Early Astronomy History: Timeline

EARLY HISTORY (2700 B.C. – 1600 A.D.)

Early Astronomy: Predicting Eclipses, Determining Equinoxes and Solstices

2700 B.C. (Stonehenge, England) – stones marked solstices and equinoxes; Aubrey holes predicted eclipses

2000 B.C. [Sumerians] – earliest constellations (bull, lion, scorpion); base 60 system

2000 B.C. [Babylonians] – Pythagorean Theorem

1000 B.C. [Egyptians] – helical rising of Sirius; 12 month, 30 day calendar; sundial

1000 B.C. [Chinese] – counting boards

700 B.C. – 50 A.D. [Babylonians] – planetary positions and eclipses

600 B.C [Pre-Greek: Thales of Miletus] – solar eclipse prediction, Saros Cycle; constellations as known today

600 B.C. (Miletus, Greece) [Anaximander] – shadow from stick t calculate the length of the year; life originated in water, evolved from simpler forms

500 B.C [Pythagoras of Samos] – spherical moon, spherical-moving Earth

450 B.C [Empodocles] – water thief to argue that air must be so finely divided that it’s invisible

400 B.C. [Chinese] – sunspots

400 B.C. [Democritus] – atoms, large number of other worlds, Milky Way aggregates of light from other galaxies

4th Century B.C [Plato] – proposed Uniform Circular Motion of Planets; spherical Earth

350 B.C. (Athens, Greece) [Aristotle]– model of the solar system: spherical universe centered on solid spherical Earth (geocentric view); moon between Earth and Sun; all objects are from the four elements – earth, water, fire, and air; earth and heaven to be subject to two different sets of laws

300 B.C. (Alexandria) [Euclid] – most prominent mathematician; “Elements”: geometry; conic sections

310-250 B.C. [Aristarchus of Samos] – relative distances and sizes of the Moon and the Sun; Sun at the center of the solar system (heliocentric view); used Earth’s shadow to measure the size of the moon

200 B.C. (Alexandria) [Eratosthenes] – measured earth’s size using simple geometry and scientific process

130 B.C. [Hipparchus of Rhodes] – star maps; star catalog of 850 stars, precession; epicycles

150 A.D. [Ptolemy] – fixed Aristotle’s model with the epicycle theory: planets move in epicycles (small circular paths around which the planets move); the centers pf epicycles are along the deferent (big circle)

250 A.D. [Mayans] – “place-value” number system

500 A.D [Hyptia] – first known woman astronomer, librarian of Alexandria

500 A.D. [Chinese] – solar wind; comets: tail of comets always point away from the Sun

6th – 9th Century A.D. [Persian and Arabic Astronomy] – “Al-Sufi”: Book of Stars Showing Orion Nebula; “Al-Battani”: Non-circularity of Earth’s Orbit

10th Century A.D. [Mayans] – Dresden Codex, Venus tables, eclipse tables

10th Century A.D. [Chinese] – star map showing 26 sections

1054 A.D. [Chinese] – supernova: remnant traced to Crab Nebula

1100 A.D. [Pueblo Native Americans] – Sun Dagger

1270 A.D. [Samarkand] – star catalog

Mid-1400’s A.D. (Germany) [Regiomontanus] – “Ephemeris”; “The Nuremberg Chronicle” – planetary positions and comet charts

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Why Does Earth Have Seasons?

SEASONS

In the northern hemisphere in summer, the Sun rises in the northeast, stays high overhead at noon, and sets in the northwest. In the winter, the Sun rises in the southeast, stays low in the southern sky at noon, and sets in the southwest. Seasons are caused by the Earth’s tilt of rotational axis to the ecliptic and not by the Earth’s distance to the Sun. The Spring (Vernal) Equinox is the first day of spring (third week in March), when the Sun crosses the Celestial Equator the first time in the year. The Autumnal Equinox is the first day of Fall (third week of September), when the Sun crosses the Celestial Equator six months later. The Summer Solstice is the first day of summer (third week in June), the longest day of the year, and when the Sun is at its highest point in the ecliptic. The Winter Solstice is the first day of winter, the shortest day of the year, and when the Sun is at its lowest point in the ecliptic.

2012 Dates:

Vernal Equinox = March 20, 2012

Summer Solstice = June 20, 2012

Autumnal Equinox = September 22, 2012

Winter Solstice = December 21, 2012

Prehistoric Astronomy

Prehistoric Astronomers

As one of the oldest sciences, astronomy flourished in prehistoric times. Hunter-gatherers realized the importance of recognizing seasons, moon phases, annular events, and the apparent movement of the Sun. The early peoples divided the skies into the North Celestial Pole, a single point about which stars move around in the sky, and the South Celestial Pole. The Celestial Equator is the half-way line between the Celestial Poles and also a projection of Earth’s equator into the sky. 3,000 years ago, the Babylonians discovered the 360° circle, which is a base 60 system that originated from 365 days in a year. The five ancient planets are Mercury, Venus, Mars, Jupiter, and Saturn. The North Star is the star closest to the North Celestial Pole— currently Polaris. Because of precession, or the wobble of Earth’s rotational axis that sweeps out a circle in 26,000 years, the extension of Earth’s North Pole points to a different North Star during the motion. Helical rising is the first day each year when a particular star can first be seen just before dawn; helical setting, then, is the last day of the year when the star can be seen at dusk.  The ecliptic is the apparent path of the Sun in the sky and the zodiac is the path of planets within a zone of 18 degrees wide-centered on the ecliptic. Hunter-gatherers and early settlers utilize knowledge of these ideas to farm, navigate, and survive.

What are Eclipses?

ECLIPSE: An eclipse occurs when one object blocks another. Eclipses occur on Earth because the Sun’s size to the Moon’s size is equal to that of the Sun’s distance to Earth to the Moon’s distance to Earth.

SOLAR ECLIPSE: A solar eclipse occurs when the Moon, between the Sun and Earth, blocks out t he Sun.

LUNAR ECLIPSE: A lunar eclipse when the Earth’s shadow falls on the Moon’ the Earth is between the Sun and the Moon.

  • Total and partial lunar eclipses are much more common than total and partial solar eclipses because the Earth is more likely to block the Sun’s light than the Moon is.
  • Lunar eclipses can also be seen on over a greater area than solar eclipses.
  • Since the Moon’s orbit is tilted 5 degrees more than the Earth’s orbit, eclipses do not occur every month; sometimes, the Moon is too high or too low.
  • Umbra: (total eclipse) the innermost and darkest of the shadows, light source is completely blocked
  • Penumbra: (partial eclipse) only a portion of the light source is blocked
  • Antumbra: (annular eclipse) the occluding body appears entirely with the disc of light

FUTURE ECLIPSES:

November 13-14, 2012 = Total Solar Eclipse

November 28, 2012 = Penumbral Lunar Eclipse