Cycles In The Solar System - Science Lessons for Grade 5 Students
A pattern of change that repeats itself over and over is called a cycle.
We are familiar with the start of the day with the sun appearing to the east and ending the day with it setting in the west. This is an example of a cycle that occurs daily. This cycle is the cause for day and night to occur, which is one of those natural phenomena that is fundamental to human life on earth.
What causes the Sun to rise and set? Why does this cycle repeat every day?
Although the Sun appears to move across the sky, the day and night we experience is caused by the movement of the Earth. The Earth is always moving. One way it moves is by spinning. The way the earth spins or rotates is similar to the way a basketball spins on your finger. An imaginary line called axis runs from the North pole to the South pole. The earth rotates from West to East. Thus it appears that the Sun rises in the east and sets in the west.
Day and night is caused by the rotation of the Earth about its axis. It takes the Earth a period of 24 hours to complete one rotation. During this time, part of the Earth faces towards the sun and part of the earth faces away from the sun. The part of the earth facing towards the sun experiences daytime. The part of the earth facing away from the sun experiences nighttime.
In countries near the equator, there are about 12 hours of daylight and 12 hours of darkness every day. In countries far from the equator, the hours of daylight and darkness vary throughout the year.
The Earth’s revolution
As the Earth rotates about its axis, it also moves in a path around the Sun. You can think of the path the Earth takes around the Sun as the path you take when you run around an athletics track. The path the Earth takes around the sun is called its orbit. One complete orbit around the Sun is called a revolution.
It takes the Earth 365 ¼ days to make one revolution around the Sun.
In our calendar there are usually 365 days in one year. Every four years we add one extra day, making 366 in total. The year when an extra day is added is called a leap year.
The Earth and the Moon
Have you ever noticed that the Moon appears to change shape at different times of the month? Why do you think this happens?
The Moon revolves around the Earth. Each revolution takes about 28 days. As the Moon revolves around the Earth, the shape of the Moon appears to change. This is because at different times of the month, we see different parts of the illuminated moon.
A full moon occurs when the Earth is between the Sun and the Moon. During a full Moon, we see the Moon as a full circle.
A new Moon occurs when the Moon is between the Sun and the Earth. We cannot see a new Moon because the illuminated side of the Moon is not facing the Earth.
The Solar System
The Sun and all of the bodies that revolve around it make up our Solar System. The sun is a star at the centre of the Solar System. It is also the largest body in the Solar System. It is the main source of light and heat energy on Earth.
The Solar System was formed roughly 4.6 billion years ago from the collapse of a huge interstellar molecular cloud. As you can imagine, the vast majority of the system’s mass is concentrated in the Sun, while most of the remaining mass is contained in the giant planet Jupiter.
Besides the Earth and the Moon, there are other bodies that we can see in the Solar System.
The Planets
There are eight planets in our Solar System. In order from the closest to the farthest from the Sun, they are
1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune
(Till 2006, it was believed that there were 9 planets, with the 9th being called Pluto. However, Pluto is now classified as a dwarf planet. Although it is in orbit around the Sun and has a nearly round shape, Pluto is not big enough to exert orbital dominance and clear the neighbouring region of other objects. It was the International Astronomical Union (IAU) that demoted Pluto from the status of a planet to that of a ‘dwarf planet’ in 2006. Thus, it was decided that the Solar System contains only 8 planets.)
Like the Earth, all of the planets rotate about an axis and revolve in an orbit around the Sun. The time it takes to complete a rotation and a revolution is different for each planet.
Do you think it will be difficult for you to remember the names of the planets? Do not worry. The saying below is a good way to remember the names and order of the planets.
‘My Very Energetic Mother Just Served Us Noodles.’
The first letter of each word is the same as the first letter of each planet.
Mercury
Mercury is the smallest planet in the Solar System and the closest planet to the Sun. It takes Mercury 88 days to revolve around the Sun and 59 days for one rotation about its axis. Mercury has no moons.
Venus
Venus is the fourth smallest planet in the Solar System. It takes Mercury 225 days to revolve around the Sun and 243 days for one rotation about its axis. Venus has no moons.
Earth
Earth is the only planet in the Solar System that is known to contain life. It takes Earth 365 ¼ days to revolve around the Sun and 24 hours for one rotation about its axis. Earth has one moon.
Mars
Mars is the third smallest planet in the Solar System. It takes Mars 689 days to revolve around the Sun and 24.6 hours for one rotation about its axis. Mars has two moons.
Jupiter
Jupiter is the largest planet in the Solar System. It takes Jupiter 12 years to revolve around the Sun and 10 hours for one rotation about its axis. Jupiter has more than 60 moons.
Saturn
Saturn is the second largest planet in the Solar System. It takes Saturn about 30 years to revolve around the Sun and 11 hours for one rotation. Saturn has more than 60 moons.
Uranus
Uranus is the second farthest planet from the Sun. it takes Uranus 84 years to revolve around the Sun and 16 hours for one rotation. Uranus has 27 moons.
Neptune
Neptune is the farthest planet from the Sun. it takes Neptune 165 years to revolve around the Sun and 16 hours for one rotation. Neptune has 13 moons.
Life in the solar system
Of all the planets, only one is known to contain life – Earth. What are the characteristics of Earth that makes it suitable for life?
The distance from the Sun to the Earth is 150,000,000 km. This distance means that the temperatures on Earth are suitable for life to exist. If the Earth was too close or too far away from the Sun, living things could not survive.
Earth is also the only planet in the Solar System that has water and an atmosphere containing the gases oxygen and carbon dioxide. Living things need water and the gases in the atmosphere to survive.
Other objects in the Solar System
Comets
Comets are balls of ice and dust that orbit the Sun. Most comets are too small or too far away to be seen from Earth. Some comets can be seen as they pass close to the Sun during their orbit. Their long tails reflect sunlight, making them easy to see.
Asteroids
Large rocks that orbit the Sun are called asteroids. Asteroids can vary in size from only a few metres to more than 200 kilometres wide, but all of them are much smaller than the planets. There are a number of asteroids in our Solar System. Most of the asteroids in the Solar System can be found in the main asteroid belt between the orbits of the planets Mars and Jupiter.
Man-made objects in the Solar System
Along with natural bodies such as planets, comets and asteroids, there are also many man-made objects in space. Such objects include satellites, space shuttles, and the International Space Station (ISS). The International Space Station was launched from Kazakhstan in 1998.
Communication satellites are man-made objects that send and receive information to and from Earth. They are used in telecommunication, television, the internet, and Global Positioning Systems (GPS).