Reasons for the seasons - Rebecca Kaplan

Summary

This script explores the misconceptions about the Earth's seasons, revealing that only two regions experience four distinct seasons. Contrary to popular belief, the Earth's elliptical orbit and proximity to the sun do not directly cause seasonal changes. Instead, the axial tilt of 23.5 degrees is the primary factor, affecting daylight hours and warming effects. The script explains how the Earth's tilt and position relative to the sun lead to varying daylight and solar energy, impacting temperatures more than the length of daylight alone. It concludes by highlighting the astronomical intricacies behind the changing seasons.

Takeaways

• 🌐 The Earth's orbit is nearly a perfect circle, contrary to common exaggerated depictions.
• 📉 In January, Earth is actually 5 million kilometers closer to the sun than in July, despite it being winter in the northern hemisphere.
• 🌍 Seasons are not determined by Earth's distance from the sun, but by the axial tilt of 23.5 degrees.
• 🌞 The axial tilt causes variations in daylight hours, affecting temperatures and creating seasons.
• 🕒 Longer daylight hours in summer lead to an overall warming effect, while shorter hours in winter result in cooling.
• 🌅 The maximum solar height changes during the year, affecting the intensity of solar energy received.
• 🏙️ Locations further north receive more daylight hours in summer, but this doesn't necessarily make them hotter.
• ❄️ The North Pole, despite 24 hours of daylight in summer, remains cold due to the spread-out and less intense sunlight.
• 🌡️ Solar energy per square kilometer increases as the sun gets higher in the sky, affecting temperature more than just daylight hours.
• 🌎 Seasons are reversed in the northern and southern hemispheres due to Earth's tilt and revolution around the sun.
• 🌈 Understanding the astronomical complexity behind seasonal changes allows us to appreciate the beauty and science of each season.

Q & A

What was the speaker's childhood perception of the seasons?

The speaker perceived seasons as distinctly different, with December and January being cold and snowy, April and May full of flowers, July and August hot and sunny, and September and October marked by colorful leaves.

Why would the speaker have thought someone was crazy for saying that one-third of Earth's population had never seen snow?

The speaker would have thought this was crazy because their childhood understanding of the world included the idea that snow was a common experience during certain seasons.

In which two regions on the planet does seasonal change with four distinct seasons occur?

The script does not specify the exact regions, but it implies that these regions are limited and that even in these regions, the seasons are reversed.

What did Johannes Kepler discover about planetary orbits that was significant?

Johannes Kepler discovered that planetary orbits are elliptical and that the sun is not at the center of the orbit, which solved many mathematical problems related to planetary orbit measurements.

Is Earth's orbit perfectly circular?

No, Earth's orbit is very nearly a perfect circle but technically an ellipse, with the sun not exactly at the center.

Why is it incorrect to say that winter happens when the Earth is further away from the sun?

It's incorrect because the Earth is actually closer to the sun in January than in July by 5 million kilometers, despite it being the middle of winter in the northern hemisphere.

What is the phenomenon where summer and winter occur simultaneously on the surface of the planet?

This phenomenon occurs due to the Earth's axial tilt and revolution around the sun, causing opposite seasons in the northern and southern hemispheres, such as winter in Connecticut and summer in New Zealand.

What is the axial tilt of the Earth and how does it affect the seasons?

The Earth's axial tilt is 23.5 degrees from vertical. This tilt, combined with the Earth's spin and revolution around the sun, causes variations in daylight hours and temperature, leading to the change of seasons.

How does the length of daylight hours during summer affect the warming effect in regions like Hartford, Connecticut?

In summer, regions like Hartford, Connecticut experience 15 hours of daylight and 9 hours of darkness, leading to an overall warming effect as the area warms up for longer than it cools down.

Why isn't the North Pole the hottest place on Earth during northern summer despite receiving 24 hours of daylight?

