Astronomy 9/24/2015

Brad Hansen PAB 3-913 1-3:30 Thursdays

TA: Lynnie Saade: TBD Office Hours: TBD

Scientific Methodology

Ancient Greeks:

Thales- adopted notion of objective reality based on physical laws that could be discovered and tested. “Model of Nature”

Anaximander – reasoned that the Earth was a cylinder because the sky moves North to South but does not move East to West.

Pythagoras – taught that Earth was a sphere, and Eratosthenes evaluated the size of the Earth

Geocentric Model

Greeks believed that the earth was at the center of the celestial spheres

The Planets, including the sun and Moon, did not rotate the same way as the stars, so they needed their own spheres.

They ran into the problem of retrograde motion, when earth overtakes Mars, Mars would go backwards in its orbit.

They considered the heliocentric model but rejected it because they could find no evidence for parallax.

Epicycles

Greeks introduced the idea of epicycles.

The Ptolemaic model was the most detailed epicyclical geocentric model and was accepted for almost 1500 years.

Copernicus

Eventually, people began to see the inaccuracies in the epicycle model

Nicolas Copernicus created the heliocentric model

Copernicus also formulated the “Copernican Principle”, which states that we occupy no special place or time in the Universe.

His models wasn’t that much more accurate than Ptolemy’s because he still used circles to describe planetary orbits.

Kepler

Johannes Kepler was assistant to Tycho Brache who built his own observatory.

Kepler inherited his data and came up with the Kepler’s three laws of Planetary Motion

1. Orbits of all planets are ellipses, with the sun at the focus.2. Speed in the orbit is such that it sweeps out equal areas in equal time.3. Provides a mathematical formula relating the period of the orbit to the distance from the Sun.

Galileo

Galileo was first true experimental scientist, and first to use telescope.

Detailed observations of the moon, noticing the presence of spots and craters. He observed Jupiter and noticed that Jupiter had moons.

He noted the Venus underwent phases, but the orientation suggested motion around the Sun, not the Earth.

The Nature of Modern Science

Discovery Science: Data gathering. The first step in investigating a phenomenon is simply to gather as much data as you can.

Hypothesis- Driven Science: Propose ideas to be tested by experiments and observations.

Systematic posing of hypotheses and tests will eventually lead to a theory or model that describes the underlying principles that give rise to the observations.

Observation > Questions > Hypothesis > Prediction > Test

Modern Science is driven by observations

When a model is supported by many observations and several tests it is often referred to as a Theory.

Sometimes there are many models that can explain extant data. Usually the simplest one is correct. “Occams Razor”

Testability is an essential part of a scientific theory, and usually the most important distinction with pseudoscientific enterprises.