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TAKE HOME VERSION OF SKY-LAB #1 OR AN EXTRA CREDIT LAB
THE SKY AND CONSTELLATION TOUR:
2. USING SKY CHARTS
GET A COPY OF THE PRE-LAB OF THE FIRST SKY-LAB
READ AND UNDERSTAND THAT PRE-LAB – YOU WILL NEED TO KNOW ALL THE TERMS IN IT
The Sky #2  Extra Credit Lab  1
CONSTELLATIONS, STAR NAMES, AND STAR CHARTS
Just as the United States is divided into 50 states, the sky is divided in 88 irregular regions called
constellations. Constellations make finding objects in the sky easier. Just as specifying that Staten Island
is in the state of New York, we specify for example that Betelgeuse is in Orion. However, there are also
reasons why we use right ascension and declination (i.e., exact coordinates) as you will find out.
Actually, professional astronomers only use the exact coordinates.
The stars that make up the constellations are not actually physically associated but are just patterns that
resemble or honor animals, mythological characters, etc. Many of the constellation names are Greek in
origin (e.g., Orion, Hercules and Andromeda), while others are more contemporary in nature (e.g.,
Microscopium and Telescopium). The Stars are named using several different systems. The brighter
stars all have ancient names, while fainter ones are known by “number” only (although you can name
those stars after someone - as a Christmas present). Apart from using “popular” star names (like
“Sirius”, or even weirder ones like Zubenelgenube or Zubenesschamali), amateur astronomers use the
names of constellations, and designate stars in that constellation by Greek letters. The brightest star is
“alpha”, α, the second brightest one beta, β, then gamma, γ, etc (For the Greek alphabet check the
ToolKit). Thus Sirius, the brightest star in Canis Major, is also known as “Alpha Canis Majoris”.
Sometimes, you’ll see this abbreviated as “αCMa”. Similarly, Betelgeuse is called Alpha Orionis (or
αOri) and Rigel Beta Orionis (βOri). In the constellation charts the brightest stars correspond to big
blobs, while fainter ones correspond to smaller blobs.
You will be using charts like this in the lab. Just as we produce maps from the globe, we also produce
charts from the celestial sphere. The diagram below shows how these charts relate to the celestial
sphere. Imagine that you peel the celestial sphere just like you would
peel an orange. Make a cut along the dotted line B, peel off the
cap, and then view the cap from above. This corresponds to
the SC-2 chart. Similarly take the part of the peel from
between the lines A & A’, flatten it out, and you get
the SC-1 chart.
2  Extra Credit Lab  The Sky #2
PART I: USING SC-1 AND SC-2
a) Find the Pole star. What is its “proper” name, and what is its other name?
_________________________ and _________________________
b) Give the names (like Alpha Centaurus) of the following stars:
(Hint: Use the Greek Alphabet, which you can find in the ToolKit)
the 6th brightest star in Taurus ____________________
the 15th brightest star in Leo ____________________
the 21st brightest in Auriga ____________________
c) Locate (using the constellation charts) and give the “proper” names of:
Kappa Orionis ____________________
Alpha Bootis ____________________
Beta Ursae Majoris ____________________
c) Give both names for the two “Pointer Stars” in the Big Dipper that (when a line is drawn through
them) point towards Polaris, the pole star.
Pointer Star 1: _________________________ and _________________________
Pointer Star 2: _________________________ and _________________________
e) Which of the following stars is brightest and which faintest?
δ Auriga
γ Taurus
η Canis Majoris
__________
__________
__________
f) Using only the SC-1 chart locate and list 4 star clusters
_________________________ _________________________
_________________________ _________________________
g) Using only the SC-1 chart locate and list 4 nebulae
_________________________ _________________________
_________________________ _________________________
i) Using only the SC-2 chart locate and list 3 galaxies
_________________________ _________________________
_________________________ _________________________
The Sky #2  Extra Credit Lab  3
PART II:
THE SKY DURING DIFFERENT SEASONS
Have you noticed that different stars are visible during different seasons? Let’s figure out why this is.
Look at the diagram below. Let’s ignore the rotation of the EARTH around its own axis (only for now)
and consider the motion of the EARTH around the Sun.
Imagine that there are some aliens out there ― on a planet that is still unknown, but that is orbiting
around Arcturus. Arcturus is in the constellation Boötes and is visible in the summer. In fact, in the
evenings in June it is the brightest star within about 20 degrees of your ZENITH. So if you wanted, you
could wave to the aliens.
Half a year later, sometime in December, you want to wave at the aliens again ― but Arcturus is not up.
Look at the diagram below, and convince yourself that the sun would blind you when trying to locate
Arcturus.
You can do this game with any other star too, and the sky appears to change with the seasons. Clearly,
the stars do not move ― but the sky appears to move because of the EARTH’s motion around the sun.
4  Extra Credit Lab  The Sky #2
SEASONS & CONSTELLATIONS
Let’s only consider stars that are in constellations along the ecliptic. The diagram below is the same as
the previous diagram. In June, at midnight, when you look towards the ecliptic, you see that Sagittarius
is transiting, but if you want to look at Sagittarius in December, you would have to look through the sun,
and you’d be blinded.
The Sky #2  Extra Credit Lab  5
WHICH CONSTELLATION IS UP?
1. The table below summarizes which constellation in the zodiac you would see at midnight.
Complete the Table.
