[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:13.90,0:00:14.82,Default,,0000,0000,0000,,When I was a kid,
Dialogue: 0,0:00:14.82,0:00:16.13,Default,,0000,0000,0000,,my understanding of the seasons
Dialogue: 0,0:00:16.13,0:00:18.12,Default,,0000,0000,0000,,was that December and January were cold
Dialogue: 0,0:00:18.12,0:00:19.63,Default,,0000,0000,0000,,and covered with snow,
Dialogue: 0,0:00:19.63,0:00:21.97,Default,,0000,0000,0000,,April and May were bursting with flowers,
Dialogue: 0,0:00:21.97,0:00:24.57,Default,,0000,0000,0000,,July and August were hot and sunshiny,
Dialogue: 0,0:00:24.57,0:00:28.77,Default,,0000,0000,0000,,and September and October were a kaleidoscope of colorful leaves.
Dialogue: 0,0:00:28.77,0:00:30.23,Default,,0000,0000,0000,,It was just the way the world worked,
Dialogue: 0,0:00:30.23,0:00:31.90,Default,,0000,0000,0000,,and it was magical.
Dialogue: 0,0:00:31.90,0:00:33.32,Default,,0000,0000,0000,,If you had told me back then
Dialogue: 0,0:00:33.32,0:00:35.19,Default,,0000,0000,0000,,that one-third of Earth's population
Dialogue: 0,0:00:35.19,0:00:36.86,Default,,0000,0000,0000,,had never seen snow
Dialogue: 0,0:00:36.86,0:00:40.74,Default,,0000,0000,0000,,or that July 4th was most definitely not a beach day,
Dialogue: 0,0:00:40.74,0:00:42.40,Default,,0000,0000,0000,,I would have thought you were crazy.
Dialogue: 0,0:00:42.40,0:00:45.41,Default,,0000,0000,0000,,But in reality, seasonal change with four distinct seasons
Dialogue: 0,0:00:45.41,0:00:48.04,Default,,0000,0000,0000,,only happens in two regions on the planet.
Dialogue: 0,0:00:48.04,0:00:49.04,Default,,0000,0000,0000,,And, even in those two,
Dialogue: 0,0:00:49.04,0:00:50.58,Default,,0000,0000,0000,,the seasons are reversed.
Dialogue: 0,0:00:50.58,0:00:51.58,Default,,0000,0000,0000,,But why?
Dialogue: 0,0:00:51.58,0:00:53.42,Default,,0000,0000,0000,,A lot of people have heard of an astronomer
Dialogue: 0,0:00:53.42,0:00:54.90,Default,,0000,0000,0000,,called Johannes Kepler
Dialogue: 0,0:00:54.90,0:00:57.34,Default,,0000,0000,0000,,and how he proved that planetary orbits are elliptical
Dialogue: 0,0:00:57.34,0:01:00.09,Default,,0000,0000,0000,,and that the sun is not at the center of the orbit.
Dialogue: 0,0:01:00.09,0:01:02.01,Default,,0000,0000,0000,,It was a big deal when he figured this out
Dialogue: 0,0:01:02.01,0:01:03.35,Default,,0000,0000,0000,,several hundred years ago.
Dialogue: 0,0:01:03.35,0:01:05.89,Default,,0000,0000,0000,,His discovery solved a lot of mathematical problems
Dialogue: 0,0:01:05.89,0:01:07.18,Default,,0000,0000,0000,,that astronomers were having
Dialogue: 0,0:01:07.18,0:01:09.17,Default,,0000,0000,0000,,with planetary orbit measurements.
Dialogue: 0,0:01:09.17,0:01:12.32,Default,,0000,0000,0000,,While it's true that our orbit's not perfectly circular,
Dialogue: 0,0:01:12.32,0:01:14.27,Default,,0000,0000,0000,,those pictures in our science books,
Dialogue: 0,0:01:14.27,0:01:15.77,Default,,0000,0000,0000,,on TV, and in the movies
Dialogue: 0,0:01:15.77,0:01:17.11,Default,,0000,0000,0000,,give an exaggerated impression
Dialogue: 0,0:01:17.11,0:01:19.36,Default,,0000,0000,0000,,of how elongated our orbit is.
Dialogue: 0,0:01:19.36,0:01:22.74,Default,,0000,0000,0000,,In fact, Earth's orbit is very nearly a perfect circle.
