The Equinox

The Earth's terminator rewpressnts a fixed reference to the Sun and
can be demarcated by the direction of the arrows over the course of an
annual orbit -

http://www.honeysucklecreek.net/imag...6689creth1.jpg

http://www.mhhe.com/physsci/astronom...ages/04f15.jpg

The global unequal lengths of the natural noon cycles,supposing axial
rotation is constant or near enough constant, represent a longitudinal
change in the motion of the Earth,this can be observationally
confirmed using the sequence of images from Uranus -

http://astro.berkeley.edu/~imke/Infr..._2001_2005.jpg

With axial rotational orientation at almost 90 degrees to the change
in orbital orientation,it is fairly easy to isolate the orbital
component in Uranus however as axial orientation and rotation runs
almost parallel to the orbital change on Earth it is very difficult to
discern save the unequal lengths of the natural noon cycles.

In the representation demonstrating Keplerian orbital geometry,it is
possible to gauge the longitudinal orbital orientational change
against the fixed orientation of the Earth's terminator at the
Equator.

There is no advantage in maintaining 'axial tilt' as a pseudo-
dynamic,the fact that local rotations and orientations can blot out
larger motions is probably the main reason why the false perception
still remains -

http://www.astronomy.org/programs/se...ns-general.gif