Can someone please explain why the tilt of the Earth's axis cause different day lengths?

Question

Can someone please explain why the tilt of the Earth's axis cause different day lengths?

Answer 1

Not so easy without good diagrams.  The link given by the first answer is lousy.  

IF the Earth's axis was parallel to its orbit then once a year the axis would be pointing directly at the sun from the North pole.  If you quickly flew south, at the equator the sun would be on the horizon, and further south there would be no sunrise that day.  6 months later the South pole would be pointing at the Sun, the sun would be overhead there all day and at the north pole there would be no sunrise.

So this "sort of" explains why the tilt changes the day's length.  

Our tilt isn;'t that much so we need to get close to the North or south pole to have days without sunrise.  The tilt determines the arc the Sun makes across the sky, in the Northern Hemisphere in the Summer the arc is closer to East to straight overhead to West at sunset while in the Winter the arc is from the East South East to a little (more) South of right over head to the West South West at sunset.

If the axis was perpendicular to the orbital plane, days would be the same length all year.  BUT remember that the days at the Equator would still be longest.  

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I've linked a little article that maybe is a bit more helpful.  Where the heck are the Java applets IDK.  On the second page there is a diagram  of Sun & Earth Winter and Summer and a "little man" standing on the Earth.  Picture the Earth turning about its axis both on the "summer earth" and on the "winter earth".  can you see why the man has more daylight in the summer?  Remember the earth spins around its axis and NOT perpendicular to a line between the sun and the earth.

Answer 2

http://www.lpi.usra.edu/education/skytel...

The above image should help illustrate it.  Near the spring and autumn equnoxes, all the earth receives about the same amount of daylight daily, for the "tilt" is perpendicular to where the light from the sun is coming from.

At the solstices, however, the farther from the equator you get, the larger difference in sunlight you will receive (per day).  This is due to one pole or the other (depending on the season) is pointed closer to the sun.  Within the arctic and antarctic circles, the sun actually "Never sets" for a certain amount of days (depending on how far beyond that line you go).  The sunlight essentially "wraps around" the poles...  if you are shy of these lines, but still a distance from the equator, the sunlight will be close to perpetual, but not quite, because it actually does set.