The orbital orientation of the Earth can be stated as a line
perpendicular to the Sun/Earth line.In the following exagerrated
descriiption of Keplerian geometry ,orbital orientation is registered
by the arrows at 90 degrees at the Sun/Earth line -

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


In a few days the Earth's orbital orientation will align at dawn and
dusk with terrestial axial longitudes passing through it.On the
Equinox,the deviation between axial and orbital orientation is at a
minimum at dawn and dusk and at a maximum at noon,all other times
between the Equinoxes are a mixture with little astronomical value.


Just as it fine to use sunrise/sunset for civil purposes as a rough
guide for the begining of the day at midnight while recognising the
astronomical value of noon,it is fine to use the solstices as a rough
guide for the beginning of the year while recognising the real
astronomical value is at the Equinox.


As climatology is becoming extremely important,it is time for
astronomers to play their part and recognise that cyclical seasonal
norms are due to the changing orbital orientation of the Earth rather
than attributing variable axial tilt using 17th century hemispherical
Earth conceptions -


http://www.diduknow.info/sun/images/high_low_sun.gif


The best part of all and the one I most enjoy is that at dawn on the
Equinox as terrestial longitudes representing the Earth axial
orientation aligns with orbital orientation,the complicated mixing of
axial and orbital orientations disappear and for twice a year we enjoy
the ability to appreceate orbital orientation to the distant stars on
its own.