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.