1. How we came about the knowledge of what is out there in space.
Celestial History
How we came about the knowledge of what is out there in space.

2. For thousands of years, people have looked up into the sky, and observed what they saw, using their observations to keep track of the time of the day, and the time of the year.

3. Early Astronomy
1500 B.C.  British Isles: the Stonehenge was made, which is a collection of giant stones that mark the direction of the sun.
1300 B.C.  China: astronomers observed the night sky in depth, and calculated the length of a year to be 365 ¼ days.
BC (before Christ) or BCE (before Common Era)
AD (anni domini in the year of the lord in latin) or CE (Common Era)

4. Continued….
B.C.  This was the time of Aristotle, a Greek philosopher and astronomer. He supported the idea of a Earth centered model of the universe, along with his mentor, Plato. Around A.D.  Ptolemy, Greco-Egyptian mathematician and astronomer, developed the geocentric model into what we now see it as.

5. Early 1500’s
In roughly 1514, Nicolaus Copernicus developed the heliocentric model of the universe, although he was not the first to mark the theory. He went against the Church in supporting this model, so he was not well supported.
Copernicus was German.

6. Early to Mid 1600’s
About 100 years later, in about 1632, Galileo Galilei, an Italian astronomer, used a telescope to gather more proof in support of Copernicus’s heliocentric model. He observed moons around Jupiter, which proved that not everything revolves around the Earth.

7. The Milky Way
Ancient Greek philosophers proposed that the Milky Way may be a vast collection of stars.
Galileo used his telescope in 1610 to prove that it was made up of countless stars.
In 1755 Immanuel Kant proposed it was held together by gravity, and that the solar system was imbedded within.
The Milky Way is a huge whirlpool that rotates once ever 200 million years & has 100 billion stars.
It belongs to a cluster of at least 40 galaxies.

8. Inertia Galileo Newton This law states:
In Galileo’s time, he was the first to be credited with the idea of inertia.
To recap, inertia is the resistance to a change in motion
Sir Isaac Newton, however, is credited with formalizing the idea into a law, known as Newton’s 1st Law, or the Law of Inertia.
This law states:
A body in motion will remain in motion, and a body at rest will remain at rest, unless acted upon by an outside force.
Larger mass = more inertia
Smaller mass = less inertia

9. The Milky Way is part of the Drion Spur

10. Gravity holds together our Milky Way galaxy.
There are two factors that affect the pull of gravity, mass and distance. ~more mass = greater gravitational pull ~less mass = less gravity - closer = more gravity - farther = less gravity

11. The Celestial Police
By the 1800’s, scientists predicted that there was a planet between Mars and Jupiter.
The celestial police was a group formed to try to find it.
In 1801, an astronomer outside of the group found a “body” in the region and named it Ceres.
Within a short time, 100 had been found, and it was realized that they could not be planets because of their small size, so they called them asteroids.
We now call this area, that contains millions of asteroids, the Asteroid Belt.

12. Kuiper Belt
In 1950, astronomer Gerard Kuiper predicted the existence of a belt of large objects beyond the orbit of Neptune, but the first belt object wasn’t discovered until 1992.
-We now know that this region starts beyond Neptune, and extends past Pluto, and contains icy debris.

13. What We Know Today In our solar system we have: 8 official planets
One major star, the sun, that everything revolves around
5 dwarf planets
181 moons
~4.6 billion years old
Dwarf planets = Ceres, Pluto, Eris, Makemake, and Haumea
181 moons as of october 2008; 173 orbit the planets, 8 orbit the dwarf planets
We have 1 moon, mars has 2, jupiter has 67, saturn has 62, uranus has 27, neptune has 14, pluto has 5
-mercury and venus have none, most likely because of their proximity to the sun

14. The Planets The close planets: The far planets:
Mercury, Venus, Earth, Mars
Terrestrial planets  solid, rocky surfaces
The far planets:
Jupiter, Saturn, Uranus, Neptune
Called the Jovian planets, or gas giants
Made of mostly helium and hydrogen gasses
Less dense
Jovian from the Roman God Jupiter, or the archaic name Jovia.

15. Relative Size of the Planets