The solar system
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The Solar System. How did the solar system form?. The nebular theory (or accretion hypothesis) is the most widely accepted explanation. NEBULAR THEORY A nebula is an extremely large cloud of dust and gas.

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How did the solar system form
How did the solar system form?

  • The nebular theory (or accretion hypothesis) is the most widely accepted explanation.


  • A nebula is an extremely large cloud of dust and gas.

  • The nebula is unstable, and begins to collapse around different regions because of an unequal distribution of matter.

Nebular theory
Nebular Theory

  • As the nebula collapses around different areas of high mass, the gravitational attraction of these regions grows, which attracts more and more material.

  • These points where the matter collects become stars.

  • For this reason, nebulae are often called stellar nurseries.

Nebular theory1
Nebular Theory

  • As matter collects unevenly around the center, it begins the whole mass spinning. (PROTOPLANETARY DISK)

  • Most of the mass (99%) collects in the center forming the Sun.

  • The rest of the mass (1%) flattens into a spinning disk of dust and gas around the Sun.

Nebular theory2
Nebular Theory

  • Within the disk, areas of higher mass attract more and more material (accretion).

  • This accretion forms “planetessimals”, or the beginnings of planets.

Nebular theory3
Nebular Theory

  • When accretion is finished, we are left with our solar system.

The sun
The Sun

  • The Sun is the star at the center of our solar system.

    • Made mostly of hydrogen (92.1%) and helium (7.8%)

    • Nuclear fusion produces the Sun’s energy

    • About 1.3 million Earth’s could fit inside the Sun

      • 1.4 million km in diameter (109 times larger than Earth)

    • 5500 °C (9900 °F)


  • Law of Universal Gravitation

  • All objects with mass exert a gravitational force on the objects around them.

  • Strength of force depends on the masses of the objects and the distance between them.

  • Because of the Sun’s great mass, all other objects in the solar system orbit around it.


  • A planet:

    • Orbits the Sun

    • Has a spherical shape

    • Is significantly more massive than the objects around it

  • There are 8 planets in our solar system

    • Inner planets

    • Outer planets

Inner planets
Inner Planets

  • The four planets closest to the sun (inside the asteroid belt)

    • Mercury, Venus, Earth, Mars

  • Smaller size (than the outer planets)

  • Rocky (Terrestrial)

    • Mostly iron core

    • Solid outer crust

Outer planets
Outer Planets

  • The four planets farthest from the Sun (outside the asteroid belt)

    • Jupiter, Saturn, Uranus, Neptune

  • Larger size (than the inner planets)

    • Called “gas giants”

  • Ice and gasses

Dwarf planets
Dwarf Planets

  • Like a planet…

    • Made of rock and ice

    • Spherical shape

    • Orbits the Sun

  • But not a planet!

    • Orbits near other similarly sized objects.


  • Small, rocky objects that orbit the Sun

  • Millions found in the asteroid belt between the orbits of Mars and Jupiter

  • Between one meter and several hundred thousand meters in length

  • Usually not spherical


  • Relatively small ball of gas, dust, and ice

  • Orbits the Sun

    • Usually an extremely elliptical orbit

  • Come from outer parts of the solar system

  • Sometimes called a “shooting star”

    • NOT A STAR!!!

Measuring distances
Measuring Distances

  • Because of the great distances between objects in our solar system, we use a larger than usual measurement…

  • AU – Astronomical Unit

    • The average distance between Earth and the Sun

    • 150 million kilometers (150,000,000 km)

Geocentric model
Geocentric Model?

  • It was once believed that Earth was the center of the universe and all other objects revolved around it.

  • Geo = Earth

  • Centric = Center

Heliocentric model
Heliocentric Model

  • Helio = Sun

  • Centric = Center

  • In the 1500’s, Copernicus proposed that Earth and other planets revolve around the Sun

    • Though the Sun was later observed NOT to be the center of the universe!

  • Supported by evidence collected as technology allowed further investigation.

Planetary orbits
Planetary Orbits

  • Kepler discovered that planetary orbits are elliptical rather than circular

  • Planets move faster when they are closer to the Sun, and slower when they are farther from the Sun.

  • Sun at one focus.