Credit/Permission: For text, © David Jeffery. For figures etc., as specified with the figure etc. / Only for reading and use by the instructors and students of the UNLV astronomy laboratory course.
Sub Tasks:
Sub Tasks:
Sub Tasks:
Each group member OR each group as specified by the
instructor
should print out the figure below
(local link /
general link: field_of_view_inversions.html)
and complete it
by drawing the point inverted
and axis reflected
(the 2-d analog of plane reflected)
versions of the field of view (FOV)
which contains the Alien.
The point inversion
can be done easily using two printouts and rotating one 180° and
tracing
on the other.
The axis reflection
is tricky to understand in a sense, but
it is just what happens in Image 1 of the figure above
(local link /
general link: optics_reflection_plane.html).
It's probably best to just to use your artistic skill to do the
axis reflection.
But it can be done with tracing
too plus some trickery.
Trace the
FOV without the
star diagonal (but with
the Alien
point inverted already drawn)
on the back of the printout.
That will effect the axis reflection.
Then trace that tracing
to a separate sheet of paper, and then
do the final tracing
from the separate sheet of paper to the printout
for the FOV with
the star diagonal.
But make sure the completed
FOV with
the star diagonal
has the
Alien in the RIGHT PLACE on
the reflection axis,
NOT shifted off the reflection axis,
etc.
Append the printout to your report form. Each group should have a printout.
Sub Tasks:
What is our
C8
finderscope specification
and what does it MEAN? HINT: Look at the
C8
on display in the classroom if there is one and click on
Wikipedia: Finderscope: Function and Design.
Complete the following procedure for centering an object in the
field of view (FOV) of
a C8:
Sub Tasks:
Sub Tasks:
To prep for having real observations, let's apply the
FOV timing formula to some synthetic observations.
Remember, just round off the declination
values to the nearest degree.
Sub Tasks:
Look at the figure
local link: sky_swirl_polaris_ehrenbuerg.html
below and watch the accompanying
videos.
The star trails each take
the same time to form in the
long-exposure image
and have the same angle
around the celestial axis.
But the field of view (FOV)
angular diameter
is an angular diameter
subtended at the observer
and is the SAME for any
declination.
So as you go to higher in declination
(i.e., get closer to the
celestial axis)
it takes a longer star trail
and thus a longer
transit time
to transit the
FOV.
In fact, the transit time
is infinite at the
celestial axis.
Do you understand why now? Y / N
Some time before observations get the
instructor
to give your group a hands-on
intro to the C8's.
The instuctor could call you up for the intro or you could take the initiative in getting him/her to give
you the intro.
You or a group member has had the intro. Y / N
You or a group member has at least mostly covered all the sub tasks below. Y / N
Sub Tasks:
For more detailed information, see
Telescope
Operating Procedure for Instructors
or
Telescope
Operating Procedure for Instructors, pdf.
Each group will need a sky map
to help locate the star choices for tonight's observations.
Sub Tasks:
Write down the two star choices for tonight's observations and their
declinations.
Sub Tasks:
This takes a little practice.
Time 1: _______ m _______ s = ______________ m with decimal fraction.
If NO observation, use: 1:20.
Time 2: _______ m _______ s = ______________ m with decimal fraction.
If NO observation, use: 1:22.
Time 3: _______ m _______ s = ______________ m with decimal fraction.
If NO observation, use: 0:22.
Average Time: ________________ m with decimal fraction
Note if any of the 3 timings differ from the others by more than 20 seconds,
then you probably have made some error.
Repeat the timing in this case or neglect the out-of-trend observation in the average time calculation.
Evaluate the FOV timing formula
(which is linked to its name)
to get
the FOV
angular diameter.
Remember to give the units, arcminutes (').
Result: _____________________
This measurement was done with our standard 40 mm
eyepiece.
Make sure that the first star
is very well centered before proceeding. The new
eyepiece has
a smaller FOV
and it is easy to lose the
star
and NOT find it again.
However, it doesn't really matter since any
star in the vicinity of
the first star will do as well
for the measurement.
Now remove the standard eyepiece just
loosening the screws NOT taking them out---if you take them out you will drop them
and they'll roll into the crevices and we'll NEVER get them out.
Put the standard eyepiece
in the box designated for doing that so it is safe.
But, if your
instructor
allows it, you can put it on the base right by the pillar
and the electrical connection in an upright position
so it is safe and will NOT roll off.
Put the new eyepiece
in and tighten the screws enough so that the
eyepiece is snuck---but don't
grind the screws in.
What is the focal length
of the new eyepiece?
_________________
Time 1: _______ m _______ s = ______________ m with decimal fraction.
If NO observation, use (i) 2:01, (ii) 1:21, (iii) 0:57, OR (iv) 0:40 as your
instructor designates.
Time 2: _______ m _______ s = ______________ m with decimal fraction.
If NO observation use (i) 1:59, (ii) 1:18, (iii) 0:56, OR (iv) 0:37 as your
instructor designates.
Time 3: _______ m _______ s = ______________ m with decimal fraction.
If NO observation use (i) 2:05, (ii) 1:25, (iii) 1:01, OR (iv) 0:43 as your
instructor designates.
Average Time: ________________ m with decimal fraction
Note if any of the 3 timings differ from the others by more than 20 seconds,
then you probably have made some error.
Repeat the timing in this case or neglect the out-of-trend observation in the average time calculation.
Evaluate the FOV timing formula
(which linked to its name)
to get
the FOV
angular diameter.
Remember to give the units, arcminutes (').
Result: _____________________
Time 1: _______ m _______ s = ______________ m with decimal fraction.
If NO observation use 4:05.
Time 2: _______ m _______ s = ______________ m with decimal fraction.
If NO observation use 4:00.
Time 3: _______ m _______ s = ______________ m with decimal fraction.
If NO observation use 3:55.
Average Time: ________________ m with decimal fraction
Note if any of the 3 timings differ from the others by more than 20 seconds,
then you probably have made some error.
Repeat the timing in this case or neglect the out-of-trend observation in the average time calculation.
Evaluate the FOV timing formula
(which linked to its name)
to get
the FOV
angular diameter.
Remember to give the units, arcminutes (').
Result: _____________________
At the end of the observing:
If you are the last section observing and NOT otherwise, you:
Have we have done all these things? Y / N
Complete the following table using your own calculated values
and values obtained from other groups.
EOF
The red laser dot is powered by
a little lithium battery
which is frequently dead.
The star pointer
can still be used, but you have stand a meter or so off from it and
get a little practice.
Some nights, yours truly can do this pretty niftily, other nights, no luck.
Mark the two star choices on your printed out
sky map in such a way that
you can see them easily outside.
________________________________________________________________
Table: C8 telescope specifications for available eyepieces
________________________________________________________________
focal length magnification approximate
(mm) (X) fields of view
(arcminutes = ')
________________________________________________________________
40
25
18
12.5
9
________________________________________________________________