The Solar system - Social Studies - Standard Four
Meaning of Solar System
The solar system is the arrangement of the sun and planets and other celestial bodies.
It is the arrangement of heavenly bodies that around the sun.
The solar system is composed of the sun, planet, asteroids, comets, satellites and meteorites.
The sun is the closest star to the Earth.
Planets
Planets are relatively large heavenly bodies that move around the sun.
Each planet follows its own path called orbit.
There are eight planets in the solar system. These are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Planets are grouped into two groups. These are terrestrial and jovian planets.
Terrestrial planets are those with solid rock surfaces. These are Mercury, Venus, Earth and mars.
Jovian planets are the ones that are made up of gaseous surfaces. These are Jupiter, Saturn, Uranus and Neptune.
The only planet that supports life is the Earth.
1. Mercury
It is the first planet from the sun.
It is the smallest and hottest of all planets. It's about 4670 0C.
It is the closest to the sun.
It takes about 88 days to complete one rotation around the sun.
2. Venus
It is the second planet from the sun.
It takes about 225 days to revolve around the sun.
It has no moon.
It is the brightest planet.
3. Earth
It is the third planet from the sun.
It is the only planet that living things can survive.
It takes 365 or 366 days to complete one rotation on its orbit.
It takes 24 hours (one day) to complete a rotation on axis.
70% of the Earth is covered by water.
4. Mars
It is the fourth planet from the sun.
It takes about 685 days to complete rotation around the sun.
It has very low temperature.
It has two moons.
5. Jupiter
It is the fifth planet.
It is the largest planet.
It takes about 12 years (about 4331 days) to complete one revolution around the sun.
6. Saturn
It is the sixth planet from the sun.
It is the second largest planet.
It takes about 30 years (about 10,980) to go round the sun.
It has more than 30 moons.
7. Uranus
It is the seventh planet.
It takes about 80 years (about 28,300) to go round the sun.
8. Neptune
It is the eighth planet from the sun.
It takes about 165 years to go round the sun.
It is the furthest planet from the sun.
Characteristics of planets
1. They all revolve around the sun.
2. Each planet takes a particular time to complete one rotation.
3. Planets have spherical shape.
4. Planets do not generate their own light, but they reflect light from the sun.
5. Some planets have natural satellites while others do not have satellites.
6. Planets are of different sizes.
7. Planets are of different distance from the sun.
8. They revolve around the sun in anticlockwise direction.
Dwarf planets
1. These are celestial bodies that resemble planets but do not have all the characteristics of planets.
2. Dwarf planets are too small compared to other planets.
3. Dwarf planets are Pluto, Ceres and Eris.
Asteroids
These are celestial bodies but are not planets.
They revolve round the sun between the orbits of Mars and Jupiter because asteroids do not have specific orbit.
Comets
These are small celestial bodies formed of rocky materials with ice and gases. When we see them at night, they appear to have bright tails.
There are small celestial bodies formed from broken comets. These may sometimes fall on the Earth surface. Their names change to meteorites when they fall on the Earth.
A good example of meteorites is the one at Mbozi in Songwe region.
Natural light in the environmental
Natural light is the one which is not made by man but appears naturally.
The main source of light is the sun which rises in the East and sets in the West and make up a day time.
When the sun sets, the Earth becomes dark which is the night time.
Other forms of natural light are stars which produce light at night time.
The moon does not produce its own light but reflects light from the sun.
Moon takes 28 days/month to go around the Earth.
Differences between the sunlight and the moonlight
| Sunlight | Moonlight |
| The sun has its own light. | The moon reflects light from the sun. |
| Bright at day time. | Bright at night. |
| Has strong energy. | Its energy is weak. |
| Helps in the formation of rain. | Does not help in the formation of rain. |
| Helps plants to make their food. | Does not help in photosynthesis. |
Importance of the sun
1. Gives us light and heat.
2. Enables the body to make vitamin D.
3. Hold all planets on their orbits by its gravitational force.
4. Used in generating solar energy.
5. Source of moonlight.
6. Helps in the formation of rain.
7. Used to dry crops and clothes.
