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A Timeline of Astronomy

Central Astronomy, 2019-20

Before Recorded History

Prehistoric Foundations of Astronomy

Hopi petroglyphs in Arizona track the passage of time/seasons

  • Early cultures identified celestial objects with gods and spirits.

Stonehenge in England marks the Winter Solstice (shortest day of year)

  • Related the movements of these objects to phenomena such as rain, drought, seasons, tides, et cetera.

  • Earliest astronomers were likely priests or shamans who related celestial movements to manifestations of the divine (pretty much the definition of astrology btw).
  • Designed ancient structures (Stonehenge) and calendars based on observations of Sun and Moon.
  • Solstices and equinoxes crucial to agricultural societies.

Descent of Kukulcan during Vernal and Autumnal Equinoxes

BC

Astronomy

Temple of Kukulcan, Chichen Itza, Mexico

BC Astronomy

Jantar Mantar Observatory, Jaipur, India

  • 750 BC: Mayans discover 18.6 year cycle in the rising and setting of the Moon, created the first almanacs, devise a pretty epic calendar.
  • 400 BC: Babylonians use the zodiac to divide the heavens into twelve equal segments of 30 degrees each to better record and communicate information about position of celestial bodies.
  • FYI: the Sun has shifted almost one full constellation since the Zodiac was created. So if you have lived your life thinking you are an Aquarius, the Sun was probably in Capricornus when you were born :P
  • Zodiac is a segment of the sky in an area of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year.

BC Astronomy (continued)

  • 387 BC: Plato promotes the harmonic rhythm of all celestial objects that rotate in perfect circles around the Earth.
  • Around the same time, Aristotle proposes the Earth is spherical, based on observations of eclipses, movements of stars, ships sailing over the horizon, infinity other things that prove the Earth is NOT flat.
  • 270 BC: Aristarchus of Samos proposes heliocentrism, gets pushed into the lockers and all his Snapstreaks go cold.
  • 270 BC: Eratosthenes estimates the circumference of the Earth to within 1% accuracy.
  • https://www.khanacademy.org/partner-content/big-history-project/solar-system-and-earth/knowing-solar-system-earth/a/eratosthenes-of-cyrene
  • Circumference of Basketball Experiment
  • 6 BC: Some random Persian astronomers/astrologers observe a planetary conjunction on the Sabbath of April 17, 6 BC, hop on their camels, ride to Bethlehem in search of a baby.

The Renaissance

Nicolas Copernicus (1473-1543)

  • Proposed a heliocentric universe, improved on models of predecessors such as Aristarchus of Samos.
  • Calculated relative distances to planets.
  • Published his ideas in the influential De Revolutionibus Orbium Coelestium. This book was banished by the Roman Catholic Church for nearly 300 years.
  • Was a major science boss, refused to ever get married or have children.

The Copernican Model

  • Much simpler and more elegant than the geocentric model.
  • Could be used to accurately measure distances between planets and sun.
  • Explained retrograde motion in a much more natural way.

Buuuuuut...........

  • Could not predict planet positions any more accurately than previous models.
  • Could not explain lack of parallax motion of stars.
  • Didn't pass the Aristotelian "common sense" test.

Tycho Brahe (1546-1601)

  • Danish nobleman, made significant number of observations of stars and planets throughout his career, all with the naked eye.
  • Recorded the appearance of comets and supernovae, most notable the appearance of a bright "new star" in 1572.
  • The Tycho supernova remnant is still visible today.
  • Had beef with his cousin over who was a superior mathematician. Engaged in a drunken sword duel in which he lost part of his nose.
  • Was a mentor to Johannes Kepler, who thought Brahe's model of the universe was mistaken.
  • Mysteriously died in 1601. The main suspect was Kepler.

Galileo Galilei (1564-1642)

  • Father of Observational Astronomy.
  • Observed the heavens with telescopes of his own design.
  • Scientific contributions to Heliocentrism put him at odds with the church. Investigated by Roman Inquisition for heresy and placed on house arrest.
  • Designed a simple experiment for proving that gravity causes all objects to fall at the same rate.

Major Astronomical Discoveries

  • Four Galilean moons of Jupiter.
  • Rings of Saturn.
  • Observed that Venus exhibited a full set of phases similar to that of the Moon, pwning the Geocentric model of the universe.
  • Made topographical maps of lunar mountains and craters.

Johannes Kepler (1571-1630)

  • Key figure in 17th Century scientific revolution.
  • Invented an improved version of the refracting (or Keplerian) telescope.
  • Mother, Katharina, was imprisoned and tried as a witch. Witches aren't real. The prosecution's case fell apart.
  • Defined three laws of planetary motion that improved upon the Copernican heliocentric theory.

Kepler's Laws of Planetary Motion

  • 1: The orbit of every planet is an ellipse with the Sun at one of the two foci.
  • 2: A line joining a planet and the Sun sweeps out equal areas during equal intervals of time.
  • 3: The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

Newton & Halley

Isaac Newton (1642-1727)

  • Pioneered modern studies of motion, optics, and gravity.
  • Realized no mathematical methods existed for calculating the gravitational force of a spherical body. Kept calm, casually invents calculus.
  • Combining his 3 laws of motion with Law of Universal Gravitation guided astronomy for next 200 years and are still applied in modern space flight.
  • These laws revealed a "clockwork universe," allowing one to predict all future astronomical motions from detailed knowledge of current motions, positions and forces. Astrology is officially declared dead.

Edmund Halley (1656-1742)

  • Set up an observatory on Saint Helena island in south Atlantic, cataloged over 341 stars of the Southern Hempisphere.
  • Observed the transit of Mercury, proposed that the transit of Venus could be used to calculate absolute size of the Solar System.
  • http://www.exploratorium.edu/venus/question4.html
  • Lent Isaac Newton bread to publish Philosophiæ Naturalis Principia Mathematica.
  • Calculated orbits of comets, demonstrating that they have an eliptical orbit around the Sun (next pass of Halley's Comet in July 28, 2061.
  • Captained an exploration ship whose crew mutinied, research on Earth's magnetic field led him to propose a Hollow Earth theory.

Hubble

Edwin Hubble (1889-1953)

  • Played crucial role in establishing fields of extragalactic astronomy and observational cosmology.
  • Discovered that many objects previously thought to be clouds of dust and gas and classified as "nebulae" were actually galaxies beyond the Milky Way.
  • Discovered evidence that universe is expanding:
  • Objects ~10 megaparsecs away from Earth are redshifted.
  • Hubble Space Telescope named in his honor.

The Hubble eXtreme Deep Field (XDF) may have observed a region of sky just 1/32,000,000th of the total, but was able to uncover a whopping 5,500 galaxies within it: an estimated 10% of the total number of galaxies actually contained in this pencil-beam-style slice. The remaining 90% of galaxies are either too faint or too red or too obscured for Hubble to reveal, and observing for longer periods of time won't improve this issue by very much. Hubble has reached its limits.

The most distant galaxy ever discovered in the known Universe, GN-z11, has its light come to us from 13.4 billion years ago: when the Universe was only 3% its current age: 407 million years old. But there are even more distant galaxies out there, and we all hope that the James Webb Space Telescope will discover them. Hubble's wavelength range sets a fundamental limit to how far back we can see: to when the Universe is around 400 million years old, but no earlier.

2019

An Important Event

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