Tiresias: How to make a prophet
When the ill-fated Oedipus Rex summoned the blind prophet Tiresias to ask him the causes of Thebes' plague, the sightless soothsayer told him in a roundabout way that the king, himself, was to blame. It turned out that Oedipus had, indeed, killed his father and married his mother, as the Delphic Oracle had prophesied. As the gods loathed both patricide and incest -unless they, themselves were the ones committing either act-the plague would only end after Oedipus was expelled. Oedipus was sorry he asked. Years earlier, Liriope asked Tiresias if her then infant son, Narcissus -we encountered him last week- would live a long life. "Yes," Tiresias assured her. "But only if he never knows himself." The irate Liriope considered this answer so cryptic and unhelpful that she was also sorry she asked. Many years later, when Tiresias was dead and residing in the Asphodel meadows, Odysseus -we saw him last week, too-ventured into the underworld to consult him on how to survive his now famed Odyssey. Tiresias offered invaluable advice, including ways to cope with the dreaded Scylla and Charybdis. In that instance, Odysseus was quite pleased to hear what Tiresias had to say. Those are just three out of many times when Tiresias' assistance was requested by those seeking sage advice
As Tiresias was arguably the mythological world's most celebrated prophet, it might come as a surprise to learn that he wasn't born to be one. Instead, he was made a prophet in a particularly strange way. One day the young and sighted Tiresias was wandering around Mount Cyllene when he happened upon two copulating snakes. Repulsed, Tiresias separated them with a stick and then tossed them away from each other. Hera observed this violent act and angrily transformed Tiresias into a woman. As a female, Tiresias eventually served as a priestess of Hera and gave birth to Manto, who matured to become a revered prophetess. After seven years of living as a woman, Tiresias once again encountered two copulating snakes Though still disgusted, she did not interfere. Her restraint appeased Hera who then returned Tiresias to male form.
Many years later, Hera was chastising her husband Zeus for his innumerable infidelities. He defended his indiscretions by claiming that physical intimacy was all to the woman's benefit and for men was, in his words "mostly just work." (Fool.) Appalled by that claim, Hera called forth Tiresias, who was still serving Hera in a religious capacity. As he had lived as both male and female, Tiresias was believed to have been uniquely qualified to resolve the dispute. "Who benefits most from the coital act," Hera asked him. Tiresias replied,
"If love's pleasures count as ten,
thrice three go to women, only one to the men."
While Zeus chortled heartily, Hera became incensed and punished Tiresias with permanent blindness. Although Zeus could not restore his sight as that would require negating another Olympian's punishment, he did gift Tiresias with the power of prophecy: second sight. Tiresias quickly cultivated this divine ability and soon became a prophet of note, though not always a popular one. One could regard him as the "Gandalf" of the Cadmus family. The blinded prophet Tiresias was present through all seven generations of the Cadmus household. He was first advisor to Cadmus and then appeared in many of the tragedies that occurred to his cursed descendants. He finally perished after the Cadmus line was ultimately destroyed in the Seven Against Thebes war in which Oedipus' two sons (and brothers) killed each other in a battle over the Thebian throne.
THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian Date: 245953.16
Julian Date: 245953.16
2019-2020: CXXV
THE DAILY ASTRONOMER
Monday, April 13, 2020
Remote Planetarium 11: A Tourist's Guide to the Planets
Greetings!
Welcome back. I know you missed us, but not nearly as much as we missed you. Today we're going to embark on something of a field trip. Granted, we'll all be far apart from one another as social distancing is the current custom. In fact, you'll be at home pretending you're with us. Our aim is to introduce you to just a few of the many breathtaking vistas within our solar system. Yes, we mean that literally as we'll have no oxygen to enjoy.
First things first, however.
We're standing in an empty parking lot (the only kind that exists presently) with, of all things, a roll of toilet paper! Yes, we actually found one. We also have a softball. One might wonder why would a solar system tour begin with such items? Simple. Before we explore the planets, we need to understand their sizes relative to the Sun and to each other. You see, we planetarium fools often show off solar system models like this one:
We're standing in an empty parking lot (the only kind that exists presently) with, of all things, a roll of toilet paper! Yes, we actually found one. We also have a softball. One might wonder why would a solar system tour begin with such items? Simple. Before we explore the planets, we need to understand their sizes relative to the Sun and to each other. You see, we planetarium fools often show off solar system models like this one:
Bright, cheerful, neatly arranged and, of course, likely stolen. Thank you, VectorStock. Such a model does present the planet in their proper order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The problem is that it isn't to scale, not by a long chalk.* Hence, the toilet paper and softball. It will help us put the solar system into perspective.
