Transcript Slide 1
There are 2 different motions involved in this diagram.
The first is the daily motion of the sun as it rises in the east
There are 2 different motions involved in this diagram.
The first is the daily motion of the sun as it rises in the east and then sets in the west at 15 °/hr.
Since the June path is longer than the December path the sun is in the sky for more hours in the summer than in the winter.
D e c J u n
But there is also the annual change in the position of sunrise and sunset.
In June the sun rises north of east and sets north of west.
June Sunset position D e c N o v t O c S e p A u g l J u J u n June Sunrise position
And in December it rises south of east and sets south of west.
Then, after the winter solstice, the sunrise and sunset positions begin moving north until it is summer once again.
December Sunset position December Sunrise position D e c J a n F e b M a r A p r M a y J u n
The Sun follows the middle path on both the Vernal and Autumnal Equinoxes. On the equinoxes the sun rises due east and sets due west everywhere on Earth and everywhere there are 12 hours of daylight and 12 hours of night.
When the Sun’s path touches this line it has reached its highest point in the sky for the day.
the
zenith
. That time is called
solar noon.
That point is called
The protractor shows the noon
altitude
of the sun. For example, the altitude of the noon sun in NY on June 21 st is about 70 ⁰.
J u n e
The noon altitude in NY on December 21 st is only about 23 ⁰
D e c
The higher the noon altitude of the Sun, the greater the intensity (strength) of the
insolation
(sunlight).
That’s why the noon sun is so much more intense in June........
Than in December.
D e c J u n e
There are two reasons why it’s warmer in summer than in winter: First, the sun is higher in the sky (more intense insolation) in the summer than in the winter.
And second, in the summer the Sun is in the sky for more hours a day which means more time for the Earth to soak up the rays and get warm.
But only about 9 hours and15 minutes on December 21st New York city receives more than 15 hours of insolation on June 21 st .
That’s a difference of nearly 6 hours of daylight!
D e c J u n
Notice that a red pole has been placed in the center of the field. You may be asked to draw the shadow of that pole at noon on any given day.
For example, draw the shadow of the pole at noon on March 21 st .
First, find the Sun’s path for March 21st. (It’s the one in the middle) Then use a straight edge or ruler to lightly draw a line from Sun’s noon position, the
zenith
..... past the tip of the pole, to the ground (dotted line.)
Now draw a line (the shadow) from the base of the pole to the dotted yellow line.
Now let’s draw the shadow of the pole as it would appear at noon on December 21 st .
Find the December 21 st path. December 21 st has the fewest hours of daylight so it must be the shortest path. Now draw a line from the December zenith, past the tip of the pole, to the ground.
Draw the shadow from the bottom of the pole to the yellow line.
Notice that the December shadow (red line) is much longer than the March shadow (blue line).
As the altitude of the Sun increases, the length of a shadow decreases.
In the summer the Sun is here at noon.
In the winter it is here.
On any other day it must be somewhere in between.
But on how many days is the Sun directly overhead, 90 °, at noon?
The Sun is never directly overhead anywhere in the United States (except for Hawaii)!
Lastly, let’s look at the relationship between the position of the sunrise in NYS and the location on the Earth where the Sun’s rays are directly overhead, 90 °.
When the Sun rises
north
of east in NYS as on the summer solstice.......
its direct rays fall on the Tropic of Cancer, 23.5
°
north.
When the Sun rises due east as it does on both
equ
inoxes.....
its direct rays fall on the
equ
ator And when the Sun rises
south
of east in NYS as on the winter solstice.... its direct rays fall on the Tropic of Capricorn, 23.5
°
south
What you must understand and know how to do....
For both solstices and both equinoxes.........................
> Know the location of sunrise and sunset > Know the approximate altitude of the Sun at noon.
> Know when the intensity of insolation is least and when it is greatest > Know the relationship between the altitude of the Sun and shadow length > Know how to draw the shadow of a pole on a given date > Know where (latitude) the Sun’s direct rays are falling on the Earth > Know when the duration of insolation is greatest and when it is shortest > Be able to draw the path of the Sun for a given date > Know that the Sun is never directly overhead anywhere in New York