Why do we have night and day? Why do daylength’s change? The Earth In Space Why do we have night and day? Why do daylength’s change?

Understanding Night and Day Day and night is the absence or presence of sunlight shining on the surface of the globe! It is caused by the spinning of the Earth on its axis There are some strange things that you should be aware of, as well as what causes them!

The tilt of the Earth The Earth spins on an axis. This is an imaginary line running through the middle of the Earth from North to South pole. The important thing to note about the axis, is that it is tilted 23.5o from the vertical. The tilt causes different daylengths depending on latitude on the Earth’s surface The following animation demonstrates this. The coloured dots represent locations on the surface of the Earth that are in the same time zone.

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So, what did you see? The animation shows the Northern Hemisphere tilted towards the Sun. This is the position that it would be in on the Summer Solstice (21 June) What do you notice about the blue circle? What do you notice about the red circle? What would happen to daylength if the green dot moved north? What would happen to daylength if the green dot moved south? How would the diagram be different if the Southern Hemisphere was tilted towards the Sun? When would this happen? Click to run animation again

East and West How does the Sun appear to move across the sky during the day? NOON is when the Sun is HIGHEST in the sky. Because the Earth SPINS, the Sun moves across the sky. The Sun RISES in the EAST. The Sun SETS in the WEST.

Length 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.

Seasons We have seen that on any given day, the amount of daylight varies between different locations on the Earth’s surface However, even at a single location the length of daylight varies over a year This is as a result of the Earth’s orbit around the Sun This also results in the Seasons

Seasons (2) You might expect that the reason it is warmer in the Summer is because we are closest to the Sun at this point However, at Summer and Winter the Earth is at its two furthest points from the Sun The Earth is nearest the Sun at the Spring equinox and the Autumn equinox

Terms to remember Summer solstice – longest day ( approximately the 21 June) Winter solstice – shortest day (approximately the 21 December) Equinox – daytime is same length as night time.

The path of the Earth round the Sun March North and South getting equal amounts of sunlight Spring in North. Autumn in South N S March North and South getting equal amounts of sunlight Spring in North. Autumn in South N S N S N S N S N S N S June June N S Northern hemisphere points towards the Sun Longer days  Warmer Summer in North! Winter in South N S 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 Northern hemisphere points away from the Sun Shorter days  Colder Winter in North. Summer in South N S N S N S N S N S N S N S N S N S N S December December 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. North and South getting equal amounts of sunlight Autumn in North. Spring in South North and South getting equal amounts of sunlight Autumn in North. Spring in South October October

Why is it summer when the northern hemisphere is tilted 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