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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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
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.
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.
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.)
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.)
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
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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