First, put the softball on the ground. It represents the Sun. You're welcome to paint it yellow, provided you know it isn't actually yellow. (We'll explain why next week when we turn our attention Sun ward.) Next, place one end of the toilet paper next to the softball and then roll it out. Each sheet represents one million miles. Mercury will be half the size of a paperclip hole located 36 sheets away. It will be much farther away than one would expect. We should note that in this model we'll be placing the planets at their average distance. Recall that planets travel along elliptical orbits and their distances from the Sun change continually.
Venus will be 67 sheets away and will be the size of a paperclip hole.
Earth will be 93 sheets away and also the size of a paperclip hole.
Now, stop for a moment and observe. The Softball-sized Sun is surrounded by three minuscule holes at vast distances from it. Earth is hardly even visible!
We continue:
Mars will be 142 sheets away and will be about 3/4 the size of a paperclip hole
Mars will be 142 sheets away and will be about 3/4 the size of a paperclip hole
Jupiter is 484 sheets away and the size of a hole at the center of those old 33 1/3 records.
Saturn 887 sheets; Uranus 1,784; Neptune 2,794 and finally Pluto 3,675 sheets.
Granted, we're not expecting you to roll out all the toilet paper even if you could somehow gain possession of so much without legal consequence.
Just know that the Sun represents more than 99% of the solar system. The planets and their moons are just little motes trapped inside its immense gravity well.
We begin our rapid planet trek, skipping Earth, which is so boring.
MERCURY
Be careful if anybody invites you to spend a day on Mercury. Days on the first world last nearly two Earth months! Although this planet rotates slowly, as it is the first planet, it revolves rapidly. With an average speed exceeding 160,000 miles an hour, Mercury completes an orbit in approximately 88 days. Consequently, a Mercurian would see only two sunrises a year! Unsurprisingly, Mercury's surface bakes under a Sun that appears 2.5 times larger than the Sun we see on Earth. Its daytime temperature exceeds 700 degrees F, hotter than a pizza oven. However, as Mercury lacks an atmosphere apart from whispers of sodium vapor, its night side is frigid with temperatures around -200 degrees F: a nearly 1000 degrees day-night temperature range. On the bright side, Mercury surface gravity is significantly less than Earth. A 200 lb Earthling would weigh in at 74 pounds on Mercury.
DOWNSIDES:
- Absolutely no oxygen to breathe
- High radiation levels
- You'd cook in the day time and freeze at night
VENUS
Let's face it: Venus was a disappointment. Seen from Earth, the second world is so beguilingly beautiful we associated it with Venus, the Roman counterpart to Aphrodite, goddess of love and beauty. Moreover, many astronomers assumed its surface would be lush and verdant: a tropical paradise extending from pole to pole. They based this hopeful assumption on Venus' close proximity to the Sun and its pervasive cloud cover. It seemed to have the two fundamental ingredients required for any true rain forest. Fierce heat and abundant rainwater. While it possesses the first, it lacks the second. Its thick carbon dioxide atmosphere not only traps heat, but produces clouds that pour forth sulfuric acid rains. The temperature exceeds 900 degrees F from pole to pole and the surface pressure is 90 times greater than Earth's sea level pressure. The only known visitors to this world were the Venera spacecraft the Soviet Union launched in the 1980's. Though these vessels were metallic and shielded, they lasted less than half an hour before Venus destroyed them.
DOWNSIDES:
- What Hell must be like, but without the Black Sabbath music
- Crushing pressure
- Furious heat
- the rain consists of the same acid used in car batteries
- Oh, and you would NEVER see the Sun!
One "upside": Venus's gravity is almost as strong as Earth's so you would be able walk around on Venus just you do here, except, well, you'd be dead before you could take your first step.
Interesting note: Venus's day equals 117 days, more than half the length of its year. It also rotates backward relative to the other planets. Of course, one can't really tell the difference between night and day, anyway, and since the temperature is constantly high, Venus has no real seasons, either.
