# How Seasons Work

Why summer and winter happen: how Earth's tilted axis changes how directly sunlight hits each hemisphere through the year\. Distance from the Sun plays little part\.

By happy\-finch\-6b5c5fa0

Topic: Earth & Geography

[Open the interactive Jig](https://ask.jig.com/j/VxTVZRQ7DOmM)

## Transcript

### 1. A year around the Sun

Earth travels around the Sun once a year, spinning once a day as it goes\. Along the way most places get warm summers and cold winters\. The reason is not distance\. It is a lean\.

One trip around the Sun takes about 365 and a quarter days\.

### 2. Earth leans

Earth spins around its axis, an imaginary line through the North and South Poles\. That axis is tilted about 23\.5 degrees, and it keeps pointing the same way all year\. Look at the four ghost Earths: every axis is parallel\.

The north end of the axis points almost exactly at the North Star\.

### 3. June: the north leans in

Around June 21 the northern half of Earth leans toward the Sun\. The Sun climbs high in northern skies and days are long, so it is summer there\. Near the North Pole the Sun does not set at all\.

At this solstice the Sun is straight overhead at the Tropic of Cancer, 23\.5 degrees north\.

### 4. Direct light is stronger

These two beams of sunlight are the same size and carry the same energy\. The northern beam hits the ground almost head\-on and makes a small, bright patch\. The southern beam arrives at a slant and spreads over a bigger patch, so each spot gets less warmth\.

Slanted light also travels through more air before it reaches the ground\.

### 5. December: the south's turn

Six months later Earth is on the other side of the Sun\. The axis still points the same way, so now the southern half leans in\. It is summer in Australia and Argentina while the north has winter\.

The two halves of Earth always have opposite seasons\.

### 6. Equinox: an even share

In March and September the tilt points along Earth's path, neither toward the Sun nor away\. Sunlight falls evenly on both halves, so day and night are each about 12 hours long almost everywhere\.

Equinox means equal night\.

### 7. Closer is not warmer

Many people think summer comes when Earth is closest to the Sun\. In fact Earth is closest in early January, about 147 million kilometres away, and farthest in early July, about 152 million\. Watch the pins marked near and far\.

The path is almost a perfect circle, so the distance changes by only about 3 percent\.

### 8. Your turn: turn the year

Drag Earth along its brass track, or use the slider, and watch the seasons change\. See the snow spread across the northern lands in winter, and the poles take turns in sunlight\.

Over about 41,000 years the tilt slowly rocks between about 22\.1 and 24\.5 degrees\.