Early Models of the Universe
Pythagoreans (500 B.C.)
•Believed the stars, planets, sun, and moon were
attached to crystalline spheres which rotated
around the Earth.
•Geocentric- everything moved around the Earth.
Aristotle (350 B.C.)
•Believed the Earth is motionless at the center of
the universe and all the stars and planets
revolved around it.
•Stars and planets moved in circular paths.
•Geocentric
Ptolemy (140 A.D.)
• Expanded Aristotle’s theories to try to account for “retrograde
motion” of the planets
• Planets traveled in smaller circular paths as they traveled around the
Earth (epicycles and deferents) Geocentric
• Popular model of the universe for 1,500 years.
Copernicus (1543)
• Sun at the center of universe and the planets orbit the sun.
Heliocentric.
• Solved the problem of “retrograde motion”
• Theory did not immediately replace Ptolemy’s theory.
Tycho Brahe (1600)
• Favored an Earth-centered universe different from Ptolemy’s theory.
• Thought that other planets revolved around the Sun, and that the sun
and moon revolved around Earth.
• His theory was incorrect, but made many precise observations of
planets and stars.
• Geocentric
Johannes Kepler (1609)
• Mathematician
• Tycho’s assistant
• Used Tycho’s observational data to develop laws of planetary motion.
• Kepler’s 3 Laws of Planetary Motion
• Law of Ellipses
• Law of Equal Areas
• Law of Periods
Galileo Galilei (1609)
• First person to use telescope for astronomical observations
• Discoveries:
• Galilean Satellites (Jupiter’s moons)
• Craters on the moon
• Sunspots on the Sun
• Phases of Venus
• Favored Copernicus’s theory over Ptolemy’s
Isaac Newton
• 1687
• Explained why planets orbit the Sun, and why moons orbit planets.
• Newton’s Law of Motion
• Newton’s Law of Gravitation
• Completed the work of Copernicus, Tycho, Kepler, and Galileo
MODEL OF THE UNIVERSE
PHYSICAL SCIENCE 4TH WEEK 1
1. discuss how Greeks knew that the Earth is round;
2. describe how Eratosthenes produced the
measurement of Earth’s circumference;
3. cite examples of known astronomical phenomena
before the advent of telescopes;
2/8/20XX 11
Equivalent to the
Earth’s north pole
Equivalent to the
Earth’s south pole
Equivalent to the
Earth’s latitude
(N & S location)
Equivalent to the
Earth’s longitude
(E & W location)
Path which the
sun appears to
take the celestial
sphere
Point in which the
ecliptic intersects
with celestial
equator
Lunar Eclipse:
SEM
Solar Eclipse:
SME
Ancient
Assyrian Egyptian
Babylonian
kept track of the…
Dark spot
comets meteors
of the sun
developed calendar
based on the movement
Venus Navigation
DIURNAL
SUN VENUS
MOON MERCURY
MARS JUPITER SATURN
PLANETES
ANNUAL
MOTION
ZODIAC A bond of thirteen constellations
collectively called zodiac can be
ECLIPTIC seen in the ecliptic
There are 13 constellations in the sky the Sun regularly
visits over a year: Capricornus, Aquarius, Pisces, Aries,
Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius,
Sagittarius, and Ophiuchus.
EQUINOXES An equinox occurs at the start of
the spring and fall.
SOLSTICES The solstice occurs during the
summer and the winter.
Occurs on March 21 (Vernal
EQUINOXES equinox) and on September 23
(Autumnal equinox). Occurs on
SOLSTICES June 21(Summer Solstice) and on
Dec 22 (Winter Solstice).
PRECESSION
Precession is defined as the slow change in
the direction of Earth's rotational axis.
Precession is akin to a planet's "wobble,"
just as a spinning top sometimes wobbles
during its rotation.
Hipparchus 1500 BC
gyroscope.
Retrograde motion of Mars as seen in the
celestial sphere
Epicycle used by Ptolemy to explain
retrograde motion
As a planet moves around on its epicycle, the center of the epicycle
(called the ``deferent'') moves around the Earth. When its motion
brings it inside the deferent circle, the planet undergoes retrograde
motion.
Tycho Brahe
Johannes Kepler
Tycho Brahe
A Danish astronomer continuously
and precisely recorded the position
of the sun, moon, and planets for
over 20years using instruments
that are like a giant PROTRACTOR.
Johannes
Kepler
Law of Ellipse: each planet's orbit
about the Sun is an ellipse. An ellipse
somewhat flattened circle.
It is closed curve in which the sum of
the distances from any point on the
ellipse to foci (two points inside)
constant.
Johannes
Kepler
Law of Equal Areas: A line joining a
planet and the sun sweeps out equal
areas in space in equal intervals of
time. A planet moves fastest when it is
nearest to the sun
Johannes
Kepler
Law of Harmony: the square of
planet’s orbital period (years) is
proportional to the cube of the
semimajor axis of its orbit (AU) or
2
P = a3
