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Course
1421.90L
Subject
Astronomy
Date
Apr 29, 2024
Type
Pages
8
Uploaded by noneya12456
Physical Science 1421
Seasons
Equipment Needed
Quantity
Equipment Needed
Quantity
Seasons Simulator (NAAP) - UNL
Astronomy
1
Seasons Excel File
1
The purpose of this laboratory activity is to study how the position of the Earth in space, the Earth’s
tilt, direct light, and indirect light combine to produce a phenomenon that we call Seasons.
Part 1: Background
Position of Earth in Space
The shape of the Earth is an ellipsoid; however for most practical educational purposes we
approximate its shape to a sphere. It can be divided into two hemispheres, the Northern Hemisphere and
Southern Hemisphere. On the top of the Northern Hemisphere is the North Pole and the bottom of the
Southern Hemisphere is the South Pole. The Earth’s axis is an imaginary line running from the North to
the South poles. The Earth spins on its own axis all the time, turning around completely once every 24
hours. The rotation of the Earth about its axis is what provides us with the alternation between day and
night. What do you think makes the seasons happen?
Direct and Indirect Light
The Earth is actually tilted 23.5
o
from the plane of the ecliptic (the plane the planets orbit about the
Sun). It should look like this:
Figure 1 the Earth
Figure 2 Light as it hits the surface.
In the left (Figure 2), the light is striking the paper at an angle. That is, it is shining on the surface
with indirect light. In the right, the light is striking the paper perpendicularly. That is, it is shining as a
direct light. Direct light produces more heat (gives more rays per area and therefore more energy per
area) than indirect light (where light striking a surface at an angle spreads out).
Length of Day and Night
During the year the length of a day changes, due to the tilt of the Earth. The Sun rises earlier in the
summer than in the winter and sets later in the summer than in the winter. The table below gives the time
of sunrise and sunset for three latitudes.
0
o
latitude
30
o
N latitude
60
o
N latitude
Date
Sunrise
Sunset
Sunrise
Sunset
Sunrise
Sunset
Jan. 1
6:00
18:08
6:56
17:12
9:02
15:06
Feb. 1
6:10
18:18
6:51
17:37
8:15
16:13
Mar. 1
6:09
18:16
6:28
17:58
6:55
17:30
Apr. 1
6:00
18:07
5:49
18:19
5:24
18:45
May 1
5:53
18:00
5:17
18:37
3:56
19:59
June 1
5:54
18:01
5:00
18:56
2:48
21:08
July 1
6:00
18:08
5:02
19:05
2:40
21:26
Aug. 1
6:02
18:10
5:18
18:55
3:36
20:34
Sep. 1
5:56
18:03
5:44
18:22
4:50
19:10
Oct. 1
5:46
17:53
5:53
17:45
6:03
17:36
Nov. 1
5:40
17:48
6:13
17:14
7:24
16:04
Dec. 1
5:45
17:54
6:38
17:00
8:35
15:03
Table 1
Sunrise and sunset times at different latitudes throughout the year
The Seasons
As mentioned in the previous section, the Earth’s rotation axis is tilted 23.5
o
throughout the year
pointing the same direction in space. The Earth moves around the Sun once every year. It follows an
elliptical orbit. This means that it goes almost in a circle around the Sun, but gets a little further away at
some times. The path it takes is like an oval.
p. 2
Figure 3 Orbit of Earth around the Sun
As you can see, because the Earth is tilted, some parts of it get direct light while other parts get
indirect light. Therefore, the amount of heat that the Earth’s surface receives is not evenly distributed.
Figure 4 shows that when the Northern hemisphere is tilting towards the Sun, sunlight falls most
directly on it. This is
Summer
in the Northern Hemisphere. As the Earth moves around to the other side
of the Sun the Northern Hemisphere is tilted away from the Sun therefore light falls indirectly on it. It is
Winter
in this hemisphere.
Notice that the exact opposite is happening in the Southern hemisphere. When the Northern
Hemisphere has Summer, the Southern Hemisphere has Winter. Now, how do we determine which has
Spring and which has Fall? This is simple:
Spring
follows Winter and
Fall
follows Summer!
