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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) Helios means “sun” 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 Heliocentric Theory. Helios means “sun” 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.

3Types of Galaxies 1. Spiral 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?