In Canada and the rest
of the northern
hemisphere, the first
day of the summer season
is the day of the year
when the Sun is farthest
north (on June 21st
or 22nd).
This day is known as the
Summer Solstice.
The declination of the
Sun on the summer
solstice is known as the
tropic of cancer (23°
27'). In the Southern
hemisphere,
winter and summer
solstices are exchanged
so that the summer
solstice is the day on
which the Sun is
farthest south.
A common misconception
is that the earth is
further from the sun in
winter than in
summer. Actually, the
Earth is closest to the
sun in December which is
winter in the
Northern hemisphere.
As the Earth travels
around the Sun in its
orbit, the north-south
position of the Sun
changes over the course
of the year because of the
changing orientation of
the Earth's tilted
rotation axes. The dates
of maximum tilt of the
Earth's equator
correspond to the Summer
Solstice and
Winter Solstice, and
the dates of zero tilt
to the
Vernal Equinox and
Autumnal Equinox.
The reason for these
changes has to do with
the Earth's yearly trip
around the sun. For part
of the year the Earth's
North Pole points away
from the sun and part of
the time toward it. This
is what causes our
seasons. When the North
Pole points toward the
sun, the sun's rays hit
the northern half of the
world more directly.
That means it is warmer
and we have summer.
The day of the summer
solstice is the longest
day of the year. The
length of time elapsed
between sunrise and
sunset on this day is a
maximum for the year.
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