You could
almost think of them as opposites. The word "solstice" comes
from the Latin roots "sol," meaning sun, and "sistere," meaning
"stationary." That refers to the fact that during a solstice,
the sun rises and appears to stop in the middle of the sky for a
while before it sets. As a result, the summer solstice is the
longest day of the year.
If you are on the
opposite side of the globe from that sunny standstill, you would
experience a winter solstice, the longest night of the year. The
winter solstice occurs on December 21 or 22 in the Northern
Hemisphere and on June 20 or 21 in the Southern Hemisphere. The
summer solstice occurs on June 20 or 21 in the Northern
Hemisphere and on December 21 or 22 in the Southern Hemisphere.
The word "equinox,"
comes from the Latin roots "aequus," meaning equal, and "nox,"
meaning night. On the equinox, day and night last for exactly
the same amount of time. Spring equinox means spring has
arrived. The vernal equinox happens about March 21 in the
Northern Hemisphere and September 23 in the Southern Hemisphere.
The autumnal equinox occurs near September 23 in the Northern
Hemisphere and March 21 in the Southern Hemisphere.
Picture the Earth as
it circles the sun. Our planet does not sit directly upright as
it rotates; its axis of rotation is actually tilted by about
23.4 degrees, always pointed in the same direction in space. In
the same way you get more sun on your shoulders if you are
sitting up in your beach chair than you will if you are lounging
flat, some areas of the Earth get more sunlight depending on
where its axis is pointing. That, in turn, depends on where the
planet is in its revolution around the sun.
For example, when it's the winter solstice in the Northern
Hemisphere, the Earth is at a point in its revolution where its
axis points away from the sun and the Northern Hemisphere gets
the least amount of sunlight. If you were standing at the North
Pole, you wouldn't get any sunlight at all. The Southern
Hemisphere, on the other hand, would get its biggest helping of
sunlight all year, making it the summer solstice there. In
Antarctica, the sun never sets during this period.
Whereas the Earth's
axis is tilted directly toward or away from the sun during a
solstice, it's tilted directly askew from the sun during an
equinox. To use the sunbathing example again, it's as if you
rotated your body parallel to the towel clockwise you get the
same amount of sun on your front and back as if you had rotated
the other way. At this time, the sun is directly above the
equator, and that means that day and night are of equal length.
But not for long: A new season is upon you, which means shorter
nights (or days!) and more (or less!) sunlight to enjoy.