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ASTRONOMY 3130: A Guide to Scientific Presentation
(Your Lab Write-Ups)
While most students will have had experience writing up lab reports from
high school science courses, for some students this may be the first
time they have been asked to present the results of a experiment
according to the standard structure adopted by most scientists for
reporting research. Therefore, this webpage gives
both a general outline of what is expected for lab write-ups in this
class, but also specific examples relating to the work in this first lab
of the semester. Other lab reports you hand in this semester should
follow this general format.
While I will not give you everything
that should be included in your first lab write-up, enough will be given
that you can adopt much of the skeletal structure given here and need only
fill in details around it. However, do not just hand back this guide
with notes written on it! Rewrite any of the following guide that
you adopt into your own version of the report. Note also that you
are expected to supply your own data for this work!
All reports are expected
to be typed or word-processed, with graphs and figures inserted in the
proper place or clearly referenced from the text of your report.
If the report style that follows
seems mystifying or even arcane, I invite you to spend some time
leafing through scientific journals (e.g., The Astrophysical
Journal Letters) to see that, in general, the approach we are requesting here is
the same as that followed in the professional literature.
You should keep this guide to writing up lab reports for use throughout the
The basic structure of your lab reports should be as follows:
I. COVER PAGE
Somewhere near the beginning of the Lab, perhaps on
a cover page, list your name, your group name (e.g., ``Group 1"), and the
names of the people
in the group with whom you took (and reduced/analyzed) the data. In labs
where you will take images or other data, you should also list where those
data are stored.
What is the scientific reason for undertaking the
lab activities? In a professional context, the scientist would have no
problem writing down the purpose of an experiment because he/she will
have been motivated to do it by some burning question or hypothesis they
want to answer. In this class,
however, where you are being given a set of activities to do, it may not seem
so obvious at the onset what the purpose is. However, by reading through the lab
before doing the experiment and then undertaking the activities it should become
obvious what are the fundamental scientific points we are trying to have you
address. What you put down for the ``Purpose" section of the lab report is
thus an important indicator of how well you understood the scientific
principles of the lab.
We want to know that YOU know the scientific purpose of the lab.
Please do not put as your purpose something like
``The purpose was to learn about telescopes". Yes, this is an ancillary goal
of the lab, but we are trying to train you in the methods of professional scientists.
A professional astronomer would never write in one of their research papers
something like ``We undertook the measurement of the radial velocity variations in
the star Gamma Scropheles because we wanted to learn how to use a spectrograph"!
Thus, for example, in the first lab of the semester, we would expect a purpose something like
"The goal of this experiment is to determine: (1) the relationship between the
field of view and magnification for different eyepieces used with a given
telescope, and (2) the relationship between field of view and aperture
diameter with a given telescope and eyepiece.''
This section of your report should be a
simple description of the general procedures followed
for each part of the experiment (please do not just reiterate the instructions of the
lab, but rather explain briefly the general idea of what was done and why). The point
of this part of the lab is to describe how the experiment was carried out at a
level of detail sufficient for a colleague to be able to reproduce the general procedures
independently (though not necessarily copy exactly everything you did).
This does not need to be long, but it should give a general idea of what was done
and the techniques
used. You should also give information on the date(s) of observations and
the name of the telescope and instrument used. Weather information (e.g., seeing
conditions, clouds, moon phase) is also standard information astronomers give
in their reports.
Here is an example of the kind of thing we are looking for:
"Observations were carried out on the night of UT 30 August 2012
using the 6-inch Clark refractor at McCormick Observatory and the Doghouse
eyepiece and aperture stop set.
The sky was not photometric;
some high cirrus clouds were noted, but we were still
able to see bright stars. There was a waning crescent moon in the east. There was
no wind and the atmosphere was calm, as evidenced by only slow
scintillation ("twinkling") of stars.
