Assignment A2 Instructions & Worksheet (1)
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Feb 20, 2024
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Assignment 2: Observing the effects of the Earth’s Rotation
Because the earth spins on its axis, the overall motion of the sky (in general) seems to go from east to
west in 24 hours (ignoring the circular motion of the stars near the celestial pole). The most obvious
effect is the sun’s slow motion across the sky during the day. During your nighttime observing sessions,
you should note how most objects move in the same or a similar slow westward movement. Part 1 – Observing the Rising or Setting of an Object
To see the slow rotation of the sky yourself, find a bright constellation or star in the eastern, southern, or
western sky and position yourself so this object is lined up next to a tree, power line, or edge of a
building, if possible. Measure the altitude and azimuth of the object and record this in the data table
provided below. Sketch the constellation and the objects near it on the horizon. While you wait for this
time to pass, you can work on other assigned objects in other activities. Observe this constellation again 3 hours later from the same spot. You should easily see a change in the
position of the object due to the slow movement of the sky as it turns above your head (in actuality, it is
the Earth that is doing the moving, not the sky). Measure the altitude and azimuth of the object a second
time and enter this information into the appropriate data table below your first observation. Draw a
second sketch on of the constellation and objects near it on the horizon.
Don’t forget to record your data in the table provided below. Also, write a description of the
observations that showed the rotation of the sky on the appropriate Observing Record Form for
Assignment 2. Record everything asked for in the table.
Part 2 – Observing the Circumpolar Constellations
Ursa Major, Ursa Minor and Cassiopeia are a few of the circumpolar constellations and are constellations
that appear to circle around Polaris. Once you have identified these circumpolar constellations:
record the locations in azimuth and altitude
draw a picture of the shapes and relative positions of the Big Dipper (in Ursa Major), Little Dipper
(in Ursa Minor) and Cassiopeia relative to Polaris and the horizon. Include Polaris and the
horizon in your sketch.
Record the date, time and your location on the drawing and in the data table on Observing Record
Form for Assignment 2 as well. You will need this information later.
To observe how the Earth’s rotation affects what we see in the night sky, observe these circumpolar patterns again three hours or more after your first observation
. While you wait to do the second observation, you can work on the other assigned objects that are visible in the sky.
After an hour or so, you should detect a change in the location of these circumpolar patterns.
Make another sketch of the positions of these patterns
Measure their positions in altitude and azimuth.
Record the name, date, time, altitude and azimuth of your second observation of each object in the appropriate data table
.
Describe on the Observing Record Form for Assignment 2 what you learned about the effects of
the earth's rotation on constellations in the northern sky from your two sketches.
For clarity – in Assignment 2, I am looking for you to perform TWO observations of a constellation in one night, separated by at least 3 hours. I also want you to make TWO observations of the locations of the Big Dipper, the Little Dipper, and Cassiopeia relative to Polaris and the Horizon in one night. These observations must also be separated by at least 3 hours as well.
Observation Record Form for Assignment 2 – Unit A
Part 1: Data log
for observing a constellation in the east, south, or west over 180 minutes
Constellation
observed
When Observed
Position in Sky
Change in position from the first observation
Date
Time
Minutes
since 1
st
obs
Azimuth
Altitude
0
First Observation
Sketch of first observation:
Sketch of second observation:
Write a description below of the motion of a constellation near the eastern or western horizon over a span of 180 minutes:
Part 2: Data log
for observing circumpolar constellations in the sky over 180 minutes
Constellation
observed
When Observed
Position in Sky
Change in position from
the first observation
Date
Time
Minutes
since 1
st
obs
Azimuth
Altitude
Sketch of first observation:
Sketch of second observation:
Write a description of the motion of the circumpolar patterns observed over a span of 180 minutes:
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