and determined that the starfield shift was consistent with
Einstein's predictions. The Eddington expedition confirmed that space-time
is curved and Albert Einstein became a world-wide celebrity literally
overnight.
[image: 0_K_tYN4NbxjACv4RG.png]
Space and time then truly became space-time in the public consciousness as
well as in physical reality. As we now know, however, the Eddington
Expedition was only the first stages in our new understanding of a cosmos
that is not only stranger than we imagine, but far stranger than we can
imagine.
We'll offer more strangeness tomorrow....
*Actually, Newton also predicted that star light would also be shifted by
the Sun's gravity because he perceived starlight as consisting of small
massive particles. Newton's shift was about one half that of Einstein's
prediction.
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