for use with the simulation Four seasons - solstices and equinoxes; single view
from the materialworlds Solar System simulations
© materialworlds.com 2002
The Four seasons - solstices and equinoxes; single view simulation shows the Earth orbiting the Sun.
Compared to the size of the orbit the Sun is magnified 36 times and the Earth 6000 times - not just just make it visible, but also to show which areas of the Earth the Sun illuminates.
The tilt control also helps see where there's daylight - and adds to the 3D appreciation of the Earth's orbit and spin axis.
The "View every: ¼ hour / day / week" control adjusts the time that elapses between each snapshot of the simulation.
"¼ hour" shows the actual rotation of the Earth - missed with the "day" interval that shows the same part of the Earth facing the Sun.
The "step" checkbox briefly pauses the simulation between each snapshot - removing any illusion of continuous movement.
You can estimate the length of day or night for a part of the world at a particular time of year by counting the number of ¼ hour intervals it is in light or darkness (with "step" active). If the region you're interested in lies on or near one of the circles of equal latitude displayed (equator, tropic or arctic/antarctic circles) you could instead estimate the proportion of the circle in darkness or light.
1. As the Earth goes around the Sun, what do you notice about the direction of tilt of the Earth's axis of rotation? Is it fixed or does it move - to point the same way towards the Sun (or in some other way)?
2. Set the "view every" time interval to "day". Pause the simulation at the June solstice, switch the viewing interval to ¼ hour and set the simulation to Play. At the June solstice:
a) which part of the world is in constant daylight?
b) which part of the world is in constant darkness?
c) where is the Sun directly overhead at midday?
d) at the North Pole, what angle is the Sun from the horizon?
e) does anywhere in the world have equal days and nights?
3. As the Earth moves to the September equinox, what happens to:
a) day length North of the equator?
b) day length South of the equator?
c) day length at the equator?
4. At the September equinox:
a) what is true about day length anywhere in the world?
b) At the North and South Poles, where is the Sun in the sky?
5. What happens as the Earth moves from the September equinox to the December solstice?
6. What happens from the December solstice through to the June solstice?