[image: 1_MI6MyiERSjPzPbXSjmgqbw.jpeg]

*Sisyphus:  The Rock Roller*
At times, the gods could be temperamental in their dealings with mortals.
They rapidly avenged slights, demanded atonement for transgressions even
from those who didn't commit them, and severely punished hubris.
 Tantalus' example illustrates that these punishments were often as
excruciatingly painful as they were exquisitely creative.  We remember that
he was condemned to perpetual hunger and thirst in Tartarus, the
underworld's punitive region.   Also relegated to Tartarus was Sisyphus,
pictured above.    Whereas Tantalus condemned himself with his mad
arrogance and murderous tendencies, Sisyphus, as we shall see, simply
outsmarted the Olympians.
       Sisyphus was the founder  and king of Ephrya, now known as Cornith.
 He was hardly a beloved ruler owing to his iron-fisted rule and his
propensity to quickly dispatch those who gave offense.   This type of
murderous tendency did not incur the gods' wrath because Sisyphus was a
king presiding over a volatile populace.    They deemed such ruthlessness a
regrettable necessity.    Trouble truly began for Sisyphus when he spied a
large eagle overhead carrying the nymph Aegina in its talons. He knew very
well that eagle was Zeus in disguise.   When Aegina's father Asopus, the
river god, traveled to Ephyra in search of her, Sisyphus told him that Zeus
had assumed the form of an eagle and spirited her away.  In exchange for
this information Asopus drew forth a spring in Ephyra that has never since
run dry.     When he learned that Sisyphus had informed on him, Zeus became
so enraged he commanded Thanatos, the god of death, to collect him.   When
Thanatos arrived at the palace, Sisyphus did not run as all the others had
done, but instead greeted him warmly.   He offered Thanatos refreshments in
accordance to xenia, the ancient code governing the conduct between host
and guest.  Bound also by xenia, Thanatos accepted the offerings but warned
Sisyphus that they would have to depart for the underworld very soon.
During the pleasant exchange that ensued, Sisyphus persuaded Thanatos to
show him the bindings he used to trap the dead.  Once the bindings were
revealed, Sisyphus quickly grabbed them and bound Thanatos securely.
During the days he kept Thanatos tied up in his home, nobody died.
 Mortally wounded soldiers continued to move and the grievously ill and
elderly remained miserably Earthbound.   Ares, the god of War, realized
that Thantos had been imprisoned and went to release him.  Knowing that his
death was now imminent, Sisyphus instructed his wife, the Pleiad Merope,
to  leave his body above ground.  "Do not offer prayers or perform any
rituals," he asked.   Although perplexed, Merope followed  her husband's
instructions.  After he died, his body was not interred.  As a consequence,
Sisyphus remained on the shores of the River Styx instead of being conveyed
to the other side on Charon's ferry.  He then prayed to Persephone, goddess
of the underworld, who came to him on the shore. "My wife neglected my body
and gave me no honors," he protested.  "She is forgetful at times.   I
implore you to allow me to return home for just one day to remind her of
the duties she is bound to perform."    Induced to pity, Persephone
released him.  "You will be summoned back in one day," she informed him
before he left.    Sisyphus returned to the upper world, but did not see
Merope at all.  Instead, he fled into concealment and managed to elude
death until he grew so old and weak he could run no more.     Exasperated
by Sisyphus' craftiness and deceit, Zeus condemned him an eternity of
pushing an immense boulder up a steep mountain.   Each day he hoisted the
boulder up to the summit and while he slept overnight, the boulder rolled
back down to the base.    Every day for all time Sisyphus must perform this
exhausting and futile labor.    A punishment well suited for one accustomed
to using his brain instead of his brawn.

THE SOUTHWORTH PLANETARIUM
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Julian Date: 245967.16
2019-2020:  CXXXV

I have decided to make a slight change to our syllabus.    Today's topic
will pertain to comets. We'll discuss asteroids tomorrow   Combining them
both made for such a long article laden with so many images the system kept
rejecting it.      My apologies for the shift.    Thursday's topic will
pertain to moons.     "Space Weather" will be our focus on Monday.
THE DAILY ASTRONOMER
Tuesday, April 28, 2020
Remote Planetarium 22:   Comets

[image: Lspn_comet_halley.jpg]

Once, and not too long ago, comets terrified humanity.     They served as
celestial harbingers of doom whose sudden appearance presaged war, famine
or some other catastrophe.     They engendered such fear, perhaps, because
they were unpredictable. They materialized out of the darkness, grew
brighter and more distinctive before ultimately vanishing into the same
boundless black from whence they came.  These "hairy stars," as they were
called owing to the long tails formed in their wake, didn't abide by the
same regular schedule that dictated the planetary motions.   Like dire
news, itself, comets arrived with little or no warning.

