Question

What would be the effect on the seasons and the northern and southern hemispheres if Earth were not tilted?

Answer 1

Imagine the equator. Constantly at 90+ degrees, so its always summer, this would be the same thing for the northern and southern hemispheres but it would always be fall or spring, at the same time!. Summer and winter are caused by the title of the earth as it goes around the sun, when its winter in the north is summer in the south, and same for if they flip. So without the tilt there would be no winter or summer it would be I guess spring or fall all year long.

http://en.wikipedia.org/wiki/File:Earth_tilt_animation.gif

http://en.wikipedia.org/wiki/Axial_tilt

Those links will help. :)

Hope I helped you learn something new today! :)