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Solstice vs. equinox
Question:
What is the difference between solstice and equinox?
Answer:
The words solstice and equinox refer to four specific days in the year—one in each of the
four seasons. A solstice occurs in summer and winter; an equinox, in spring and fall.
Solstice
The word solstice comes from the Latin words sol (sun) and stitium (standstill). At the
solstice, the sun appears to "stand still". What does this mean?
During the winter and spring months in the northern hemisphere, the sun rises at a more
northerly point on the horizon each day. When the sun reaches its extreme northerly point,
it rises above the line of latitude known as the Tropic of Cancer (about 23.5° north of the
equator). In the northern hemisphere, that day marks the summer solstice, the longest day
of the year and the beginning of summer.
For a few days before and after the solstice, the change in position of the sunrise is so slight
that the sun seems to come up at the same point on the horizon each day. Thus, it appears
to stop or "stand still" for a few days before it changes direction and begins to rise farther
and farther to the south each day. When the sunrise reaches its extreme southerly point, it
is directly over the Tropic of Capricorn (about 23.5° south of the equator). In the northern
hemisphere, that day marks the winter solstice, the shortest day of the year and the first
day of winter.
In the northern hemisphere, the summer solstice happens on or around June 21, and the
winter solstice happens on or around December 22. (Of course, because the seasons are
reversed below the equator, the southern hemisphere enjoys its summer solstice around
December 22 and experiences its winter solstice around June 21.)
Equinox
The word equinox comes from the Latin words aequus (equal) and nox (night). At the
equinox, the night is almost equal in length to the day. Why does this happen?
After the winter solstice, as the sun rises farther and farther to the north, the days in the
northern hemisphere grow longer, while the nights grow shorter. Midway through this
process, at the spring equinox, the daytime and nighttime hours are almost equal. After the
summer solstice, the longest day of the year, the process is reversed. The days grow
shorter and the nights longer, until they are once again almost equal, at the fall equinox.
The spring equinox (called the vernal equinox) happens on or around March 21, and the fall
(or autumnal) equinox happens on or around September 23.
Vocabulary
If you plan to read more on this topic, the following terms may help you:
(solar) altitude:
the height of the sun relative to the horizon
autumnal equinox:
a brief period when day and night are basically equal in duration,on or around
September 23
axial tilt:
the number of degrees the Earth leans toward or away from the sun, measured from
its axis; the Earth has an axial tilt of about 23.5° at all times
axis:
an imaginary line that goes through the centre of the Earth, from the North Pole to
the South Pole
equator:
an imaginary line that can be drawn around the Earth at its middle
horizon:
a point where the Earth and sky seem to meet
line of latitude (or parallel of latitude):
an imaginary line that can be drawn around the Earth, parallel to the equator (that
is, the same distance from the equator at every point) The latitude of the equator is
0° and the latitude of the North and South poles is 90°.
line of longitude (or meridian of longitude):
an imaginary line that can be drawn around the Earth, starting at the North Pole and
going to the South Pole
northern hemisphere:
the half of the Earth that is north of the equator
orbit:
the path followed by a planet (or star) around another planet (or star)
Polaris:
the North Star
southern hemisphere:
the half of the Earth that is south of the equator
summer solstice:
a brief period when the sun does not appear to move, on or around June 21
Tropic of Cancer:
the latitude line at 23.5° N (north)
Tropic of Capricorn:
the latitude line at 23.5° S (south)
vernal equinox:
a brief period when day and night are basically equal in duration, on or around
March 21
winter solstice:
a brief period when the sun does not appear to move, on or around December 22
zenith:
the point in the sky directly overhead; the highest point above the horizon