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Tycho Brahe (1546-1601)Tycho Brahe (1546-1601)(right around Galileo)(right around Galileo)

Born Born Tyge Ottesen Tyge Ottesen BraheBrahe (I can’t say (I can’t say that correctly)that correctly)

Last of the great Last of the great astronomers who astronomers who came before the came before the invention of the invention of the telescopetelescope

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What’s the deal with Tycho’s nose?What’s the deal with Tycho’s nose?

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Tycho’s lifeTycho’s life

Born as a twin, but his brother diedBorn as a twin, but his brother died

His uncle took him away from his family His uncle took him away from his family when he was two, but his real parents when he was two, but his real parents were apparently all right with this.were apparently all right with this.

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Tycho’s lifeTycho’s life

Observed the total Observed the total solar eclipse of 1560solar eclipse of 1560

So impressed by the So impressed by the fact that it had been fact that it had been predicted that he predicted that he developed an interest developed an interest in Astronomyin Astronomy

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Tycho’s lifeTycho’s life

Became discouraged Became discouraged when he couldn’t find when he couldn’t find any 2 astronomical any 2 astronomical charts that agreed charts that agreed with each otherwith each other

Set out to complete Set out to complete his own astronomical his own astronomical chart of the night skychart of the night sky

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Tycho’s Observatory on the Island of HvenTycho’s Observatory on the Island of Hven

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Tycho and the supernova of 1572Tycho and the supernova of 1572

A new star appears in theconstellation Cassiopeiaand temporarily becomesas bright as the planetVenus

- why is a new star important?

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Tycho’s contributionsTycho’s contributions

Observed the supernova of 1572Observed the supernova of 1572

Showed that the comet of 1577 was Showed that the comet of 1577 was beyond the earth’s atmospherebeyond the earth’s atmosphere

Accumulated years of careful observations Accumulated years of careful observations of the apparent motions of the planets in of the apparent motions of the planets in the skythe sky

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Tycho’s ContributionsTycho’s Contributions

Made incredibly Made incredibly detailed catalogues of detailed catalogues of the sky over a period the sky over a period of 25+ years!of 25+ years!

Was able to detect Was able to detect stellar parallax!stellar parallax!

All withoutAll without the aid of the aid of a telescope!!!a telescope!!!

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Tycho’s own model of the solar Tycho’s own model of the solar system was not a successsystem was not a success

The sun goes around the earthand the otherplanets go aroundThe sun

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At one point, he was so famous and rich, At one point, he was so famous and rich, he was said to own 1% of the entire wealth he was said to own 1% of the entire wealth of Denmark (in 1580)of Denmark (in 1580)

Held large parties at his castle, and had a Held large parties at his castle, and had a dwarf named Jepp sit under the tabledwarf named Jepp sit under the table

Tycho = a strange duckTycho = a strange duck

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Tycho = a strange mooseTycho = a strange moose

Had a tame moose as Had a tame moose as a peta petThe moose died after The moose died after drinking too much drinking too much beer at a party and beer at a party and falling down the stairs falling down the stairs (the story doesn’t say (the story doesn’t say why the moose was why the moose was indoors at all, perhaps indoors at all, perhaps he knew some good he knew some good moose jokes)moose jokes)

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Tycho’s DeathTycho’s Death

““Bladder myth” generally believed to be Bladder myth” generally believed to be falsefalse

Sick for 11 days after the banquetSick for 11 days after the banquet

Perhaps………..Perhaps………..

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High levels of Mercury were found in samples of High levels of Mercury were found in samples of Tycho’s hair recentlyTycho’s hair recently

Tycho himself was an alchemistTycho himself was an alchemist– He would have known Mercury can killHe would have known Mercury can kill

After Tycho’s death, Kepler took Tycho’s 25 years After Tycho’s death, Kepler took Tycho’s 25 years of observations and used the data to calculate his of observations and used the data to calculate his 3 laws of planetary motion!3 laws of planetary motion!– Tycho was Tycho was veryvery secretive with his notes! secretive with his notes!

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R.I.P. Rockstar AstronomerR.I.P. Rockstar Astronomer

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But Tycho’s observations paved the But Tycho’s observations paved the way for way for Johannes KeplerJohannes Kepler (1571- (1571-

1630, born in Stuttgart, Germany)1630, born in Stuttgart, Germany)

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Kepler: a mystic and a Kepler: a mystic and a mathematicianmathematician

Uses Tycho’s Uses Tycho’s observations to try to observations to try to come up with a better come up with a better model of the motions model of the motions of the planetsof the planets

Mysterium cosmographicum (The Sacred Mystery of the Cosmos)

1919

Kepler: the man, the myth, the Kepler: the man, the myth, the legendlegend

Dabbled in the Dabbled in the philosophical side of philosophical side of Astronomy and Astronomy and AstrologyAstrology– At that time, they were At that time, they were

one in the sameone in the same

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Kepler’s music of the spheresKepler’s music of the spheres

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But Kepler was not wackoBut Kepler was not wackoHe came up with 3 laws of He came up with 3 laws of

planetary motionplanetary motion

First LawFirst Law– Planets move in Planets move in

elliptical orbits with the elliptical orbits with the sun at one focus of the sun at one focus of the ellipseellipse

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An ellipse looks like an elongated circle

What is an Ellipse?

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Kepler’s First Law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus.

What are Kepler’s three laws of planetary motion?

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No more uniform circular motionNo more uniform circular motion

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Kepler’s Second Law: As a planet moves around its orbit, it sweeps out equal areas in equal times.

means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.

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Kepler’s third lawKepler’s third law

a is the semi-major axisof the ellipse

For a circle a isequal to the radius

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Kepler’s third lawKepler’s third law

P = periodP = period

a = semi-major axis (radius for a circle)a = semi-major axis (radius for a circle)

PP22 = constant X a = constant X a33

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For a planet orbiting the sunFor a planet orbiting the sun

Measure P in earth yearsMeasure P in earth years

Measure a in AU (astronomical units, Measure a in AU (astronomical units, Earth to sun, as we’ll see)Earth to sun, as we’ll see)

– ThenThen

PP2 2 = a= a33

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ExamplesExamples

Earth a =1 gives P = 1Earth a =1 gives P = 1

Jupiter a = 5.2 AUJupiter a = 5.2 AU

PP22 = a = a33 = (5.2) = (5.2)3 3 = 141= 141

P is the square root of 141, which is about 11.9P is the square root of 141, which is about 11.9

So it takes Jupiter about 11.9 years to go once So it takes Jupiter about 11.9 years to go once around the sunaround the sun

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KeplerKepler

By getting rid of uniform motion in circles By getting rid of uniform motion in circles Kepler got rid of epicyclesKepler got rid of epicycles

His laws of planetary motion predicted the His laws of planetary motion predicted the motions of the planets more accurately motions of the planets more accurately than either Ptolemy or Copernicusthan either Ptolemy or Copernicus

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R.I.P. F.D.G.R.I.P. F.D.G.

Gustavus Adolphus’ (King of Sweden) army Gustavus Adolphus’ (King of Sweden) army destroyed the churchyard where Kepler was destroyed the churchyard where Kepler was buried, so we don’t actually know where his grave buried, so we don’t actually know where his grave is anymore. Sad day.is anymore. Sad day.