Theme 3 Part 2 – Revolutionary Times: Copernicus and Tycho

Brahe

ASTR 101Prof. Dave Hanes

Revolutionary Times

A Few Aspects to Note

The invention of the printing press provided the ability to promulgate new ideas freely

These were times of great artistic and literary creativity

The Protestant Reformation (Martin Luther) questioned the ultimate authority of the then-dominant religious order in Europe

The European discovery of the New World marked the dawn of an age of adventurous exploration

The Principal Astronomical Players

Copernicus – the idea (early 1500s)

Tycho Brahe – the observations (late 1500s)

Kepler – the analysis and empirical laws (1620s)

Galileo – the proof (early 1600s)

Newton- the physics (late 1600s)

Copernicus: Proposed a Heliocentric Solar System

Not himself a keen observer of the heavens!

Motivated mainly by a wish for simplification; he dislikedthe contrived Ptolemaic model.

He hesitated to publish for fear of persecution.

De Revolutionibus Orbium Coelestium

(On the Revolutions of the Heavenly Spheres)

Tycho BraheAn unusual life, from youth to death:

Lost his nose in a duel, had a fake one made

Apparently a very cantankerous man.

Died of a burst bladder after a banquet

He was inspired by and wrote abouta‘nova’ – a ‘new’ star – appearing

wherenone had been seen before. (It is nowrecognized to have been a

‘supernova,’ anexploding star at its death.)

Mapping the Pattern of Stars

First, a definition:the meridian runs across the sky from North to South,through the zenith (your overhead point). It divides the Eastern half of the sky from the Western half.

Think of the meaning of AM and PM: ‘ante’ (before) and ‘post’ (after) meridiem

The Behaviour of Stars

Measuring the Stars:a Meridian Transit

Build a big instrument like that shown, oriented exactly North-South.

No need for a telescope!A straight stick or narrowhollow tube will do. It has to be free to swing up and down.

Measure Two Coordinates

1. Raise or lower the movable stick to point it at each star in turn as it passes through the meridian. Differences in this ‘up-down’ sense tells you which stars are farther North or South in the sky.

2. Use a clock. If Star A passes through the meridian before Star B, then Star A is to the West of Star B (by a measurable amount, given by the difference in time).

(The third coordinate, the star’s distance from us, is unknown!)

Now Accumulate Some Data!

1. Repeat this exercise many, many times to get a precise, detailed map of the sky as defined by the fixed stars. (The stellar patterns don’t change perceptibly over human lifetimes.)

2. Make similar measurements, night after night, to see how the moving dots of light (the planets) change position over time.

Tycho at work

A Model of his Home at Uraniborg, in Denmark

(he was very generously supported by the ruler)

One Particular Contribution

Tycho observed a comet, and invited others in various far-flung locations to describe what they had seen.

From the lack of measurable parallax, he proved that the comet was farther away than the moon – not an atmospheric effect, as some had maintained.

The comet had to be moving through the realm of the planets, metaphorically shattering Ptolemy’s ‘crystalline spheres.’

Tycho’s Most Important Contributions

He accumulated lots and lots of data (really a first in any scientific endeavour) arising from

precise repeated measurements, using

the very best instruments possible, built to exacting standards [but still no telescopes]; and

he hired Kepler to analyze the data!

Tycho’s Legacy

Tycho believed in a hybrid model, with a static Earth, with the moon and sun orbiting us, but all the other planets orbiting the sun

(This would explain why we see no stellar parallax.)

His dying wish (to Kepler)was that he might be proven right.http://www.youtube.com/watch?v=3cutaPj7qMY&feature=

related

The Shakespearean Connection

Tycho’s coat of arms bears the names of two important ancestors: Rosenkrantz and Guildenstern (left side)

Characters with these names appear in Hamlet, and indeed Shakespeare’s plays have various subtle allusions to the questions raised by the “Copernican revolution”