Even though the North Pole receives 24 hours of daylight, the sunlight is spread out and delivers less energy due to the low angle of the sun, and the area has a lot of cooling to make up for from the 6 months of darkness.

How does the angle of the sun in the sky affect the amount of solar energy an area receives?

The amount of solar energy an area receives changes based on the sun's height in the sky. When the sun is higher, as during the summer months and at noon on the summer solstice, more solar energy per square kilometer is delivered.

What is the significance of the Earth's tilt towards the sun during summer and away from the sun in winter?

The Earth's tilt towards the sun in summer allows for more direct sunlight and longer daylight hours, increasing the solar energy received and causing warming. In winter, the tilt away from the sun results in less direct sunlight and shorter daylight hours, leading to cooling.

Outlines

00:00

🌏 Understanding Earth's Seasons

This paragraph delves into the misconceptions about Earth's seasonal changes and explains the scientific reasons behind them. It starts with a personal anecdote about the traditional view of seasons and then challenges this by presenting the fact that only two regions on Earth experience four distinct seasons, and even then, they are reversed. The script introduces Johannes Kepler's discovery of elliptical orbits to explain the Earth's varying distance from the sun throughout the year. Contrary to a common misconception, it clarifies that Earth is closer to the sun in January than in July, debunking the idea that winter is due to increased distance from the sun. The paragraph also highlights the simultaneous occurrence of summer and winter on opposite hemispheres and introduces the concept of Earth's axial tilt as a key factor in season formation. The Earth's 23.5-degree tilt and its consistent orientation during revolution around the sun are emphasized as the primary reasons for seasonal variations.

05:01

🌞 The Role of Daylight and Solar Energy in Seasons

This paragraph continues the discussion on Earth's seasons by focusing on the role of daylight hours and solar energy. It explains how the Earth's axial tilt affects the number of daylight hours a region receives, leading to more daylight in summer and less in winter. The example of Hartford, Connecticut, is used to illustrate how longer periods of sunlight during summer lead to an overall warming effect, while the opposite occurs in winter. The paragraph also addresses the variation in daylight hours as one moves further north, using Alaska's Juneau and the North Pole as examples to show the increase in daylight hours during summer. It then refutes the simplistic idea that more daylight hours directly correlate with higher temperatures, pointing out that the angle at which sunlight strikes the Earth also affects the amount of solar energy received. The script concludes by emphasizing the complexity of the astronomical factors that contribute to the beauty and variety of Earth's seasons.

Keywords

💡Seasons

Seasons refer to the four distinct periods of the year characterized by particular weather conditions and natural phenomena. In the video, the concept of seasons is introduced as a magical part of the world's workings, with the speaker reminiscing about their childhood understanding of the typical weather associated with each season. The video goes on to challenge this notion by explaining the astronomical reasons behind the seasons, rather than the simplistic view of weather patterns.

💡Axial Tilt

Axial tilt, also known as obliquity, is the angle between a planet's rotational axis and its orbital axis. The Earth's axial tilt of 23.5 degrees is crucial for the creation of seasons. The video explains that this tilt, combined with the Earth's orbit around the sun, results in varying amounts of daylight and solar energy received at different latitudes throughout the year, which in turn causes the seasonal changes.

💡Orbit

Orbit refers to the path that an object in space takes around another object due to gravity. Johannes Kepler's discovery that planetary orbits are elliptical, not perfectly circular, is mentioned in the video. Although Earth's orbit is nearly a circle, its slight elliptical shape means that the distance between the Earth and the sun varies slightly over the course of a year, affecting the intensity of sunlight received.

💡Daylight Hours

Daylight hours are the measure of time during which an area receives sunlight. The video emphasizes that the number of daylight hours changes with the seasons due to the Earth's axial tilt and orbit. Longer daylight hours in the summer lead to more warming, while shorter daylight hours in the winter result in more cooling, contributing to seasonal temperature differences.

