Two of Earth's movements make our days and nights as well as our seasons. These movements are rotation and revolution. The earth spins, turns & rotates on its axis, an imaginary line running through its poles. As a result, half of our planet experiences daylight while half is always in darkness. We have day when we face the sun, our parent star. We have night when we spin away from the sun into our shadow. The earth always casts a shadow. What we call night is simply this shadow, and we spin in and out of it. The sun does not rise, nor does it set. Sunrises and sunsets are illusions caused by Earth's rotation. It is we who are moving. The sun stays put. Twilight occurs in the evening and morning because the sun's rays are reflected to the ground by the top of our atmosphere. We see sunlight when the sun itself is not visible.
The earth revolves, orbits & goes around the sun. We call one trip around the sun a "year." Because of this movement, stars appear to rise 4 minutes earlier each night. Again, this is an illusion. What happens is, we view the starry panorama from different angles as we orbit. We see different stars at night on opposite sides of our orbit. Constellations (which exist only in our minds) become identified with seasons. Floating in space, we would see all the stars and constellations at once. Bob Berman compares our simultaneous rotation and revolution to patting our heads while rubbing our stomachs.
Another illusion is the apparent movement of the sun's arc north and south during the course of a year. It is Earth revolving around the sun that gives this impression.
Historically, great importance has been attributed to solstices and equinoxes. Stonehenge, 90 miles west of London, is an ancient observatory associated with solstices and equinoxes.
1 Summer solstice - The sun's arc is overhead at the Tropic of Cancer, which runs off the tip of Florida. This is as far north as it gets. The Northern Hemisphere has its longest days and shortest nights around June 21.
2 Autumn equinox - The sun's arc is overhead at the equator on its way south. Days and nights are equal everywhere around September 21.
3 Winter solstice - The sun's arc is overhead at the Tropic of Capricorn, which runs through Australia. This is as far south as it gets. The Northern Hemisphere has its shortest days and longest nights around December 21.
4 Spring (vernal) equinox - The sun's arc is overhead at the equator on its way north. Days and nights are equal everywhere around March 21.
Different parts of the earth receive different amounts of the sun's energy over the course of a year. Earth's axis is tilted 23 1/2 degrees to the plane of its orbit, so when it is summer in the United States, it is winter in Australia. Earth's axis always points in the same direction. On one side of our planet's orbit, the Northern Hemisphere tilts toward the sun while on the other side, it tilts away from the sun. Earth's tilt resulted from an impact by a large object, the same impact that created the moon.
Many people are immersed in ancient perceptions, the thinking of Aristotle and Ptolemy. They are hampered by a Biblical bias. The Bible is a hodgepodge of superstition written between 1500 B.C. and 100 A.D. by 40 authors. Its influence on western civilization has been enormous. Scientific knowledge came hard! The ancient Greeks had science (Aristarchus and Eratosthenes) before Europe plunged into a thousand year dark age. It took Copernicus in Poland and Galileo in Italy to start a Renaissance in astronomy. Copernicus figured out that the earth goes around the sun, not the other way around. Galileo supported heliocentrism after watching moons circle Jupiter, proving that not everything circled the earth.
All life on earth depends on the sun. Life thrives more abundantly on parts of the planet that receive most of the sun's energy. The tropics (those areas closest to the equator) get the most sunlight, so we can expect life there to be diverse. We can expect less life close to the poles, where there is less sunlight. We are made of sunlight! We are frozen energy grown to consciousness.
When we eat or put gas in our trucks, we use energy from the Big Bang. All energy originated from the Big Bang. Chlorophyll turns sunlight into food, and plants give off oxygen, making animal life possible.
Species like the big snakes evolved near the equator as did the more exotic species of birds and insects. They received plenty of the sun's energy.
Races evolved over a thousand generations. Light skinned people evolved closer to the North Pole, where the sun's rays are slanted. Dark skinned people evolved closer to the equator, where the sun's rays are more direct.
Sleep is a mini-hibernation, night being a mini-winter. Plants and animals evolved in such a way as to cut back during periods of reduced sunlight. Trees shed their leaves.
Earth sits in the habitable zone, where it is not too hot and not too cold. Liquid water exists, and therefore life. Venus and Mars lie outside the habitable zone. Venus experienced runaway heating. Mars experienced runaway cooling.
