EARTH SUN RELATIONSHIP

Note: Please refer to the GETTING STARTED lab module to learn tips on how to set

up and maneuver through the Google Earth ( ) component of this lab.

KEY TERMS

The following is a list of important words and concepts used in this lab module:

Analemma Equation of time Solstice

Aphelion Equinox Sphericity

Axial parallelism Insolation Subsolar point

Axial Tilt International Date Line Sun Angle

Circle of illumination NDVI Sun-fast, Sun-slow

Coordinated Universal Time (UTC) Perihelion Time zones

Daylight saving time Revolution

Declination of Sun Rotation

LAB MODULE LEARNING OBJECTIVES

After successfully completing this lab module, you should be able to:

● Compute differences in time between two location

● Recognize and demonstrate how time zones work

● Differentiate the changes in the circle of illumination over the course of a

year

● Identify and describe the reasons for the seasons

● Infer vegetation as an indicator for seasonality

● Read and interpret an analemma

● Calculate the Sun’s declination for a given location and date

● Compute the equation of time for a given location

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INTRODUCTION

This lab module examines fundamental Earth-Sun relationships. Topics include time

zones, the equation of time, analemma, declination, solstice and equinox, the

reasons for seasons, and the seasonal migration of the subsolar point. While these

topics may seem disparate, you will learn how they are inherently related.

The modules start with four opening topics, or vignettes, found in the

accompanying Google Earth file. These vignettes introduce basic concepts related to

Earth-Sun relationships. Some of the vignettes have animations, videos, or short

articles that will provide another perspective or visual explanation for the topic at

hand. After reading each vignette and associated links, answer the following

questions. Please note that some components of this lab may take a while to

download or open, especially if you have a slow internet connection.

Expand EARTH-SUN RELATIONSHIPS, and then expand the INTRODUCTION

folder. Double click Topic 1: Earth-Sun Relations.

Read Topic 1: Earth-Sun Relations.

Question 1: Looking at the maps, which of the following best showcases the

uneven balance of insolation – and resulting seasonality – on planet Earth?

A. Most of the northern hemisphere is free of ice and snow year round

B. Most of the northern hemisphere is covered in ice and snow year round

C. Most of the northern hemisphere shows ice and snow advancing in the

July

D. Most of the northern hemisphere shows ice and snow retreating in July

Read Topic 2: Reason for Seasons. (Note: If you are having issues watching

the animation, please check to see if the movie has been downloaded rather than

automatically playing via the webpage)

Question 2: Why does each hemisphere receive the same amount of energy

from the Sun on the March and September equinoxes?

E. The subsolar point is aligned with the Tropic of Cancer

F. The subsolar point is aligned with the Tropic of Capricorn

G. The subsolar point is aligned with the Equator

H. The subsolar point is aligned with the North Pole

Read Topic 3: Time Zones.

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Question 3: What was the main reason for instituting standard time (time

zones)?

A. To end confusion in communities using their own solar time

B. To help astrologers forecast urban growth patterns

C. To reaffirm England’s world dominance

D. To validate the Meridian Conference of 1884

Read Topic 4: Human Interactions.

Question 4: Name 3 reasons ancient cultures used stone structures or

modified natural formations regarding Earth-Sun or Earth-Moon relationships.

A. To chart seasons, create calendars, and celebrate birthdays

B. To monitor eclipses, mark deaths, denote holidays

C. To chart seasons, monitor eclipses and create calendars

D. To celebrate birthdays, mark deaths and denote the end of days

Collapse and uncheck the INTRODUCTION folder.

GLOBAL PERSPECTIVE

I. Coordinated Universal Time (UTC)

The Earth is divided into 24 time zones, one for each hour of the day. Earth’s 24

time zones are approximately 15° wide – a width calculated from the number of

degrees in a sphere divided by the number of hours in a day (360°/24hr =

15°/hour). Noon (12pm) occurs roughly when the Sun is at its highest point in the

sky each day. For example, noon in New York is three hours before noon in Los

Angeles because there is (approximately) a three hour difference in when the Sun

is at its zenith.

Expand the GLOBAL PERSPECTIVE folder and then expand and select the

Universal Time Coordinated folder.

Time zones are as much a Sun-Earth relationship as they are a human construct

used to standardize time. The Prime Meridian – which signifies 0 degrees latitude

and passes through Greenwich, England – is the starting reference line for time

zonation. Time zones are relative to Greenwich Mean Time (GMT) or more

appropriately, the Coordinated Universal Time (UTC). Examples are New York City,

USA in the winter at UTC -5 (or 5 hours behind UTC), or Manila, Philippines at

UTC+8 (or 8 hours ahead of UTC). In other words, when it is 8am in New York, it is

9pm in Manila.

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As you can see in Google Earth, time zones do not always follow straight lines from

pole to pole because of political, economic, or geographic reasons. Time zone

anomalies include the following:

Time Zone Anomaly Example

Time zone extends far greater or lesser

than 15 degrees.

China is one time zone.

Time zones shifts significantly eastward

or westward.

Iceland shifts 2 time zones to be UTC 0.

Time zone does not follow the 1-hour

system. Instead, a partial time-zone unit

is used.

Newfoundland, Canada is 3:30 UTC

(summer 2:30 UTC), while Nepal is 5:45

UTC

Double-click São Paulo, Brazil. You might have to pan northward to find the

time zone label near the Equator.

Question 5: In what UTC time zone is this city located?

A. UTC -2

B. UTC -3

C. UTC +2

D. UTC+3

Question 6: If UTC 0 time is 1pm, what is the standard time for this city?

A. 10 AM

B. 11 AM

C. 3 PM

D. 4 PM

Double-click Cape Town, RSA. You might have to pan northward to find the

time zone label near the Equator.

Question 7: In what UTC time zone is this city located?

A. UTC -1

B. UTC -2

C. UTC +1

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D. UTC+2

Question 8: If UTC 0 time is 1pm, what is the standard time for this city?