Transcript The Birth of Modern Astronomy

Astronomy
Astronomy
is the study of the planets and other
objects in space.
The “Golden Age of Astronomy” occurred during
600 – 150 B.C. when the ancient Greeks used
observations, instruments, and geometry and
trigonometry to make the first discoveries of space.
During this time, Aristotle (384 – 322 B.C.) was the
first person to determine that Earth was round based on
the curved shadow left on the surface of the moon when
Earth fell between the sun and the moon. His belief was
abandoned in the Middle Ages.
Models of the Solar
System



Geocentric Model – The Greeks determined that
the moon, the sun, and the known planets at that
time (Mercury, Venus, Mars, and Jupiter) orbited
Earth.
Heliocentric Model – Aristarchus (312-230
B.C.) was the first Greek to believe in a suncentered universe.
Ptolemaic System – Claudius Ptolemy
published his 13-volume work in 141 A.D. He
used the geocentric model, but was the first to
explain retrograde motion (the planets move
eastward in the sky, appear to stop, move
backwards, and then resume its eastward
movement).
The Birth of Modern
Astronomy


Nicolaus Copernicus (1473-1543) – The
first major astronomer to make
advancements since Ptolemy. He was the
first to determine that Earth is a planet and
that the sun is the center of the universe.
Tycho Brahe (1546-1601) – He convinced
King Frederick II to build an observatory in
Copenhagen. Here, Brahe invented
measuring devices (telescopes had not yet
been invented) and made the most
accurate observations of several planets,
especially Mars.
The Birth of Modern
Astronomy (2)

Johannes Kepler (1571-1630) – Studied under
Brahe and continued his work by using math to
develop 3 laws of planetary motion.
 The path of each planet around the sun
is an ellipse. There are 2 “centers” – 1
at the sun and 1 at the other end of the
ellipse.
 There is an imaginary line over which
the planet travels. This ellipse is
traveled in the same time interval
every time it orbits and the planet
moves more quickly when traveling
around the sun and slower at the other
end of the ellipse.
 P2 = a3 (P = the time it takes the
planet to complete 1 orbit; a =
distance of the planet to the sun)
The Birth of Modern
Astronomy (3)

Gallileo Galilei (1564-1642) – was the
great Italian astronomer and was the first
to use the telescope. He made 5 major
discoveries.
The discovery of 4 satellites (moons)
around Jupiter.
The discovery that planets are circular
disks, not just points of light.
Venus has phases (just like our moon
does).
The sun has sunspots (dark spots).
The Birth of Modern
Astronomy (4)

Sir Isaac Newton (1642-1727) – developed
the Law of Universal Gravitation.
 The gravitational pull is a result of the
mass of the object and the distance
between 2 objects.
 The greater the mass of an object, the
greater the gravitational pull. (Weight
does not mean the same as mass – the
mass of an object will never change;
however, the weight of an object is a
result of the mass and the gravitational
pull of the planet. This is why your weight
will change when you are on another
planet.)
 The force of gravity and the tendency to
orbit on a straight-line is the result of the
elliptical orbits that were discovered by
Kepler.
Assignment

Solar System Introduction Worksheet