Geography 410/510—Assignment 1 - Portland State University



Earth-Sun Relationship

Due Date: Tuesday October 15, 2002

NAME ___________________

1. Introduction

The purpose of this assignment is to introduce you to some of the important aspects of earth-sun relationship. In class I showed the seasonal path of the earth using the globe and slide projector (sun). Make sure that you need to understand these fundamental relationships by drawing the relative positions of the following features: Earth’s axis, North and South Poles, Equator, circulation of illumination, subsolar point, Tropic of Cancer and Capricorn, Arctic and Antarctic Circles. Use the circles provided in the next section to draw these. (each 1 point, 10 points total for each diagram)

2. Sun angle

As you recall, the earth’s axis remains a constant tilt with respect to the solar system as the Earth revolves (axial parallelism). Thus, the latitude of the subsolar point, known as the Sun’s declination, changes with seasons, and the angle of the sun’s rays striking any given place on Earth changes throughout the year.

As I told you in class, the noon sun angle can be estimated by the simple formula

90 º - latitude (± declination of the Sun)

In other words, for equinox conditions, when the subsolar point is at the Equator (declination = 0º), the noon angle for any place on earth is simply 90 º - latitude

For solstice conditions,

If the sub-solar point is “in” the hemisphere of the place in question, add 23.5º

If the sub-solar point is “out” the hemisphere of the place in question, subtract 23.5º

*** Angles should NOT exceed 90º !!!.

EQUINOXES – March 21 or September 23

At what latitude is the noon sun directly overhead on this date? ___________

What is the noon sun angle (altitude) for

90 ºN ________ 23.5 ºS ________

66.5 ºN ________ 40 ºS ________

40 ºN ________ 66.5 ºS ________

23.5 ºN ________ 90 ºS ________

0 ºN ________

Sun’s Rays

OUR SUMMER SOLSTICE – June 21

At what latitude is the noon sun directly overhead on this date? ___________

What is the noon sun angle (altitude) for

90 ºN ________ 23.5 ºS ________

66.5 ºN ________ 40 ºS ________

40 ºN ________ 66.5 ºS ________

23.5 ºN ________ 90 ºS ________

0 ºN ________

Sun’s Rays

OUR WINTER SOLSTICE – December 22

At what latitude is the noon sun directly overhead on this date? ___________

What is the noon sun angle (altitude) for

90 ºN ________ 23.5 ºS ________

66.5 ºN ________ 40 ºS ________

40 ºN ________ 66.5 ºS ________

23.5 ºN ________ 90 ºS ________

0 ºN ________

Sun’s Rays

3. Day length

The duration of solar energy received at a location is a function of the length of time in the Sun above the horizon.

3.1 On what dates are the lengths of day and night exactly equal for all locations on the globe?

________________ & __________________

At the June 21 solstice (our summer solstice)

3.2 What portion of the Earth’s surface is exposed to the Sun’s rays for 24 hours?

____________________________________

3.3 What portion receives no radiation in a 24 hour period?

____________________________________

3.4 Day length at the Equator will be _____hrs

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