Originally Posted by Sumo
Here's a very simplified answer, and something most 5th graders have learned.
We live on a planet.
This planet is called Earth.
The Earth rotates around the sun. (this has been proven, btw)
The Earth also spins on an axis.
This axis is not vertical, but tilted.
This tilt means that at any time during the year, either the northern or the southern hemisphere will be the recipient of more of the sun's energy.
When the energy is most direct on a certain hemisphere, that part of the earth will experience summer.
In Australia, this falls in line with a month on our calendar that is called January.
I hope this helps.
For more information follow this link....... https://www.google.com/
This is a fine explanation but misses one key point -- that the tilt of the rotation axis to the plane of the Earth orbit does not change as Earth goes around the sun. In any case, while not too complicated, I doubt most people would be able to produce this explanation right away.