Download What is the difference between geocentric and heliocentric theories?

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9 planets
Geocentric vs Heliocentric
• “Geo” means Earth
• “Helio” means sun
Ancient Observations
• The ancient Greeks
observed the sky and
noticed that the moon,
sun, and stars seemed to
move in a circle around the
Earth.
• It seemed that the Earth
was not moving and
everything in the heavens
revolved around the Earth.
• As it turned out, it was very
difficult to prove that the
planets did not revolve
around the Earth without
leaving the planet.
Geocentric Theory
• Ancient Greeks such as
Aristotle believed that
the universe was
perfect and finite, with
the Earth at the exact
center.
• This is the geocentric
theory, which stated,
the planets, moon,
sun, and stars revolve
around the Earth.
Ptolemy (85-165 AD)
• In AD 140 the Greek
astronomer Ptolemy
revised the geocentric
model to explain all
the planetary motions.
• His model had the
planets move in little
circles that also
moved in bigger
circles.
• This belief persisted
for about 1500 years.
Copernicus (1473-1543)
• In the early 1500’s
the polish
astronomer
Copernicus
suggested that the
Sun, not Earth, was
the center of the
solar system and the
planets revolved
around it.
• This is the
 Helios means “sun”
Heliocentric Theory.
in Greek.
Galileo (year 1609)
• One of the first to
use a telescope to
see objects in
space
Isaac Newton (1687)
• Showed that all
objects in the
universe attract
each other by
gravity
What is a galaxy?
• A galaxy is a large grouping of stars,
gas, and dust in space that are held
together by gravity.
1. Spiral
3Types of
Galaxies
3. Irregular
2. Elliptical
Spiral Galaxies
• Shaped like flattened
disks with one or
more spiral arms.
• Our galaxy, Milky Way, is
a spiral galaxy.
• Our solar system is
located in one of the spiral
arms.
Elliptical Galaxies
• About 1/3 of all galaxies.
• massive, round blobs of stars.
• Round or elliptical in shape.
• Contain very little gas or dust.
• Because of little gas, no new
stars are forming.
• The largest and smallest
galaxies are elliptical galaxies.
Irregular Galaxies
• No defined shape
• Do not fit into any other
category.
• Chaotic mix of stars, gas
and dust
• Usually found near large
spiral galaxies who may
be distorting their shape.
THINGS IN OUR SKY!!!
• A natural
satellite is any
celestial body in
space that orbits
around a larger
body.
Meteorite, Meteoroid, Meteor?
What’s the difference?
Meteorite vs. Meteoroid
• Meteoroid = while in space a meteorite is
called a meteoroid
• Meteorite = a small rock or rocky grain that
strikes Earth’s surface
• So the difference is just based on where
the rock is when you are describing it
Meteor
• Sometimes called a
“Shooting Star”
• When a meteorite
enters Earth’s
atmosphere, friction
causes them to burn
up, producing a
streak of light
Comets
• Bodies in space made up of ice, dust,
small gritty particles
• Sometimes called “dirty snowballs”
• When close to the sun, ice vaporizes,
producing a spectacular streak of gas,
referred to as a “tail”
• Many in a regular orbit around the sun
Comets
Famous Comets
• Comet Hale-Bopp
• Halley’s Comet
• Comet Kohoutek
Asteroids
• An irregularly shaped
rocky object in space
(like a space potato)
• May be the shattered
remains of objects left
over from the time
when the planets
were formed
How big are asteroids?
• Larger than meteoroids
• (In fact, the main difference between
meteoroids and asteroids is their size.)
• Size ranges from 10 feet across to bigger
than a mountain
Asteroids
• Approx. 150,000 asteroids in the Solar
System
• Most are in a band that orbit the sun
between Mars and Jupiter (Asteroid Belt)
• Why are there all of those asteroids
between Mars and Jupiter and not another
planet?