Remember that the Earth is tilted all the time that it
is moving around the Sun. The Earth moves around the Sun once every year. It
follows an elliptical orbit. This means that it goes almost in a circle around
the sun, but gets a little further away at some times. The path it takes is like
Now, take your orange again, tip it like before and hold
it at arms length, keeping it tipped. Slowly turn around in a circle. Notice how
the tilt stays the same. The Northern hemisphere is always tipped toward you.
This is NOT how the earth moves.
Put your orange down for a minute and walk around a
chair. The way you would normally do it, you would walk around with one side of
you facing the chair the whole time. I want you to do it a different way. Place
the chair between you and a window. Leave enough space between it and the window
so you can walk around it. Start on the opposite side to the window, facing the
chair AND the window. Now walk around the chair, all the way, but keep facing
the window. Don't turn round (this means you will be walking backwards at some
point, so be careful). THAT is how the Earth moves around the sun. Now do it
again, holding the orange at your side, starting with the top of the orange
facing towards the chair. As you walk around, notice that the part of the orange
facing the chair changes. First the Northern Hemisphere points to the chair (or
Sun), then the tilt is sideways, with neither hemisphere pointing at the Sun,
then the Southern hemisphere points at the Sun (when you are walking backwards)
and finally neither hemisphere points at the Sun again. Then you are back to the
beginning and the Northern hemisphere is pointing at the Sun again.
It is very difficult to make a model to show this. You
can make a good model, but you would need the Earth to follow a rectangular
orbit in order to keep the tilt of the Earth correct. If you let it follow an
elliptical orbit you would need gears and all sorts of things to keep it right.