naap_basic_coordinates_and_seasons_sg (1)
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Dec 6, 2023
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Basic Coordinates & Seasons – Student Guide
There are three main sections to this module: terrestrial coordinates, celestial equatorial
coordinates, and understanding how the ecliptic is related to seasons on the Earth. Each of these
sections has its own simulator(s). The background material necessary to utilize these tools is
contained in each section.
Terrestrial Coordinates
Work through the explanatory material on
units of longitude and latitude
,
finding longitude and
latitude
, and
a bit of history
(optional).
Open the
flat map explorer
.
Familiarize yourself with the cursor and how it prints out the longitude and latitude of the
active map location.
Note that you can vary the central meridian of the map (i.e. change its longitude). Use the
“shift map” arrows at the top of the simulator to affect large rapid changes. Use the shift-
click feature of the cursor for finer control.
Note what information is accessible through the
show cities
and
show map features
check
boxes.
Center the cursor on your present location. Click the open Google Maps button to launch
the Google Map tool focused on this location. Experiment until you get a good feeling for
the Google Map’s capabilities and then close this window. (Note that you must be
connected to the Internet to make use of this feature.)
Question 1: Use the flat map explorer to complete the following table. You are encouraged to try
and predict the answers and then use the map’s cursor and other features to check the accuracy of
your estimates.
Location
Longitude
Latitude
Southern tip of Greenland
88.2º E
22.6º N
Prime Meridian
51.8º N
46.6º W
Tropic of Capricorn
McMurdo Station, Antartica
77.2º W
38.5º N
149.1º E
35.5º S
NAAP – Basic Coordinates & Motions 1/9
Question 2: Determine which of the 50 states defines the farthest extent of the United States in
each of the 4 map directions.
Direction
State
North
South
East (there are two ways
of thinking about this)
West
Question 3: The exact coordinates of Wisconsin’s State Capitol Building are 89.38422º W and
43.07472º N. What are these exact coordinates in sexagesimal notation? Show your calculation
in the box below. (You can use the Google Map tool to check your answer.)
Open the
globe explorer.
You are encouraged to use the Terrestrial Coordinate Explorers
link which opens both simulators at the same time for the following two questions.
Familiarize yourself with the features noting that they are very similar to those in the flat
map explorer.
Question 4: A) Where is the south pole on the
flat map explorer
? What is its shape?
B) Where is the south pole on the
globe explorer
? What is its shape?
C) Your answers to parts A and B should be different. Explain why.
NAAP – Basic Coordinates & Motions 2/9
Question 5: Compare the relative sizes of Greenland and Australia in the two maps? The true
values of the surface areas for these countries are Greenland (2.2 million km
2
) and Australia (7.7
million km
2
). Does each map demonstrate these true values?
Celestial Equatorial Coordinates
Work through the introductory material on the page entitled
Celestial Equator, Declination,
Right Ascension
.
Open either the
Flat Sky Map Explorer
or the
Sky Map Explorer
.
Familiarize yourself with the same set of features (cursor movement, shifting the map,
decimal/sexagesimal) that were available on the previous maps.
Make sure that you understand what each check box does.
Question 6: Where is the star Polaris located on this map? What are its coordinates?
Question 7: Find the constellation known as the “Big Dipper” shown in the box below and
measure the right ascension and declination of the two stars indicated. Note that the Big Dipper
is located at a declination of around +60º.
NAAP – Basic Coordinates & Motions 3/9
RA
DEC
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Question 8: Which direction is east on the flat sky map? Relate this to a coordinate of the
celestial equatorial system (Right Ascension or Declination).
Question 9: Complete the following table of positions on the ecliptic.
Ecliptic Location
Approximate Date
Right Ascension
Declination
Vernal Equinox
March 21
Summer Solstice
June 21
Autumnal Equinox
December 21
Question 10: Write out a description of the ecliptic on the flat sky map. What does the shape look
like? Describe the ecliptic in terms of its average and range of declination values.
Seasons and the Ecliptic
Work through the introductory material on the page entitled
Orbits
and Light
.
Open the
Seasons and Ecliptic Simulator
.
Note that there are three main panels (left, upper right, and lower right) each of which
have two different views. Controls run along the bottom of the simulation that affect
NAAP – Basic Coordinates & Motions 4/9
RA
DEC
more than one panel. Click animate and then move through the six views to get an
overview this simulator’s capabilities. We will address each of these six views separately.
Experiment with the various methods to advance time in the simulator. You may click the
start animate/stop animation button, drag the yearly time slider, or drag either the sun or
the earth in the left panel to advance time.
Note that this animation does not illustrate the rotation of the earth. Because the
timescales of rotation and revolution are so different, it isn’t possible to effectively show
both simultaneously.