In the year 12 BCE, a comet seemed to hover over Rome. According to the
historian Cassius Dio, its arrival preceded the death of the beloved
statesman Marcus Agrippa.  In AD 451, a cometary apparition was said to
have brought about the defeat of Attila the Hun.    In AD 837, a brilliant
comet lit up the sky and left a tail that stretched more than 60 degrees!
  Louis the Pious, King of the Franks and son of the inimitable
Charlemagne, was said to have devoted himself to prayer and penance for he
knew the comet's arrival would bring about the death of a prince.     Louis
died three years later.

[image: Comete_Tapisserie_Bayeux.jpg]

The image above is take from the Bayeux Tapestry, an 11th century tapestry
depicting the Battle of Hastings in the year 1066.  Here we see a
mysterious comet appearing high above the fray: an ominous sign for Harold
II, but a joyous one for William the Conqueror.

A 1222 cometary apparition might have inspired Gengis Khan to shift his
ambitions toward Europe.    In 1456 a comet attended the Siege of Belgrade
in which the then dominant Ottoman Empire invaded the Kingdom of Hungary.

A comet appeared in 1531, but no calamity ensued.
A comet appeared in 1607, but again, it didn't prefigure any disaster.
The comet that appeared in 1682 wasn't followed by excessive bloodshed,
either.   It did, however, come to the attention of Edmond Halley
(1656-1742), a contemporary of Isaac Newton (and purportedly the one person
who got on with him.)

[image: Edmond_Halley_072.jpg]
*Edmond Halley*
Using observational data collected from the cometary apparitions of 1531
and 1607, Halley concluded that they were not three separate comets, but
the same comets that periodically returned to the inner solar system.
Based on his analysis, Halley predicted the comet would return in 1759.
 Indeed, the comet did appear in late 1759, delayed somewhat by
gravitational interactions with Jupiter.    Having died in 1741, Halley
didn't live to see his prediction proven correct.    However, the comet
that visited in 1759, 1682, 1607, 1531, 1456, 1222, 1066, 837, 451 and 12
BCE now bears his name:  Halley's Comet.  It revisits the inner solar
system every 76 years.  Its last visit occurred in 1985-86  It will return
in 2061.   (Note; we didn't include every Halley's Comet visit since 12 BCE
in the previous section.)

[image: unnamed.jpg]
Comets follow highly elongated orbits around the Sun.    They originate
from two different regions beyond the planets.    Short period comets
(those with orbital periods equal to or less than 125 years) originate in
the *Kuiper Belt*. Longer period comets come out of the Oort Cloud.   The
*Oort Cloud *is a spherical region of cometary nuclei from which all long
periods comets originates.     Unlike the Kuiper Belt, which is
concentrated along the solar system's plane and begins just beyond Pluto's
orbit, the Oort Cloud envelopes the solar system.      The Oort Cloud is
also significantly larger and more distant:  it begins around 2,000 AU from
the Sun and extends out to about 50,000 AU.  (An AU, or astronomical unit,
equals Earths' mean distance from the Sun, or approximately 93 million
miles.) Astronomers haven't directly observed either the Kuiper Belt or
the Oort Cloud, because neither of them are solid structures.    Instead, a
collection of cometary nuclei comprises the Oort Cloud and Kuiper Belt.

Dutch-American astronomer Gerard Kuiper (1905-1973) observed that short
period comets traveled along paths that were limited to a region around the
ecliptic plane, or the plane defined by Earth's orbit.   From these
observations he concluded that short period comets must originate from a
belt of nuclei encircling the solar system.

Dutch astronomer Jan Oort (1900-1992) observed that long period comets were
not as restricted as the short period comets.  Long period comets were
observed to originate from various points all around the solar system, not
just the ecliptic.  From these observations, Dr. Oort deduced the existence
of the Oort Cloud -which consists of a series of shells- far beyond the
planets.     We now believe that this cloud consists of billions, or
perhaps even trillions, of cometary nuclei: fragments of the early solar
system trapped in frozen storage far from the Sun.

ANATOMY OF A COMET
[image: ahearn_anatomy.jpg]

Comets rarely ever sport tails.     For instance, if we were to visit
Halley's comet right now* we would find it dark, barren and tail-less.
Comets consist primarily of ice and dust.   Comets only form tails when
they infiltrate the inner solar system.  Each comet produces two tails; a*
dust tail* and an *ion tail.*    The Sun's heat melts the comet's surface
ices, producing a tail of liberated dust motes. The ion tail consists of
charged particles repelled by the solar wind.       These tails extend out
of the coma that envelopes the nucleus.  While the nucleus tends to be only
a few miles in diameter, a comet's tail can sometimes extend more than a
million miles!

Comets are the repository of the early solar system.   Like asteroids, they
are the remnants that did not become incorporated into the other planets or
moons.    Even though our solar system is more than 4.5 billion years old,
it still harbors innumerable comets as well as asteroids, which will be our
focus tomorrow.

 *The most famous comet is now beyond Neptune and due to turn around in
December 2023.
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