Astronomy 161 – Spectroscopy Lab Introduction: The light of celestial objects contains much information hidden in its detailed color structure. In this lab we will separate the light from some sources into constituent colors and use spectroscopy to find out the chemical constitution of known and unknown gases. The same procedure is used for starlight, telling us what its source is composed of. The baseline is a laboratory experiment with known materials, and later we can compare the unknown to what we already know. Hot, glowing bodies like a light bulb, or the Sun, glow in all the colors of the spectrum. All these colors together appear as white light. When such white light hits a prism, or a raindrop, or a diffraction grating, colors get separated according to their wavelength. Red, with its wavelength of 600 nm to 700 nm, is deflected least and ends up on one edge of the spectrum – or the rainbow when sunlight hits a raindrop after a storm. Blue, wavelength around 400 nm, is the other end of the visible spectrum. An infinite number of elementary colors are located between these two edges, each corresponding to its own wavelength. An incandescent light bulb radiates a continuous spectrum. All colors are present in this “thermal glow”, and it is impossible to tell what the chemical composition of the source is. However, other physical processes produce different spectra. A fluorescent light tube works, crudely speaking, on the principle of lightening. Electrons rush from the negative pole to the positive pole inside, and hit gas atoms in the tube, making them emit light. This sort of light contains only a few colors, and is called “emission spectrum”. When we separate the colors of such light, only a few bright “emission” lines appear, each in its own color (and wavelength). Each sort of an atom will emit light at its own particular set of wavelengths. When we analyze the emission spectrum of an unknown source, we can compare the colors of its spectral lines to known spectral lines we see in a laboratory, and tell which substance matches. The color of spectral lines is directly related to the structure of the atoms. Electrons can jump from one orbit around the atomic nucleus to another, giving off the difference in energy levels in the form of light. The wavelength (color) of light is related to the amount of energy freed up between the old and the new orbit. In this laboratory we will measure the wavelengths of spectral lines from a few gases, which are easy to put inside a discharge tube. Other chemical elements would have different spectra. In the spectroscope that we use in this laboratory, a diffraction grating (many parallel black lines drawn very tightly on a little piece of film) breaks up the light entering through the input slit into colored lines. Each color corresponds to a wavelength, measured in nanometers (1 nm = 10-9 m). Instructions: In  this  investigation   ...

1. Astronomy 161 – Spectroscopy Lab
Introduction:
The light of celestial objects contains much information hidden
in its detailed color
structure. In this lab we will separate the light from some
sources into constituent colors and use
spectroscopy to find out the chemical constitution of known and
unknown gases. The same
procedure is used for starlight, telling us what its source is
composed of. The baseline is a
laboratory experiment with known materials, and later we can
compare the unknown to what we
already know.
Hot, glowing bodies like a light
bulb, or the Sun, glow in all the colors of
the spectrum. All these colors together
appear as white light. When such white
light hits a prism, or a raindrop, or a
diffraction grating, colors get separated
according to their wavelength. Red, with
its wavelength of 600 nm to 700 nm, is
deflected least and ends up on one edge of
the spectrum – or the rainbow when sunlight hits a raindrop
after a storm. Blue, wavelength
around 400 nm, is the other end of the visible spectrum. An
infinite number of elementary colors
are located between these two edges, each corresponding to its
own wavelength. An
incandescent light bulb radiates a continuous spectrum. All

2. colors are present in this “thermal
glow”, and it is impossible to tell what the chemical
composition of the source is.
However, other physical processes produce different spectra. A
fluorescent light tube
works, crudely speaking, on the principle of lightening.
Electrons rush from the negative pole to
the positive pole inside, and hit gas atoms in the tube, making
them emit light. This sort of light
contains only a few colors, and is called “emission spectrum”.
When we separate the colors of
such light, only a few bright “emission” lines appear, each in its
own color (and wavelength).
Each sort of an atom will emit light at its own particular set of
wavelengths. When we analyze
the emission spectrum of an unknown source, we can compare
the colors of its spectral lines to
known spectral lines we see in a laboratory, and tell which
substance matches.
The color of spectral lines is directly
related to the structure of the atoms. Electrons
can jump from one orbit around the atomic
nucleus to another, giving off the difference in
energy levels in the form of light. The
wavelength (color) of light is related to the
amount of energy freed up between the old and
the new orbit. In this laboratory we will measure
the wavelengths of spectral lines from a few
gases, which are easy to put inside a discharge
tube. Other chemical elements would have
different spectra.
In the spectroscope that we use in this
laboratory, a diffraction grating (many parallel

