Download Lab Manual part 2

Physics 44
Lab Manual
Part II
Fall 2004
Instructor: Francis Wilkin
Contents:
page
Lab #3: The Celestron C4.5 Telescope
2
Lab #4: Astrophotography and Filters in Observations of the Sun and Moon
5
--------------------------------------------------------------------------------------------------------------------Lab #3: The Celestron C4.5 Telescope.
This is a Newtonian Reflector. Explain what that means.
A. Setting-up and Using The C4.5 for Viewing with Eye:
1. To ensure that the telescope is oriented properly, you need to first find the North Pole star
The easiest way is to find the Big Dipper, and then follow the line indicated by the last
two stars in the pan of the dipper. This line points to the North Pole star (Polaris). You
know you've found Polaris if it is also the first star in the Little Dipper and you can be
sure that you have the Little Dipper if its pan is pouring into the Big Dipper and the Big
Dipper's pan pours into the Little Dipper.
2. Set-up the tripod:
Find the leg with the 'N' on it and line up this leg with the North Pole.
Using the wing-nuts, attach the triangular tray to the brackets that are half-way up the
legs of the tripod.
3. Mount the telescope onto the tripod as instructed:
Note the loose metal rings on the telescope and that these rings have nuts with knobs.
These nuts go into screw holes in the brace at the top of the tripod. As you mount the
telescope, be sure that the eyepiece holder and finder-scope are toward the outside of the
telescope. That is, you want the nuts to be on the opposite side of the telescope from the
eyepiece and finder scope.
4. Get familiar with the telescope and its parts: Identify each of the following.
a. The front of the telescope is the end by the eyepiece holder. (Do you understand
why the eyepiece is by the front of the telescope?) There should be a dust cover on the
front that easily pops off. Be sure not to lose this cover, or any dust cover (such as those
on the finder scope) for that matter.
b. RA and Dec axes. Note that the telescope can swing about two different axes. When
the telescope swings about its middle like a baton, it is swinging about the DEC axis; and
when part of the mount moves with the telescope as it swings around perpendicularly to
the first swing, then the telescope is swinging about the RA axis.
c. Locks and fine-adjust knobs. Each of these two axes has lock handles, which you use
to fix the telescope in position when you want. These handles are silver. There is a third
similar looking lock handle. This third lock handle has tape on it, to help distinguish it
from the RA and DEC lock handles, and locks the altitude of the telescope (described
below). It should be obvious to you when you turn the handles when they are locked. To
unlock, you only need to turn these handles a 1/2 turn counterclockwise. There are also
black knobs, which enable you to turn the telescope on these axes more slowly and with
more control. These are the fine-adjust knobs. They are used when you have the
telescope close to, but not at, the position you want it to be. These knobs are used, for
example, to help center an object in the field of view (either in the telescope or the finder
scope).
d. Altitude axis and lock. The whole mount (everything but the tripod) can move on a
third axis. This determines the “altitude” of the main axis of the telescope mount, i.e. the
angle above the horizon (or above the level) that the axis points. Except for the initial
alignment of the mount with the North Pole (step H.) you should keep this movement
locked. The altitude lock handle has tape on it, to remind you to leave it alone.
e. Finder scope. The miniature telescope attached to the big telescope (and that looks
like a parasite fish following a whale) is known as the finder scope and is used for getting
the celestial object of interest into the field of view of the telescope. The finder scope,
with its low magnification, has a much larger field of view than the telescope. So, it is
much easier to line up the telescope to get a particular object into the field of view of the
finder scope than it is to get into the field of view of the telescope. Once you get the
object into the field of view of the finder scope, you can adjust the position of the
telescope using the fine-adjust knobs to get the object at the center of the cross hairs of
the finder scope. Then, if the finder scope is properly aligned, that object should be in the
field of view of the telescope.
f. Eyepiece holder and focus knob. The telescope will not already have an eyepiece.
The holder for the eyepiece should be obvious. Notice that it has a little set screw to lock
onto the eyepiece when you put it in. On the eyepiece holder right by the telescope is the
focus knob. Every single time that you put in a new eyepiece you will need to re-focus.
