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400th Anniversary of Galileo
400th Anniversary of Galileo

Telescope Observations that Changed the World

Galileo made a number of observations that could not be explained with the accepted theories of the day. Old beliefs had to be re-examined.

The visual observations made by Galileo and the work of Nicolaus Copernicus, Tycho Brahe and Johannes Kepler toppled the Earth-centered view of the universe, replacing it with the heliocentric (Sun centered) model. The previous and long-held assumption that the heavens were perfect in form was suddenly in doubt.

2009 marks the 400th anniversary of Galileo's observations. Over the next few month's we will use Starry NightŪ to relive the exciting discoveries that changed forever our view of the universe and our place in it. We encourage educators to follow along with us in their classrooms.

Discovery One: Jupiter and its Moons

Galileo?s first observations of Jupiter on January 7, 1610, revealed three "stars" in line with Jupiter's equator. Galileo was not concerned by this observation as he believed they were fixed background stars.


January 7, 1610

But on the very next day, he found a different arrangement:

January 8, 1610

Galileo was puzzled by this observation and his thoughts were concerned with how Jupiter itself had moved relative to the fixed background stars.

Further observations over the next few days revealed that these "stars" continued to change their arrangement around Jupiter. Galileo knew that these changes could not be attributed to Jupiter itself and came to the astonishing realization that these three 'stars' were moving around Jupiter.

You can follow in Galileo's footsteps using Starry NightŪ. Begin by downloading the file Jupiter1610.snf. Open this file with Starry NightŪ (File-Open). Starry NightŪ will display the night sky as seen by Galileo 400 years ago on January 7, 1610.

Compare what you see in Starry NightŪ with Galileo's sketch on January 7, 1610. How many "stars" or more accurately moons, do you see around Jupiter? How do your observations in Starry NightŪ compare to Galileo's?

Advance the time by one day and compare the view in Starry NightŪ with Galileo's sketch on January 8, 1610.

How do your observations compare with Galileo's? Hint: Galileo's telescope had a field of view of about 15 arc minutes.

On January 13th, 1610 Galileo discovered an additional "star" which had escaped his earlier observations. These four "stars" are now know as the Galilean moons of Jupiter.

Stay tuned to next month as we continue to relive the discoveries made by Galileo that changed our view of the universe.

February 2009

Date Taken: 06/08/2011
Author: Herb Koller
Category: Archives

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