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101L
Subject
Astronomy
Date
Feb 20, 2024
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Uploaded by BrigadierLightning2983
Name: Pan Lu
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 _______shorter____. (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 ___the same___. 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?
_approximately April 19 – May 13____ (C)
On July 4
th
at midnight, the constellation _____ Sagittariusis_______ is on the
observer’s meridian. (D) At sunrise on Christmas Day, the constellation on the observer’s meridian is
__Virgo_______. 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
NAAP – Motions of the Sun 1/7
Z
Location Object Meridional Altitude Equator (lat = 0
°
) Sirius(dec = -16
°
) 74
Location Object Meridional Altitude Lincoln NE (lat = 41
°
N) Summer Solstice Sun 72.5
Z Location Object Meridional Altitude Iquique, Chili (lat = 20
°
S) Sirius(dec = -16
°
) 86
°
NAAP – Motions of the Sun 2/7
N S Z N S N S
Location Object Meridional Altitude Ann Arbor, MI ( lat = 42ºN) Capella ( dec = +46º) 94
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 continually repeat. o
If you select step by day
, time will leap forward in 24 hour increments
and the time of day will not change. NAAP – Motions of the Sun 3/7
Z N S 20
°
CE 70
°
16
°
MA = 70
°
+16
°
= 86
°
SCP Z N S
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•
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 meridinal altitude of the sun
throughout the year. 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 meridinal 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
58.2
301.8
Autumnal Equinox
49.5
89.4 270.4
Winter Solstice 25.6
121.8
238.2
Now use the results from the table above to help you draw the 3 paths in the horizon
diagram below. Label each path. NAAP – Motions of the Sun 4/7
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 value would increase from 60 degrees to 63.4 degrees in two weeks later.
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? For the Sun to be at the zenith, one needs to be located between 23.5◦ North Latitude
(Tropic of Cancer) and 23.5◦ South Latitude (Tropic of Capricorn) .
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
Does not rise
Does not set
Autumnal Equinox
19
90
270
Winter Solstice -12.5
Does not rise
Does not set NAAP – Motions of the Sun 5/7
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 doesn’t 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? To witness the sun rising every day, you need to move to a latitude below 66.5 º N.
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 0º June 21 6:04
18:05
12:01
Sept 21 5:50
17:55
12:05
Dec 21 6:00
18:00
12:00
41º June 21 4:35 19:35 15:00 Sept 21 5:50
17:55
12:05
Dec 21 7:30
16:35
9:05
66.5º June 21 0:25
23:45
23:20
Sept 21 5:50
17:50
12:00
Dec 21 11:45
12:20
0:35
90º June 21 Always rise
Does not set
24:00
NAAP – Motions of the Sun 6/7
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Sept 21 Always rise
Does not set
24:00
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? Sunlight is best described as a seasonal phenomenon, but it can also be considered a daily
occurrence. The variation in sunlight is more noticeable between seasons than on a daily
basis. Latitude significantly influences sunlight, with near-equator regions receiving
consistent sunlight, while poles experience extremes with 24-hour daylight in summer and
complete darkness in winter.
NAAP – Motions of the Sun 7/7