MARS
Mars was something of a disappointment as well, we must admit. Whereas Venus was supposed to have been like Tahiti on a global scale, Mars was supposed to have been a Tolkienesque world replete with imposing castles, elegant princesses and a vast community of monstrous creatures and even the occasional sorcerer. Well, blah! As far as we can tell, Mars is devoid of life, though it might have harbored microbial life in the distant past when the planet's surface was much wetter. Mars is a cold, barren desert world that also lacks the oxygen we need to life. However, it does possess water ice at its pole that would prove useful to us if we could hold our breath long enough to reach it.
Mars was something of a disappointment as well, we must admit. Whereas Venus was supposed to have been like Tahiti on a global scale, Mars was supposed to have been a Tolkienesque world replete with imposing castles, elegant princesses and a vast community of monstrous creatures and even the occasional sorcerer. Well, blah! As far as we can tell, Mars is devoid of life, though it might have harbored microbial life in the distant past when the planet's surface was much wetter. Mars is a cold, barren desert world that also lacks the oxygen we need to life. However, it does possess water ice at its pole that would prove useful to us if we could hold our breath long enough to reach it.
Unlike the first two planets, Mars does have natural satellites. Two of them: Phobos and Deimos, two captured asteroids whose names mean "Panic" and "Fear." Those are appropriate nicknames as Mars was named for the Roman god of War. As Mars is coated in iron oxide (rust), it appears reddish in our sky. Our conflict-weary ancestors likely associated that color with blood, hence the name.
UPSIDES
- Mars contains the solar system's largest mountain. Olympus Mons. It towers 72,000 feet above the Martian surface and its base is as large as the state of Missouri
- Mars is also scarred by the solar system's grandest canyon, the Valles Marineris. Extending more than 2500 miles across the Martian surface, this immense canyon can reach of depth of about four miles. Earth's celebrated Grand Canyon could fit neatly inside one of its offshoots chasms.
- Its surface gravity equals that of Mercury so you'd weigh less on the fourth world.
DOWNSIDES
- Yet, again, no air for us to breathe
- Cold! Cold! Cold! The highest temperature possible temperature is around 50 degrees. It is only that warm around the equator in summer
JUPITER
Now we're moving into new territory, into the realm of the gas giants. We can divide the planets into two categories. The "terrestrial" planets: Mercury, Venus, Earth and Mars and the "gas giant" planets: Jupiter, Saturn, Uranus and Neptune. Pluto doesn't fit neatly into either category.
The gas giants rapidly rotate, contain thick atmospheres that are utterly unlike those enshrouding our planet, and all of them are surrounded by an absurd number of moons.
Jupiter get high marks for aesthetic beauty owing to its kaleidoscopically colorful cloud forms. We are most intrigued by its "Great Red Spot," a storm larger than Earth which has been raging for centuries. It is possible that Giovanni Cassini observed it in the 17th century. We do know that the Great Red Spot has been tearing through the Jovian atmosphere since at least 1830, making it the most durable known storm in the solar system. (Even the most persistent hurricane on Earth lasts for only about a month.)
One minor problem: Jupiter offers no surface on which to walk. If we tried to "stand" on Jupiter, we'd be consumed by its turbulent clouds and would perish in an instant. We could try to wander about any of its 79 known moons. Yes, 79! Jupiter boasts more attendant moons than any other planet. It is sensible that the fifth planet would be so well endowed as it is the solar system's most massive planet. In fact, it is more massive than all the other planets put together.
DOWNSIDES
- Even if we could stand on Jupiter, its gravity field is immensely strong. A 200 pound person would weigh 508 pounds on Jupiter
- Again, the lack of oxygen thing.
- True, Jupiter has plenty of moons, but only a few would be visible from Jupiter's cloud tops
- COLD! COLD! COLD! About -235 degrees F along the top of Jupiter. However, because of the enormous pressures, Jupiter's core is hotter than the Sun's surface, more correctly known as its "photosphere."
UPSIDES
- It is Earth's protector. As Jupiter is so massive, it has often diverted many incoming comets away from the inner solar system. We have likely sustained fewer impacts due to Jupiter's presence.
- Has a ring, though it is exceedingly difficult to observe.
SATURN
The one we've been waiting for. A+ in the looks category. Saturn is the the famous ringed world that is almost one billion miles from the Sun. Like the other gas giants, Saturn lacks a solid surface so bang goes our hope to stroll under its majestic rings. Although those rings look solid when seen from a distance, they actually consist of billions of small particles ranging in size from dust grains to railroad box cars. It is also surrounded by more than 60 moons, one of which, Titan- harbors an atmosphere that might well be similar to that of the early Earth.
