next we are going to investigate why we have seasons on planet Earth the two takeaway points from this unit are that seasons happen because of differences in intensity of incoming solar radiation to earth and differences in the length of time radiation has received basically Sun angle and the number of daylight hours have you ever heard someone say that we're closer to the Sun in the summer and farther from the Sun in the winter this is not true and it's also not what causes our seasons earth does revolve in an elliptical path around the Sun every 365 days one year Earth rotates every 24 hours or every one day but the earth is closest to the Sun in January and farthest from the Sun in July if you live in the northern hemisphere that means the earth is closest to the Sun in winter and farthest from the Sun in summer this means we need another explanation for why we have seasons on planet Earth it turns out the amount of energy provided by the Sun changes based on the angle of incidence of that solar radiation so if the Sun is high in the sky it's providing more concentrated radiation versus when it's low in the sky look at the two flashlights in the left image the flashlight that is shining straight down on Earth's surface is creating light over a smaller circle therefore the light at every point on that circle is more intense the fresh light shining down at an angle has light that's spread out over a larger oval so the light is more diffuse across that oval this is the same thing that happens with the Sun where high Sun angle means concentrated radiation and low Sun angle means diffused we know this to be true because when it's summer and the Sun is very high in the sky we know that we feel the intensity of that Sun much more and we're more prone to sunburns and other adverse consequences from the high Sun angle why does this happen it happens because earth is rotating around the Sun on a tilt if you focus in on the summer solstice June 21st in this diagram you can see that the north is tilted slightly toward the Sun at the summer solstice for the northern hemisphere the northern hemisphere is tilted toward the Sun at the angle of twenty three and a half degrees which is our current tilt as we go throughout the course of the year the tent doesn't change it remains at a constant twenty three and a half degrees but the position of the earth with respect to the Sun changes and so if you look at the Winter Solstice December 21st you now see that the North Pole is tilted twenty three and a half degrees away from the Sun the pole isn't shifting but the position of the earth is translating with respect to the Sun therefore when we're tilted toward the Sun at the summer solstice we're receiving more direct solar radiation and at the winter solstice less direct solar radiation if you think about it we will also receive more hours of daylight at the summer solstice compared to the winter solstice because of that tilt let's zoom in on the zoo the June solstice again the Sun is directly overhead in the northern hemisphere with a much higher sun angle than in the southern hemisphere this is the longest day of the year for the northern hemisphere and the shortest day of the year for the southern hemisphere the Sun is directly overhead on the Tropic of Cancer but still relatively high in this in the sky for the rest of the northern hemisphere if you are located in below the Antarctic Circle near the South Pole you're tilted away from the Sun to the point where you're not even receiving any sunlight throughout the day you have 24 hours of darkness on the other hand if you're closer to the North Pole north of the Arctic Circle you have 24 hours of sunlight constant Sun have you ever been to Alaska and experienced seasons that were more extreme like this with almost an entire day of sunlight in the summer or total darkness in winter it's the same idea here's the length of day for Portland Oregon between sunrise and sunset for the 15th of every month you'll do something similar to this in lab when you investigate sun angle this week if you check out the table you can see that the length of day varies from January at about 9 hours to June at more than 15 hours the longest days of the year and so you can see that during closer to the summer solstice we indeed have our longest days and near the winter solstice we have our shorter days just as we would expect given our position in the northern hemisphere this graphic shows an even more detail how we how then hours of daylight changes as we vary between the equator and the pole if you're at 90 degrees at the North Pole you can see that you get a huge amount of sunlight six months of sunlight in June and zero hours of sunlight at the December solstice just as we discussed previously for the Arctic Circle if you're closer to the equator your sunlight is pretty consistent for the entire year because the tilt does not affect you as much if we look at our global temperatures we see that the position of the Sun has a direct effect on where it's warmer and colder around the globe this map shows temperatures in Fahrenheit global average and we can see that near the equator the temperatures are much warmer than near the poles near the equator there are places that have average yearly temperatures greater than 80 degrees whereas near the poles there are places that have averaged nearly temperatures closer to zero degrees this is because the equator receives consistently much more direct sunlight throughout the year than the poles poles have really extreme seasons but they don't last for very long this means an in general it's always warmer near the equator and colder near the pole this leads to an energy imbalance on planet Earth there's always extra heat being gained in the tropics and heat escaping near the poles but we don't find that our tropical areas are constantly getting hotter and hotter and our plows are constantly getting colder and colder so something else needs to happen here on earth we need some mechanisms to transfer heat between the equator and the pole so that earth can stay at a stable temperature there are many ways that this heat transfer happens but two of the biggest are our circulation patterns in the atmosphere in the ocean in other words our winds and our ocean currents which move heat from the equator toward the pole in the next video you will learn more about how why the winds blow and which direction our global winds tend to circulate