name THE SKY AND CONSTELLATION T - Tufts University

name

THE SKY AND CONSTELLATION TOUR

USING THE CELESTIAL SPHERE AND CONSTELLATION CHARTS

ANONYMOUS "ID", COELIFER ATLAS, 1559, ENGRAVING, ? X ? CM, IN WILLIAM CUNNINGHAM, THE
COSMOGRAPHICAL GLASSE, LONDON, JOHN DAY, 1559.

Book stored at the Wipple Library at the University of Cambridge.

The Sky #1  Lab 3  1

PART I

FINDING THE POLE STAR

a) If this is an evening lab and if the sky is clear go outside and try to find the Big Dipper and Polaris.
b) Here is cartoon drawing of a part of the sky — without the constellations lines drawn in. After all,

that’s what the sky looks like! Bright stars are represented by big dots, and fainter stars by smaller
ones. In the pattern below find the Big Dipper, Cassiopeia, and Polaris. Play the game of connect-
the-dots, and identify the remaining constellations.

2  Lab 3  The Sky

PART II

THE CELESTIAL SPHERE

Have you noticed that the night sky appears to be different if you travel much further north, or south?
You still see the same constellations, but they will appear to be at a different location on the night sky.
Also, if you follow the stars motions throughout the night, the stars will follow different paths. In this
exercise you will learn to how your location on Earth affects where you see Polaris. You will also learn
to visualize the motions of the stars on the night sky.

1) Orienting yourself

Imagine you are standing somewhere on Earth (let’s take Boston), and you are looking up. The point
directly above you is the Zenith. Perpendicular to the Zenith, all the way around you is the Horizon.
As illustrated in the Figure below, position the Celestial Sphere so that the Zenith of a miniature
person standing on the Globe in Boston (see below) point to the same Zenith as you standing in the
classroom (turn the Celestial Sphere until Boston is at the top and pointing to the ceiling).

Zenith of the person on the Globe Your
in the Celestial Sphere. Zenith
(Top of
Points to the top of the ceiling. Ceiling)

You in the
astronomy lab –
looking at the
celestial sphere in

front of you.

The proportions in this Figure are “a little off”.

The Sky #1  Lab 3  3

2) Identifying where is what on the CELESTIAL SPHERE

Grab on of the Celestial Spheres provided by your instructor. Before you start filling out the Table
on the next page make sure you can locate the following on the Celestial Sphere in front of you.

a) On that CELESTIAL SPHERE where is
The ZENITH and the HORIZON
The Earth’s EQUATOR and the CELESTIAL EQUATOR
The NORTH & SOUTH CELESTIAL POLES

b) Which numbers on the CELESTIAL SPHERE are telling you:
Your LONGITUDE and LATITUDE
The RIGHT ASCENSION and DECLINATION of a stat in your ZENITH
What is the ALTITUDE of a Star in your ZENITH (show the angle)

c) Chose any star on the CELESTIAL SPHERE, spin the sphere and watch the path of that star. Next,
imagine yourself standing on the Globe inside the CELESTIAL SPHERE – watch how the star rises
above the horizon, reaches its highest, and then sets below the horizon. The path of the star
should look somewhat similar to the path of the star in Figure 4 of the Pre-Lab.

3) Correlating various Angles

Imagine you are standing on the North Pole, then in a city at a latitude of 60, at 30 degrees and
finally at the equator. Identify specific angles and compare these angles to other angles on the
Celestial Sphere. Complete the table on the next page. Below is an explanation of the meaning of
every column of that table.

Column A) Take the CELESTIAL SPHERE and orient it in such a fashion that the EARTH’S NORTH POLE
points towards the ceiling. Now imagine you’re standing on the NORTH POLE ― (on the
small EARTH) and you’re looking straight up.

Column B) Your LATITUDE.
Column C) Locate POLARIS. What is the ALTITUDE of Polaris? Write this into the table.
Column D) Identify the ZENITH and the HORIZON on the Celestial Sphere in front of you. Identify a

star in your ZENITH. What is the DECLINATION of that star?
Column E) Determine the angle between the star in your ZENITH and POLARIS?
Column F) Determine the angle between your HORIZON and the CELESTIAL EQUATOR.
Column G) Compare the angle between the star in your ZENITH and POLARIS to the angle between

your HORIZON and the CELESTIAL EQUATOR. Determine the difference between these
angles.
Column H) Compare the angle between your HORIZON and the CELESTIAL EQUATOR to your
LATITUDE. How are the two angles related? Add both angles and write into the table.
Column I) Compare the ALTITUDE of POLARIS to your LATITUDE. Determine the difference between
these angles and write that into the table.