3. black lines drawn very tightly on a little piece of
film) breaks up the light entering through the input slit into
colored lines. Each color corresponds
to a wavelength, measured in nanometers (1 nm = 10-9 m).
Instructions:
In
this
investigation
you
will
use
a
diffraction
grating
to
examine
the
bright
line
spectra
of
several
light
sources
and
then
use
this
information

4. to
identify
an
unknown
light
source
by
its
spectrum.
The
electrodes
of
the
source
tube
are
at
HIGH
VOLTAGE.
Do
not
touch
them
(or
you,
too,
can
glow

5. in
the
dark).
A.
Looking
at
the
hydrogen
source
through
the
grating
you
should
see
three
or
four
bright
lines
on
each
side
of
the
source.
If
your
equipment
is

6. aligned
properly
these
should
fall
on
the
meterstick.
Using
the
appropriate
color,
draw
each
of
these
lines
on
the
spectrum
chart
provided.
Be
sure
to
mark
the
position
of
each
of
these

7. lines
to
the
nearest
centimeter.
B.
In
addition
to
the
general
appearance
of
the
spectrum
determined
in
part
A
we
need
something
a
little
more
quantitative.
We
will

8. find
the
average
distance
of
each
line
from
the
source,
which
should
be
at
the
50
cm
mark
in
the
middle
of
the
stick.
If
the
red
lines
lie
on
the
meterstick
at

9. 25
cm
and
77
cm,
for
example,
these
distances
would
be
77
cm
-­‐
50
cm
=
27
cm
50

10. cm
-­‐
25
cm
=
25
cm
and
the
average
distance
of
the
red
line
would
be
27
cm
+
25
cm

11. =
26
cm
2
Make
these
calculations
for
each
of
the
hydrogen
lines

12. and
enter
the
numbers
on
the
chart.
C.
Repeat
these
procedures
for
neon
and
mercury
tubes.
Be
careful
when
changing
the
tubes.
Always
turn
the
power
switch

13. off
first
and
allow
the
tube
to
cool
down
before
attempting
to
handle
it.
For
neon
you
should
see
a
great
many
lines.
Pick
the
five
brightest
lines
for
analysis.
Remember,

14. the
whole
idea
is
to
make
a
picture
of
the
most
conspicuous
lines
of
neon,
the
ones
most
likely
to
show
up
if
neon
is
present
in
the
unknown.
D.

15. Now
repeat
this
procedure
for
one
of
the
unknowns.
The
unknown
might
be
one
of
the
elements
you
have
already
examined
or
a
mixture
of
two
of
them.
On
your
chart
be

16. sure
to
give
its
identifying
number.
(The
unknowns
are
not
all
the
same.)
By
comparing
its
spectrum
with
those
you
have
already
plotted
can
you
identify
what
element
or
elements
this
tube

17. contains?
LABGROUP: SECTION:
SOURCE:

18. SOURCE:
SOURCE:

19. SOURCE:
The Sun is a hot glowing body and gives off a continuous
spectrum. However, atoms in
its cooler atmosphere absorb particular wavelengths of light.
Recall that in the exercise above,
the atoms were emitting at particular wavelengths of light. In
fact, if an atom were in the
atmosphere of the Sun, it would absorb the same wavelengths of
light it emits in the emission
tubes.
Below is a simplified version of the Sun’s spectrum. Use this
spectrum to determine the
two dominant elements that make up the Sun.
Two dominant elements in the Sun:
_______________________________________________

20. 1
LAB: PHASES OF THE MOON & ECLIPSES
Names: _________________________ ,
____________________________
Section: _________
Introduction: The Moon orbits the earth about once a month.
Half of the Moon’s surface is always illuminated by the sun.
But the fraction of the Moon’s
illuminated face that is visible from Earth will change according
to the Moon – Earth – Sun
alignment at a given time.
Using the Styrofoam ball as the Moon, a flashlight as the Sun
and your head as the Earth make
observations and design experiments to simulate the phases of
the Moon. Answer the following
questions:
1- Is the bright side of the Moon facing toward the Sun, or away
from it? Indicate in the
sketch below the lit side of the Moon (shade with your pencil
the dark side, leave the lit
side white).

