Motions_of_the_Sun
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School
Fayetteville Technical Community College *
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Course
151
Subject
Astronomy
Date
Apr 3, 2024
Type
docx
Pages
7
Uploaded by SuperHumanFlower13366
Name: Janae Watson
Motions of the Sun – Student Guide
Seasonal Motion
Work through the explanatory material on Sidereal vs. Synodic and
Seasons and the
Zodiac
. All of the concepts that are covered in these pages are used in the Paths of the
Sun Simulator.
Question 1:
For each of the following statements respond shorter, the same, or longer. (A) If the Earth revolved more rapidly, its sidereal day would be the same
.
(B) If the Earth revolved more rapidly, it solar day would be longer
.
(C) If the Earth rotated more rapidly, its sidereal day would be shorter
. (D) If the Earth rotated more rapidly, it solar day would be shorter
.
Question 2:
Use the Zodiac Explorer to answer the following questions. (A)
On May 25
th
, the sun is in the constellation of Taurus
.
(B)
What would be a good time of year to observer the constellation Aries? October
.
(C) On July 4
th
at midnight, the constellation Sagittarius
is on the observer’s
meridian.
(D) At sunrise on Christmas Day, the constellation on the observer’s meridian is
Scorpius
.
Daily Motion with Seasonal Effects
Work through the explanatory material on Meridional Altitude and
Sun Paths.
Question 3:
Complete the following table on meridional altitudes. You are encouraged to
check your answers with the meridional altitude explorer, but you should make every
effort to solve these problems yourself first. Note that part D is completed for you.
Location
Object
Meridional Altitude
North Pole (lat = 90
°
N)
Betelguese (dec. = +7)
7
°
Location
Object
Meridional Altitude
Equator (lat = 0
°
)
Sirius(dec = -16
°
)
74
°
MA: 0
°
+7
°
=7
°
NCP
90
°
-0
°
-7
°
CE
Z N S SCP
NCP
MA: 90
°
+(-16
°
) =74
°
-90
°
--16
°
CE
Z N S 0
°
Location
Object
Meridional Altitude
Lincoln NE (lat = 41
°
N)
Summer Solstice Sun
72.5
°
Z Location
Object
Meridional Altitude
Iquique, Chile (lat = 20
°
S)
Sirius(dec = 16
°
)
86
°
MA: 49
°
+23.5
°
=72.5
°
49
°
CE
23.5
°
41
°
NCP
°knm
N S Z N S 20
°
CE 70
°
16
°
MA = 70
°
+16
°
= 86
°
SCP
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Location
Object
Meridional Altitude
Ann Arbor, MI ( lat = 42ºN)
Capella ( dec = +46º)
86
°
Paths of the Sun Simulator This simulator allows you to simulate the path of the sun for any date during the year, for
any latitude on the Earth. Spend some time familiarizing yourself with the simulator –
most of the controls are fairly intuitive and similar to those in the preceding modules.
•
Practice using the yearly slider to move to different dates during the year.
•
Practice using the map to move to different latitudes during the year.
•
Note that the simulation lists the right ascension, declination, azimuth, and altitude
for the sun at all times.
•
Note that some advanced features such as the sidereal time, hour angle, equation
of time, and the analemma are available in a box in the lower left in this
simulation, but will not be covered in this guide.
•
Note that there are three different animation modes.
o
If you select continuous
, time will move forward in a natural fashion. You
may adjust the rate at which time passes using the animation speed slider.
You may modify this mode with the loop day
check box, which will cause
the sun’s motion for the current day to repeat continuosly.
o
If you select step by day
, time will leap forward in 24-hour increments
and the time of day will not change.
•
Special care should be taken to make sure that you understand what is being
simulated at all times. This is especially true in regard to discriminating between
the yearly and daily motion of the sun.
o
Move to a middle United States Latitude like 35
°
N. Click show ecliptic
and show month labels
. This is the sun’s yearly path on the celestial
sphere and is denoted by a white circle in the simulator. Note that it
crosses the blue celestial equator on the equinoxes.
o
Change your time to noon (12 pm) and animate the simulator in the step
by day mode. You can watch the changing meridional altitude of the sun
throughout the year.
