Day & Night and The Seasons

Day and Night

What causes day and night?

What causes day and night?

The Earth doesn't just orbit around the Sun – it also spins, or rotates. Imagine a line that runs through the Earth from the North Pole to the South Pole. This line is called an axis. The Earth rotates on its axis from west to east.

What causes day and night?

The rotation of the Earth is what causes the change between day and night. At any time, half of the Earth is bathed in light from the Sun and experiences daylight. The other half of the Earth faces away from the Sun and experiences night. As the Earth rotates, a location moves to the sunlit side and then back to the shadowed side. We experience this as the Sun rising, crossing the sky and setting.

What causes day and night?

The time taken for any planet to rotate once on its axis is a day. On Earth, a day is 24 hours because this is how long it takes for our planet to rotate once.

Multiple Choice

A day on Earth is 24 hours long.

This is the time it takes for...

• The Sun to rotate once on its axis

• The Earth rotates on its axis

• The Earth to orbit once around the sun

• The Sun to orbit once around the Earth

Multiple Choice

"Orbiting" means the same as "rotating"

• True

• False

Multiple Choice

As countries move out of the sunlight, they experience a...

• Sunrise

• Sunset

Multiple Choice

At any one time, what percentage of Earth is experiencing night?

• 20%

• 35%

• 50%

• 70%

Open Ended

If the Earth rotated faster, what would happen to the length of a day? Explain your answer.

Open Ended

Different planets rotate at different speeds. For example, Saturn takes 10 hours and 42 minutes to complete one rotation on its axis.

Imagine if it was possible to live on Saturn. How would this length of rotation affect your daily life?

Does the Moon play a role?

Discussion...

The Moon doesn't produce its own light.
It reflects light from the Sun.
So, when you see the moon at night, it’s the sunlight bouncing off the moon’s surface.

The Moon orbits Earth and is visible during both the day and night, but it doesn’t affect the occurrence of day or night.

The Moon and its role...

Open Ended

If the Earth did not have a moon, would we still have day and night? Would there be any differences? Explain your response.

Things to remember...

• The cause of Day and Night is the rotation of the Earth as it orbits around the Sun - it is not the orbiting that causes Day and Night but it is the rotation of Earth.

• The Moon does not have a role in Night time apart from reflecting the light from the Sun so that our nights are not completely dark.

• A full day on Earth is 24 hours which is how long it takes the Earth to make 1 whole rotation on its axis.

The Seasons

As children, we often learn that there are four seasons: summer, autumn, winter, spring... But this isn't true everywhere in the world. For example, people living in the tropics experience just two seasons: wet and dry.

Depending on where you live, you probably experience dramatically different weather at different times of the year. It might be hot for months on end. Then the heat fades and you can't leave the house without a heavy coat.

The Seasons

Open Ended

Briefly explain the seasons we experience here where we live...

Why do we have seasons?

The Earth orbits the Sun once a year and the orbit isn't a perfect circle. Sometimes the Earth is closer to the Sun and at other times it is further away. So... could this explain the seasons?

Multiple Choice

If the seasons really were caused by how close the Earth was to the Sun then...

• Both hemispheres would have summer at the same time

• The southern hemisphere would have summer when the northern hemisphere is in winter

• There would be no autumn or spring

• There would be no seasons at all

Open Ended

Explain why the the northern hemisphere has summer at the same time that the southern hemisphere has winter.

Multiple Select

Two factors that make summer warmer than winter are...

• The sunlight is more direct

• The Earth is closer to the Sun because of its elliptical orbit

• The Earth's axis is more tilted in summer

• There are more daylight hours or longer days

Open Ended

Imagine that a comet hit the Earth and increased its tilt to an angle of 35°
How would this be likely to affect the seasons?

The other planets in the Solar System also spin or rotate as they orbit the Sun. So each planet has an axis of rotation. And Earth is not the only planet with a tilted axis.

In fact, most of the planets are tilted and have four seasons like Earth. Mercury is the only planet that has no tilt. Its axis is at a right angle to the orbital plane.

Open Ended

If Earth's axis changed to have the same tilt as Uranus's, how do you think this would affect us? Describe some of the effects you might see.

Things to remember

1. Earth's Tilt Causes Seasons: The Earth's axis is tilted at about 23.5 degrees. This tilt causes different parts of the Earth to receive more direct sunlight at different times of the year, creating the seasons.
   

2. Seasons in Both Hemispheres: When it's summer in the northern hemisphere, it's winter in the southern hemisphere, and vice versa. Spring and autumn are also reversed in the two hemispheres.

Things to remember

3. Daylight and Sunlight Intensity: In summer, there are more daylight hours, and sunlight is more direct, making it warmer. In winter, there are fewer daylight hours, and sunlight is less direct, making it colder.
   

4. Common Misconceptions: The seasons are not caused by the Earth's distance from the Sun. Although the Earth's orbit is elliptical, the slight distance change does not significantly affect temperatures. Instead, the Earth's tilt is the main reason.

Things to remember

5. Other Planets: Most planets in the Solar System also have tilted axes, leading to seasons like Earth's. However, planets like Mercury, which has no tilt, do not experience seasons.