The Earth and the Solar System | High School Geography

- [Definition: A theory is a set of reasoned ideas intended to explain facts or events ]
The theories explaining the origin of the solar system include:

1. Passing Star Theory
2. Collision Theory
3. Nebula Cloud Theory
4. Supernova/explosion Theory

- A star with a greater gravitational pull passed near the sun
- It attracted large quantities of gaseous materials from the sun
- The materials split, cooled and condensed to form planets
- The planets were set in orbit by the passing star

Weaknesses of the Passing Star Theory

- Doesn't explain the origin of the sun and star.
- Minimal chance of a star approaching another
- Materials would disperse than condense

- Star with greater gravitational pull passed near the sun
- It attracted large quantities of gaseous materials
- The materials split into portions
- Large portions collided with smaller ones and swept them to form planets.

Weaknesses of the Collision Theory

The weakness resemble those of the Passing Star Theory.

- There was a slowly rotating cloud of dust and gas called Nebula
- It cooled and began to contact
- Rotation speed increased and successive rings of gaseous materials were formed.
- The rings condensed to form planets
- The central gaseous material remained as the sun

Weaknesses of the Nebula Cloud Theory

- The origin of nebular is not explained.

Evidence of the Nebula Cloud Theory

- Rotation and revolution of planets in anticlockwise direction
Below is an illustration of the Nebula Cloud theory:

- There was a violent explosion of a star.
- A cloud of dust (nebular) remained from the star.
- There was fast movement of the cloud due to the force of explosion.
- Rotation speed increased due to gravitational attraction
- The cloud flattened into a disc.
- The matter began to accumulate towards the centre to form a protosun (Check definition below) which later began to shine.
- The rest of the cloud collapsed to form planets.
[Definition: Protosun - the gaseous cloud that underwent gravitational collapse to form the sun]

Weaknesses of the Explosion Theory

- Doesn't explain the origin of the star
- Doesn't explain the cause of explosion

As you can see, all these theories have their weaknesses. That is the common denominator among them.

Our solar system consists of an average star we call the Sun and the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids, and the interplanetary medium. The Sun is the richest source of electromagnetic energy mostly in the form of heat and light in the solar system.
The whole solar system, together with the local stars visible on a clear night, orbits the centre of our home galaxy, a spiral disk of 200 billion stars called the Milky Way galaxy.
The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits.
Next, lets learn more about the composition of the Solar System including the characteristics of the planets and more on other celestial bodies.

- A natural satellite
- Receives its light from the sun and reflects it onto the earth.
- It revolves around the earth
- Takes 29.5 days to complete one revolution around the earth
- Its orbit is almost circular
- As it revolves around the sun it appears in various shapes ranging from crescent/new moon, half moon, gibbons moon and full moon.
- Has gravitational pull which causes the rising and falling of the ocean level
- As the moon orbits around the earth it creates an event called eclipse.

Eclipse

- Phenomenon occurring when the rays of the sun are blocked from reaching the earth or the moon.

Solar/Sun Eclipse

- The moon comes between the earth and the sun
- The moon's shadow is cast on the earth
- The sun appears to be covered by darkness

Lunar/moon Eclipse

- The earth comes between the moon and the sun
- The earth's shadow is cast on the moon
- The moon appears to be covered by darkness

- A star with a greater gravitational pull passed near the sun
- It attracted large quantities of gaseous materials from the sun
- The materials split, cooled and condensed
- Heavier materials collected at the centre to form the core
- Less dense materials collected around the core to form the mantle
- The lightest materials formed the crust

- The shape of the earth is called geoid/ovoid/oblate spheroid due to being an imperfect sphere by being wide at the equator and flat at the poles

Proofs/Evidence That the Earth Is Spherical

1. If one moves towards the east in a straight line he will end up where he started.
2. All the planets are spherical so the earth being one of them is also spherical.
3. Places in the east see the sun earlier than those in the west.
4. Satellite photographs taken from space show that the earth is like a sphere.
5. The earth's horizon appears curved when observed from a very high point like a tower.
6. When a ship is approaching the smoke is seen first, then the mast and finally the whole ship.
7. During the moon eclipse the earth casts a spherical shadow on the moon.

- Equatorial diameter is 12756km
- Equatorial circumference is 40085km
- Polar diameter is 39995km
- Surface area of the earth is 510×10⁶ km²
- Water covers 73%. of the earth's surface.

The earth is an extensive topic.Next We will explore rotation, revolution, calculating local time and the internal and external structure of the earth including the atmosphere.