Why Polar Seasons Are Extreme
Understand how Earth's axis, tilted about 23.5 degrees, causes polar seasons as Earth travels around the Sun. Each pole has months with the Sun above the horizon and months with it below. Seasonal changes in sunlight and temperature affect sea ice and animals that use it.
What a learner can do afterwards
- Explain that Earth's axis is tilted at about 23.5° and this tilt causes the extreme polar seasons
- Explain that each pole leans toward the Sun for about half the year and away for about half, producing long periods with the Sun above or below the horizon
- Connect the seasonal cycle to at least one animal behaviour, such as migration or sea ice retreat affecting hunting
1 · Read
You know about midnight sun and polar night. Earth's axis is an imaginary line through its poles, around which Earth spins. Imagine Earth's yearly path around the Sun lying on a flat sheet. A line standing straight out of that sheet is the reference. Earth's axis leans about 23.5 degrees from that line.
During its yearly trip, Earth's axis keeps pointing nearly the same way in space. Each pole leans toward the Sun for about half the year and away for about half. In polar summer, sunlight reaches the pole throughout Earth's daily spin. Deep in polar winter, the Sun stays below the horizon. Twilight can still bring some light.
When the North Pole leans toward the Sun, the South Pole leans away. Their seasons are opposite. Earth's distance from the Sun changes a little during the year. Both poles share that change, so it does not explain their opposite seasons. Earth's tilt does.
Sea ice generally grows in colder months and shrinks in warmer months. Polar bears hunt seals from sea ice. Where summer sea ice disappears, some bears spend time on land until ice returns. Other bears stay with remaining sea ice. A bear's hunting places can change as the ice changes.
Earth's tilted axis causes opposite polar seasons. Each pole has months of sunlight and months with the Sun below the horizon. Changing sea ice affects hunting places.
Four original readings written for this dataset.
More to read
Two ends of one axis
Earth spins around an imaginary line through its North and South Poles. This line is its axis. The axis is tilted, and it keeps pointing nearly the same way during Earth's yearly trip around the Sun.
For part of the year, the North Pole leans toward the Sun while the South Pole leans away. Later, the South Pole leans toward it while the North Pole leans away. The two poles have opposite seasons.
At each pole, the Sun stays above the horizon for about half the year and below it for about half. These are approximate lengths. Elsewhere in the polar regions, the periods without sunrise or sunset are shorter.
A day without sunrise
A day still has 24 hours when the Sun never rises. During deep winter at a pole, the Sun stays below the horizon throughout those hours.
Below the horizon does not always mean a pitch-black sky. Air can scatter sunlight and give the sky some light while the Sun itself is hidden. We call this twilight.
In polar summer, the Sun remains above the horizon through the whole day and night. The yearly change comes from Earth's tilted axis as Earth travels around the Sun.
Keep the globe pointing one way
Ask an adult to help you use a globe and a cool lamp. Keep the lamp in one place to represent the Sun. The globe's tilted axle represents Earth's axis.
Choose a direction in the room for the axle to point. Move the globe around the lamp while keeping the axle pointing that way. On one side, the North Pole leans toward the lamp. Across the circle, it leans away.
Slowly spin the globe at each position. Watch whether its North Pole stays lit or stays in shadow. Keep hands and the globe away from the lamp. This model shows the effect of tilt, not the real sizes or distances.
Summer feeding and autumn travel
Some geese raise their young in the Arctic summer. The long daylight gives parents many hours to find food for their chicks.
As autumn arrives, days shorten and water begins to freeze. Many birds travel south to places where they can still find food and open water. They may return north in spring.
This regular movement between seasonal homes is migration. Not all geese make the same journey, and some populations do not migrate. Seasonal changes affect different animals in different ways.
2 · Watch
Take it off screen
Where it sits
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.