Reasons for the seasons simulator

What this simulator shows

Earth's axis is tilted about 23.5° and points the same way in space all year, toward the North Star. The left picture shows Earth's orbit from a slight angle, with the Sun in the middle; tap a month to move Earth there. The right picture is a close-up from the side, with the Sun to the left, so you can see which hemisphere leans toward the Sun. The coral line marks the latitude of the place you choose: New York City, London, Quito on the equator, or Sydney.

• In June the Northern Hemisphere leans toward the Sun: long days, a high noon Sun, summer. The Southern Hemisphere has winter.
• In December it is the other way around.
• At the March and September equinoxes neither hemisphere leans toward the Sun, and day and night are about 12 hours everywhere.
• The readout gives the day length and how high the Sun gets at noon, worked out for the 21st of each month (the 20th or 22nd at the equinoxes).

The big misconception

Most people, adults included, think summer happens when Earth is closer to the Sun. Earth's orbit is very nearly a circle. Earth is actually nearest the Sun in early January, about 91.4 million miles away, and farthest in early July, about 94.5 million miles. If distance caused the seasons, both hemispheres would have summer together. Instead, Sydney has summer while New York has winter. Many textbook pictures make the orbit look like a long oval, which feeds the mistake; this one keeps it close to a circle.

The tilt matters in two ways. The hemisphere leaning toward the Sun has longer days, and the Sun climbs higher in its sky, so the same sunlight is spread over a smaller area and heats the ground more.

A 10-minute seasons activity

• Ask: "Why is it hot in summer?" Note the answer without correcting it.
• Pick June, then December. Look at the axis in both pictures. Ask what stayed the same.
• With New York City chosen, read the day length in June and December.
• Switch to Sydney in the same two months. Ask: "Could distance explain this?"
• Open Is it about distance? and come back to the first answer together.

Where this fits in school

• US, grade 5: NGSS 5-ESS1-2 asks students to graph patterns in day length, shadows and the night sky.
• US, middle school: NGSS MS-ESS1-1 asks students to model the Earth-Sun-Moon system to explain seasons as well as phases and eclipses.
• England, Key Stage 3: pupils learn about the seasons and Earth's tilt, and day length at different times of year in different hemispheres.

Learning more

Earth and space science is part of Eurekami's skill map. Lessons draw diagrams like these live and talk them through, and the AI tutor asks guiding questions when a student is stuck, so they do the reasoning themselves.