Figure 4 Position of the Earth relative to the Sun. The seasons are written for the northern
hemisphere.
Summary
Most places on Earth experience four seasons every year. These are
Spring
,
Summer
,
Fall
(or
Autumn) and
Winter
. Here we are going to find out why we have different seasons.
The seasons are caused by a combination of two things:
A.
Earth’s axis is tilted as it moves around the Sun.
p. 3
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B.
Direct sunlight produces more heat than indirect light.
Note: Although there are changes in the distance between the Sun and Earth during the year (because of
the Earth’s elliptical orbit), these changes are relatively small (that is, Earth’s orbit around the Sun is
almost circular). As a consequence of this, in the case of Earth, the changes in surface temperature
during the year are due to the changes in the directness/indirectness of the Sun’s light as Earth orbits
around it. The effect on temperature due to changes in Sun-Earth distance is negligible compared to the
effect on temperature due to the changes of directness/indirectness of the sunlight during the year.
Part 2: Lab Activity
Length of Day and Night
A. Graph 1
Start with the 30
°
latitude data from the table and make a rectilinear graph, showing the
length of the day and night for the city of Houston (Texas) at latitude 30
o
N, using Table 1 and
following the steps below:
1.
Open the document titled Seasons.xlsx in Blackboard.
2.
Click the 30
°
latitude tab on the bottom left of the page.
3.
Fill out the column for the sunrise at 30
°
latitude using Table 1. Make sure that you convert
the time into hours only. This is done by dividing the minutes by 60. Add the quotient to the
hours.
ex.
Convert the minutes by dividing by 60.
6:56 -
= .933333
or .93 mins.
56
60
3
6.93 is the new value you will enter into the table in Excel. You must convert all the mins first,
leave the hours the same.
(note: leave the hours in military time)
4.
Fill out the column for “Sunset at 30 latitude”.
5.
Entering the converted times into the table will begin to input the points on the Graph. once
you enter the times for “Sunrise” and “Sunset”, answer the questions in the lab report section.
B. Graph 2
p. 4
Sunrise
6:56
Complete the rectilinear graph you have started so it shows the time of sunrise and sunset
for each of the three latitudes of Table 1. Follow the steps bellow:
6.
Repeat step 2 and 3 for the sunrise and sunset at 0
°
and 60
°
latitude. To complete the two
graphs be sure to click the appropriate tabs. Once you are done with the graphs, answer the
questions in the lab report section.
The Seasons
In this section of the lab you will use “Seasons Simulator (NAAP) - UNL Astronomy”
Go to the URL
https://astro.unl.edu/classaction/animations/coordsmotion/eclipticsimulator.html
1.
In the simulator, be sure that the “orbit view” and “show subsolar point” are checked.
2.
Next, make sure the “labels” is clicked as well. By clicking on the labels tab, you will be able to see
where the sun is when it is directly above Earth. You may also move the little stick figure up or
down depending where the Sun is directly above. This will help with answering some of the lab
report questions.
A. Summer Solstice
With your mouse, position it on the sliding tab at the bottom, click and move the tab to the June
21, known as the Summer Solstice position (shown in Fugure 4 as “Summer”)
p. 5
The Summer Solstice is the most northern position of the Sun during the year. At this time,
we have the longest day in the Northern Hemisphere.
Click on “start animation” and observe how the light shines on the Arctic Circle, the Tropic
of Cancer, the Equator, the Tropic of Capricorn, the Antarctic Circle and the regions in between.
Let the animation run for two months, after this time, the earth begins to tilt. Stop the animation
and move the tab back to June 21
st
to restart.
Answer the questions in the lab report section.
B. Fall Equinox
Change the date to September 21. This is the relative position of the Earth and the Sun on
September 21 or the Autumnal (Fall) Equinox position (shown in the Figure
4 as “Autumn”). The Autumnal (Fall) Equinox corresponds to the Sun’s position as it crosses
the celestial equator going south. At the equinoxes, day and night are equal in length.