(Question: Since everything in the sky is essentially infinitely far away, and so the
focus should always be set to infinity, why would you need to refocus when putting
in a different eyepiece?)
g. Setting circles. Note the two silver dials. These are the DEC and RA dials, generally
referred to as setting circles. These dials will enable you to determine what RA and DEC
the telescope is pointing to and therefore will enable you to find faint objects. The RA
setting circle should spin freely, so don't let its looseness concern you. Note also that the
RA numbers are the red ones, not the black.
5. Install the Eyepiece
Insert a long-focal length eyepiece into the eyepiece holder and lock it down. A long
focal-length means that it has poor magnification, and therefore a large field of view. You
will find it very hard to get an object in the center of the field of view using the highest
power eyepiece, so you should always start with a long-focal length eyepiece. Once you
have the object in the center of the field of view of the lower power eyepiece, then you
can put in the higher power eyepiece.
6. Align the Finder Scope
The alignment of the finder scope with the telescope is very important. If the finder
scope is not well aligned, you will find it very difficult to find any object. So, this is a
very important step. However, once the finder scope is aligned it will probably stay
aligned for a long time. If the finder scope has been aligned within the last year, you
should find that the finder scope IS already aligned and so this step will be only a check.
But, you should always take the few minutes necessary to check that it is indeed aligned.
You never know who the last bozo to mess with the telescope was, and you’ll save
yourself a lot of agony if you discover the finder scope is misaligned before you try to
use it to center an object. Find a distant, bright, and easy to see object (such as a distant
street light) and move the telescope so that the object is in the center of the field of view
of the telescope (you'll probably need to focus) and lock the axes. Then check the finder
scope. If the object is not exactly in the center of the cross hairs of the finder scope then
you need to adjust the finder scope. To do so, use the three set screws on the finder
scope. You'll need to loosen one screw to turn another.
7. Move to the desired object by Star-Hopping. What is Star-Hopping? “Star-Hopping:” Study
your star chart that contains the object you wish to view. Take note of the brightest stars
that are near your object. Identify those stars in the sky. Move your telescope to point at
one of those brightest stars. Use the double-eye method to confirm that the telescope is
aimed at the correct star. Then, map out a route on the star chart that gets you to the
desired object by hopping from star to star, as if they are stepping stones in a stream. In
general, you’ll want to start with the brightest stars, and hop to slightly fainter stars...until
you’re close enough to the desired location that a small movement of the telescope in the
correct direction will get you to the desired object. Try to follow those hops with your
telescope, using the double eye method as much as possible. When you get good at this
method, you can find almost any object within a few minutes.
C. Exercises (after successfully lining up with North Pole): (Be sure to take careful logs)
Fall Term (2004):
1. With a low-power eyepiece, point the telescope at the Double Cluster (Chi and Eta Persei).
How does the image of these clusters compare with what you saw on your photographs
with an ordinary camera? Look at the clusters with binoculars. Which of the three
situations gives you the best view? Why?
2. Point the telescope to Deneb (see sky and planet locator). What do you see. Describe in
detail your observations.
3. Try to find M13 (If it is still high enough in the sky). M13 is the “cluster” shown on the Star
and Planet Locator and its coordinates are listed below. What do you see? What is
M13, as explained in your text (see Figure 15.10, p. 456, and read pp. 455-456)?
Mention any significant pieces of information regarding this object.
5. If is late enough in the term and in the evening, use your star and planet locator to find
Saturn. Point your telescope at Saturn and look at it in awe for as long as you like.
Describe what you see? Look carefully and take note of all features that you can identify.
You can refer to your textbook to identify all that you see. Draw pictures for your
report.
6. Point the telescope to M31. M31, which is more commonly known as the Andromeda
Galaxy, is the “galaxy” shown on the Star and Planet Locator in the constellation of
Andromeda. What do you see? What is M31? Mention any significant discoveries
regarding Andromeda (ask your instructor if you don’t know).
7. If you have time try finding the Ring Nebula (M57). When you first get it in your scope it
may look like a star, but when you study it carefully with a high power eyepiece you will
see that it is a little different. Describe what you see. What is the Ring Nebula (see
section 13.6).
