Presentation on theme: "Why do we have night and day? Why do daylength’s change?"— Presentation transcript:
1 Why do we have night and day? Why do daylength’s change? The Earth In SpaceWhy do we have night and day?Why do daylength’s change?
2 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 axisThere are some strange things that you should be aware of, as well as what causes them!
3 The tilt of the EarthThe 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 surfaceThe following animation demonstrates this. The coloured dots represent locations on the surface of the Earth that are in the same time zone.
60 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
61 East and WestHow 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.
62 Length of DayThe 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.
63 SeasonsWe have seen that on any given day, the amount of daylight varies between different locations on the Earth’s surfaceHowever, even at a single location the length of daylight varies over a yearThis is as a result of the Earth’s orbit around the SunThis also results in the Seasons
64 Seasons (2)You might expect that the reason it is warmer in the Summer is because we are closest to the Sun at this pointHowever, at Summer and Winter the Earth is at its two furthest points from the SunThe Earth is nearest the Sun at the Spring equinox and the Autumn equinox
65 Terms to rememberSummer solstice – longest day ( approximately the 21 June)Winter solstice – shortest day (approximately the 21 December)Equinox – daytime is same length as night time.
66 The path of the Earth round the Sun MarchNorth and South getting equal amounts of sunlightSpring in North. Autumn in SouthNSMarchNorth and South getting equal amounts of sunlightSpring in North. Autumn in SouthNSNSNSNSNSNSJuneJuneNSNorthern hemisphere points towards the SunLonger days WarmerSummer in North! Winter in SouthNSNorthern hemisphere points towards the SunLonger days WarmerSummer in North! Winter in SouthNorthern hemisphere points away from the SunShorter days ColderWinter in North. Summer in SouthNorthern hemisphere points away from the SunShorter days ColderWinter in North. Summer in SouthNSNSNSNSNSNSNSNSNSNSDecemberDecemberIt takes 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 sunlightAutumn in North. Spring in SouthNorth and South getting equal amounts of sunlightAutumn in North. Spring in SouthOctoberOctober
67 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