💡Summer Solstice

The summer solstice is the day with the longest period of daylight in the year in the respective hemisphere. The video notes that the summer solstice occurs on June 21st in the northern hemisphere and December 21st in the southern hemisphere. During this time, the sun is at its highest point in the sky, resulting in the maximum amount of solar energy per square kilometer.

💡Winter

Winter is one of the four seasons, characterized by cold weather and typically snow or ice in many regions. The video dispels the myth that winter occurs when the Earth is further from the sun. Instead, it explains that winter in the northern hemisphere, including cold regions like Connecticut, happens when the Earth is actually closer to the sun than in July, due to the axial tilt and the angle at which sunlight hits the Earth.

💡Solar Energy

Solar energy is the radiant energy emitted by the sun that can be harnessed by the Earth. The video explains that the amount of solar energy received by the Earth's surface changes based on the sun's position in the sky, which is influenced by the Earth's tilt and orbit. More direct sunlight results in greater energy delivery, contributing to warmer temperatures.

💡North Pole

The North Pole is the northernmost point on Earth, located in the Arctic region. The video uses the North Pole as an example to illustrate that despite receiving 24 hours of daylight during the summer months, the region remains cold due to the low angle of the sun's rays, spreading out the energy and resulting in less warming effect compared to areas further south.

💡Sun Angle

Sun angle refers to the angle at which sunlight strikes a surface, which affects the amount of energy absorbed. The video explains that when the sun is at a higher angle in the sky, as it is during the summer months, more solar energy is delivered per square kilometer. Conversely, a lower sun angle, as experienced at the poles, spreads out the energy, delivering less warmth.

💡Seasonal Change

Seasonal change is the transition from one season to another, marked by shifts in weather, temperature, and daylight hours. The video discusses how seasonal change is not uniform across the globe and is a result of the Earth's axial tilt and orbit. It emphasizes the astronomical complexity behind these changes, which are not solely due to the Earth's distance from the sun.

💡Global Variation

Global variation refers to the differences in climate and environmental conditions across the Earth. The video highlights that not all regions experience the four distinct seasons as described in the speaker's childhood understanding. It points out that only two regions on the planet have this type of seasonal change, and even then, the seasons are reversed in the southern hemisphere.

Highlights

Childhood perception of seasons as distinct and magical.

Contrary to childhood belief, only 2 regions on Earth experience four distinct seasons.

Seasons are reversed in those two regions.

Johannes Kepler's discovery of elliptical orbits and the sun's position.

Earth's orbit is nearly a perfect circle, contrary to common depictions.

Earth's distance from the sun varies slightly throughout the year.

Contrary to intuition, Earth is closer to the sun in January than in July.

Simultaneous occurrence of summer and winter on opposite sides of the planet.

Earth's axial tilt as the main reason for the seasons.

The axial tilt causes variation in daylight hours and temperature.

Summer warming effect due to longer daylight and shorter cooling time.

Winter cooling effect due to shorter daylight and longer cooling time.

Increased daylight hours in summer as one moves further north.

The North Pole receives 24 hours of daylight in summer but remains cold.

Solar energy varies based on the sun's height in the sky.

Direct overhead sun in summer increases solar energy per square kilometer.

The angle of sunlight affects the amount of energy delivered to Earth.

Appreciation of the astronomical complexity behind seasonal changes.

Transcripts

Transcriber: Andrea McDonough Reviewer: Jessica Ruby

When I was a kid,

my understanding of the seasons

was that December and January were cold

and covered with snow,

April and May were bursting with flowers,

July and August were hot and sunshiny,

and September and October were a kaleidoscope of colorful leaves.

It was just the way the world worked,

and it was magical.

If you had told me back then

that one-third of Earth's population

had never seen snow

or that July 4th was most definitely not a beach day,

I would have thought you were crazy.

But in reality, seasonal change with four distinct seasons

only happens in two regions on the planet.

And, even in those two,

the seasons are reversed.

But why?