To measure fields of view we used the transit time of stars across
the center of the field of view through the eyepiece. For all measurements the star
which has J2000.0 coordinates (α, δ) = (19h51m, 8o53'),
The transit times were then converted to field of view angles, after
accounting for the declination of the star. The same observer (Jane Doe) made
the observations of ingress and egress of the star from the field of view
and signaled start and stop times to John Smith, who used a digital watch
to time the transit.
We first measured the transit time (field of view) three times each for the
32 mm eyepiece, the 12.5 mm and the 7.4 mm
eyepieces, respectively, on the 6-inch refractor, and one
time for the finder scope.
We then made three measurements of the transit time (field of view) using the 7.4 mm
eyepiece but with the telescope stopped down to a 3-inch aperture. The results of these
observations are presented below."
In this section you should present all of the results of
your observations and analysis, including the measured data, your
calculations, graphs, and answers to the questions put forth in the Lab handout.
mark clearly in your write-up the number of the question (e.g., ``Question 1" or ``Point (3)")
when you answer it, to help make it easier for us to find your answers when
grading this assignment. We don't want
to hunt for your answers. Therefore, the structure of
your results section should more or less mirror the order and
outline of the lab instructions. Make sure to answer all of the
questions asked in the lab. Please note:
The skeleton of a results section for this particular lab might look something like this
(obviously, you should use your own numbers and the ones provided here are just
Part 1: Field of View Versus Magnification
- All data taken should be neatly tabulated when possible.
- Show your calculations so that if there is a mistake
in your answer, we can tell whether it was a simple math error
or a more worrisome conceptual or measurement error.
- Graphs should have clearly labeled and graduated axes. Make sure the dependent
variable (the part of the experiment you measured) is on the ordinate and the
independent variable (the part of the experiment you set --- e.g.,
the eyepiece focal length) is on the abscissa.
- If you include figures (e.g., graphs) and tables at the end of your report, each
should be labeled clearly (e.g., "Figure 1", "Table 3") and referred to by that label
in the text of your report.
- Please endeavor to record in your lab report only significant digits. Just
because your calculator puts out six decimals of precision on some calculation does not mean
that they are all meaningful and should be recorded. Have a good idea of to what precision
you can trust your measurements and calculations.
We will discuss more about significant digits as the semester progresses.
(Question 1) The focal ratio of the Clark 6-inch refractor is given by
the formula f\# = F/D where F is the focal length of the objective and
D is its diameter. Thus....(fill in your own words here).
(Question 2) According to Whittaker's rule, the estimated upper limit to
magnification is given by m < D in mm. This would imply that the maximum
useful resolution of the 6-inch telescope is m=..., though
Roy & Clarke, in their book Astronomy: Principles and Practice,
point out that with smaller apertures it is possible to exceed
Whittaker's rule. An estimate for the lower limit on useful magnification
is given by....
(Question 3) The magnifications of the eyepieces can be found
magnification = FLobjective / FLeyepiece = 1830 mm / FLeyepiece,
from which magnifications of 73X for the 25 mm eyepiece
and 203X for the 9 mm eyepiece are obtained. The exit pupils
can be determined from ....
Table 2 below includes the expected magnification and exit
pupil expected for each eyepiece. We note that all of the exit pupils
are smaller than the typical human eye pupil (7 mm); this means....
For all measurements of the field of view we used the star
Altair, which has J2000.0 coordinates (α, δ) = (19h51m, 8o53').
Table 1 shows the results of these measurements (Question 5).
Table 1: Field of View Measurements for Different Eyepieces
We estimate that the error on the Table 1 measurements is about 3 seconds
with the 25 mm eyepiece, but maybe a little better (1 or 2 seconds) with
the 9 mm eyepiece (Question 6) because the quickness
of the star's apparent motion makes it easier to tell when it is in and out
of the field of view in the latter case.
The error comes about because it is difficult to judge precisely when
the star enters and exits the field of view, and there is an imprecision
and delay in conveying the occurrence of those events to the timekeeper.