Coordinates of stars and objects of interest:
star or object
RA
Dec
Double Cluster
02h 22.3m
57o 6.5’
Altair
19h 44.8m
08o 52’
Deneb
left for you to determine as an exercise
M13 (Hercules cluster)
16h 41.7m
36o 28’
M31 (Andromeda Galaxy) 00h 42.7m
41o 15’
M57 (Ring Nebula)
18h 53.5m
33o 02’
D. Dismantling
1. Remove the eyepiece and puts its lens cover(s) on and give all your eyepieces to the
instructor.
2. Put covers back on: the front of the telescope, both ends of the finder scope, and on the
eyepiece holder.
3. Take the telescope off the mount.
4. Take the tripod tray off (and put the wing nuts back onto the tripod to keep from losing the
wing nuts).
5. Carry all the parts back to the storage room and help put them away.
Lab #4: Astrophotography and Filters: Observations of the Sun and Moon
Before coming to lab, read pages 188-192, 330-338 in the text and consider the following end of
chapter questions. Chapter 6: “Questions for Review” #2, 3, and 4, “Problem” #2. Chapter 11:
“Questions for Review” #1, 12, 13, 15, 20, and 21; “Test Yourself” #2 and 3.
I. Familiarize Yourself with the New Equipment:
A. Filters: Some filters, including a “moon filter,” are inserted by screwing into the eyepiece.
and some, such as “solar filters,” are mounted on the front of the telescope. A solar filter must
mount on the front because the intensity of the Sun’s radiation can heat and deform the optics of
the telescope, so it is important to filter out most of the Sun’s radiation before it enters the
telescope. While in the lab room, practice installing the different types of eyepieces.
B. Attaching the Camera to the Telescope.
Try to get the same camera you used in lab #2B, so that the knobs will be somewhat familiar
to you. In the first camera lab, you were taught about three adjustments on the camera: the
focus, the f-stop, and the exposure time. When you mount a camera onto a telescope, you won’t
be using the lens since the telescope will be your lens. So, you don’t need to worry about the
focus and f-stop...but be sure you remember how to adjust the exposure time and what the
numbers on the dial actually mean. There is need now to understand two other settings on the
camera. These are how to tell the camera what speed film you’ve loaded and then how to read
the camera’s meter for the suggested exposure time. Each camera is different with regards to
this adjustment, so you’ll need to learn about your camera in particular.
The procedure for attaching the camera to telescope is complicated. There are two different
set-ups: one for using the camera instead of an eyepiece (called “focal plane photography”) and
one for using the camera in combination with an eyepiece (for greater magnification pictures). A
written description would be very hard to follow, so take careful notes on the instruction in the
classroom.
NOTE: There are many small parts involved in these set-ups that can easily get mixed up.
You’ll need to be sure to keep them straight. I suggest that each person be given responsibility
for different attachments, i.e. person A be responsible for attaching and keeping track of the
pieces of the “tele-extender,” person B be responsible for the “T-mount” (one small piece, but
which is easily mixed up with other small pieces). VERY IMPORTANT: Don’t use your
strength to force any item to screw into another. All screw attachment take little force, but
wrong match-ups can (and have been, in the past) be forced. DO NOT USE your strength to
make anything happen.
Bring outside: a C4.5 telescope, eyepieces, a Moon filter, a Solar filter, a loaded (with 100 ASA
film) camera, a shutter release cable, a T-mount, a tele-extender, and a T-mount adapter.
II. Observations of the Sun.
Warning: Do not attempt any observations of the Sun of any sort without guidance. The
radiation from the Sun when focused with a telescope can destroy your eye as well as the
optics of a telescope. (Take note of the all the bold face instructions below.)
