Major Changes in AstronomyWithin last 400 years:
-- Earth is not the center-- Universe is immense
Within last 200 years:-- Appreciate the age of the universe
Within the last 50 years:-- Universe is not static-- Contains truly bizarre objects
Within the last 10 years:-- Many planets around other stars-- Water elsewhere in the solar system
History
Aim: What was the study of Astronomy like long ago?
Why did humans first study Astronomy?
• Mark time and cycles• Predict season change for planting crops• Navigation• Curiosity… need to explain phenomena
Early Astronomy
Earliest known records show astronomical interest.
Many ancient cultures built sites and kept records on astronomical data.
3,000 BC - Stonehenge built (aligned with solstice and lunar eclipses).
Big Horn Medicine Wheel
Caracol Observatory - Mayans
Calendar
Our calendar marks movements in our solar system.
Year - one Earth revolution around Sun.Month - one Moon revolution around EarthDay - one Earth rotation
Early PhilosophersAristotle (350 BC) - Geocentric model. Why?
Because it explained observations
Geocentric Model:
Earth at the center of universe. Everything revolves around Earth.Universe is unchanging and static.
Geocentric Model
Observations it explains: -- The stars, sun, and planets appear to revolve
around the Earth each day.
-- Earth does not appear to move… no constant wind.
-- No parallax.
Parallax
How do we determine distances in space?
Simple way is triangulation. If you know two angles and one side, trigonometry does the rest.
Parallax = apparent movement of object when observer’s location moves.
Parallax
Early Philosophers
Aristarchus of Samos (310- 230 BC)
** Earth and all planets orbit Sun.
- idea rejected by later philosophers because they conflicted with Aristotle.
How Big?
Eratosthenes - Greek mathematician (200 BC)
• Invented Latitude and Longitude.
• Measured Earth’s circumference.
Eratosthenes
How Round?
Earth is an oblate spheroid.
Early Philosophers
3. Hipparchus - (150 BC) =
-- first astronomer-- developed trigonometry
-- first star chart-- discovered precession-- possibly developed the astrolabe
Precession
Earth “wobbles” on its axis like a spinning top.
Every 26,000 years Earth completes one wobble.
Caused by Moon’s gravity.
Hipparchus Star Catalog
Farnese Globe
Astronomical Clock
• Antikythera Mechanism (150 BC)
• Made by Greeks
• 31 gears – give sun, moon, 5 planets, eclipses.
• As complex as a 19th century clock.
Early Astronomers
Claudius Ptolemy - (140) = Sophisticated geocentric model.
-- made geocentrism the standard model.
-- very complicated with 80 epicycles.
-- explained Mars retrograde motion.
Early Astronomers
Nicolaus Copernicus - (1473 – 1543) = Heliocentric Model
-- Sun is at the center of universe.
-- Simple and elegant… no epicycles
-- Not accepted until Galileo
Early Astronomers
Tycho Brahe (1546 – 1601) = Measured movements of planets and stars.
-- made most accurate star charts
-- based ideas on actual observations
-- Sun and Moon orbit Earth, but other planets orbit Sun.