The earth whips around the sun in 365 1/4 days. Seasons come and go. Today is April 1 by my calendar. It is spring, and there is more sunlight. Days and nights are getting warmer. This trend will continue through the summer solstice. People will be outdoors, and baseball season will be in full swing. May and June are the best times of the year. Flowers bloom, and nature is reborn. The Kentucky Derby is run the first Saturday in May. But perfection is short-lived! It gets hot after the 4th of July. People set off fireworks, which are nerve-racking and a waste of money. August brings scorchers but also the Perseid meteor shower. I counted 351 meteors the night of August 11 and morning of August 12, 1964. I saw many "scratches" which were so dim, I did not count them. Suddenly, students return to school as our planet continues along its 585 million mile orbit at 67,000 miles an hour. It is the autumn equinox, and days and nights are equal. I find myself avoiding football, something that takes effort in Nashville as avoiding basketball takes effort in Louisville. Earth's axis is tilted 23 1/2 degrees and always points in the same direction as our planet circles its star. The sun's arc across the sky appears gradually lower as we journey through the fall months. The final days of October witness a dramatic change! The Northern Hemisphere points away from the sun, and we get less of the the sun's energy while spending more time in our planet's shadow. Plants and animals cut back, preparing for the coming cold. Death is in the air! People celebrate Halloween and the spooky side of nature. November hits hard! It is our most depressing month and the one in which President Kennedy was assassinated. People eat turkey on Thanksgiving and start shopping for Christmas. It is Jesus and Santa! The winter solstice is around December 21. The sun's arc across our sky is at its lowest. We tilt away from the sun as its rays hit us indirectly. We have snow and icy roads! Electric bills are high. It takes time for the planet to cool, so the first day of winter is not the coldest time. The coldest days and nights are generally the first week of January. Ironically, we are closer to the sun in January than we are in July. People ring out the old year and ring in the new. Arbitrary numbers provide a way of measuring time! We plow through the tunnel of November, December, January & February on our way back to spring. Earth keeps orbiting the sun headed for the next vernal equinox. Pitchers and catchers meet the middle of February. It is spring training again, and the New York Yankees convene in Florida for the Grapefruit League. The Cactus League is in Arizona. Baseball teams play 30 exhibition games before the season begins. Starting lineups and pitching rotations are set. Days and nights are equal again as nature renews itself. Grass grows. Flowers bloom. Trees sprout new leaves. It is a cycle, and although it will not continue forever, it will go on as long as the sun remains stable. Billions of years in the future, it will be a different story. The sun will expend its energy and become a red giant. Its outer portion will be given off, and its core will shrink to become a white dwarf. Life on Earth will end. Astronomers know this because they see it happening to other stars. Life is robust for a while. In the long run, it is fragile and tenuous. Our existence, whatever it is, is at once a comedy and a tragedy.
Astronomy: Thoughts On A Couch
Round and round the sun we go! 67,000 miles an hour in a 585 million mile orbit. Seasons come and go based on Earth's 23 1/2 degree tilt to the plane of its orbit, a tilt resulting from our planet being hit during the solar system's infancy. The earth spins, turns & rotates from west to east, spinning 365 1/4 times while making one trip around the sun. Whoever figured that out was a genius! Man devised calendars as ways of keeping track of time. Years, decades, centuries & millennia were recorded. If a person lives to be 80, he or she will live 960 months. Earth always casts a shadow into space, and any particular location continually spins in and out of that shadow, which we call night. Calendars play with words and numbers. There are 12 months because that is the number of moon cycles in a year. 30 days have September, April, June & November. Other months have 31 except for February, which has 28 except during leap year when it has 29. The extra day is added every 4th year to account for the 1/4 day. Beginning the new year on January 1 is a civil event, not an astronomical one. Past civilizations have begun their new years on different dates. We divide our years into 52 weeks. Weeks have 7 days because of the sun, moon, & 5 classical planets: Mercury, Venus, Mars, Jupiter & Saturn. Earth was not thought to be a planet. The planets were associated with gods. Earth's axis, an imaginary line extending from the North Pole through the South Pole, always points in the same direction as Earth goes around the sun. We experience the vernal equinox, summer solstice, autumn equinox & winter solstice. Equinox means equal nights. Everywhere on the globe! The sun's arc appears to shift north and south during the period we call a year. It is an illusion, one of many in astronomy. The sun stays put as we circle it. It is we who are moving, and it is our tilt that makes the sun's arc appear to move north and south in the sky. Calendars go up on the wall and come down. People celebrate birthdays and holidays. They may not mean much but do give a sense of continuity. Astrology is superstition, not science. Astrologers believe personalities depend on what "sign" the sun is "in" when a person is born. Nonsense! For one thing, the constellations (signs) are illusions. For another, the sun is not "in" constellations. It is only in the direction of stars trillions of miles away. Furthermore, there are 13 constellations in the zodiac. Astrology fails to account for Ophiuchus the Serpent-Bearer. The sun, moon & planets appear to stay inside the zodiac because of the flatness of our solar system. All its objects are in the same plane because the solar system coalesced from a spinning cloud of hydrogen left over when the sun formed. The sun was massive enough for the temperature and pressure at its core to start thermonuclear reactions. Hydrogen fuses into helium and so on. Lighter elements are produced inside stars. Heavier elements are produced when massive stars go supernova. The sun emits energy in the form of heat and light. We know that of our galaxy's 400 billion stars (suns), 3 quarters of them are red dwarfs. These are "cool stars," which burn slow and last a long time. Barnard's star, the second closest star after the Alpha Centauri system, is an M red dwarf. Stars and planets are globes, spheres & balls. These are the shapes with the smallest surface areas. If objects have enough mass, they will have enough gravity to pull themselves into these shapes. Objects like asteroids do not have enough mass. Globular clusters contain millions of stars and lie outside the plane of the Milky Way. They are very old and remain intact because they are outside the chaos of the Galaxy. Open star clusters lie along the plane of the Milky Way and disperse after a few million years. The Pleiades and the Hyades in Taurus are open clusters. In Greek mythology, they were half-sisters, daughters of Atlas. There is nothing easy about astronomy, and I have 20 books on my shelf. I have 60 titles in 2 bibliographies. I do not get under the night sky like I did as a teenager, which is okay. I have star maps in my head. I have attended a number of star parties since 1996, and it is always good to hang out with astronomers. I have a plan for going to Greece. It was the ancient Greeks who codified the original 48 constellations, although they were influenced by Mesopotamian shepherds in the Euphrates Valley. Greek myths have survived because the shenanigans of the Olympian gods and goddesses are still interesting. I learned mythology in high school Latin, then applied it to the night sky after my parents bought me telescopes. I sometimes think astronomy is a waste because it takes us out of the world. Still, it is real knowledge.