Month / Date
June 21
July
August
September 21
October
November
December 22
January
February
March
April
May
constellation
transiting at midnight
Sagittarius
Capricorn
Aquarius
Pisces
Aries
Taurus
Gemini
Cancer
Leo
…
…
…
of
that constellation
18 hours
20 hours
22 hours
0 hours
2 hours
4 hours
…
…
…
…
…
…
RIGHT ASCENSION
Sun would be seen
in this constellation
Gemini
Cancer
Leo
Virgo
…
…
…
…
…
…
…
…
2. Answer the following questions:
In March, which constellation would you be able to see best at midnight?
_________________
What is the RA of that constellation?
_________________
In May, which constellation would transit at midnight?
_________________
What is the RA of that constellation?
_________________
Today, which constellation is transiting at midnight?
_________________
What is the RA of that constellation?
_________________
In which constellation would you find the sun today?
_________________
What is the RA of that constellation?
_________________
3. Do you get the idea? Explain below how RA correlates with the season.
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
4. How many hours in RIGHT ASCENSION does each month correspond to?
_________________
And one week corresponds to hour many minutes in RIGHT ASCENSION?
_________________
6  Extra Credit Lab  The Sky #2
PART III
USING SKY CHARTS TO OBSERVE THE SKY
You will be using all the information you learned in the last section to figure out in during which season
and during what time of night you will be able to observe which stars. Use the constellation charts SC-1
and SC-2. In particular check out SC-1. The x-axis corresponds to right ascension (RA), and the y-axis
to declination (DEC). We said previously, that stars with a RA of 0 hours will be transiting on
September 21 at midnight. But let’s assume we want to observe at 8 p.m. at night, i.e., 4 hours before
midnight. Thus stars with a RA of -4 hours, or with an RA of 20 hours (i.e., 24-4 = 20 hours) will be
transiting.
Now check the SC-1 chart. On the x-axis you see “RA”. Find all stars that have an RA of 20 hours.
Below “20h” on the x-axis you find a date (in a smaller script) - it says September 20. So at 8 p.m. in the
evening of September 20, stars with an RA of 20 hours are transiting.
Using the previous Table and/or the SC-1 chart answer the following questions:
[Note the SC-1 chart shows transits at 8pm, not at midnight!]
Write down today’s date.
Which stars are transiting at 8 p.m. today?
Which stars are transiting at 8 p.m. on August 21?
Give the name of a star that will transit today at 10 p.m.:
Give the name of a star that will transit on August 21 at 10 p.m.:
Which constellation is transiting at midnight on June 21?
Which constellation is transiting at 2AM on June 21?
Which constellation is rising at 2AM on June 21?
Which constellation is setting at 2AM on June 21?
On which date will Capella transit at midnight?
On which date will it transit at 8 p.m.?
At which time will Capella transit today?
At what time, today, will Betelgeuse transit?
At what time, today, will the Andromeda Galaxy (M31) transit?
The Sky #2  Extra Credit Lab  7
A QUIZ QUESTION #1
1. It is midnight. What season is it? Explain.
2. At what time would Vega be transiting in the above picture? Explain
8  Extra Credit Lab  The Sky #2
QUIZ QUESTION #2
Hold the picture at arms
length right in front of
you. Imagine that this
picture is part of the
landscape in front of
you. Imagine that the top
of the picture somewhat
curves around you.
Image taken from the
Anglo Australian
Observatory at
http://www.aao.gov.au/images.html
1. At what latitude is this observatory? [You may consult your textbook. Check out the diagrams with
the star trails.] Circle one of: 0, 10, 20, 30, 45, 60, 90 degrees. Explain how you arrived at this answer
2. What direction is the photographer facing? Circle one of E, W, N, S, SW, SE, NW, NE. Explain.
3. For how long was the shutter of the camera left open? Circle one of 1sec, 1min, 10 min, half an hour,
one hour, two hours, 5 hours, 10 hours, 24 hours. Explain your answer.
The Sky #2  Extra Credit Lab  9
LAB-REPORT
IF YOU DO THIS LAB FOR EXTRA CREDIT, HAND IN THE ENTIRE LAB, INCLUDING YOUR PRE-LAB.
State the purpose of the Lab
Explain how the position of a star depends on the time of observation
Explain how the position of a star depends on the season
What have you learned from this Lab, and how useful do you think this information will be to you.
10  Extra Credit Lab  The Sky #2
Now apply what you learned from this Lab. The Star Vega has a
o
DECLINATION of 39 .
RIGHT ASCENSION
of 18h 40m and a
a) Determine at what time Vega will transit tonight (state your date). Show every step of how you
reach your conclusion. [Explain in words how you arrive at your answers, then, do some additions
and/or subtractions.]
b) Make a drawing of the Celestial Sphere similar to the Figure in the quiz question #1; insert the
position of Vega at its transit, and then draw its path throughout the night.
c) Calculate the ALTITUDE of Vega during transit. Explain how you would determine this. [This tests if
you understand the general concepts of the Celestial Sphere and whether you can visualize the
motion of Vega in the sky.]
d) If you think that you should be able to see Vega, go outside and look at the night sky — check if
your answers and drawings coincide with what you see.
The Sky #2  Extra Credit Lab  11
Here are small versions of the
charts; get the full size version from
your instructor.