The average timing and standard deviation for the 9 mm eyepiece are 51 +/- 1 seconds
and for the 25 mm eyepiece are 140.3 +/- 2.5 seconds (Question 7).
The standard deviations
calculated here are similar to our estimates above of about 1-2 seconds
for the 9 mm eyepiece and 3 seconds for the 25 mm (Question 7).
The timings above can be converted to an angular field of view using the
FOV(arcminutes) = FOV(minutes) * 15 cosδ .
(Question 8) Thus, we obtain a field of view of
51s (1m/60s)(15)(cos(8.9o)) = 12.6 arcminutes
for the 9 mm eyepiece and an error of
1s (1m/60s)(15)(cos(8.9o)) = 0.2 arcminutes .
140.3s (1m/60s)(15)(cos(8.9o)) = 34.7 arcminutes for the 25 mm eyepiece and an error of
2.5s (1m/60s)(15)(cos(8.9o)) = 0.6 arcminutes.
Finally, for the finder scope one gets:
802s (1m/60s)(15)(cos(8.9o)) = 198 arcminutes = 3.3o.
(Question 9) The derivation of this conversion formula is...
(I can't give you all the answers!)
Thus the results of this experiment are as summarized in Table 2:
Table 2: Field of View Versus Magnification
| eyepiece || time (seconds) |
| 9 mm (trial 1) || 51
|| 9 mm (trial 2) || 50
|| 9 mm (trial 3) || 52
| 25 mm (trial 1) || 140
|| 25 mm (trial 2) || 143
|| 25 mm (trial 3) || 138
|finder scope || 802
We note an interesting correlation in these data between magnification and
field of view, which is that .....
Part 2: Field of View Versus Magnification
(Question 10) In the second part of the lab
we check field of view timings using the same
eyepiece but different telescope apertures. We use the 9 mm eyepiece
for these measurements and find (using the 9 mm data for the 6-inch
aperture from the table above) the results given in Table 3.
Table 3: Field of View Measurements with Different Apertures and 9 mm Eyepiece
| eyepiece || magnification || field of view (arcmin) || exit pupil (mm) |
| 9 mm || 203 || 12.6 +/- 0.2 || 0.75 |
| 25 mm || 73 || 34.7 +/- 0.6 || 2.1 |
For the 9 mm eyepiece and the 6 inch aperture the
timing measured is 51 +/- 1 sec and this corresponds to 12.6 +/- 0.2 arcmin.
For the 3 inch aperture we find an average time of 51.3 +/- 1.5 seconds
and this corresponds to
51.3s (1m/60s)(15)(cos(8.9o)) = 12.7 arcminutes
for the 9 mm eyepiece and an error of
1.5s (1m/60s)(15)(cos(8.9o)) = 0.4 arcminutes.
The results of this part of the experiment can be summarized as shown in Table 4.
Table 4: Field of View Versus Magnification
| aperture (inches) || time (seconds) |
| 6 (trial 1) || 51 |
| 6 (trial 2) || 50 |
| 6 (trial 3) || 52 |
| 3 (trial 1) || 53 |
| 3 (trial 2) || 50 |
| 3 (trial 3) || 51 |
(Question 11) Interestingly, within the errors, the 3 inch aperture
and the 6 inch aperture give the same result! Clearly there
is no dependence of field of view on aperture of the telescope, though,
as we found above, there is a dependence on the magnification.
(Question 12) The one aspect of the optical configuration that has not
changed throughout our experiment is ..... Thus, this aspect of the telescope
cannot have had any bearing on the variations we observed with our set-up.
This is as expected, because the variations we found in Tables 1 and 2 are due to .....
(Question 13) The expected relationship between field of view and magnification
is .... because ... We see that our data in Table 2 support this, because, as may be seen in our plot of field of view as a function of magnification shown in Figure 1, ...
The relationship in our data is not exact, but this is because of the imprecision of
our measurements. Within the 0.2 arcmin and 0.6 arcmin errors
in our measured fields of view, the expected trend is found in our data.
