March 9 2006 - Autumnal Equinox
The Southern Hemisphere Autumnal Equinox occurs on March 21 at 06:26 am.
Brian Carter, Senior Astronomer at the Carter Observatory says, “this is when the Sun moves from the Southern Hemisphere
into the Northern Hemisphere”.
The Earth orbits the Sun, at a tilt of about 23½, which is the cause of the seasons. In our Summer, the South Pole is
tilted towards the Sun and the North Pole is tilted away. We therefore get longer days and the Sun rises higher in our
sky, which means we get warmer weather. Conversely, in our Winter, the South Pole is tilted away from the Sun so our
days are shorter and the Sun is lower in our sky, hence the colder temperatures.
At the two equinoxes, in March and September, the Earth is vertical in relation to the Sun. This means that the Sun goes
directly overhead at the equator and the Sun is on the horizon all day at both poles. At other places one would expect
that the time between Sunrise and Sunset would be 12 hours. This is not quite true because the Earth’s atmosphere
refracts (bends) the Sun’s rays upwards causing the day to be slightly longer.
For more information about this subject, or any other astronomical issue contact
Brian Carter, Senior Astronomer.
ENDS