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The Earth In SpaceThe Earth In SpaceWhy do we have night and day?Why do we have night and day?
Why do daylength’s change?Why do daylength’s change?
Understanding Night and DayUnderstanding Night and Day
Day and night is the absence or presence Day and night is the absence or presence of sunlight shining on the surface of the of sunlight shining on the surface of the globe!globe!
It is caused by the spinning of the Earth on It is caused by the spinning of the Earth on its axisits axis
There are some strange things that you There are some strange things that you should be aware of, as well as what should be aware of, as well as what causes them!causes them!
The tilt of the EarthThe tilt of the Earth
The Earth spins on an axis. This is an imaginary The Earth spins on an axis. This is an imaginary line running through the middle of the Earth from line running through the middle of the Earth from North to South pole.North to South pole.The important thing to note about the axis, is The important thing to note about the axis, is that it is tilted 23.5that it is tilted 23.5oo from the vertical. from the vertical.The tilt causes different daylengths depending The tilt causes different daylengths depending on latitude on the Earth’s surfaceon latitude on the Earth’s surfaceThe following animation demonstrates this. The The following animation demonstrates this. The coloured dots represent locations on the surface coloured dots represent locations on the surface of the Earth that are in the same time zone.of the Earth that are in the same time zone.
DAYDAYNIGHTNIGHT
SUNLIGHT
12 midnight
DAYDAYNIGHTNIGHT
SUNLIGHT
2am
DAYDAYNIGHTNIGHT
SUNLIGHT
3am
DAYDAYNIGHTNIGHT
SUNLIGHT
4am
DAYDAYNIGHTNIGHT
SUNLIGHT
6am
DAYDAYNIGHTNIGHT
SUNLIGHT
8am
DAYDAYNIGHTNIGHT
SUNLIGHT
10am
DAYDAYNIGHTNIGHT
SUNLIGHT
12 noon
DAYDAYNIGHTNIGHT
SUNLIGHT
2pm
DAYDAYNIGHTNIGHT
SUNLIGHT
3pm
DAYDAYNIGHTNIGHT
SUNLIGHT
4pm
DAYDAYNIGHTNIGHT
SUNLIGHT
7pm
DAYDAYNIGHTNIGHT
SUNLIGHT
9pm
DAYDAYNIGHTNIGHT
SUNLIGHT
11pm
DAYDAYNIGHTNIGHT
SUNLIGHT
12 midnight
DAYDAYNIGHTNIGHT
SUNLIGHT
2am
DAYDAYNIGHTNIGHT
SUNLIGHT
3am
DAYDAYNIGHTNIGHT
SUNLIGHT
4am
DAYDAYNIGHTNIGHT
SUNLIGHT
6am
DAYDAYNIGHTNIGHT
SUNLIGHT
8am
DAYDAYNIGHTNIGHT
SUNLIGHT
10am
DAYDAYNIGHTNIGHT
SUNLIGHT
12 noon
DAYDAYNIGHTNIGHT
SUNLIGHT
2pm
DAYDAYNIGHTNIGHT
SUNLIGHT
3pm
DAYDAYNIGHTNIGHT
SUNLIGHT
4pm
DAYDAYNIGHTNIGHT
SUNLIGHT
7pm
DAYDAYNIGHTNIGHT
SUNLIGHT
9pm
DAYDAYNIGHTNIGHT
SUNLIGHT
11pm
DAYDAYNIGHTNIGHT
SUNLIGHT
12 midnight
DAYDAYNIGHTNIGHT
SUNLIGHT
2am
DAYDAYNIGHTNIGHT
SUNLIGHT
3am
DAYDAYNIGHTNIGHT
SUNLIGHT
4am
DAYDAYNIGHTNIGHT
SUNLIGHT
6am
DAYDAYNIGHTNIGHT
SUNLIGHT
8am
DAYDAYNIGHTNIGHT
SUNLIGHT
10am
DAYDAYNIGHTNIGHT
SUNLIGHT
12 noon
DAYDAYNIGHTNIGHT
SUNLIGHT
2pm
DAYDAYNIGHTNIGHT
SUNLIGHT
3pm
DAYDAYNIGHTNIGHT
SUNLIGHT
4pm
DAYDAYNIGHTNIGHT
SUNLIGHT
7pm
DAYDAYNIGHTNIGHT
SUNLIGHT
9pm
DAYDAYNIGHTNIGHT
SUNLIGHT
11pm
DAYDAYNIGHTNIGHT
SUNLIGHT
12 midnight
DAYDAYNIGHTNIGHT
SUNLIGHT
2am
DAYDAYNIGHTNIGHT
SUNLIGHT
3am
DAYDAYNIGHTNIGHT
SUNLIGHT
4am
DAYDAYNIGHTNIGHT
SUNLIGHT
6am
DAYDAYNIGHTNIGHT
SUNLIGHT
8am
DAYDAYNIGHTNIGHT
SUNLIGHT
10am
DAYDAYNIGHTNIGHT
SUNLIGHT
12 noon
DAYDAYNIGHTNIGHT
SUNLIGHT
2pm
DAYDAYNIGHTNIGHT
SUNLIGHT
3pm
DAYDAYNIGHTNIGHT
SUNLIGHT
4pm
DAYDAYNIGHTNIGHT
SUNLIGHT
7pm
DAYDAYNIGHTNIGHT
SUNLIGHT
9pm
DAYDAYNIGHTNIGHT
SUNLIGHT
11pm
So, what did you see?So, what did you see?
