No More Boring Science Presents:
Constellations by season and
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Coordinates in the sky:
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An
Astronomy
Lab
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LAB: Constellations by Season and Coordinates in the sky
Part A: Coordinates in the Sky
1. Consider the imaginary constellation “Pezaglis”
which has the 4 stars shown the table to
Stars of Pezaglis
the right.
Name
Declination
Right
a. Plot these points on the Mercator Map
Ascension
b. Connect the stars with lines, in order
Alpha
40°
23h
given including a line from delta back to
Beta
40°
1h
alpha.
Gamma
70°
1h
c. Label the stars with the correct Greek
Delta
70°
23 h
symbol
d. Plot these same points on the Polar Map, again connect the stars.
e. Now, use a “Celestial Sphere” to see what shape it would be in the sky.
2. Discussion: You will probably find that the “shape” of the constellation is different on
the two maps. Briefly, which map do you think more closely represents how it would
appear in the sky (equivalently on a celestial sphere) to you eye? Explain your reasoning.
3. Consider two more stars: epsilon at (70°, 4h) and zeta at (70°, 16h).
a. Plot them on the Mercator Map. Label with correct Greek symbols.
b. Using a ruler, connect them with a straight line (i.e. the shortest path).
c. How many degrees apart are they (on the Mercator Map)? ___________________
[Hint: 1 hour is equivalent to 15°]
d. Explain how you arrived at your answer to part c
4. Plot these same stars on the Polar Map.
a. Using a ruler, connect them with a straight line. Label with correct Greek symbols
b. How many degrees apart are they (on the Polar Map)? ___________________
c. Explain how you arrived at your answer to part b.
5. Discussion: Are the distances you measured on the two maps the same? Which map
probably represents what you would see in the sky? Again, use a “Celestial Sphere” to
resolve any interpretation issue of the correct “line” to draw between the two stars. [Are
the lines you drew on the two maps representing the same thing?]
POLAR MAP PROJECTION
MERCATOR MAP PROJECTION
PART B – Constellations by Season
1. Using the provided seasonal star maps, locate Polaris on each map. N on the map represents the northern
horizon. Does the position of Polaris relative to the northern horizon change throughout the year?
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2. Locate the Big Dipper on the winter map. Note that two stars in the Big Dipper are labeled pointers. If a line
connecting the pointers is continued to the right, to which star does the line point?
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How can the Big Dipper be used to find direction in the northern hemisphere?
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3. Locate on the winter map the three closely spaced stars in the middle of Orion. If a line is drawn through
these stars and continued to the left, toward which constellations does it point?
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4. Name the constellation in which each of the following stars in located:
Polaris ____________________________________________________________________
Antares ___________________________________________________________________
Vega _____________________________________________________________________
Spica _____________________________________________________________________
Betelgeuse __________________________________________________________________
Rigel ______________________________________________________________________
Arcturus ___________________________________________________________________
5. For each constellation listed in the Data Table, identify its general location (N, E, NE, NW, Zenith and so forth)
on the Autumn, Winter, Spring, and Summer maps.
Data Table
Constellation
Autumn
Winter
Spring
Summer
Boötes
Lyra
Orion
Pegasus
6. Explain why the position of Polaris does not change relative to the northern horizon during the year.
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7. Explain how the stars and constellations can serve as landmarks for other stars and constellations.
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8. Look over the data you collected in procedure step 5. Which season provides the best viewing of each
constellation? Explain.
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SEASONAL POLAR MAPS
SEASONAL POLAR MAPS
TEACHER KEY – Part A
1 a) and 1 b)
1c) and 1d)
δ
γ
α
β
γ
β
δ
α
1e) This constellation is a perfect square in the sky.
1 hour RA = 15 degrees. The width of the constellation is from 23 h to 1 h, so the total right ascension is 2 h. 2 h = 30 degrees wide.
The declination goes from 40 degrees to 70 degrees, so the height is 30 degrees.
If this constellation is 30 degrees wide and 30 degrees high, then it is a square.
2) Basically, the closer constellation is to the zenith (to directly overhead), the more accurate the polar projection is. The closer the
constellation is to the horizon, the more accurate the Mercator projection is.
3a) and 3b)
ζ
ε
3c) the two points are 12 h apart, so 180 degrees.
3d) 16 h – 4 h = 12 h.
1 h = 15 degrees
12 h * 15 = 180 degrees
4a)
4b) 40 degrees. Because you can measure across the pole, which gives you
an angular distance from 70 – 90 – 70.
5) They are not the same. On the Mercator map, we measured around the
pole, shown here in green on the polar map. On the polar map, we
measured across the pole.
ζ
ε
TEACHER KEY - Part B
1) No, Polaris stays at the same distance from the northern horizon the entire year,
even when the other stars around it change.
2) The big dipper points to Polaris. Big Dipper can be used to determine which
direction is north.
3) The stars in Orion’s belt point to Canis.
4) Polaris – Ursa Minor (little dipper), Antares – Scorpios, Vega – Lyra, Spica - Virgo,
Betelgeuse – Orion, Rigel - Orion, Arcturus - Boötes
5)
Constellation
Boötes
Autumn
No visibility
Winter
No Visibility
Lyra
West
No Visibility
Orion
Pegasus
East
Zenith
(overhead)
West
Zenith
(overhead)
Spring
Zenith
(overhead)
No Visibility
No Visibility
No Visibility
Summer
West
Zenith
(overhead)
East
No Visibility
6) Polaris is very, very close to the north celestial pole, which is what all the other stars
appear to rotate around
7) By knowing the location of a specific constellation or bright star, you can memorize
directions and distances to other, fainter constellations (like locating Canis from
Orion)
8) Boötes – Spring
Summer – Lyra
Autumn – Pegasus
Winter - Orion