Dialogue: 0,0:01:22.74,0:01:25.78,Default,,0000,0000,0000,,However, because Earth's orbit is technically an ellipse,
Dialogue: 0,0:01:25.78,0:01:27.37,Default,,0000,0000,0000,,even though it doesn't look like one,
Dialogue: 0,0:01:27.37,0:01:29.87,Default,,0000,0000,0000,,and the sun isn't quite exactly at the center,
Dialogue: 0,0:01:29.87,0:01:31.46,Default,,0000,0000,0000,,it means that our distance from the sun
Dialogue: 0,0:01:31.46,0:01:33.12,Default,,0000,0000,0000,,does change through the year.
Dialogue: 0,0:01:33.12,0:01:34.11,Default,,0000,0000,0000,,Ah-ha!
Dialogue: 0,0:01:34.11,0:01:37.50,Default,,0000,0000,0000,,So, winter happens when the Earth is further away from the sun!
Dialogue: 0,0:01:37.50,0:01:39.34,Default,,0000,0000,0000,,Well, no, not so fast.
Dialogue: 0,0:01:39.34,0:01:41.40,Default,,0000,0000,0000,,The Earth is actually closer to the sun
Dialogue: 0,0:01:41.40,0:01:43.32,Default,,0000,0000,0000,,in January than we are in July
Dialogue: 0,0:01:43.32,0:01:45.76,Default,,0000,0000,0000,,by 5 million kilometers.
Dialogue: 0,0:01:45.76,0:01:48.02,Default,,0000,0000,0000,,January is smack-dab in the middle
Dialogue: 0,0:01:48.02,0:01:49.65,Default,,0000,0000,0000,,of the coldest season of the year
Dialogue: 0,0:01:49.65,0:01:51.26,Default,,0000,0000,0000,,for those of us up north.
Dialogue: 0,0:01:51.26,0:01:52.40,Default,,0000,0000,0000,,Still not convinced?
Dialogue: 0,0:01:52.40,0:01:53.52,Default,,0000,0000,0000,,How about this:
Dialogue: 0,0:01:53.52,0:01:55.61,Default,,0000,0000,0000,,Summer and winter occur simultaneously
Dialogue: 0,0:01:55.61,0:01:57.23,Default,,0000,0000,0000,,on the surface of our planet.
Dialogue: 0,0:01:57.23,0:01:58.57,Default,,0000,0000,0000,,When it's winter in Connecticut,
Dialogue: 0,0:01:58.57,0:02:00.19,Default,,0000,0000,0000,,it's summer in New Zealand.
Dialogue: 0,0:02:00.19,0:02:01.82,Default,,0000,0000,0000,,So, if it's not the distance from the sun,
Dialogue: 0,0:02:01.82,0:02:03.11,Default,,0000,0000,0000,,what else could it be?
Dialogue: 0,0:02:03.11,0:02:04.53,Default,,0000,0000,0000,,Well, we need to also need to know
Dialogue: 0,0:02:04.53,0:02:06.32,Default,,0000,0000,0000,,that the Earth doesn't sit straight up.
Dialogue: 0,0:02:06.32,0:02:07.62,Default,,0000,0000,0000,,It actually tilts.
Dialogue: 0,0:02:07.62,0:02:09.41,Default,,0000,0000,0000,,And that axial tilt of the Earth
Dialogue: 0,0:02:09.41,0:02:12.29,Default,,0000,0000,0000,,is one of the main reasons for the seasons.
Dialogue: 0,0:02:12.29,0:02:14.20,Default,,0000,0000,0000,,The Earth spins on an axis
Dialogue: 0,0:02:14.20,0:02:17.17,Default,,0000,0000,0000,,that's tilted 23.5 degrees from vertical.
Dialogue: 0,0:02:17.17,0:02:19.55,Default,,0000,0000,0000,,At the same time, the Earth revolves around the sun
Dialogue: 0,0:02:19.55,0:02:23.09,Default,,0000,0000,0000,,with the axis always pointing in the same direction in space.
Dialogue: 0,0:02:23.09,0:02:24.17,Default,,0000,0000,0000,,Together with the tilt,
Dialogue: 0,0:02:24.17,0:02:26.15,Default,,0000,0000,0000,,the spinning and revolving causes the number
Dialogue: 0,0:02:26.15,0:02:28.26,Default,,0000,0000,0000,,of hours of daylight in a region to change
Dialogue: 0,0:02:28.26,0:02:29.43,Default,,0000,0000,0000,,as the year goes by,
Dialogue: 0,0:02:29.43,0:02:30.94,Default,,0000,0000,0000,,with more hours in summer
Dialogue: 0,0:02:30.94,0:02:32.95,Default,,0000,0000,0000,,and fewer in winter.