The animation shows the Northern Hemisphere tilted The animation shows the Northern Hemisphere tilted towards the Sun. This is the position that it would be in towards the Sun. This is the position that it would be in on the Summer Solstice (21 June)on the Summer Solstice (21 June)What do you notice about the blue circle?What do you notice about the blue circle?What do you notice about the red circle?What do you notice about the red circle?What would happen to daylength if the green dot moved What would happen to daylength if the green dot moved north?north?What would happen to daylength if the green dot moved What would happen to daylength if the green dot moved south?south?How would the diagram be different if the Southern How would the diagram be different if the Southern Hemisphere was tilted towards the Sun? When would Hemisphere was tilted towards the Sun? When would this happen?this happen?
Click to run animation again
East and WestEast and West
The Sun RISES in the EAST.
NOON is when the Sun is HIGHEST in the sky.
The Sun SETS in the WEST.
How does the Sun appear to move across the How does the Sun appear to move across the sky during the day?sky during the day?
Because the Earth SPINS, the Sun moves across the sky.
Length of DayLength of Day
The Sun is at a higher angle in the sky in summer than in winter. This means the Sun is ABOVE THE
HORIZON longer in summer than in winter. So, in summer, the days are longer and the nights are
shorter, compared to winter.
SeasonsSeasons
We have seen that on any given day, the We have seen that on any given day, the amount of daylight varies between amount of daylight varies between different locations on the Earth’s surfacedifferent locations on the Earth’s surface
However, even at a single location the However, even at a single location the length of daylight varies over a yearlength of daylight varies over a year
This is as a result of the Earth’s orbit This is as a result of the Earth’s orbit around the Sunaround the Sun
This also results in the SeasonsThis also results in the Seasons
Seasons (2)Seasons (2)
You might expect that the reason it is You might expect that the reason it is warmer in the Summer is because we are warmer in the Summer is because we are closest to the Sun at this pointclosest to the Sun at this point
However, at Summer and Winter the Earth However, at Summer and Winter the Earth is at its two furthest points from the Sunis at its two furthest points from the Sun
The Earth is nearest the Sun at the Spring The Earth is nearest the Sun at the Spring equinox and the Autumn equinoxequinox and the Autumn equinox
Terms to rememberTerms to remember
Summer solstice – longest day Summer solstice – longest day ( approximately the 21 June)( approximately the 21 June)Winter solstice – shortest day Winter solstice – shortest day (approximately the 21 December)(approximately the 21 December)Equinox – daytime is same length as night Equinox – daytime is same length as night time. time.
The path of the Earth round the The path of the Earth round the SunSun
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Northern hemisphere points towards the Sun
Longer days Warmer
Summer in North! Winter in South
Northern hemisphere points away from the Sun
Shorter days Colder
Winter in North. Summer in South
June
December
October
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March North and South getting equal amounts of sunlight
Spring in North. Autumn in South
North and South getting equal amounts of sunlight
Autumn in North. Spring in South
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It takes 365.25 days for Earth to orbit the Sun. Because of the .25 day, we add an extra day to our year every four years – a leap year.
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S
N
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N
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Northern hemisphere points towards the Sun
Longer days Warmer
Summer in North! Winter in South
Northern hemisphere points away from the Sun
Shorter days Colder
Winter in North. Summer in South
December
October
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March North and South getting equal amounts of sunlight
Spring in North. Autumn in South
North and South getting equal amounts of sunlight
Autumn in North. Spring in South
June
Why is it summer when the Why is it summer when the northern hemisphere is tilted northern hemisphere is tilted towards the Sun?towards the Sun?
• When the northern hemisphere is tilted towards the Sun, the Sun is at a higher angle in the sky and the Sun’s rays are less spread out. They have a greater heating effect.
•In northern winter the Sun is at a lower angle in the sky because the northern hemisphere is tilted away from the Sun. The Sun’s rays are more spread out and have a lower heating effect than in summer.
•Don’t forget that there are also longer days when it is summer, so there is more time for the Sun to warm the Northern hemisphere
