Why won't there be seasons if the earth was not tilted 23.5 degrees?

Answer 1

Season exist because the earth's axis (the line passing through the planet connecting the north and south poles) is not perpendicular to the plane in which Earth orbits. Go to http://www.srh.noaa.gov/jetstream//global/global_intro.htm and look at the picture. In December, the Southern Hemisphere is pointed more toward the sun, while the Northern Hemisphere is pointed more away. The Northern Hemisphere receives less sunlight than the SH, and thus it is colder. The reverse is true in June: the NH receives more sunlight and the SH less. If the angle of inclination were 0 degrees, the two hemispheres would receive equal amounts of sunlight throughout the year. It's not correct to say that there would be NO seasons if the Earth were not tilted at 23.5 degrees. What is true is that the seasons would be more uniform at a lower angle, and more severe at a higher angle. In fact, the Earth slowly moves between angles of 22 and 24.5 degrees (it takes us 40,000 years to move from 22 to 24.5 and back to 22 degrees!), and this seemingly small difference has taken the Earth back and forth between ice ages ("glacials") and non-ice ages ("interglacials").

Answer 2

Seasons occur because the Earth's tilt affects the angle at which sunlight strikes different parts of the Earth, causing variations in temperature. If the Earth was not tilted, the amount of sunlight received by each hemisphere would be constant, leading to a lack of distinct seasons.