On the other hand we expect the aperture of the telescope at fixed focal length
to have no bearing on the field of view because... Table 3 shows this
to be the case, within the errors of the measurements.
(Question 14) From our work we now see that lower magnifications correspond
to larger fields of view. Thus, finder scopes are designed to have low
magnification because this gives them higher fields of view, and this
is important because...
(Question 15) The results of this experiment are subject to the imprecision in being able
to gauge timings of stars crossing the field of view. There are several
ways that our methodology may introduce measurement errors. One we discussed
above is the uncertainty in determining precisely when the star enters and
leaves the field of view and the delay in conveying this information from
the observer to the timekeeper. This is complicated by the atmospheric effects
on stars, which make them rapidly wander in their apparent position with time.
Yet another source of error is...(I'll leave this for you to figure out!).
| aperture (inches) || field of view (arcmin) |
| 6 || 12.6 +/- 0.2 |
| 3 || 12.7 +/- 0.4 |
What scientific conclusions do you draw from your experiments?
Did your results conform to your expectations? Your conclusions sections should
address the scientific questions raised in your PURPOSE section.
In this lab, the scientific conclusions might be something like:
We find that the relationship between field of view and magnification is...
for eyepieces used on the same telescope. This is expected theoretically because...
We also find that there is no relationship between field of view and the aperture
of the telescope, however this only holds for a telescope of fixed ____________________
and eyepiece because....
You might also note any other scientific findings that you did not expect in
setting out to do the experiment, for example,
It was also noted that with higher magnification the stars appeared
to move around a lot more. This is because the higher magnification also
means that the image wander of the stars from the atmosphere is magnified.
Finally, PLEASE INCLUDE A PHOTOCOPY OF THE NOTES TAKEN AT THE TELESCOPE. Note, this is
to help us decipher potential problems with what you have done. We will NOT
ordinarily look at this for grading, so do NOT use this photocopy to present your
results. Please assemble your measurements and other important data
into an orderly fashion (e.g., tables) for the RESULTS section.
Other tips and common mistakes in lab reports:
- The word "data" is plural for the word "datum".
Thus "The data are...", not "the data is...".
And, "We added one more datum to the analysis."
- Although your English and writing teachers probably have warned you about
excessive use of passive voice, in scientific writing it is very common
to use the passive voice to avoid excessive first person writing. Also, it is common
to discuss your results in the present tense, e.g., "The timings are
converted to angles..." rather than "The timings were converted to angles...".
The idea is that you are leading the reader through a process as if it is
happening at the moment. Finally, it is common for science writers to use the
"royal we" when they mean the first person singular "I", though this is not
- Make sure to include all proper units along with your answers, e.g.,
not "51" but "51 seconds" for a timing measurement.
- Make sure that your graphs, especially ones generated by a computer,
do not include lines "connecting the dots". In general, plots we make in this
class will be ``scatter plots", where you will be plotting points corresponding
to individual measurements of a dependent variable y versus an independent
variable x (e.g., the measured field of view as a function of the magnification)
in the hopes of finding some smooth trend (a line, or a curve) that might
characterize a relationship between them. It is acceptable to attempt
to find that smooth trend (for example, through linear regression fitting)
and plot that, but you should not consider your points to have such
good precision that every bump and wiggle in the trend of y with x is meaningful.
- Be clear about the difference between minutes and seconds of time (which
are used, for example, in right ascension) and arcminutes and arcseconds
(which are used, for example, in declination). For that matter, be
careful of the use of identical symbols " for arcseconds and inches and ' for
arcminutes and feet. For this reason, astronomers tend to write out
"inches" and "feet" to be clear. Often coordinates are written in the
format "10:04" or "10:04:21", and in this case it is assumed (from the
context) that the first number is hours (right ascension) or degrees (declination),
the second number is minutes of time (right ascension) or arcminutes (declination),
- Please make use of spell and grammar checkers on your
computer whenever possible!!
Aug 2012 by srm4n