Dialogue: 0,0:02:32.95,0:02:35.94,Default,,0000,0000,0000,,So, when the sun is shining on the Earth, it warms up.
Dialogue: 0,0:02:35.94,0:02:38.48,Default,,0000,0000,0000,,After the sun sets, it has time to cool down.
Dialogue: 0,0:02:38.48,0:02:39.35,Default,,0000,0000,0000,,So, in the summer,
Dialogue: 0,0:02:39.35,0:02:42.49,Default,,0000,0000,0000,,any location that's about 40 degrees north of the equator,
Dialogue: 0,0:02:42.49,0:02:44.11,Default,,0000,0000,0000,,like Hartford, Connecticut,
Dialogue: 0,0:02:44.11,0:02:45.91,Default,,0000,0000,0000,,will get 15 hours of daylight each day
Dialogue: 0,0:02:45.91,0:02:47.93,Default,,0000,0000,0000,,and 9 hours of darkness.
Dialogue: 0,0:02:47.93,0:02:50.10,Default,,0000,0000,0000,,It warms up for longer than it cools.
Dialogue: 0,0:02:50.10,0:02:52.22,Default,,0000,0000,0000,,This happens day after day,
Dialogue: 0,0:02:52.22,0:02:54.41,Default,,0000,0000,0000,,so there is an overall warming effect.
Dialogue: 0,0:02:54.41,0:02:56.24,Default,,0000,0000,0000,,Remember this fact for later!
Dialogue: 0,0:02:56.24,0:02:57.94,Default,,0000,0000,0000,,In the winter, the opposite happens.
Dialogue: 0,0:02:57.94,0:03:00.03,Default,,0000,0000,0000,,There are many more hours of cooling time
Dialogue: 0,0:03:00.03,0:03:01.24,Default,,0000,0000,0000,,than warming time,
Dialogue: 0,0:03:01.24,0:03:04.70,Default,,0000,0000,0000,,and day after day, this results in a cooling effect.
Dialogue: 0,0:03:04.70,0:03:06.83,Default,,0000,0000,0000,,The interesting thing is, as you move north,
Dialogue: 0,0:03:06.83,0:03:10.25,Default,,0000,0000,0000,,the number of daylight hours in summer increases.
Dialogue: 0,0:03:10.25,0:03:13.38,Default,,0000,0000,0000,,So, Juneau, Alaska would get about 19 hours of daylight
Dialogue: 0,0:03:13.38,0:03:17.60,Default,,0000,0000,0000,,on the same summer day that Tallahassee, Florida gets about 14.
Dialogue: 0,0:03:17.60,0:03:20.38,Default,,0000,0000,0000,,In fact, in the summertime at the North Pole,
Dialogue: 0,0:03:20.38,0:03:22.56,Default,,0000,0000,0000,,the sun never sets.
Dialogue: 0,0:03:22.56,0:03:26.06,Default,,0000,0000,0000,,OK, then, it's all about daylight hours, I've got it!
Dialogue: 0,0:03:26.06,0:03:29.08,Default,,0000,0000,0000,,Well, no, there's another important piece to this puzzle.
Dialogue: 0,0:03:29.08,0:03:30.96,Default,,0000,0000,0000,,If daylight hours were the only thing
Dialogue: 0,0:03:30.96,0:03:32.60,Default,,0000,0000,0000,,that determined average temperature,
Dialogue: 0,0:03:32.60,0:03:34.52,Default,,0000,0000,0000,,wouldn't the North Pole be the hottest place
Dialogue: 0,0:03:34.52,0:03:36.16,Default,,0000,0000,0000,,on Earth in northern summer
Dialogue: 0,0:03:36.16,0:03:38.11,Default,,0000,0000,0000,,because it receives 24 hours of daylight
Dialogue: 0,0:03:38.11,0:03:40.58,Default,,0000,0000,0000,,in the months surrounding the summer solstice?
Dialogue: 0,0:03:40.58,0:03:41.91,Default,,0000,0000,0000,,But it's the North Pole.
Dialogue: 0,0:03:41.91,0:03:43.46,Default,,0000,0000,0000,,There's still icebergs in the water
Dialogue: 0,0:03:43.46,0:03:44.75,Default,,0000,0000,0000,,and snow on the ground.
Dialogue: 0,0:03:44.75,0:03:46.43,Default,,0000,0000,0000,,So, what's going on?
