Transcript History of Astronomy

History of Astronomy
Pre-AP student notes
Aristotle
384 BC – 322 BC
•Thought
the universe was
stable, and always will be
•Believed in a geocentric
universe, where the planets
revolved around the Earth
•Believed the entire universe
was the same as the solar
system, did not understand
the vastness of space
Aristarchus
310-230 BC
•Was
the first astronomer to
believe in a heliocentric (sun
centered) universe
•Nobody believed him 
•First attempt at measuring
the distance from the Earth
to the moon, and accurately
did so
•His ideas of a heliocentric
universe went unsupported
by astronomers and the
general public
Aristarchus’ moon
measurement
calculations
Ptolmey 90168 (AD)
A
Roman astronomer who wrote in Greek
Began writing a star catalog, naming and
describing the stars in the night sky
Huge supporter of geocentric models of
the universe
At the time, astronomers were confused
about why the planets wandered the sky in
unpredictable patterns (unlike stars.)
Ptolmey explained the structure of the
universe in terms of epicycles, complicated
planetary movements in circles as they
orbit the Earth
This geocentric model of the universe was
accepted for many, many years
Copernicus: Ancient
Greek astronomer
First
to explain why Earth has seasons
Copernicus took the guesswork out of understanding the
universe, and was the first to apply evidence and the scientific
method
The church banned Copernicus’ books and saw him as a
troublemaker, causing upset in the way we believed our Earth
was central to the universe
During his lifetime, he was never given recognition for his
heliocentric model of the universe
100 years after he died, his model was accepted and people
changed their way of thinking from geocentric (Earth centered)
to heliocentric (sun centered.)
This huge change in people’s perceptions (that the Earth is not
central or all that important in the grand scheme of things) is
now referred to as the Copernican Revolution
Galileo
Galilei
Came 100 years after Copernicus
Made his own telescope and improved it
First to point the telescope at the sky
Discovered Jupiter’s 4 largest moons: Io, Europa, Ganymede, and
Calisto… these are called the “Galilean moons” now
Popularized the Copernican view of a heliocentric universe
Wrote his books in Italian (instead of Latin) so everyone can read them,
not just the scholars
The church warned him to stop writing books about how the universe
was heliocentric… his books were banned and Galileo was put on house
arrest (This didn’t stop him.)
Finally after the threat of being burned at the stake (like Giordino Bruno
was,) Galileo stopped writing.
Galileo’s finest accomplishments:
1. Discovered Galilean moons of Jupiter
2. Discovered mountains and valleys on the moon
3. perfected the telescope , first to point it skyward
4. Discovered that Venus has phases, like the moon does
5. Observed sunspots on the sun (NEVER look at the sun.)
Tycho
Brahe
Wealthy Danish nobleman who loved to party with friends
Built his own observatory in his house
Was the best naked eye astronomer who has ever lived,
made accurate measurements of the distances of planets and
stars with no telescope
Very eccentric – had a pet moose that he let roam his house
(it was fed some beer at one of his parties and then fell down
the stairs and died)
1573 witnessed a supernova and was the only astronomer at
the time to maintain that it was a distant phenomenon…
others believed it was something occurring as nearby as the
moon. Tycho used parallax to demonstrate to others that it
was not a local occurance.
Tycho and one of his friends had a duel to settle an
argument, Tycho lost his nose (hint: don’t duel in the dark)
and had a set of false noses he wore in public… some of them
gold, silver, and copper.
Tycho remains to this day the best naked eye astronomer
that ever lived
Large lunar crater named after him
Came up with his own model of the universe and was
convinced that Copernicus was wrong… died of kidney disease
while trying to prove his model was better than Copernicus
Enlisted the help of his assistant, Johannes Kepler, to try to
prove his model was more correct than Copernicus’ model of
the universe.
Johannes Kepler
Friends
with Galileo
Was Tycho Brahe’s assistant
Tycho had told him “Let not me have lived in vain” because he wanted Kepler to prove
the Copernican model wrong, and convince everyone that the Brahe model was right. It
wasn’t.
Kepler, a physicist at heart, came up with 3 laws of planetary motion from studying
Brahe’s measurements…
1.Planets do not follow circular orbits, but instead follow elliptical orbits… most are
barely elliptical but Pluto was the most elliptical
2.A line joining a planet and the Sun sweeps out equal areas during equal intervals of
time… this means as a planet is nearing the sun, it speeds up and whips around the sun
then slows again
3.3.The square of the orbital period of a planet is directly proportional to the cube of the
semi-major axis of its orbit. (p squared = a cubed)
Women in Astronomy – Harvard’s
computers
•Williamina
Fleming was a housekeeper for a Harvard professor named
Edward Pickering, who became angry at his assistant and told him “My maid
could do a better job than you.” Sympathetic to the cause of women’s
rights…. Pickering hired Williamina to study the spectral classes of stars. She
classified stars according to spectral type, A through Q.
•Antonia Maury: worked on classifying stars and creating a master stellar
catalog.
•Henrietta Leavitt: worked to study the magnitude of stars (brightness) and
was the first to study Cephied variable stars (stars that do not maintain their
brightness, and instead repeat a cycle of bright and dim.)
•Annie Jump Cannon: rearranged the classification system of stars to reflect
temperature…. Created the OBAFGKM system.
•Caroline Herschel (sister to William Herschel, discussed on the next slide, an
astronomer who discovered 2 moons of Saturn, and discovered infared
radiation and built many telescopes) discovered 8 comets and 3 nebulae,
and helped William build the world’s best telescopes of the time
William Herschel – German astronomer
1738-1822
Herschel became most famous for the
discovery of the planet Uranus in
addition to two of its major moons,
Titania and Oberon. He also discovered
two moons of Saturn and infrared
radiation. Finally, Herschel is less known
for the twenty-four symphonies that he
composed.
Herschel was a telescope builder,
building many telescopes in his lifetime.
His 40 foot telescope with a 49.5 inch
mirror (which he cut and polished
himself) helped him discover a moon of
Saturn the first night he used it.
Herschel’s
40 foot
telescope
Edwin
Hubble
Edwin Powell Hubble (November
20, 1889 – September 28,1953)
was an American astronomer who
profoundly changed understanding
of the universe by confirming the
existence of galaxies other than our
own, the Milky Way.
He also discovered that the degree
of "Doppler shift" (specifically
"redshift") observed in the light
spectra from other galaxies
increased in proportion to a
particular galaxy's distance from
Earth. This relationship became
known as Hubble's law, and helped
establish that the universe is
expanding.