About 1 hour before sunset, set-up the Celestron C4.5 telescope, but be sure not to aim it
towards the Sun accidentally during setup. You don’t need to worry about aligning the
telescope mount with the North Pole. But, you do need to put in a long focal length eyepiece and
focus the telescope on a very distant object. Then place a solar filter over the front of the
telescope and put a lens cap on the finder scope. Swing the telescope so that it is pointed
towards the Sun. To aim it at the Sun, look at the shadow of the barrel of the telescope and try to
get the shadow to be that of only the round end of the barrel (i.e. so that the shadow of the length
of the barrel disappears). To check the alignment better, for a brief moment, take the cap off
the finder scope and place your hand behind finder scope and note whether there is a very bright
spot centered in the circular image on your hand. DO NOT LOOK THROUGH THE
FINDERSCOPE WITH YOUR EYE!!! If you aligned the telescope with the shadow properly,
you should see a bright spot, but it might not be centered. Fine adjust the telescope so that the
bright spot is centered and place the cap back onto the finder scope. Now, provided that you
do still have the solar filter over the front of the telescope (CHECK FIRST! If you didn’t really
get the filter right it have might fallen off), look through the eyepiece of the telescope. The Sun
should look a dull orange. With the long focal-length eyepiece in, you should see the edges of
the Sun. You may also see some dark spots somewhere on the Sun. These are called sunspots.
Observations:
A. How many sunspots do you see? Draw the pattern of sunspots.
B. Center on the largest spot and put in a high-power eyepiece. What is the shape of the spot?
Comment on any interesting detail that you see.
C. Considering that the diameter of the Sun is about 100x the diameter of the Earth, roughly
estimate the size of the spot relative to the size of the Earth.
D. In your report, discuss what a sunspot is and why it looks black (read pp 338 + section
11.5 in your text).
III. Observations of the Moon:
Set-up the Celestron C4.5 telescope:
1. Move the telescope away from the Sun and towards the Moon, and take off the solar filter and
the cap to the finder scope.
2. Put in a long focal length eyepiece and focus the telescope (check again).
3. Check the alignment of the finder scope.
4. Roughly align with the North Pole.
5. Point the telescope at the Moon (which is in “First Quarter Phase,” meaning that you see half
of the side of the moon that you see is lighted).
A. Take a quick look at the Moon through the low-power eyepiece. Then remove the eyepiece,
screw a Moon-filter into the eyepiece, and put the eyepiece back in. Look at the Moon again.
Comment, in your report, on the purpose of the Moon filter.
B. Study the Moon and take note of the shadows. In particular, note the lengths of the shadows
as you look at different spots on the Moon. Where are the shadows the longest? Why?
(Ask your instructor if confused).
C. Compare the terrain of the dark regions to that of the light regions. When Galileo first looked
at the Moon through a telescope, he called the dark regions “maria”, which is latin for “seas.”
Can you see why he called them that? (Note, they are not really seas, but Galileo thought
that they might be.)
D. Put in a high-power eyepiece (with moon filter). What is the focal length of your high-power
eyepiece? What fraction of the Moon can you see in the field of view with this eyepiece?
Considering the diameter of the Moon is about ½o in the sky, what is the field of view with
the high-power eyepiece? Estimate the field of view of the low-power eyepiece by using the
ratio of the focal lengths.
IV. Telescopic Photos of the Moon:
A. Attach the camera as instructed in lab and rebalance the telescope.
B. Align the telescope with the Moon again and focus the camera
C. Looking through the camera’s viewfinder, position the telescope for your desired picture.
NOTE: there may now be two focus knobs, the one on the telescope and the tele-extender
tube, whose length can be adjusted. You should be able to get the image into focus with a
number of different combinations of these two adjustments, but the size of the image will
vary. Play with the two focuses to get the largest image in focus.
D. Try to read the camera’s meter for the suggested exposure time. Take five pictures at
different exposure times, centered on the suggested exposure time.
E. Replace the low-power eyepiece with a high-power eyepiece. Take five pictures in the
middle of the moon at the “terminator” (the boundary between shadow and light on the
moon), and five pictures at one of the poles, and five pictures of the limb (the outer edge).
BE SURE to check the view through the camera before each exposure (with the high-power
eyepiece the Moon will appear to move a lot in a short period of time).
V. Afterwards.
After you get your pictures developed, take note of and comment on how well the camera’s
suggested exposure time worked. What exposures worked best? Include your photos with your
report. You can get them back to keep after your instructor has graded the lab (or you can keep
the negatives and get prints made again...you can even make posters if you like).