Our solar system

Our solar system

by Roy Mathews

​Our Solar system

Our solar system consists of the sun (the star), the eight major planets, their natural satellites (moons), asteroids (space rocks), and ​comets. A star and all the heavenly bodies that orbit around it make a solar system. The sun's gravitational pull keeps these objects in fixed paths called orbits. The nuclear reaction which powers the sun releases an enormous amount of heat and light energy. Planets and their moons shine only because they reflect sunlight.

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​The inner planets (Mercury, Venus, Earth, and Mars) are called terrestrial or earth-like planets while the outer planets (Jupiter, Saturn, Uranus, and Neptune) are gas giants. All planets except Mercury and Venus have natural satellites or the moon. Our earth has only one moon.

​Sun and all the planets originated from a cloud of gas and dust called the solar nebula. This gas cloud or nebula started to collapse and the particles were pulled together by the gravitational force. The central part became the Sun and the rotating cloud around the Sun became a flat disc. Planets were formed from this disc.

​Paths along which the planets revolve around the sun are called their orbits. orbits of most planets in our solar system have the shape of an ellipse (oval).

​The distance between planets and also the distance between the planets and the sun are not very great when compare with the distance between stars. The distances in the solar system are usually measured in a unit called the astronomical unit (AU). One AU is the distance between the earth and the sun, which is approximately 150 million kilometers.

​Distances in outer space, between stars, are so great that the astronomical units are too small. For such measurements, we use another unit, the light-year. This is the distance traveled by a beam of light in a year. Light travels 300,000 km per second in a vacuum. In a year it travels about 9.5 trillion kilometers.

Multiple Choice

Which one of the following is a gas giant?

• Mars

• Jupiter

• Venus

• Mercury

Multiple Choice

Which one of the following is a terrestrial planet?

• Mercury

• Jupiter

• Saturn

• Uranus

Multiple Choice

How many planets are in our solar system?

• Seven

• Six

• Eight

• Five

Multiple Choice

How many terrestrial planets are there in our solar system?

• One

• Two

• Three

• Four

Multiple Choice

What is another term used to describe space rocks?

• Asteroids

• Comets

• Satellites

• Nebula

Multiple Choice

What star is closest to our Earth?

• Sun

• Proxima Centauri

• Sirius A

• Alpha centauri

Multiple Choice

Any object that orbits a star can be called a:

• satellite

• Planet

• comet

• moon

Multiple Choice

The natural satellite of a planet is called:

• asteroids

• moon

• comets

• shooting stars

Multiple Choice

The distance between the sun and the earth is around:

• 150 km

• 15 million km

• 150 million km

• 150 million cm

Open Ended

Our earth has one natural satellite while planet mars has two. Describe what a natural satellite is.

Open Ended

Describe the major differences between the inner planets and the outer planets.

Open Ended

Describe what a light-year is. Explain why this unit is used in astronomy.