Science Sunday: The Reason for the Season As I’m writing this
it’s late evening, and I have been spending a few days at home.
Funny thing is, even though I’m going to bed soon, the Sun isn’t
setting. Actually, it won’t set for at least another month.
During that time, it will circle the sky, dip a bit up and down,
but never go under the horizon. So, how does that work? The
axial tilt, or obliquity, of the Earth is defined as the angle
between the rotational axis and the orbital axis. Presently, the
axial tilt is at about 23.5 degrees, a number that varies
slightly over a 41 000 year cycle. Other astronomical bodies
have different tilts, where some vary a lot over time. The
stability of the Earth’s axial tilt is largely because of the
presence of our Moon. Without it, the Earth would most likely
tip drunkenly back and forth between different degrees of
obliquity. This would not happen overnight, but it has been
theorized that a greatly varying tilt would not be positive for
the evolution of higher species. Thi