THE UNIVERSE

THEORIES ABOUT THE ORIGIN OF THE SOLAR SYSTEM

NEBULAR THEORY1. Developed by Pierre-Simon Laplace in 17962. Suggests that the Solar System began from

rotating clouds of dust and gas called NEBULA.3. Gaseous rings then formed from rapidly rotating

nebula. Later, materials in the rings condensed. 4. Further condensation of gaseous rings resulted in

the formation of planets, with the sun at the center.

PROTOPLANET HYPOTHESIS

Proposed in 1949 by Gerald P. KuoperIt states that the Solar System began also with a

great cloud of dust and gas. Gravity pulled most of the cloud materials around the center. The compressed materials became so hot to form the sun. The remaining materials formed a single disk around the sun. The disk rotated slowly with the sun. friction within the disk caused the materials to form several eddies.

These eddies shrunk into more compact masses called protoplanets which later became the planets and their moons.

The remaining uncollected cloud materials were the comets, meteoroids and planetoids.

PLANETESIMAL THEORY The planetary system was formed from

materials removed from the sun by great gravitational attraction. The gaseous projection was pulled from the sun by tidal action caused by a passing star.

The projection became masses of gases which revolved around the sun. at first, the masses were very hot. They cooled and contracted and became solid bodies of varying sizes and distances from the sun.

The larger bodies attracted smaller ones and became planets. The smaller bodies became asteroids, meteors and satellites of planets.

GALAXIES

A galaxy is a concentration of billion of stars held together by their mutual gravitation.

The SPIRAL GALAXY

Our Sun lies in a spiral galaxy called Milky Way. Its disk is 2000 light-years thick and nearly 100,000 light-years in diameter.

The Solar Systemand its members

THE SUN• Sun, closest star to Earth. The Sun is a huge mass

of hot, glowing gas. The strong gravitational pull of the Sun holds Earth and the other planets in the solar system in orbit. The Sun’s light and heat influence all of the objects in the solar system and allow life to exist on Earth.

• Rotating sphere of hot gases. Its rotation varies from 25 days at the equator and 36 days near the poles.

• Hans Albrecht Bethe figured out from his studies that the sun’s energy comes from changing hydrogen gas to helium gas (NUCLEAR FUSION)

THREE MAJOR PARTS OF THE SUN

CORONAHalo of white light we see around

the run during total eclipse. It is the outermost region of the sun’s atmosphere.

Its temperature reaches about 1 to 1.5 million degrees Celsius.

Holes appear in the Corona, which allows electrically charged particles to flow into space

CHROMOSPHERE

A dense layer of colored gases above the photosphere. Its temperature reaches to about 10 000 degrees Celsius.

PHOTOSPHERE

a bright, thin layer of visible light. It is a sea of gases with a temperature of about 6000 degrees Celsius. Most of the light we receive comes from this layer.

The planetsAsteroidsMeteoroidsCometsSatellitesDwarf Planets (Pluto, Ceres, Eris)