As days lengthen and nights shorten after the Winter Solstice, the Vernal
Equinox marks the point where day and night are of the
same length. After the Equinox, days will continue to grow longer until they reach
a maximum at the Summer Solstice in June.
This fixed inclination means that, as the Earth travels around the Sun, each pole is
sometimes angled towards the Sun, and sometimes angled away. From the Sun's perspective,
the Earth 'tilts' backward and forward each year, and it is this 'tilt' that causes the
Many of the Earth'sliving systems have adapted to the
planet's astronomical cycles. Both of these organisms - butterfly and flower - have developed their
own responses to the Vernal Equinox and the climatic changes it brings with it.
When a pole is oriented towards the Sun, its hemisphere has six months where the Sun is
high in the sky, and days are longer than nights (that is, summer). For the other six months, the pole
is tilted away from the Sun, which is low on the horizon, and nights are longer than days (winter).
These differences are more noticeable at higher latitudes: at the poles themselves, the
effects are extreme, and result in months of daylight followed by months of darkness.
The equinox is the point where one season turns to the other. The word is
Latin for 'equal night' and refers to the fact that, on the equinox, day and night are
of equal length. There are two equinoxes each year, with the vernal equinox usually occurring on
21 March. Vernal comes originally from the Latin word for 'bloom' - it refers to the
fact that, in the northern hemisphere, this equinox marks the end of winter and the beginning
of spring. The name is less meaningful in the southern hemisphere, where this equinox actually marks the beginning of autumn, but nonetheless the traditional name vernal is commonly retained.