Astronomy: Watching the Sky A TCNJ CCS Program
Contents • Class 1: From Astrology to Astronomy –The history of looking up at the sky. • Class 2: A Trip Through the Solar System – Planets, Moons, and Comets. Oh My! • Class 3: The Big Bang and the Universe – The history of everything • Class 4: Space Exploration– Spaceflight and a visit to the planetarium.
In the beginning… • The ancients believed that the sky was the realm of the gods. • They knew the sky well. With no TV or Internet there was nothing else to watch at night!
In the beginning… • Define terms: • Astrology : A belief system that the positions of the stars and planets provide information about personality, human affairs, and other earthly matters.
In the beginning • Astronomy: the scientific study of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earth's atmosphere.
Astronomy vs. Astrology • Astronomy and Astrology were largely the same thing. • Many cultures believed that the heavens were the realm of the gods who controlled men destinies. • Observing the heavens, however, also had very practical applications.
Ancient Astronomy Worldwide • Many ancient cultures had a highly developed art of astronomy. • This included the Chinese, Arabs, Greeks, Babylonians and Mayans.
Egyptian Astronomy • Had a 360 day calendar from earliest times. • Used movement of stars and sun to predict Nile flood. • Religious festivals timed with moon, stars, sun. • Temples built base on alignment with sky.
Alignment with Sky • Pyramids aligned with Polaris, the North Star. • Temple Amun-Re at Karnak has a passage that is only illuminated by the mid-winter’s rising sun.
Alignment • The ancients noticed that stars always rose at the same point. • Other objects like the Sun and Moon would vary with the time and season. • Monuments like Stonehenge were built aligned to certain days of the year and could act as calendars.
Sun, Moon & Planets • Do not rise and set at the same place over each day. • But the stars do!
Demo • Sunrise alignment and a tomb.
Egyptian Gods in the Sky • Sun was the god Re • Moon was Troth god of wisdom.
Ancient Constellations • A grouping of stars is a constellation. • Different ancient cultures had different constellations. • The afterlife god Osiris shares most of the same stars with our modern constellation Orion.
Some Greek Constellations • Capricorn (the goat) – Draco (the dragon)
What the Ancients Saw • All noticed that the stars seemed to be fixed on a giant sphere that turned about the earth (The “Starry Vault”) • The sun and moon moved across the sphere on similar path.
The Wanderers • Another group of objects moved across the sky in the same path as the sun and moon. • These did not always move in a consistent direction but wandered forward and back. • We call this objects planets after the ancient Greek word for wanderer.
Hairy Stars • Comets were planet-like objects with long tails that appeared at random times. • They were often associated with important (sometimes evil) events (death of a king, etc.).
Evil Omen • In 1066 the appearance of Halley’s Comet was considered an omen of the death of Harold II of England who died at the Battle of Hastings later that year.
The Zodiac • The constellations the sun, moon and planets moved through were often considered special. • Today we call this group the Zodiac.
The Zodiacs • Different cultures had different zodiacs because their constellations were different.
Greek Zodiac • The Greek Zodiac has 12 constellations: • Aries, the ram; Taurus, the bull; Gemini, the twins; Cancer, the crab; Leo, the Lion; Virgo, the Virgin; Libra, the scales; Scorpio, the scorpion, Sagittarius, the archer; Capricorn, the goat; Aquarius, the water bearer; and Pisces, the fish.
Greeks: Aristotle • Aristotle believed that the earth was at the center of a number of sphere’s. • On the outermost sphere were the stars. • Inner spheres contained the sun, moon and planets.
Geocentric System • A planetary system with Earth at the center like Aristotle proposed was geocentric. The Greek word geo means “Earth.” • Most ancient astronomers used a geocentric system.
The Greeks: The Almagest • Around 100 BC Claudius Ptolemy took Aristotle's system and put math to it. • He published this in a massive book called the Almagest. • It was the authority for astronomy for almost the next 1000 years.
The “Wanders” Problem • The old geocentric system had hard time explaining the motion of the planets. How could they make these strange loops?
Heliocentric Theory • A few ancient scholars, however, came up with the idea that the Sun, not the Earth was the center of the solar system (Such as Aryabhata a 5th century Indian astronomer). • A planetary system with the sun in the center is known as a heliocentric system. • From the Greek word Helios, which means “Sun.”
Copernicus • Around 1530 the Polish scholar Nicholas Copernicus published a book On the Revolutions of the Celestial Spheres proposing a heliocentric system. • It was a much simpler system then Ptolemy’s.
Retrograde Motion • Because both Earth & other planets are orbiting the Sun they can appear to move backwards.
Copernican Revolution • Copernicus’ claim was controversial. • Man and Earth not center of universe. • Changed our understanding of man’s place in universe.
Johannes Kepler • One of the first astronomers to adopt and defend Copernicus’ sun centered system. • Invented a basic refracting telescope.
Demo • Kepler’s Laws of Planetary Motion
Kepler’s Laws of Planetary Motion • Kepler discovered that the length of their orbit was a function of their distance from the sun. • He also realized that planets did not move in perfect circular orbits, but ellipses.
Galileo Galilei • Did not invent the telescope. • One of the first persons to use it for astronomy. • Vocal supporter of sun centered system.
Galileo’s Accomplishments • Discovered mountains on the moon in 1610. • Discovered four moons of Jupiter in 1610. • Discovered rings of Saturn in 1610. • Discovered sunspots in 1613.
Galileo and the Church • The church found the sun centered system “false and contrary to Scripture.” • Galileo was warned not to defend Copernicus’ system. • He was put on trial and forced to recant his ideas. • He spent the end of his life under house arrest.
Father of Modern Astronomy • Has been called: • Father of modern observational astronomy • Father of modern physics • Father of Modern Science
Legacy • Stephen Hawking says, "Galileo, perhaps more than any other single person, was responsible for the birth of modern science.“ • In 1992, Pope John Paul II issued a declaration acknowledging the errors committed by the Church tribunal that judged the scientific positions of Galileo.
Newton’s Gravity • Isaac Newton born on 4 January 1643. • Gravity: Every object in the universe attracts every other object. • The force is more powerful with more mass involved. • The force weakens over distance.
Law of Gravity • We are 6 times heavier on the Earth than the moon because the Earth is more massive than the moon. • If you weighed 100 pounds on Earth you would be 16.6 pounds on the moon and 236 pounds on Jupiter.
Gravity • One of the weakest forces in nature, but also one of the most long range. • Holds the planets in orbit around the sun.
Demo • Gravity vs. Electromagnetism
Homework • Read “Comet Halley: Harbinger of Death?” for next class.
Group Work: • Groups will work together to present on these topic on February 1st. • Mars: Is there a possibility of Life on Mars? • What’s the Story with Pluto? • How does a telescope work? • What is SETI?