Day Length Differences Throughout Year
I have been a secondary teacher for
many years but after my retirement I have
decided to teach primary school children (6-10
years old). I have a degree and Ph.D in physics,
but is difficult for me (!) to find an easy and
adequate way of teaching to children aged 6-7
years old about "Why days and nights have
different duration along the year"... Could you please help me?
Whenever something becomes difficult for me to teach, I tend to always
rely on an activity of some kind that will help drive ideas home. By
having the students actually do the activity and guide them to -not tell
them- the conclusions I want, I find that their learning is much
improved and they have fun in the process.
You know that the different day/night duration is a function of the tilt
in the axis of a spheroid (not perfectly spherical) Earth. So how about
putting an egg on a slowly rotating clamp, putting a dot on the egg, and
timing how long that dot stays within the light of a flashlight at
different angles of incidence? The trick is to get some kind of rotor
that will rotate the egg at a careful and consistent pace.
Greg (Roberto Gregorius)
---Or a beach ball
(Nathan A. Unterman)
It is hard to explain this concept to seven year olds. The answer should
include the idea that Earth is tilted, and that when the tilt is sharp, as
in Northern hemisp[here winter, the nights are longer. Also you might
introduce the concept that we live on a spaceship, and this is how our ship
flies through space.
David H. Levy
First, a great-big-THANK YOU for teaching!
I am not an educator and do not have any factual, tested knowledge of how
children best learn. That said, the idea that best occurs to me is not
an explanation. Rather it seems that for children that young the best
way might be through showing them with a model of the solar system.
The canonical version of this is the incandescent light bulb "sun" and
then balls as the planets to orbit the bulb. In your case, you could
have a ball mounted on something (or even just handheld) that turns at a
constant rate. Perhaps a line of constant latitude and a big spot on
the ball to represent the actual location. Then show the kids summer
with the spot inclined towards the sun and then winter on the opposite
side from the bulb. In fact, you could have a one spot for the northern
hemisphere and then a second colored spot for the southern hemisphere.
If they're capable of grasping the time difference in days/nights of the
two hemispheres and why it is summer on one half and winter on the other,
then I think you've got it.
If the ball turns slowly enough, say once every 30 seconds, perhaps you
could even have them "time" day and night in both winter and summer with
I often think children are smarter than we adults give them credit for.
As such, the bonus question would be to try and come up for a reason
why the seasons change due to the earth's inclination and not because
the "earth is closer to the sun in the summer, therefore hotter."
Understanding that the reason for hot summers and longer days is not due
to the earth being closer to the sun would be a great thing.
Lastly, sadly, I've met too many adults that do not understand this.
Michael S. Pierce
Materials Science Division
Argonne National Laboratory
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Update: June 2012