Famous Dead Guys
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Famous Dead Guys. # 6 and 7. Tycho and Kepler!. Tycho Brahe (1546-1601) (right around Galileo). Born Tyge Ottesen Brahe (I can’t say that correctly) Last of the great astronomers who came before the invention of the telescope. What’s the deal with Tycho’s nose?. Tycho’s life.

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Famous Dead Guys

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Famous Dead Guys

# 6 and 7

Tycho and Kepler!

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

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

  • Last of the great astronomers who came before the invention of the telescope

What’s the deal with Tycho’s nose?

Tycho’s life

  • Born as a twin, but his brother died

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

Tycho’s life

  • Observed the total solar eclipse of 1560

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

Tycho’s life

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

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

Tycho’s Observatory on the Island of Hven

Tycho and the supernova of 1572

A new star appears in the

constellation Cassiopeia

and temporarily becomes

as bright as the planet


- why is a new star important?

Tycho’s contributions

  • Observed the supernova of 1572

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

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

Tycho’s Contributions

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

  • Was able to detect stellar parallax!

  • All without the aid of a telescope!!!

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

The sun goes

around the earth

and the other

planets go around

The sun

Tycho = a strange duck

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

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

Tycho = a strange moose

  • Had a tame moose as a pet

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

Tycho’s Death

  • “Bladder myth” generally believed to be false

  • Sick for 11 days after the banquet

  • Perhaps………..

Kepler killed him!

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

  • Tycho himself was an alchemist

    • He would have known Mercury can kill

  • After Tycho’s death, Kepler took Tycho’s 25 years of observations and used the data to calculate his 3 laws of planetary motion!

    • Tycho was very secretive with his notes!

R.I.P. Rockstar Astronomer

But Tycho’s observations paved the way for Johannes Kepler (1571-1630, born in Stuttgart, Germany)

Kepler: a mystic and a mathematician

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

Mysterium cosmographicum (The Sacred Mystery of the Cosmos)

Kepler: the man, the myth, the legend

  • Dabbled in the philosophical side of Astronomy and Astrology

    • At that time, they were one in the same

Kepler’s music of the spheres

But Kepler was not wackoHe came up with 3 laws of planetary motion

  • First Law

    • Planets move in elliptical orbits with the sun at one focus of the ellipse

What is an Ellipse?

An ellipse looks like an elongated circle

What are Kepler’s three laws of planetary motion?

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

No more uniform circular motion

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.

Kepler’s third law

a is the

semi-major axis

of the ellipse

For a circle a is

equal to the radius

Kepler’s third law

  • P = period

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

    P2 = constant X a3

For a planet orbiting the sun

  • Measure P in earth years

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

    • Then

      P2 = a3


  • Earth a =1 gives P = 1

  • Jupiter a = 5.2 AU

    P2 = a3 = (5.2)3 = 141

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

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


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

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

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

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

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