21. 2- Sketch the Earth, Moon and Sun when the Moon is in the full
phase. What is the angle
Moon – Earth – Sun?
3- Sketch the Earth, Moon and Sun when the Moon is in the first
quarter phase. What is the
angle Moon – Earth – Sun?
2
4- If it is Waxing Crescent Moon in the Northern Hemisphere,
which phase will it be for
the Southern Hemisphere?
5- How much of the entire Moon surface is illuminated by the
Sun during New Moon?

22. a) None of the surface.
b) Less than half of the surface is illuminated.
c) Half of he surface is illuminated.
6- How much of the Moon’s illuminated surface is visible from
Earth during New
Moon?
a) None of the surface (visible from Earth) is illuminated.
b) Less than half of the surface (visible from Earth) is
illuminated.
c) Half of the surface (visible from Earth) is illuminated.
7- You observe a full Moon rising in the east. Which image
shown best represents how the Moon
will appear as it is setting?
The time for the Moon to make one complete orbit is the same
time as it takes to rotate on its
axis, and is approximately 27.3 days. As a result, the Moon
always keeps the same face
toward earth. In fact, nobody knew what was on the far side
(the side we never see) of the
Moon until it was photographed from spacecraft in the 1960’s.
8- What is the phase of the Moon when the dark side (night) and
the far side (the side we
never see) of the Moon are the same? Include a sketch.

23. 9- What is the phase of the Moon when the dark side (night)
of the Moon is facing Earth?
Include a sketch.
3
To determine how and when the various phases of the Moon
occur, we will find it useful to
look at the following diagram:
The diagram above is a view of the Moon’s orbit from the NCP
(North Celestial Pole)
perspective. When the Moon is located in its orbit in the
general direction of the sun, it
cannot be seen. Not only is it located in the bright, daytime sky,
but also the hemisphere
facing the earth is not sunlit. This is known as new Moon. At all
other positions in its orbit,

24. the Moon is visible. The changing shape of the illuminated
portion of Moon, as different
amounts of the sunlit face are seen, is known as the phase cycle.
Following new Moon, one
sees crescent phases for several days. Crescent phase is
followed by the first quarter Moon,
then the gibbous phases until full Moon is reached. This waxing
(increasing illumination) half
of the cycle is followed by the waning (decreasing illumination)
half of the cycle, returning
to the new Moon again.
S
U
N
LI
G
H
T
Full Moon
1st QTR
Waxing
Gibbous
Waxing
Crescent
New Moon

25. Waning
Gibbous
3rd QTR
Waning
Crescent
Earth
Dusk
Midnight Noon
Dawn
4
One can use the Moon phase diagram to determine rising and
setting times. (The local time
is given by the clock time directly above the observer's head.
For example, a first quarter
Moon sets around midnight).

26. Note that the Moon orbits counterclockwise (to the east) and
that the earth also rotates
counterclockwise (to the east).
I

27. nc
om
in
g
su
nl
ig
ht
Mid-
night
Dusk
Dawn
Noon
1st
QTR
Waning
Gibbous
Full
Moon
Waxing

28. Gibbous
Waxing
Crescent
New
Moon
3rd
QTR
Waning
Crescent
5
PROCEDURE:
The Moon phase diagram is a useful tool in determining where
the Moon is at a particular time
of day when the Moon is in a given phase.
Cut out the diagram on the following page and to familiarize
yourself with its use, use this
diagram to answer the questions below.
CUT ALONG THE DOTTED LINES
I
nc
om

