A planet is a celestial body that orbits a ____
In the centre of our solar system is the sun, an enormous star (which is one of the hundred billion stars that make up the Milky Way galaxy).
Revolving around the sun are 8 planets. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
EARTH AND ME
Earth formed around 4.5 billion years ago and has gone through many transitions to be what it is today.
I am one person on a planet of 7.7 BILLION human beings.
This can make me sound very small – and perhaps I am.
But size doesn’t equal importance.
And being small doesn’t mean that my actions aren’t meaningful.
Across all space and time, there has only - and will only - ever be one me.
The Earth is separated into two halves by an imaginary line called the Equator.
The half of Earth that is between the Equator and the North Pole is called the Northern Hemisphere.
The half that is between the Equator and the South Pole is called the Southern Hemisphere.
DAY AND NIGHT
When we see the sun shining in the sky it is day and when we don’t it’s night.
Where does the sun go when you can’t see it?
By observing the sun we can see that the sun rises in the East and Sets in the West.
The sun appears the move across the sky because the Earth rotates on its axis.
Axis is an imaginary straight line passing through the North Pole the centre of Earth, and the South Pole.
The movement of the Earth on its own Axis is known as Rotation.
Earth spins at 1609.34 Kilometres per hour (KPH). It takes Earth 24 hours to complete one rotation.
Earth is on a slight tilt - 23.5 degrees to be exact.
The side of Earth that is facing the sun is in daylight and the side that is facing away is in nighttime.
Now that we know that the day and night are controlled by Earth spinning on it’s axis (rotation) and its relationship with the sun.
Can you think of a reason why in Summer we have long days (more hours of sunlight) and in Winter we have shorter days (less hours of sunlight)?
why we have seasons
At the same time Earth is rotating on its axis it is also travelling around the sun. This movement around the sun is called its Revolution.
REVOLUTION : When a planet or moon travels around the body it is orbiting one time.
For Earth to make one full orbit all way around the sun it takes 365 days or one year. One orbit is known as a Revolution.
Got it so far?
So the Earth is rotating on its axis, creating day and night at the same time its also revolving around the sun.
So why in Summer do we have long days and short nights?
The reason we have seasons is a combination of the angle of the Axis and the revolution or orbit the Earth does around the Sun.
Remember the Earth is separated into two halves by an imaginary line called the Equator.
By relating the two halves, southern and northern hemisphere, and the relationship the Earth has with the sun we can see why in summer we have more hours of sunlight than in winter.
What observations can you make from the above illustration?
You may have noticed that
The Southern Hemisphere on the Earth on the left has a lot more day time than night time. Shorter nights and longer days. This must be summer for the Southern Hemisphere.
The Southern Hemisphere on the Earth on the right has a lot more night time than day time. Shorter days and longer nights. This must be Winter for the Southern Hemisphere.
Besides the sun the Moon is the most noticeable object in our sky.
Does the Moon always look the same?
The Moon changes everyday, sometimes it’s up in the day and it’s shape is always changing.
The Moon is four times smaller than Earth and it’s surface is actually pretty dark. It looks bright to us because it is sitting in full sunlight! Because the Moon is orbiting Earth the way we see it lite by the sun changes, this is what causes the moons phases.
Remember how day and night works? The half of Earth facing the sun is in day light and the half of Earth facing away from the sun is in night time! Well the Moon Works exactly the Same!!
We call the side not illuminated by the sun the dark side of the moon!
It takes the moon 27.5 days or one month to complete one revolution of Earth.
Is the Moon important to life on Earth?
The Moon has a big influence on the Earths tides.
Tides and tidal currents helps balance the temperature on Earth and help to control the climate.
Lots of animal,s both land and sea, use Lunar clues and cycles such as the phases of the Moon, to find a mate, to feed and sleep!
Remember how Earth is on a 23.5 degree tilt? The Moon helps stabilise this too!
So the Moon it vital to life on Earth.
LAYERS THAT MAKE UP EARTH
If we were to cut a slice out of the Earth, just like we cut a piece of Cake we would notice that is has layers!
To understand why the Earth has layers, we need to understand density.
Remember last week did a density experiment and looked out how the solar system formed?
Well the same thing applies to the layers that make up Earth.
Density is how compact an object is.
Put another way, density is the mass (weight) of an object divided by its volume (amount of space something takes up).