MA: 180
°
-(48
°
+46
°
) =86
°
NCP
42
°
-48
°
-46
°
CE
Z N S
o
Stop the simulation near the summer solstice. The simulator readout
should state “The horizon diagram is shown for an observer at latitude 35
°
on 21 June at 12:00 (12:00 pm)”. Think about what the sun’s path should
look like in the sky on that day.
o
Now check show the sun’s declination circle
,
which is a yellow circle in
the simulator. This is what the sun’s path in the sky would be on the
summer solstice. Note that this circle has the proper meridional altitude
(78.8
°
) and is a coaxial circle with the celestial equator (picture the
slinky).
Question 4:
Set up the simulator for Lincoln, NE which has a latitude of 41
°
N. Complete
the following chart for the meridional altitude and the rising and setting azimuths for the 3
major paths of the sun. Note that the rising azimuth can be determined by dragging the sun
(dragging in time of day mode) and reading off the azimuth when the altitude is zero.
Date
Meridional Altitude
Rising Azimuth
Setting Azimuth
Summer Solstice
72.4
58.5
301.8
Autumnal Equinox
48.6
°
89.4
°
269.4
°
Winter Solstice
25.6
°
121.7
°
238.2
°
Now use the results from the table above to help you draw the three paths in the horizon
diagram below. Label each path. Question 5:
Suppose that you are visiting Lincoln, NE and on July 10, you wake up early
and note the rising azimuth of the sun. In which direction would the value change if you
measured it two weeks later? The rising azimuth on July 10
th
would be 60° and two
weeks afterwards, it would be 63.4°. So, when it rises on the horizon on July 24
th
, it’ll be
more Southward’s.
Question 6:
Note that the sun can never be at the zenith for Lincoln (lat = 41ºN)? How far
would you need to move on the Earth to find a latitude where the sun can be at the
zenith?
You would need to move down to the tropic of cancer or lat = 23
°.
Question 7:
Set up the simulator for Nordkapp, Norway which has a latitude of 71
°
N.
Complete the following chart for the meridional altitude and the rising and setting
azimuths for the 3 major paths of the sun.
Date
Meridional Altitude
Rising Azimuth
Setting Azimuth
Summer Solstice
42.4
°
Doesn’t set
Doesn’t set
Autumnal Equinox
19.3
°
88.6
°
270.9
°
Winter Solstice
-4.4
°
Doesn’t rise
Doesn’t rise
Now use the results from the table above to help you draw the 3 paths in the horizon
diagram below. Label each path. Question 8:
Note that the sun does not rise every day from Nordkaap. How far would you
need to move on the Earth to find a latitude where the sun does rise every day? You
would need to move far enough to the Arctic, or lat = 66
°.
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Question 9:
The Paths of the Sun Simulator is also very useful for determining how long
the sun is above the horizon each day. Simply make sure that the option for dragging the
sun’s disk is set to time of day and drag the sun to the eastern/western horizon read the
clock to determine the time at which the sun rises/sets.
Latitude
Date
Rising Time
Setting Time
Total Time
June 21
6:04
18:00
11:59
0º
Sept 21
5:52
17:51
12:00
Dec 21
5:58
17:58
12:00
June 21
4:35
19:35
15:00
41º
Sept 21
5:53
17:55
12:00
Dec 21
7:27
16:30
9:03
June 21
00:25
23:38
23:13
66.5º
Sept 21
5:50
17:54
12:04
Dec 21
11:42
12:15
00:13
June 21
Doesn’t rise
Doesn’t set
00:00
90º
Sept 21
Doesn’t rise
Doesn’t set
00:00
Dec 21
Doesn’t rise Doesn’t set 0 Question 10:
Based on your answers to the previous questions, is it best to refer to
sunlight as a seasonal or daily phenomena? Does this depend on latitude? Based on my
previous answers, I think it could be both seasonal and daily phenomena that could all
depend on the latitude of your location.