Galaxy Imaging – Project Instructions
Richard Beare
Version 2.0
Summary of Activities
Planning You choose suitable galaxies to observe and when to observe them.
Observing You use the telescope (in real time or off-line) to obtain JPEG images of galaxies in
different wavebands (colours). A full colour (colour composite) image is also obtained.
Commenting You print out the images of each galaxy and comment in scientific terms on their
features, including the differences between images in different colours.
Measuring You can use the JPEG Viewer software to make simple measurements on a galaxy,
including how tightly wound the spiral arms are in a spiral galaxy.
Classifying You then classify your galaxies using a modified form of Hubble's classification
scheme.
Evaluating You think about sources of error and how the project could be improved.
What images are required
Images for this project can be obtained in either real time or off-line.
Each galaxy to be measured and classified should, at the very least, be imaged with the V and R
waveband (green and red) filters, so that a three-colour composite image can be created. In
addition, taking images using different filters, including possibly U (ultraviolet) and I (infrared) as
well, will allow you to compare the proportions of hot, blue, young stars and older, cooler, more
yellow stars in different parts of the galaxy.
JPEG images for each waveband are sent back to you straight away by the telescope software, as
well as a full colour JPEG image.
These JPEG images are all that is needed to observe and classify a galaxy. However, if you want
to carry out the full astronomical image processing required to produce a high quality image for the
Faulkes Atlas of Nearby Galaxies, you will need to make use of the FITS files returned to you
several hours after the actual observing session. Details are given as a separate project.
Faulkes Telescope Project
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Advanced planning
1 Choose suitable galaxies
Ideally these should be one that are neither too small nor too large for the field of view and
sufficiently bright to give reasonably good images given appropriate choices of exposure time. A
list of suitable galaxies can be downloaded from the resources page for this project, along with an
Observation Planner - a spreadsheet showing which galaxies are visible when.
2 Choose when to observe
Good images of faint deep sky objects such as galaxies can only be obtained when there is a low
level of background sky brightness. Such conditions are called photometric because they are
suitable for making brightness measurements of objects. To observe under photometric conditions
with the Faulkes Telescopes, you need to choose times when the Moon is not up and it is not
twilight.
3 Choose suitable filters
To obtain a true colour image you will need to produce images using the blue, green and red (B, V
and R) filters. These are broadband filters because they allow through a range of wavelengths
centred on the blue, green or red parts of the spectrum respectiveily.
However, you may also want to use the ultra-violet (U) filter to show up any bright regions
containing bright blue young stars more clearly. You might also want to use the near infra-red fliter
(I) to show up old cooler stars more clearly.
4 Choose suitable exposure times
Having chosen when to observe, and through which filters, you next need to decide how long to
observe each galaxy through each filter. The telescope software will help you do this.
5 Plan you observing slot
Draw up an observing schedule taking account of the time required for each exposure and the time
required for the telescope to slew from one galaxy to the next.
Submit this to the Telescope Control Centre and book your observing slot.
6 Save the images
Save the JPEG images you have obtained from your observing session in a suitable folder on your
computer.
Faulkes Telescope Project
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Commenting
7 Viewing images
You can use JPEG images taken in different colours (wavebands) and you can also use the full
colour images.
If you want to take your analysis further than is possible simply using JPEGs, an alternative is to
use astronomical image processing software to view the full astronomical data files (FITS files).
The advantage of doing this is that you can selectively enhance different aspects of a galaxy image
in order to study it. You could, for example, enhance less bright regions of an image so that fainter
outer parts of the galaxy can be seen clearly. However, this would saturate the bright central
regions so that no detail was visible there, so you might also want to change the settings in such a
way that detail in these regions can be studied.
Viewing galaxy FITS images
Make sure that you save the originals as well as the processed images. In some cases you may
find that it is a good idea to process an image in different ways to bring out different features (e.g.
detail in fainter outer parts, detail in bright parts of the galaxy).
