Axial Tilt and the Seasons 3D – Orbit, Day Length and Sun Angle
GeographyEarth in SpaceAges 15–16
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Sign in to playA rotatable 3D model of Earth moving along its true elliptical orbit, with the axis tilted 23.44° and always pointing the same way in space; the chosen line of latitude is orange on the day side and grey on the night side. Move through the year to read the subsolar latitude, the Earth–Sun distance, day length, noon Sun altitude and daily solar radiation at your latitude, and compare both hemispheres on a year-long graph. Set the tilt to 0° to make the seasons disappear, and notice that Earth is closest to the Sun in early January.
Lesson: Earth's orbit around the Sun and its consequences: the seasons and the variation of day length with season and latitude
What it shows
Seasons happen because Earth's axis is tilted 23.44° and keeps pointing the same way as Earth orbits the Sun. For half the year one hemisphere leans towards the Sun: the noon Sun is higher, days are longer and each square metre receives more energy. Distance matters little: Earth is closest to the Sun in early January, during the northern winter, and the change in distance alters sunlight by only about 7%. The model uses the real orbit and computes day length, noon Sun altitude and daily radiation at the top of the atmosphere.
How to use
Drag the Date slider or press Play and watch the orange latitude ring: its lit part shows how long the day is. Move Latitude to compare places, and choose a quantity for the year-long graph; click the graph to jump to a date. Press Upright axis (0°) to remove the tilt and see day length stay at 12 hours everywhere. Switch the view to Follow Earth for a close-up.
Parameters you can change
- Day of the year (1 = 1 January) 1–365 day
- Observer's latitude (negative = Southern Hemisphere) -90–90 °
- Tilt of Earth's axis 0–45 °
- Animation speed 1–60 days/s
- Year-long graph Day length, Noon Sun altitude, Daily mean solar radiation
Questions to explore
- Earth is closest to the Sun in early January, so why is it winter in the Northern Hemisphere then?
- At 50° latitude, how many hours longer is the longest day than the shortest day, and what happens at the equator?
- If the axis were tilted 45°, where would the tropics and polar circles be, and how would the seasons change?