Saturn's average temperature is about -288 degrees F, which we would expect being so far from the moon. It is also torn by fierce winds owing in part to its rapid rotation. Saturn spins on its axis once every 10.5 hours (slightly slower than Jupiter). For this reason, Saturn is the solar system's most oblate planet: thicker around its equator than at its poles.
DOWNSIDES
- Ok, you know about the lack of oxygen issue. We'll stop mentioning it.
- COLD! COLD CO... Sure, we'll stop talking about that, too
- No surface on which to wa.....ok, and that
UPSIDES
- Stand on a nearby moon and those rings will dazzle you into a stupor
- It year lasts almost 30 Earth years so you'll have plenty of times to admire any given constellation before the Sun obscures it.
URANUS
The planet every Middle School teacher hates. Uranus was named for Uranus, the Roman god of the sky. It was the first planet to have been "discovered," as all the closer planets have been known and observed since antiquity. Astronomer William Herschel discovered it on March 13, 1781. He was astonished to realize that he had found the solar system's seventh planet!
Uranus is "tipped over" on its side so that its axis almost spins along the orbital plane as opposed to being perpendicular to it. It has 27 attendant moons, far less than Jupiter and Saturn have, but still much more than the terrestrials planets lay claim to. Like the other gas giants planets, Uranus contains ample quantities of hydrogen and helium, but also harbors great stores of ammonia ice.
DOWNSIDES
- Yes, we know!
- Yes, we know!
- Yes, we know!
UPSIDES
- Miranda, one of its moon, has the distinction of having the highest cliff in the solar system: Verona Rupes. As it is nearly 20 miles high and is located on a moon with very weak surface gravity, a person who jumped off its summit would fall for more than twelve minutes! (And, alas, still die after impact.) Yes, not much of an upside.
NEPTUNE
Two astronomers, Englishman John Couch Adams and Frenchman Urbain Leverrier independently discovered Neptune in 1846 by studying the observed perturbations in Uranus's orbit. They used Newton's gravitational laws to mathematically determine its approximate location. Leverrier persuaded Johann Galle to search for the then-unknown world through his telescope, which Leverrier did not possess. Galle located the planet after only a single hour search. He found it about one degree from the position that Leverrier had pinpointed.
With an average distance of 2.8 billion miles, Neptune is the most distant of the gas giant worlds. It requires about 165 Earth years to complete an orbit. In fact, it hasn't even completed two orbits since its discovery. It is also the smallest gas giant and has fewer known moons (14) than any of the other Jovians.
Neptune was named for the Roman god of the sea, the counterpart to the Greek Poseidon. They named the seventh planet Uranus because he sired the Titans, including Saturn. Saturn sired the gods, including Jupiter, who sired Mars. The planets were arranged in order of lineage. The problem was that Uranus was born out of "Chaos," which meant nothing. So, instead of calling the eighth world nothing, it was given the name "Neptune," because of its distinctive bluish coloring. Methane, not water, produces that blue tint, however.
UPSIDE
- The surface of Neptune's largest moon, Triton spouts geysers that propel methane crystals miles high. A sight that must be indescribable.
PLUTO
Hey, none of that "it's not really a planet" talk! At some point we'll address Pluto's undeserved demotion. Now, we just want to end with Pluto, the solar system's ninth world. Discovered in 1930 by American astronomer Clyde Tombaugh, Pluto's average distance equals 3.7 billion miles. At that distance, it requires 248 years to complete one revolution around the Sun. It hasn't even finished half an orbit since its discovery.
Pluto is the smallest world and the least massive one as astronomers were able to determine after the United States Naval Observatory's James Christy discovered its largest moon Charon in 1978. Pluto is now known to have five moons and might well have others that we cannot see from our vantage point. NASA's New Horizons probe flew by Pluto in 2015 and discovered many features not visible from even the Hubble Space Telescope. Its icy surface is far more complex than once believed.
UPSIDE
- Pluto and its largest moon, Charon, have established a mutual synchronous rotation. Charon's revolutionary period equals its rotation period and that of Pluto. If one were to watch Pluto in Charon's sky, it would not appear to move at all and vice versa.
*Looking for a diversion during your isolation? Try "By the Sword Divided," a wonderful and grossly underrated BBC dramatic series produced in the 1980s and set during and then after the three 17th century English civil wars. https://www.youtube.com/watch?v=bQRVH08xZcI It is highly addictive and will make you want to use strange phrases like "not in a long chalk."
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