Name:_____________________________
Class Meeting Time__________________
Earth-Sun Relations Homework
(refer to diagram below and figs. 1-21, 1-22, & 1-23 in the text)
1. What is the latitude of the direct rays of the sun on June 21?
__________
2. (a) What is the latitude of the tangent
rays (those that just barely intercept the
earth and would appear on the horizon to
a viewer) in the Northern Hemisphere on
June 21?
_____________
(b) What is the latitude of the tangent
rays in the Southern Hemisphere on June
21? _____________
3. Why is the June Solstice associated with
Southern Hemisphere winter?
4. Notice the orientation of the circle of illumination on this day.
(a) Does the equator receive more day or night on this day?
(b) Does day become longer or shorter as you move southward from the equator?
(c) How many hours of daylight are experienced between 66.5O - 90O N on this day?
_____________
(d) Why?
Solar Angle
The direct (or overhead) rays of the sun will strike the earth's surface at the Tropic of Cancer (23.5O N)
on June 21, at the equator on the equinoxes, and at the Tropic of Capricorn (23.5O S) on December 21.
The latitude of these direct rays is called the declination of the sun. A graphic device called an
analemma (see attached Figure) allows us to determine the declination on any day of the year.
Problem:
It is valuable to know what the maximum angle of the sun will be on a given day at any location.
Higher maximum sun angles are higher energy; conversely, lower maximum sun angles are lower energy. This
angle can be calculated for any location by first calculating the total difference (in degrees) between the latitude of
your chosen location and the declination for that day. Then, subtract this number from 90. In other words: Solar
Altitude = 90 - Angular Distance . Calculate the maximum angle of the sun in Los Angeles on the following dates:
Los Angeles
Latitude
June Solstice?
September Equinox?
December Solstice?
March Equinox?
Declination
Difference*
Maximum Sun
Angle**
34 North
34 North
34 North
34 North
*This difference is in degrees only; it is not a latitude! Also, you will need to be careful when the declination is in
the Southern Hemisphere. Under this circumstance, you may NOT subtract to find the difference. THINK!!!
**Again, the answer here is in degrees only; it is not a latitude!!!!!!
Test Questions:
6. The Angle of the Sun above the horizon at noontime:
(a)
Changes 47 degrees from Solstice to Equinox
(b) Changes 47 degrees from Solstice to Solstice
(c) is the way to measure longitude
(d) is the lowest the sun will be that day
(e) stays the same throughout the year
7. The seasons are caused by:
a. The tilt of the axis of the earth with respect to the plane of the ecliptic
b. the shape of the elliptical orbit of the earth around the sun
c. The orbit of the moon around the earth
d. changes in the energy output of the sun itself
e. none of these
8. The two most important things which determine the amount of energy falling on a location in one
day are:
a. the changing strength of solar rays
b. the angle of the sun upon the surface (solar altitude)
c. the albedo of the surface
d. the duration of daylight
e. none of these
True or False (bubble in A for true, B for false)
9. Summer is the time from the Equinox to the Summer Solstice.
10. The axis of the earth points to the north star all year.
11. There are always 12 hours of daylight and 12 hours of darkness at the poles.
12. Duration of daylight and solar altitude work together to increase differences between summer and
winter.
13. Summer and winter are reversed in time between the Southern and Northern Hemispheres.
ABC
ABD
AE
N
N
A
AD
B
AC
AB
D
C
Sun
E
S
Choose your answers from the list below:
11. Tropic of Cancer
12. Arctic Circle
13. 66.5O N
14. Twenty four hours of darkness
15. Drawing showing Southern Hemisphere summer
16. Drawing showing Northern Hemisphere winter
17. Overhead rays of the sun on June 21
18. Plane of the Ecliptic
S