4  Lab 3  The Sky

A B C DE F G H I

Your Your LATITUDE ALTITUDE of DECLINATION of ANGLE between ANGLE between DIFFERENCE SUM of DIFFERENCE
location POLARIS a star in ZENITH POLARIS & HORIZON & between between
Symbol LAT ZENITH ANGLEHor–CelEq
ALTN CELESTIAL ANGLECelEq–Hor ALTITUDE of
North Pole 90o dec ANGLEZen-N EQUATOR and LATITUDE POLARIS —
 and
ANGLECelEq–Hor ANGLEHor–CelEq LATITUDE
ANGLEZen-N
+ LAT ALTN – LAT
ANGLEHor–CelEq

–ANGLEZen–N

Oslo 60o

Washington 30o
Equator 0o

Boston

Comment on this table. What correlation do you find in general? Are some of the columns always the same? What is the correlation
between your LATITUDE and the ALTITUDE of POLARIS?

The Sky  5

PART III:

THE APPARENT MOTION OF STARS IN THE SKY

With the aid of the celestial sphere figure out what the night sky looks like, where the North Pole is
relative to your location on Earth, and how the stars appear to move throughout the sky. Use the
Celestial Sphere as in Part II, but rotate the Sphere around its axis. This will show you the motion of the
stars; where they rise, where they transit (when they are at their highest point), and where they set.

For EACH of the four diagrams below, draw the following:

a) Using a black pen label the HORIZON, and N, S, E, W on the HORIZON
b) Using a blue pen label POLARIS, the N-S AXIS, the CELESTIAL EQUATOR
c) Using a red pen label your LATITUDE and the ALTITUDE of POLARIS

d) Using a green pen draw the paths of the two stars in ALL FOUR diagrams

Zenith Zenith

North Pole / 90° Oslo / 60°

Zenith Zenith

Washington / 30° Equator / 0°

6  Lab 3  The Sky

PART IV:

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.

The Sky  Lab 3  7

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.

8  Lab 3  The Sky

WHICH CONSTELLATION IS UP?

1. The table below summarizes which constellation in the zodiac you would see at midnight.
Complete the Table.

Month / Date constellation RIGHT ASCENSION of Sun would be seen
transiting at midnight that constellation in this constellation
June 21
July Sagittarius 18 hours Gemini
Capricorn 20 hours Cancer
August Aquarius 22 hours
September 21 0 hours Leo
Pisces 2 hours Virgo
October Aries 4 hours
November Taurus …
December 22 Gemini … …
Cancer … …
January Leo … …
February … …
March … … …
… … …
April … …
May

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? _________________

The Sky  Lab 3  9

PART V

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?

10  Lab 3  The Sky

QUIZ QUESTION #1

(This is the type of question that could come up in a test)

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
that the Horizon in that
picture corresponds to your
own Horizon.
Image taken from the Anglo
Australian Observatory at

http://www.aao.gov.au/images.html

1. Where (at what latitude) was this picture taken? Explain how you arrived at that answer.
[You may consult your textbook. Check out the diagrams with the star trails.]

2. Which hemisphere are you looking at? Explain.

3. The shutter of the camera was left open for several hours – for how long? Explain.

The Sky  Lab 3  11

QUIZ QUESTION #2

1) Label the following quantities: the
NORTH and SOUTH CELESTIAL
POLES; your HORIZON; your ZENITH;
your N, S, E, W; the MERIDIAN; and
the CELESTIAL EQUATOR.

2) Draw the paths of the five stars in the
diagram. Also draw arrows showing
the direction of motion.

3) Indicate which stars are always
visible, which stars are sometimes
visible, and which are never visible.
Always _______________________
Sometimes ____________________
Never ________________________

4) Take a red pen and draw the altitude
of Polaris (an angle). Then draw the
latitude of the observer in the picture.

5) Take blue pen and draw angle Polaris-to-Zenith and the angle Celestial Equator-to-Horizon. What
can you say about those angles?

6) Next add the altitude of Polaris to the angle Polaris-to-Zenith. What do you get? ________________
Then add your Latitude to the angle Polaris-to-Zenith. What do you get? ______________________

7) Compare both answers of question 6. What can you say about those angles?

8) What would happen to those angles as you travel North (i.e., as you increase your latitude?)

9) Comment on how the altitude of Polaris changes in relation to your latitude as you travel North.

12  Lab 3  The Sky

LAB-REPORT

HAND IN THE ENTIRE LAB. FOR EXTRA CREDIT DO SKY LAB #2.

1. Explain the purpose of the Lab.

2 .Let’s daydream a little. Imagine your friend invites you on a sailing trip. It’s beautiful weather, and
you’re having a good time. Then night sets in and you decide to sail a more, but the GPS brakes
down… Your friend is totally lost, but you are not…
a) Explain how you would find POLARIS.

b) But that’s not all ― you can also tell your friend where you are on EARTH. Explain how you would
determine your LATITUDE. (hint: look at the table.)

The Sky  Lab 3  13

c) Outline a method of how you could measure that angle.

d) Your friend is taken aback but is not sure whether to believe you. So, you have to convince your
friend that you are indeed correct. EXPLAIN WHY there is a correlation between your LATITUDE and
the ALTITUDE of Polaris (a diagram may also help).

3. Now you travel to Mexico. Explain in your own words how the sky in Mexico City looks different
from the sky in New York. Comment on the location of Polaris and on the paths of the stars at night.

14  Lab 3  The Sky