2 messages.---------------------------Johnnie
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: [log in to unmask] (Jim Carter)
: Re: Sunrise...Sunset...180 Degrees
: Wed, 28 Jun 1995 16:06:57 -0500 (CDT)
>
> 180 degrees from sunrise to sunset could never happen north of
> Cancer or south of Capricorn. Regardless of the time of year north of
> Cancer, sunrise is still in the southeast with sunset in the southwest,
> just at varying degrees. South of Capricorn, sunrise is always in the
> northeast and sunset in the northwest. Only between Cancer and
> Capricorn could you ever have 180 degrees from sunrise to sunset since
> it is only in that range that the Sun would ever pass directly
> overhead. At least that's as I understand it...
>
And I remember when the author of this was one of my students. Luckily, he did
not take physical geog or climatology from me. I wanted to get my copy of Wm.
Sellers, Physical Climatology, in front of me before I took on this issue. In
this classic text, dated about 1965, the author copies a number of the sun
position diagrams. Those diagrams are reproduced from an earlier
Meteorological monograph. In that monograph there is a diagram of sun position
for each 5 degrees of latitude.
These diagrams show the position of the sun relative to North for various times
of the year. They also show the height of the sun above the horizon. Sellers
also gives the equations to solve for these values.
The quote above has to be wrong. North of the Arctic Circle the sun will rise
in the north and set in the north at least twice during the year. Depending
how far north you go, the sun will never set for part of the year. So, in this
area the sun will trace out a 360 degree arc part of the year.
South of the Arctic Circle, the sun will rise in the north half of the sky from
March 22 through September 20, or so. (Applicable only in the Northern
Hemisphere.) The further north you go, the more northern the arc will be at
sunrise and sunset.
If you have not done so, let me suggest you mark the compass position of the
sun at sunrise, or sunset, for the Summer Solstice, Equinox, and Winter
Solstince. I was able to do that on my deck in Knoxville. It is interesting
to see how much difference there is in the position of the sun at sunrise and
sunset throughout the year.
And, get a copy of Sellers and look at those diagrams. They are important
tools for architectual design. I suspect the diagrams have been reproduced
elsewhere.
When I get a chance, I'll pull out my copy of Sellers, look at some topos of
NYC, and revisit this discussion. BTW; how did folks work out Stonehenge
without the use of email?
Jim Carter, Illinois State University
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: Wed, 28 Jun 1995 15:19:08 -0700
: [log in to unmask] (Paul R. Larson)
: Re: Sunrise...Sunset...180 Degrees
>----------------------------Original message----------------------------
>
>
> 180 degrees from sunrise to sunset could never happen north of
> Cancer or south of Capricorn. Regardless of the time of year north of
> Cancer, sunrise is still in the southeast with sunset in the southwest,
> just at varying degrees. South of Capricorn, sunrise is always in the
> northeast and sunset in the northwest. Only between Cancer and
> Capricorn could you ever have 180 degrees from sunrise to sunset since
> it is only in that range that the Sun would ever pass directly
> overhead. At least that's as I understand it...
>
> Eric
The above explanation misses something.
A question on my physical geography test goes as follows:
"If the vertical sun at the June solstice only reaches 23.5 degrees North
latitude, why does the early morning and late evening sun shine directly
into the windows on the NORTH side of my house, which is located at 40
degrees north latitude?"
The answer, of course, is that the path of the sun across the sky is an
arc, not a straight line. The earth is a spheriod, not a cylinder. At
solar noon on the June solstice, the sun is to the south of my position (40
degrees North latitude) at an altitude of 72.5 degrees above the horizon.
But, in the morning and evening, the sun is rising and setting in the
northeast and northwest respectively. At equinoxes the sun rises directly
east (90 degrees) at every point on the earth. (Use a globe and check it
out.) As the position of the vertical sun moves toward the north following
the March equinox, it rises in the northeast and sets in the northwest (for
the entier six month period). It then crosses the sky in an arc, reaching
its highest point at noon, as noted above. That is why streets oriented
from northwest to southeast in Manhattan are parallel to the Sun's rays at
sunset on the June solstice. At the December solstice, sunrise should be
just the opposite, or parallel to the streets from the other direction.
At this time of year in Tennessee you will note the same phenomenon. The
sun at sunrise and sunset will be illuminating the NORTH side of buildings.
Sunrise and sunset are not in the southeast and southwest from the March
equinox until the September equinox. Use a globe to help you visualize
this phenomenon. Tilt the globe as it would be at the solstice. Position
yourself as if you were the Sun, with the axis inclined directly toward
you. Then, place a small block of wood or other object, at your latitude.
Rotate the globe from sunrise to sunset. At sunrise and sunset, which side
of the block do you see?
I do not like to use the terms Summer solstice and Winter solstice, nor
Spring and Autumn equinox. These terms only apply to one hemisphere while
the other hemisphere is exactly opposite. In order to make the terms
applicable to the entire globe, I refer to them as June and December
Solstice, and March and September equinox.
I hope that this will shed some "light" on the subject.
Paul R. Larson
Assistant Professor, Geography
SC 309
Southern Utah University
Cedar City, Utah 84720
tel: (801) 865-8244
fax: (801) 865-8051
E-mail [log in to unmask]
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