The Structure of Our Solar System

Past ideas vs. Current Knowledge

Can it change over time?

• The solar system consists of the sun, nine planets, their 158 moons and a belt of asteroids and comets.

• There are over 130 satellites of planets

• Venus, Earth, Mercury, Mars and the sun are all parts of the inner solar system.

• Outer solar system consists of Neptune, Saturn, Uranus, Pluto and Neptune.

• Between the orbits of Mars and Jupiter lies the main asteroid belt.

Current Knowledge

Composition Categories

Mercury, Venus, Earth, Mars have rocky (terrestrial) terrain. This results in few satellites and rings, high density and slow orbit.

Jupiter, Uranus, Saturn and Neptune are gas (Jovian) planets. They are mostly comprised of helium and hydrogen. They are opposite of everything the previous planets. They have many satellites and rings, low density, and quick rotation.

Categories Continued

Giant planets are classified as those with a diameter greater than 48,000 km. These planets are Neptune Uranus, Jupiter and Saturn.

Size- Small planets are those with a diameter than is equal to or less than 13,000 km. These planets are Mercury, Mars, Earth, Venus and Pluto.

When and How the Solar System was Uncovered

1610- 1684 17 bodies were revealed

1781- 1789 5 more bodies were found

1846- 1898 9 major bodies discovered

1904-1978 13 major bodies

1979- 1990 27 small moons found

Past Ideas

Heliocentric Theory• Proposed by Aristarchus (270 B.C.) He thought that

the sun was in the center and all the planets except for the moon orbited around it. He thought that the moon orbited around the Earth. No one believed him at the time because

A) They didn’t think the Earth could be moving

and people wouldn’t feel it.

C) In addition, many believed that Earth had to be the center of the universe because all those people were self-center

B) People also believed that if Earth was moving there would have to be a shift in the positioning of the stars

Geocentric Theory Claudius Ptolemy proposed this theory. He then wrote 13 volumes on the motion of planets in 140 A.D. He wrote about

Epicycles- circles that the planets orbit on

Using epicycles to make backward orbits (retrograde) more visible

Ptolemy explained that retrograde was due to western drift. Western drift makes it seem as if its going backwards.

Church backed this theory and anyone who went against it was put under house arrest

Copernican TheoryCopernicus reinvented the Heliocentric theory and challenged the church’s principles

In case you forgot….. This theory stated that the sun was the center

Science revolution!!

Copernicus still used epicycles to explain motion, but it was more confusing than the Geocentric theory.

Keplerian Theory

Used flattened circles or ovals (ellipses) instead of circles for planetary orbits

No longer needed the epicycles So far the most accurate system of

finding the motion of planetsExplained motion by the 1)semi-major axis 2)the peculiarity3) the inclination 4) the longitude of the ascending bump 5) the argument of the point closest to

the approaching planet (perihelion) 6) the time of the perihelion.

Galileo

• Pioneer of observation• Developed laws of motion• Found that the Earth is not the

center by the fact that

1)spots on the sun

2) mountains on the moon

3) milky way is made up of lots of stars

4) Venus has phases

5) Jupiter has moons

Tycho Brahe

and his scientific contributions

Background Information

• Tycho had the bridge of his nose cut off in a duel, so he was replaced it with a metal plate.

• Lived on the island of Hven, which is located between Denmark and Sweden, given to him by the Danish King

• Brahe had a magnificent castle build there, and an underground observatory called Uraniburg.

• Brahe’s castle was his sanctuary and main center of his astronomy work.

Contributions

• Tycho invented and calibrated new machines for astronomical observation

• Brahe and his team observed the bodies and orbits of planets

• He also corrected his observations according to atmospheric refraction-The change in direction of a ray of light as it passes from space into the atmosphere.

Contributions Cont.

1st modern database and calculated the distance of planets and starts most accurately for his time

discovered that the sun is farther from the Moon than the Earth

supported geocentric theory found that planets are on

elliptical orbits

Contributions Continued

1572- Brahe detected a new star in CassiopeiaCassiopeia is a constellation

1577- He observed a comet and drew the conclusion that the comet is not closer to the Earth than the moon. Aristotle was wrong!

Bibliography

“Planets and the Celestial Sphere.” http://zebu.uoregon.edu/~js/ast221/lectures/lec06.html. 5/10/06

Namowitz, Samuel N. and Nancy E. Spaulding. Earth Science. Canada: D.C Heath and Company, 1994.

Greogry L. Vogt. Solar System. New York: Scholastic Inc., 2002.

Interactive sites

http://www.solarsystem.org.uk/planet10/

http://www.bbc.co.uk/science/space/solarsystem/