Transcript The Dead Guys

The Dead Guys
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Timeline
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Ancient Astronomy
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Anaxagorus (500-428 B.C.)
• Greek Philosopher
• Claim to fame…Indefinite elements in
all substances.
• Banished for saying “the sun is a red
hot stone and the moon was like the
Earth.”
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Pythagoreans (500 – 350 B.C.)
• Various students over many years.
• Original master was Pythagoras, a
mathematician.
• Credited for observing the planet Venus.
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Aristotle (384 - 322 B.C.)
• He proposed three observational proofs
that the Earth is a sphere:
– Ships disappear slowly over the horizon.
– The shape of the Earth's shadow at lunar
eclipse appears circular.
– Different stars are visible at northern and
southern latitudes.
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Aristarchus (310-230 B.C.)
• First to propose a heliocentric solar
system.
• Proposed a much larger universe than
what was originally thought.
• Studied various distances of the sun
and other planets in relation to each
other in space.
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Eratosthenes(276-192B.C.)
• Estimated how large the Earth was (250B.C.).
• The stadium, the size of a sports arena, was a
unit of distance used by the Greeks.
• Eratosthenes estimated the circumference of
the Earth to be 250,000 stadia. (40,320km)
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Calculating the Size of the
Earth
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Hipparchus of Nicea (190-120B.C.)
• Hipparchus proposed that the axis around which the heavens
seemed to rotate shifted gradually, though very slowly.
• Hipparchus concluded that the intersection marking the equinox
slowly crept forward along the ecliptic, and called that motion
"the precession of the equinoxes. " The rate is about one full
circle in 26,000 years.
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Ptolemy (100-170A.D.)
• Ptolemaic view
– The Earth is round, stationary and very small relative to
the celestial sphere of the sky.
– The stars are fixed points of light inside the celestial
sphere.
– Day and night result from the rotation of the entire
celestial system around the fixed, nonrotating Earth.
– The planets moved on small circular paths, called
epicycles.
– Combination of the planetary motions along the
epicycles and deferents produces the observed
wandering of the planets among the stars, including
the retrograde motion.
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• Earth centered or geocentric.
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Copernicus (1473-1543)
• First to promote the heliocentric system (motion of
the Earth and planets in orbit around the fixed Sun)
• He could easily explain the observed retrograde
motion of planets like Mars.
– The Sun is the center of the Solar System; the Earth and
planets orbit the Sun in circular orbits.
– Day and night are the result of the rotation of the Earth
on its axis.
– Mercury and Venus are closer to the Sun than the Earth
is.
– Only 3 motions of the Earth are needed:
1. daily rotation on its axis
2. yearly revolution around the Sun
3. wobble or libration of the Earth on its axis, accounting for
precession of the equinoxes
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• Has to do with the planets moving at different
speeds and our line of sight.
• Venus moves quicker…closer to the sun.
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Tycho Brahe (1546 - 1601)
• Is considered the best naked-eye observer of
all time!!!
• He built his observatory which became the
finest observatory in Europe.
• For 23 years Brahe, using instruments, made
some of the most accurate drawings of the
visible universe.
• 1600- Kepler joins Brahe and serves as
assistant
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Brahe
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Brahe’s Observatory
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Johannes Kepler (1571 - 1630)
• Kepler's teacher was one
of the earliest astronomers
to subscribe to
Copernicus's heliocentric
theory.
• Takes Brahe’s position
and data upon his death
• Develops and publishes 3
Laws
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Kepler’s 3 Laws
• The First Law: Planets move in ellipses with the Sun at one
focus.
– orbits are not circles
– sun is not the center
• The Second Law: The radius vector describes equal areas
in equal times (law of equal areas)
– orbits are not at constant speed
• The Third law: Period squared is proportional to distance
cubed (the harmonic law or law of periods)
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period is the time required for one orbit
distance refers to the average distance from the sun
planets further from the sun move slower
a3=p2
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Galileo Galilei (1564 - 1642)
• His most famous invention was the telescope.
• He was able to look at:
– the moon and describe its rough surface
– Discovered the four satellites of Jupiter
– Observed a supernova
– Verified the phases of Venus
– Saw the trenches on Mars
– Saw that the milky way was a collection of stars
– Discover sunspots
• His discoveries proved the Copernican system which
states that the earth and other planets revolve around
the sun. (Heliocentric)
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Isaac Newton (1642 - 1727)
• Among his achievements are:
– He showed that gravity not only makes an apple fall to the ground but
also governs the motions of planets and their satellites, and should apply
to any bodies (for example, binary stars).
• Newton formulated three important laws of motion:
(1) An object stays at rest if it is at rest or stays in uniform motion in a
straight line unless it is acted upon by some force. (inertia)
(2) When acted upon by a force, an object changes its motion in an amount
proportional to the force acting upon it, and according to the direction of
the force. (f=ma)
(3) When one object exerts a force upon a second object, the second object
exerts an equal and opposite force back on the first. (equal and opposite)
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