1. PART I: Where Are We Located?
Unit 8: Astronomy

2. I. What Objects Do We Find in Outer Space?
Put the following celestial objects in order from biggest to smallest:
Solar System Star Planet
Universe Galaxy Comet
Meteoroid Moon Asteroid

3. I. The Universe
The Universe – Commonly defined as the “Totality of everything that exists”
The universe contains everything we know of. All matter and energy is contained within our universe.
It continues in every direction and we do not see the end.
It was created between 10 and 15 billion years ago. (Best estimate is 13.7 billion years old).

4. How Was the Universe Created?
The current theory is that the universe was created from an explosion called the “Big Bang”. All the matter in the universe was concentrated into a dense sphere of hydrogen not much larger than our sun. It exploded into an expanding cloud of dust and debris from which all the celestial objects and systems we know of today formed.

6. Evidence for the Big Bang Theory:
1. Cosmic background radiation: Cosmic background radiation is radiation left over from the Big Bang. It looks like smoke filling the big spaces between celestial objects.

7. 2. A Red-Shift in the light from very distant galaxies:
When two celestial objects move away from each other the light between them is stretched, forming longer wavelengths that appear as red because red is the visible light wavelength that is longest.
When two celestial objects move towards each other the light between them is compressed, forming shorter wavelengths that appear as blue because blue is the visible light wavelength that is shortest.

8. We Only See a Red-Shift! That means all celestial objects continue to drift apart from the Big Bang!

9. Spiral, Elliptical and Irregular
II. Galaxies
Galaxies are smaller than the universe. A galaxy is a system containing billions of stars. The universe contains approx. 3,000 observable galaxies.
The Hubble Space Telescope has estimated that there may be as many as 125 billion galaxies!!!
Galaxies are classified by their shape. The three main shapes are:
Spiral, Elliptical and Irregular

11. Our Galaxy: The Milky Way

12. 3. Solar System
A solar system is defined ad the collection of planets and their moons in orbit around a sun, together with smaller bodies such as asteroids, meteoroids, and comets. 
Our Solar System formed about 4.6 billion years ago and includes our sun, eight planets, at least 141 moons, thousands of asteroids, millions of meteoroids, and many comets.
See page 15 ESRT!

14. Are the Planets Moving Backwards?
Although planets may appear like stars in the nighttime sky, even the earliest observers, watching night after night, noticed the eastward movement of these planets among the more fixed background of the stars and constellations. Periodically, some of the planets appear to stop, reverse their direction for a period of time, and then resume an eastward motion. This apparent westward (backward drift is called RETROGRADE MOTION

15. Why Does This Occur?
Retrograde motion occurs when we are observing planets farther away from the sun than we are. Because they move slower than us in orbit there are times when we pass them by in orbit, and it seems as if they are moving backwards.
This can easily be seen while observing the orbit of Mars.

17. History of the Solar System
To the earliest observers, the daily rising and setting of the Sun, Moon, Planets, and stars indicated that all celestial objects revolved around Earth. This model is called the GEOCENTRIC
model of the solar system.

18. The Geocentric Model as Described by Ptolemy:

19. *By the early 1500’s, Copernicus suggested that Earth and the other planets revolved around the Sun. This model is called the Heliocentric Model. (Sun-Centered).
Copernicus thought the Earth was in motion. Ptolemy thought the Earth didn’t move at all. Copernicus proved his theory through observations such as retrograde motion (proof of revolution) and the Foucault Pendulum (proof of rotation)

21. The Heliocentric Model

22. 4. The Planets
A planet is described as a celestial body moving in an elliptical (oval-shaped) orbit around a star.
The characteristics of the planets are affected by each planet’s location relative to the sun.
Planets composed primarily of rock formed closer to the sun where it’s heat drove off ices and gases. These planets are called TERRESTRIAL PLANETS.
The terrestrial planets are dense and rocky like Earth.

23. Terrestrial Planets

24. Farther from the Sun, where temperatures are lower, planets are composed primarily of gases. These planets are called the JOVIAN PLANETS, OR GAS GIANTS.
The gas giants are composed mostly of gas, have no solid rocky surfaces, and have a very low density.
Some of the Jovian planets, like Jupiter and Saturn, are so big that they have a tremendous gravitational pull and as a result have many moons orbiting them.

25. Jovian Planets

26. 5. Asteroids, Comets and Meteoroids:
Asteroids are defined as small rocky and/or metallic objects. There is an asteroid belt located between the orbits of Mars and Jupiter. Asteroids are debris left over from the formation of the solar system or comets that have broken apart.

28. Comets are small chunks of dust and ice with highly elongated orbits around the Sun.
Meteorites (meteoroids) are small asteroids that are broken apart by impacts with other asteroids that travel through space. Most are smaller than a pebble.
Evidence suggests that asteroids, comets and meteorites have impacted Earth, as well as other planets and moons. Only a few impact craters have been identified on earth. Earth’s atmosphere is responsible for the disappearing craters.

29. Small Metorites
A Comet
Willamette
Meteorite
Impact Crater