Start the animation and observe how the light shines on the Arctic Circle, the Tropic of
Cancer, the Equator, the Tropic of Capricorn, the Antarctic Circle and the regions in between. Let
the animation run for two months and stop, reset and start again.
Answer the questions in the lab report section.
C. Winter Solstice
Change the date to December 21. This is the
Winter Solstice
(shown in Figure 4 as
“Winter”) position. The
Winter Solstice
is the most southern position of the Sun during the year.
At this time we have the shortest day in the Northern Hemisphere.
Start animation and observe how the light shines on the Arctic Circle, the Tropic of Cancer,
the Equator, the Tropic of Capricorn, the Antarctic Circle and the regions in between.
Answer the questions in the lab report section.
Record your results in the Lab Report.
*Figures 1 and 4 by Klaus Kästle, Publisher & Editor-in-Chief, Nations Online Project
p. 6
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Name Cianna Hernandez, Anastasia Hernandez, Kimberly Hernandez, Frenesi Jimenez, Juan Pablo
Gonzalez Class ________PSCI 1421 C _____________
Date ______3/4/24_______
Part 3: Lab Report – Seasons
Length of Day and Night
A. Graph 1
From the graph answer the following questions:
1)
In which month Houston has the maximum hours of daylight? _____
_June_
________
2)
In which month Houston has the minimum hours of daylight? _
December_
_______________
3)
In which month Houston has the maximum hours of darkness?__
_December__
__________
4)
In which month Houston has the minimum hours of darkness?______
_June___
_____
B. Graph 2
1)
How many hours of daylight are there at 0
o
latitude on July 1?
12 hours and 13 minutes
2)
How many hours of daylight are there at 30
o
latitude on July 1?
14 hours and 5 minutes
3)
How many hours of daylight are there at 60
o
latitude on July 1?
18 hours and 76 minutes
4)
How many hours of daylight are there at 0
o
latitude on January 1?
12 hours and 13 minutes
5)
How many hours of daylight are there at 30
o
latitude on January 1?
10 hours and 27 minutes
6)
How many hours of daylight are there at 60
o
latitude on January 1?
6 hours and 7 minutes
The Seasons
A. Summer Solstice
1)
Which region has 24 hours of daylight?
Artic
2)
Which region has 24 hours of darkness?
Antarctic
3)
Note the direction at which the light strikes the Earth’s surface in both the northern and
southern hemispheres. Which hemisphere of the globe is having summer?
Northern
4)
Where on the Earth is the Sun directly overhead at noon?
Tropic of cancer
5)
Why is June 21 called the Summer Solstice?
p. 7
Because of the tilt of the planet's semi-axis either the northern or southern hemisphere is
moved toward the star orbits
B. Fall Equinox
1)
Where on Earth is the Sun directly overhead at noon?
Equator
2)
Why is September 21 called the Fall Equinox?
The sun crosses the plane of the Earth's equator, making night and day approximately equal
length all over Earth
3)
Note the direction at which the light strikes Earth’s surface in both the northern and southern
hemispheres. What season are we having in the Southern Hemisphere?
Spring
4)
Is there a region that has 24 hours of daylight? If so, which region?
None
C. Winter Solstice
1)
Where on Earth is the Sun directly overhead at noon?
The tropic of capricorn
2)
Which region has 24 hours of daylight?
The south antarctic circle
3)
Which region has 24 hours of darkness?
The north antarctic circle
4)
Note the direction at which the light strikes Earth’s surface in both the northern and southern
hemispheres. Which hemisphere of the globe is having summer?
The southern hemisphere is having summer while the northern hemisphere is experiencing
winter.
5)
Why is December 21 called the Winter Solstice?
December 21st is called the Winter Solstice because it is the exact moment when the half of
the earth is tilted the furthest away from the sun.
6)
If the Earth’s axis were not inclined, what would happen to our seasons?
If the earth's axis were not inclined then the earth wouldn't have any seasons.
7)
If the Earth’s axis were more inclined, what would happen to our seasons?
The more inclined the earth's axis is the more extreme our seasons would be hence each
hemispheres summer would be getting more sun and less sun when it's winter.
p. 8