Joined: 23 Sep 2012
|Posted: Fri Dec 21, 2012 10:06 pm Post subject: A few facts and myths about W solstice
|On Friday at 6:12 a.m. (EST), Earth's north pole will be at its maximum
tilt away from the sun, marking the official start of winter and shortest day
of the year for the Northern Hemisphere. If you're looking for some bright
sunshine to alleviate the winter blues, head south of the equator, which is
now enjoying its longest daylight period of the year.
Let's take a look at seven different statements to see what's true and
True or False?
1. The earth is at its farthest point from the sun on the winter solstice.
False. Earth's orbit is approaching perihelion its closest distance from
the sun in early January. In fact, the earth is about 3 million miles
closer to the sun now than in early July. Our seasons are caused by the
planet's axial tilt, which currently positions the sun's most direct rays over
the southern hemisphere. At the winter solstice, the northern hemisphere
continues to lose more incoming solar energy than it receives, which is why
winter's coldest days still lie ahead.
2. The number of daylight hours on the winter solstice depends on latitude.
True. Like the summer solstice in June, daylight hours on the winter
solstice vary greatly by latitude. Washington, D.C. sees the sun for 9 hours and
26 minutes on December 21, while in Miami the sun spends over 10½ hours
above the horizon. Barrow, Alaska, located far north of the Arctic Circle,
does not see the sun rise at all though it does still have about 3 hours of
dreary twilight at midday.
3. In the Northern Hemisphere, the sun takes its shortest and lowest path
across the sky.
True. In Washington, D.C., the winter solstice sun reaches a maximum angle
of only 27.7º above the horizon at solar noon. In the more northern city
of London, the sun takes an even shorter path, climbing only 15.1º in the
sky. And just south of the Arctic Circle, the Icelandic capital of Reykjavik
sees the midday sun climb no higher than 2.1º above the horizon.
4. The sun rises and sets at its southernmost points along the horizon on
the winter solstice.
True for all locations on earth, including areas in the tropics and
Because the Southern Hemisphere is at its maximum tilt toward the sun, our
nearest star rises and sets south of due east and due west, respectively.
The farther one travels from the equator, the more the sun will rise and
set toward the southern horizon.
5. In the Northern Hemisphere, the earliest sunset and latest sunrise are
on the winter solstice.
False. The reasons are complex, but most mid-latitude locations see their
earliest sunset a week or more before the solstice. Meanwhile, the latest
sunrise is typically not until early January. Washington, D.C. saw its
earliest sunset at 4:46 p.m. from December. 1-12, while the latest sunrise is at
7:27 a.m. from December. 31-Jan. 10. The reason for this misalignment is a
discrepancy between our clocks and the apparent motion of the sun.
6. At the Arctic Circle, the sun does not rise on the winter solstice.
False. If you stood at 66.5º north latitude on the winter solstice, you
would actually see the sun straddle the horizon for about two hours on a
clear day. This happens due to atmospheric refraction, an optical phenomenon
that allows us to see the sun even when it's just below the horizon. Only
starting around 67.4º north latitude does the sun remain completely below the
horizon, and even then there are still several hours of twilight. To
experience 24 hours of complete darkness (absence of any twilight), you would
have to travel to about 80ºN almost to the North Pole.
7. After the solstice, daylight in the Northern Hemisphere increases
faster the farther north you are.
True. The higher the latitude, the faster daylight is gained or lost on a
daily basis throughout the year. This is true whichever hemisphere you live
If you live in a northern city with very short days now, the good news is
that you'll gain daylight at a faster, more noticeable pace than places to
your south. So, even though the coldest days of winter have yet to arrive,
increasing daylight is something to look forward to.
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