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NUMBER
I.A. TITLE:
SIZING UP THE SKY (Fall)
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OBJECTIVE:
·
Make visual
observations of the night sky or celestial sphere.
·
Make
measurements using linear and angular units of measure.
·
Determine
scale in both angular and linear measure.
·
Become
knowledgeable of types of observational error.
DESCRIPTION:
Observational
astronomy, like any science, involves making measurements. In astronomy many
measurements are made of objects in the sky, a part of an imaginary sphere
known as the celestial sphere. The physical size of an object is usually
expressed in linear units such as meters or kilometers. The apparent
size or separation of objects on the celestial sphere may be more appropriately
expressed in angular units such as degrees or fractions of a circle. The angular separation of the stars in the
Summer Triangle will be estimated using a technique described by the
instructor. The ‘linear’ separation of
stars on a map will also be determined to calculate a map scale. Types of observational error will be
discussed briefly at the close of this exercise.
EXAMPLE OF USING A SCALE:
1. Examine the
large Moon Map and measure the diameter of the crater “Copernicus.” Using the
given scale at the bottom of the map, determine the diameter of the crater in
kilometers.
PROCEDURE AND OBSERVATIONS:
1.
Identify the
stars Vega, Deneb, and Altair on the star map provided. Print the name of each star adjacent to the
star.
2.
In the
appropriate boundary, print the name of the constellation containing each of
the above stars. Print the name of at
least one other constellation in its bounded region. Highlight the constellation boundaries with a
highlighter.
3.
Carefully
measure the linear distance between the stars in the Summer Triangle on the map
in this lab and enter results in table ‘A’.
Use the millimeter scale on your measuring device.
4. Go outside and determine the angular separation between each of the above stars, using a technique described by the instructor. Enter the results in table ‘B’.
5. Enter in table ‘B’ the ‘actual’ values of the angular separation between each of the Summer Triangle stars as given by TheSky. Calculate the discrepancy or percent error = 100* (Measured - Actual)/Actual and enter the results in table ‘B’.
6.
Using your
linear measurements and the computer values for angular separation, determine the map scale in degrees per millimeter for
each side of the triangle. Convert to
decimal degrees and enter your results in
table ‘C’.
Table ‘A’
SIDE OF TRIANGLE |
LINEAR
SEPARATION (mm) |
Vega to Altair |
|
Altair to Deneb |
|
Deneb to Vega |
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Table ‘B’
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SIDE
OF TRIANGLE |
VISUAL EST. ANGULAR SEP |
COMPUTER ANGULAR
SEP |
DISCREPANCY |
Vega to Altair |
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|
Altair to Deneb |
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Deneb to Vega |
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Table ‘C’
SIDE OF TRIANGLE |
Decimal
Degrees |
SCALE
o/mm |
Vega to Altair |
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Altair to Deneb |
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Deneb to Vega |
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Average
Scale ___________
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QUESTIONS/ANALYSIS:
1.
List the types
of error described by the instructor.
2.
What type of
error/s mentioned above would possibly explain the discrepancies listed in
Table ‘B’?
3. How could
you achieve greater accuracy in the angular measurements made in this exercise?
4. In Table
‘C’, was the scale the same on all sides of the Summer Triangle? If not, why do you suppose there was a
difference?
5.
Using the average
scale determined in Table ‘C’ and the map, calculate the angular separation
between Albireo and Rasalhauge
(use the map handout or TheSky to identify stars, but
do not use TheSky to find the angular
separation). Show work.
6.
Log all
observations you made this evening in your Bluebook.
7.
Complete the
SUMMARY sheet in your Bluebook. Include
what you observed,
what kind of measurements you made, and a comment on your
results.