Transcript File history of astronomy

History of Astronomy
Our Universe
• Earth is one of nine planets that orbit the sun
• The sun is one star in 100 billion stars that
make up our galaxy- The Milky Way
• Our galaxy is one of billions of galaxies in the
universe
• Views of our galaxy and Universe have
changed tremendously throughout time
Early Astronomy
• Astronomy- science that studies the universe
• Deals with properties of objects in space and the laws
through which the universe operates
Early Astronomy- Ancient Greeks
• Aristotle (384-322 B.C.)
– Concluded that Earth was round from
observations of the curved shadow on the moon
when Earth passes between sun and moon
• Eratosthenes (276-194 B.C.)
– Calculated circumference of the Earth
• Used angles of noonday sun in two locations on the
planet
Early Astronomy- Ancient Greeks
• Hipparchus (2nd century B.C.)
– Determined the location of 850 stars and
categorized them according to brightness
– He measured the length of a year and developed a
method for predicting lunar eclipses
Models of the Universe
• Greeks believed in the Geocentric model of
the universe
• Earth is the center and planets, sun, and moon orbit
around Earth
• Aristarcus (312-230 B.C.)
– First to propose a heliocentric model- Earth and
other planets orbit the sun
• Still- the Geocentric model dominated for
nearly 2,000 years
Ptolemaic System
• Claudius Ptolemy published the Ptolemaic
system in 141 A.D.
• This system accounted for the movements of
the planets, but was still a Geocentric model
which was determined to be inaccurate
• Ptolemy discovered retrograde motion
Retrograde Motion
• Planets appear to stop, reverse direction, and
resume normal motion
Modern Astronomy
• Nicolaus Copernicus (1473-1543)
– Concluded that Earth was a planet and proposed a
model of the solar system with the sun at the
center (Heliocentric)
– Tycho Brahe (1546-1601)
• Used instruments to measure the locations of
“heavenly bodies”
• His observations were far more precise than any made
before
• Johannes Kepler started his astronomy career as an
assistant to Brahe
Modern Astronomy
• Johannes Kepler (1571-1630)
• 3 laws of planetary motion
– Discovered that planetary orbit around the sun is
not in a circle but an ellipse (oval shape)
– Also discovered that speed of planets changes as
revolve around the sun
• Faster as they get closer to the sun (perihelion) slower
as it gets further from the sun (aphelion)
Kepler’s 3 Laws of Planetary Motion
• Law 1
– The path of each planet around the sun is an
ellipse, with the sun at one focus, and other focus
symmetrically opposite
Kepler’s 3 Laws of Planetary Motion
• Law 2
– Each planet revolves around the sun so that it
sweeps over equal areas in equal time intervalstherefore planets travel faster as they near the
sun
Kepler’s 3 Laws of Planetary Motion
• Solar distances of the planets can be
calculated when their periods of revolution
are known
• Distances are expressed in astronomical units
(AU)
Galileo Galilei (1564-1642)
• Created the first telescope in 1609- previous
to this invention all astronomical discoveries
were made without aid of a telescope
– Telescope magnified objects 3X
Galileo’s Discoveries
• Four moons orbiting Jupiter
– Disproved that Earth was center of universe
• Planets are circular disks and Earthlike
– Disproved that planets were points of light
• Venus has phases like the moon
– Shows that Venus orbits its light source (the sun)
• Moons surface is not smooth
• Sun has sunspots, or dark regions
– Helped to calculate the rotational period of the sun
Sir Isaac Newton (1642-1727)
1. Was the first to formulate and test the law of
universal gravitation
– This helps to explain why planets move in ellipses
and not in a straight line
• Gravity is directly proportional to mass of an object and
inversely proportional to distance
• Greater mass = Greater gravitational attraction
• Greater distance = less gravitational attraction
– Gravity Pulls objects towards the sun = elliptical
orbits