29. in
g
su
nl
ig
ht
Mid-
night
Dusk
Dawn
Noon
1st
QTR
Waning
Gibbous
Full
Moon
Waxing
Gibbous
Waxing

30. Crescent
New
Moon
3rd
QTR
Waning
Crescent
The non-shaded regions of the
moon are the illuminated regions
E W
6
10. For the following table, use your Moon phase diagram to
determine the approximate times
of moonrise, moonset, and meridian crossing for each Moon
phase.
Phase of Moon Time of Moonrise Time that Moon is on the
Meridian Time of Moonset
New Moon
1st Quarter

31. Full Moon
3rd Quarter
11- Which of the following could never happen?
a) An observer seeing a full Moon in the middle of the day
(local noon).
b) An observer seeing a new Moon in the middle of the night
(local midnight).
c) Both of the above observations are impossible for any
observer to see.
12- You and your friend are walking home from a party one
night and your friend asks
you what time it is. Neither of you are wearing a watch but you
notice that the full Moon
is at its highest point in the sky (crossing the meridian).
Approximately what time is it?
13- For some reason you awake near dawn and notice that the
Moon is halfway between
the eastern horizon and zenith. What is the phase of the Moon?
14- You are looking at the Moon shortly after sunset. Which of
the views shown below
will you never see? Why not?

32. 15- If a base were built on the near side of the Moon, would the
residents see sunrise?
Would they see ‘earthrise’ and ‘earthset’?
7
16- If a base were built on the far side of the Moon, would the
residents see sunrise?
Would they see ‘earthrise’ and ‘earthset’?
17- Does an observer on the near side of the Moon see the
Earth on phases?
18- If an astronaut on the Moon see a full Earth, what would an
observer on Earth see
when observing the Moon?
19- If the Moon is a waxing crescent what would an astronaut
on the Moon see when
observing Earth?
Lunar Eclipses

33. Eclipses occur when the Moon and the earth are aligned with
the sun, so that the shadow of
one of these falls on the other. If the earth is between the sun
and the Moon, then we have a
lunar eclipse (when the earth’s shadow falls on the Moon).
If the Moon is completely within the umbra, we have a total
lunar eclipse.
Solar Eclipses
A less common occurrence is a solar eclipse. In a solar eclipse
the Moon is aligned between
the sun and the earth. Because the Moon is smaller than the
earth, the lunar shadow never
covers the earth completely.

34. (1) S
U
N
(a) E
a
r
t
h
Penumbra
Umbra
Sun
Earth
Penumbra
Umbra
(2)
8
This figure illustrates the geometry of a solar eclipse. For
somebody standing within the
umbra, the Moon blocks the entire sun and a total solar eclipse
is viewed. In the
penumbra surrounding the umbral area only part of the sun’s
direct rays are blocked and
somebody standing within this region views a partial solar

35. eclipse.
The lunar orbit is somewhat elliptical, and the mean distance
between the earth and the Moon
varies from about 226,000 to 252,000 miles. Solar eclipses that
occur at times when the
Moon appears smaller than the sun are called annular solar
eclipses.
20- By looking at your Moon phase diagram, determine the
phase of the Moon during which a
lunar and solar eclipse can occur.
Type of Eclipse Moon Phase
Lunar
Solar

36. 21- Why don’t eclipses occur on a monthly basis? Doesn't the
Moon come between the
earth and the sun every 29.5 days?
22-
The photographs above are showing:
a) Total lunar eclipse, annular solar eclipse, partial solar
eclipse
b) Total solar eclipse, partial solar eclipse, Lunar eclipse
c) Total solar eclipse, annular solar eclipse, partial solar eclipse
Penumbra
Umbra
(3)
9
23- For the following diagrams, use a straight edge to draw the
sun’s rays that outline the
earth’s and Moon’s shadows. Label the umbra and penumbra on
each one. Be specific
on the type of eclipse (partial or total, lunar or solar, etc.)

37. Type of eclipse ________________________
Type of eclipse ________________________
Type of eclipse ________________________
SUN Earth
SUN Earth
SUN Earth