Dialogue: 0,0:03:46.43,0:03:47.37,Default,,0000,0000,0000,,The Earth is a sphere
Dialogue: 0,0:03:47.37,0:03:49.88,Default,,0000,0000,0000,,and so the amount of solar energy an area receives
Dialogue: 0,0:03:49.88,0:03:52.34,Default,,0000,0000,0000,,changes based on how high the sun is in the sky,
Dialogue: 0,0:03:52.34,0:03:54.43,Default,,0000,0000,0000,,which, as you know, changes during the day
Dialogue: 0,0:03:54.43,0:03:56.17,Default,,0000,0000,0000,,between sunrise and sunset.
Dialogue: 0,0:03:56.17,0:03:58.67,Default,,0000,0000,0000,,But, the maximum height also changes during the year,
Dialogue: 0,0:03:58.67,0:04:01.02,Default,,0000,0000,0000,,with the greatest solar height during the summer months
Dialogue: 0,0:04:01.02,0:04:04.06,Default,,0000,0000,0000,,and highest of all at noon on the summer solstice,
Dialogue: 0,0:04:04.06,0:04:06.35,Default,,0000,0000,0000,,which is June 21st in the northern hemisphere
Dialogue: 0,0:04:06.35,0:04:09.18,Default,,0000,0000,0000,,and December 21st in the southern hemisphere.
Dialogue: 0,0:04:09.18,0:04:10.86,Default,,0000,0000,0000,,This is because as the Earth revolves,
Dialogue: 0,0:04:10.86,0:04:13.23,Default,,0000,0000,0000,,the northern hemisphere ends up tilted away
Dialogue: 0,0:04:13.23,0:04:14.90,Default,,0000,0000,0000,,from the sun in the winter
Dialogue: 0,0:04:14.90,0:04:16.20,Default,,0000,0000,0000,,and toward the sun in summer,
Dialogue: 0,0:04:16.20,0:04:18.49,Default,,0000,0000,0000,,which puts the sun more directly overhead
Dialogue: 0,0:04:18.49,0:04:20.33,Default,,0000,0000,0000,,for longer amounts of time.
Dialogue: 0,0:04:20.33,0:04:23.20,Default,,0000,0000,0000,,Remember those increased summer time daylight hours?
Dialogue: 0,0:04:23.20,0:04:26.33,Default,,0000,0000,0000,,And solar energy per square kilometer increases
Dialogue: 0,0:04:26.33,0:04:28.38,Default,,0000,0000,0000,,as the sun gets higher in the sky.
Dialogue: 0,0:04:28.38,0:04:30.34,Default,,0000,0000,0000,,So, when the sun's at an angle,
Dialogue: 0,0:04:30.34,0:04:31.75,Default,,0000,0000,0000,,the amount of energy delivered
Dialogue: 0,0:04:31.75,0:04:34.96,Default,,0000,0000,0000,,to each square of the sunlit area is less.
Dialogue: 0,0:04:34.96,0:04:37.84,Default,,0000,0000,0000,,Therefore, even though the North Pole is getting 24 hours
Dialogue: 0,0:04:37.84,0:04:39.22,Default,,0000,0000,0000,,of daylight to warm up,
Dialogue: 0,0:04:39.22,0:04:41.85,Default,,0000,0000,0000,,the sunlight it receives is very spread out
Dialogue: 0,0:04:41.85,0:04:44.98,Default,,0000,0000,0000,,and delivers less energy than a place further south,
Dialogue: 0,0:04:44.98,0:04:46.60,Default,,0000,0000,0000,,where the sun is higher in the sky
Dialogue: 0,0:04:46.60,0:04:48.86,Default,,0000,0000,0000,,because it's more tilted toward the sun.
Dialogue: 0,0:04:48.86,0:04:51.03,Default,,0000,0000,0000,,Besides, the North Pole has a lot to make up for.
Dialogue: 0,0:04:51.03,0:04:53.57,Default,,0000,0000,0000,,It was cooling down without any sunlight at all
Dialogue: 0,0:04:53.57,0:04:54.94,Default,,0000,0000,0000,,for 6 months straight.
Dialogue: 0,0:04:54.94,0:04:57.70,Default,,0000,0000,0000,,So, as the seasons change, wherever you are,
Dialogue: 0,0:04:57.70,0:05:00.66,Default,,0000,0000,0000,,you can now appreciate not just the beauty of each new season
Dialogue: 0,0:05:00.66,0:05:02.42,Default,,0000,0000,0000,,but the astronomical complexity
Dialogue: 0,0:05:02.42,0:05:04.62,Default,,0000,0000,0000,,that brings them to you.