About this experiment
Move the Earth around the Sun through a whole year and watch the subsolar point travel between the tropics. Because the axis keeps pointing the same way in space, each hemisphere leans toward the Sun for half the year. Pick any latitude to see its day length and noon Sun height change with the date.
Learning goals
- Explain the seasons with axial tilt rather than distance from the Sun
- Locate the subsolar point on the solstices and equinoxes
- Describe how day length changes with latitude and date, including polar day and night
- Calculate the noon solar elevation for a given latitude and date
How to use it
- 1Press Play year, or drag the date slider, and watch the Earth move along its orbit.
- 2Click a solstice or equinox button to jump to that date.
- 3Set the observer latitude to your own city. The orange ring and dot mark it on the globe.
- 4Read the day length and noon Sun elevation, and follow the dot on the yearly daylight chart.
The model
Assumptions
- The orbit is treated as a circle, so the slight change in Earth-Sun distance is ignored.
- Day length uses the center of the Sun and ignores atmospheric refraction, which adds a few minutes in reality.
- Sizes, distances and the rotation speed are not to scale.
Try this in class
- Q1On which dates is the day exactly 12 hours long everywhere on Earth?
- Q2Move the latitude to 70° N. Find the dates of polar day and polar night.
- Q3Why is it summer in Australia when it is winter in China?
- Q4Calculate the noon Sun elevation at your latitude on the June solstice, then check it here.
Frequently asked questions
Are the seasons caused by the Earth being closer to the Sun?
No. The Earth is actually closest to the Sun in early January. The seasons come from the tilt of the axis, which changes the Sun angle and day length.
What is the subsolar point?
It is the place where the Sun is directly overhead at noon. It moves between the Tropic of Cancer and the Tropic of Capricorn over the year.
Why does the Arctic Circle sit at 66.56° N?
It is 90° minus the axial tilt. North of this line the Sun stays above the horizon all day on the June solstice.