NAAP – Basic Coordinates & Motions 5/9
Left Panel – Orbit View
Practice clicking and dragging in this panel to change the
perspective. Change the perspective so that you are
looking directly down onto the plane of the Earth’s orbit
Click labels. Note that you can see how the direct rays of
the
sun hit at different latitudes throughout the year.
Experiment with this view until you can quickly create the two views shown below. Note
that these images explain the shape of the elliptic on the celestial sphere. In the image on
the left (summer solstice) an observer on the Earth sees the sun above the celestial
equator. In the image on the right (winter solstice) an observer on the Earth sees the sun
below the celestial equator.
Left Panel – Celestial Sphere
This view shows the earth at the center of the celestial sphere. The
celestial equator and the ecliptic with the sun’s location are shown.
Note that you may click on the sun and drag it and read out its
coordinates.
Experiment with this view until you can quickly create the image to
the right – the direct rays of the sun hitting the earth on the summer
solstice.
Upper Right Panel – View from Sun
This view shows the earth as seen from the sun. It gives the best
view of the subsolar point – the location on the earth where the
direct rays of the sun are hitting. The noon observer’s location on the
Earth is indicated by a red parallel of latitude which can be dragged
to new latitudes (this affects the appearance of the lower right panel).
It is possible for the red parallel to be at an inaccessible location in
this view.
Create the image shown to the right – an observer at latitude 80°N
on the summer solstice.
NAAP – Basic Coordinates & Motions 6/9
Tip:
Note that if you
click and drag the
Earth,
you
will
change the date and
location rather than
the perspective.
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Upper Right Panel – View from Side
This view shows the earth as seen from a location in the
plane of the ecliptic along a line tangent to the Earth’s
orbit. It allows one to easily see the regions of the Earth
that are in daylight and those that are in shadow.
Dragging the stick figure allows one to very conveniently
change latitude. Dragging the stick figure on top of the
subsolar point effectively puts the observer at the latitude
where the direct rays of the sun are hitting.
Although rotation is suppressed in this simulation, keep in
mind that the stick figure is on a planet that is rotating with a
period of 24 hours about an axis connecting the north and
south poles. Thus, 12 hours later it will be on the other side
of the earth.
Set up the simulator for the image at right – the winter solstice for an observer at 80
N.
Since this observer’s parallel of latitude is located entirely in the shaded region, this
observer will not see the sun on this day.
Lower Right Panel – Sunbeam Spread
This view shows a “cylinder” of light coming from the sun. It is projected on a grid to
convey the area over which the light is spread. As this light is spread over a larger area,
its intensity decreases.
Lower Right Panel – Sunlight Angle
This view shows the angle with
which rays of sunlight are striking
the Earth. It lists the noon sun’s angle
with respect to the horizon (its
altitude).
Verify that when the noon observer is
at the latitude where the most direct
rays of the sun are hitting, the sun is
directly overhead making an angle of
90
with the ground.
Verify that when the noon observer is
at the latitude where the least direct
rays of the sun are hitting, the sun is
on the horizon.
NAAP – Basic Coordinates & Motions 7/9
Tip:
Once the stick figure
is selected you can gain
greater precision over its
motion by
moving the
mouse a distance away
from the figure.
Question 11: The table below contains entries for the coordinates for the sun on the ecliptic as
well as the latitude at which the most direct and least direct rays of the sun are hitting. Use the
simulation to complete the table.
Date
RA
DEC
Latitude of
Most Direct
Latitude of Least
Direct Ray
February 15
March 21
May 15
2.9 h
+16.5°
16.5° N
73.5° S
June 21
August 15
September 21
November 15
December 21
Question 12: Using the data in the table above, formulate general rules relating the declination of
the sun to the latitude where the most direct and least direct rays of the sun are hitting.
Question 13: The region between the Tropic of Cancer and the Tropic of Capricorn is commonly
known as the tropics. Using the sunlight data table above, define the significance of this region.
Question 14: Using the sunlight data table from question 11, define the significance of the region
north of the Arctic Circle commonly referred to simply as the Arctic.
NAAP – Basic Coordinates & Motions 8/9
Question 15: Use the simulator to complete the table below. For each latitude write a short
paragraph which describes the variations in sunlight (seasons) that are experienced at this
latitude throughout the year.
Latitude
Description of Yearly Pattern of Sunlight
0°
The noon sun’s angular height above the horizon ranges from 90° on the
vernal equinox, to 66.5° on the summer solstice, to 90° on the autumnal
equinox, and back to 66.5° on the winter solstice. Thus, the equator always
receives very direct intense sunlight throughout the year which accounts for
the very high temperatures.
23.5° N
45° N
66.5° N
90° N
NAAP – Basic Coordinates & Motions 9/9
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