8 Print the images out
You will find it helpful to print out your images so that they can be studied more easily. This will
also enable you to label them with relevant comments for inclusion in a written report, if
appropriate.
HINT If you can use a photographic quality printer and high resolution or photographic quality
paper, you will get much better results than with a cheap printer and ordinary paper.
9 Analyse the images
Examine the images carefully, looking in particular at the following features:
Examine the images carefully, looking in particular at the following features:
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whether you think that it is an elliptical galaxy or a disc galaxy (such as a spiral galaxy)
which is flattened like a disc, or whether it is hard to tell (as can sometimes be the case)
if the galaxy is a disc galaxy, whether it is face-on to our line of sight or tilted
if the galaxy is a spiral:
whether it is barred or not
the number of spiral arms, how long they are, and how tightly wound
whether the spiral arms are clearly defined, or vague and ragged in appearance
regions where there are a lot of bright, hot, young blue stars
regions where there are dark dust clouds
"H2" regions which are glowing with a pinky colour because ionised hydrogen gas is
glowing due to nearby hot young stars giving off copious amounts of ultra-violet radiation
(these regions are also known as emission nebluae)
globular clusters also containing older yellow stars
any other features you think are worth pointing out
Faulkes Telescope Project
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Measuring
10 Using the JPEG Viewer to make measurements
Details of how to use this software are given on a separate instruction sheet which can be
downloaded from the resources page for this project.
Measure the angular size of the galaxy, and any prominent features (any central bulge, prominent
dark dust cloud, etc.) in arcminutes or arcseconds (whichever is most appropriate).
If you know the distance to the galaxy (in light years or in parsecs), enter this into the JPEG Viewer
and it will calculate the actual linear size of these features (in light years or in parsecs).
Measure how tightly wound the spiral arms are if the galaxy is a spiral.
You can also use the JPEG Viewer to make simple proportional measurements on your galaxy, for
example:
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the relative size of the central bulge containing older yellow stars
the relative size of any bar
if the galaxy is an elliptical, the ratio of the major axis to the minor axis
Classifying
11 Hubble classification
Using the preceding information to decide how well each of your galaxies fits the published
properties for galaxies in the Hubble Classification. As there are several modern variations on
Hubble's original scheme, a guide to one appropriate for this project has been written for you. This
can be downloaded from the resources page for this project.
Evaluating
Comment on any sources of error that you are aware of and any ideas you have for improving on
the way that you carried out any aspect of the project, including both the observing and the
measurements you made.
Faulkes Telescope Project
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Further investigations
Faulkes Atlas of Nearby Galaxies (FANG)
If you wish to produce high quality colour images of your galaxies, you can do this by using a long
exposure time of (say) 5 minutes for each filter, or (better) you can take several colour images of
one minute per filter each and then 'stack' these (combine them together using software). The high
quality images so obtained could then contribute to the Faulkes Atlas of Nearby Galaxies which will
be a full-colour on-line atlas of galaxies that will be useful to both professional astronomers and
amateurs. For most galaxies, the images in this catalogue will be the first high quality colour
images ever obtained.
Eventually, the images will be put together to make a full colour atlas of nearby galaxies that will
make a very attractive "coffee table" book as well as being of great scientific value.
In both the on-line atlas and the book, credits will be printed alongside each image giving the name
of the school and the individuals involved in obtaining and processing the image.
Details can be obtained via the galaxy projects webpage.
Surface brightness profiles
There is a separate investigation which involves plotting surface brightness profiles of galaxies.
You may wish to do this for some of the galaxies that you have observed and classified in this
investigation. (You willl not need to repeat the initial sections of this additional investigation, as you
will already have done these things.)
Measuring spiral arms in spiral galaxies
There is a futher investigation you can carry out which involves measuring the spiral arms in any
spiral galaxies you have observed. (You willl not need to repeat the initial sections of this additional
investigation, which involve Observing, commenting and classifying, as you will already have done
these things.)
Richard Beare 21st March, 2005
Faulkes Telescope Project
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