A lot of people have heard of an astronomer

called Johannes Kepler

and how he proved that planetary orbits are elliptical

and that the sun is not at the center of the orbit.

It was a big deal when he figured this out

several hundred years ago.

His discovery solved a lot of mathematical problems

that astronomers were having

with planetary orbit measurements.

While it's true that our orbit's not perfectly circular,

those pictures in our science books,

on TV, and in the movies

give an exaggerated impression

of how elongated our orbit is.

In fact, Earth's orbit is very nearly a perfect circle.

However, because Earth's orbit is technically an ellipse,

even though it doesn't look like one,

and the sun isn't quite exactly at the center,

it means that our distance from the sun

does change through the year.

Ah-ha!

So, winter happens when the Earth is further away from the sun!

Well, no, not so fast.

The Earth is actually closer to the sun

in January than we are in July

by 5 million kilometers.

January is smack-dab in the middle

of the coldest season of the year

for those of us up north.

Still not convinced?

How about this:

Summer and winter occur simultaneously

on the surface of our planet.

When it's winter in Connecticut,

it's summer in New Zealand.

So, if it's not the distance from the sun,

what else could it be?

Well, we need to also need to know

that the Earth doesn't sit straight up.

It actually tilts.

And that axial tilt of the Earth

is one of the main reasons for the seasons.

The Earth spins on an axis

that's tilted 23.5 degrees from vertical.

At the same time, the Earth revolves around the sun

with the axis always pointing in the same direction in space.

Together with the tilt,

the spinning and revolving causes the number

of hours of daylight in a region to change

as the year goes by,

with more hours in summer

and fewer in winter.

So, when the sun is shining on the Earth, it warms up.

After the sun sets, it has time to cool down.

So, in the summer,

any location that's about 40 degrees north of the equator,

like Hartford, Connecticut,

will get 15 hours of daylight each day

and 9 hours of darkness.

It warms up for longer than it cools.

This happens day after day,

so there is an overall warming effect.

Remember this fact for later!

In the winter, the opposite happens.

There are many more hours of cooling time

than warming time,

and day after day, this results in a cooling effect.

The interesting thing is, as you move north,

the number of daylight hours in summer increases.

So, Juneau, Alaska would get about 19 hours of daylight

on the same summer day that Tallahassee, Florida gets about 14.

In fact, in the summertime at the North Pole,

the sun never sets.

OK, then, it's all about daylight hours, I've got it!

Well, no, there's another important piece to this puzzle.

If daylight hours were the only thing

that determined average temperature,

wouldn't the North Pole be the hottest place

on Earth in northern summer

because it receives 24 hours of daylight

in the months surrounding the summer solstice?

But it's the North Pole.

There's still icebergs in the water

and snow on the ground.

So, what's going on?

The Earth is a sphere

and so the amount of solar energy an area receives

changes based on how high the sun is in the sky,

which, as you know, changes during the day

between sunrise and sunset.

But, the maximum height also changes during the year,

with the greatest solar height during the summer months

and highest of all at noon on the summer solstice,

which is June 21st in the northern hemisphere

and December 21st in the southern hemisphere.

This is because as the Earth revolves,

the northern hemisphere ends up tilted away

from the sun in the winter

and toward the sun in summer,

which puts the sun more directly overhead

for longer amounts of time.

Remember those increased summer time daylight hours?

And solar energy per square kilometer increases

as the sun gets higher in the sky.

So, when the sun's at an angle,

the amount of energy delivered

to each square of the sunlit area is less.

Therefore, even though the North Pole is getting 24 hours

of daylight to warm up,

the sunlight it receives is very spread out

and delivers less energy than a place further south,

where the sun is higher in the sky

because it's more tilted toward the sun.

Besides, the North Pole has a lot to make up for.

It was cooling down without any sunlight at all

for 6 months straight.

So, as the seasons change, wherever you are,

you can now appreciate not just the beauty of each new season

but the astronomical complexity

that brings them to you.