K-6 Activities - Dudley Observatory

Objective
Early Astronomers, Activity 5-1
The student should be able to compare and discuss the work of early astronomers:
Ptolemy, Copernicus, and Galileo.
Background
Ptolemy, in his book, The Alamagest, explained the geocentric (earth-centered) theory
of the planetary motions. The planets were thought to rotate in circles (epicycles), the
centers of which described orbits around the earth. The sun and moon, also considered
planets, were believed to orbit the earth without epicyclical rotation.
Not until the year 1543 did anyone seriously challenge the idea that Earth was the
center of the universe. A Polish astronomer, Nicolaus Copernicus, argued that the
earth and the moon, along with the other five planets then known, all moved around
the sun in circles. He also said that the earth rotates and this makes the sun and stars
appear to move across the sky. Like most ideas that upset comfortable old beliefs, the
idea that earth was in motion was hard to accept. It was up to other scientists later
on, to prove that Copernicus was right.
Galileo advanced the idea that before explaining what happens, you must carefully
observe how it happens. He used a set of lenses, developed by a Dutch spectacle
maker, Hans Lippershey, to invent a telescope that made objects appear about 36
times larger. Observations with his telescope, especially the discovery of the phases
of Venus, supported the ideas of Copernicus.
Procedure
• Class discussion in the planetarium or classroom setting should center around
each of the men.
• Student reports can be assigned. Have students write news articles, in the present
tense, about the findings of these men.
Extension Activities
Students could role play and dress according to the times.
• B–63 • K–6 Activities