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8 Imaging
8.7.2 Planning
As mentioned above, to successfully complete this practical, you will need some
careful planning. Begin by starting up your planetarium software and setting it to the
time and date on which you expect to observe. Bring up the constellation boundaries
and names, have a look at what will be visible, and determine whether each object is
rising or setting. Check the position of the Moon, if there is one, as for some of your
targets, you may need to avoid it.
You will now need to look at the Messier catalogue. You need to observe at least
one open cluster, one barred spiral galaxy, an elliptical galaxy, a spiral galaxy, an HII
region or supernova remnant, a planetary nebula, and a globular cluster. Using your
understanding of what is currently visible, pick the best-placed target of each kind.
You will also need backup targets for each class of object.
Once you have selected your targets, you will need to determine the order of
observation and, based on their magnitudes, their lengths of exposure. You should
also be aware of the angular size of the objects. Some may be too small for your
camera to image, while some (for example, M31) will be too large. You should image
them in at least three bands. If you have narrow-band filters (such as OIII, Hα, and
SII), the HII region and the planetary nebula will benefit from their use. Although
the use of narrowband filters will increase integration time, low surface brightness
objects that emit strongly in these lines benefit greatly, as the sky tends not to be so
bright around forbidden lines (although emission lines are still present), improving
your signal-to-noise ratio for these sources.
8.7.3 Getting Ready
Before you leave for the observatory, make sure you have all your documentation,
your lab book, something to put your images on, such as a memory stick, and appropriate clothing. It is best to assume that it will be colder than forecast, as you can
always take a sweater off, but you can’t put on one you don’t have!
1. Once you arrive at the observatory, you need to start up the telescope and the
instrument. A member of observatory staff (or your tutor) should be able to help
you if you don’t know how to do this. The first thing you will need to do is start
the camera coolers if they are not already on, as it takes a while to bring the
camera down to operational temperature.
2. Once the camera is down to the required temperature, you will need to take
calibration frames. If you have been recently observing with this telescope and
camera and have bias, dark, and flats for the binning, and the exposure times
and filters you intend to use, then you can most likely use them instead of taking
new ones, although they may limit your exposure times. If your flats are more
than a week old, it is normally worth taking new ones. Dark and bias frames are
8 Imaging
8.7.2 Planning
As mentioned above, to successfully complete this practical, you will need some
careful planning. Begin by starting up your planetarium software and setting it to the
time and date on which you expect to observe. Bring up the constellation boundaries
and names, have a look at what will be visible, and determine whether each object is
rising or setting. Check the position of the Moon, if there is one, as for some of your
targets, you may need to avoid it.
You will now need to look at the Messier catalogue. You need to observe at least
one open cluster, one barred spiral galaxy, an elliptical galaxy, a spiral galaxy, an HII
region or supernova remnant, a planetary nebula, and a globular cluster. Using your
understanding of what is currently visible, pick the best-placed target of each kind.
You will also need backup targets for each class of object.
Once you have selected your targets, you will need to determine the order of
observation and, based on their magnitudes, their lengths of exposure. You should
also be aware of the angular size of the objects. Some may be too small for your
camera to image, while some (for example, M31) will be too large. You should image
them in at least three bands. If you have narrow-band filters (such as OIII, Hα, and
SII), the HII region and the planetary nebula will benefit from their use. Although
the use of narrowband filters will increase integration time, low surface brightness
objects that emit strongly in these lines benefit greatly, as the sky tends not to be so
bright around forbidden lines (although emission lines are still present), improving
your signal-to-noise ratio for these sources.
8.7.3 Getting Ready
Before you leave for the observatory, make sure you have all your documentation,
your lab book, something to put your images on, such as a memory stick, and appropriate clothing. It is best to assume that it will be colder than forecast, as you can
always take a sweater off, but you can’t put on one you don’t have!
1. Once you arrive at the observatory, you need to start up the telescope and the
instrument. A member of observatory staff (or your tutor) should be able to help
you if you don’t know how to do this. The first thing you will need to do is start
the camera coolers if they are not already on, as it takes a while to bring the
camera down to operational temperature.
2. Once the camera is down to the required temperature, you will need to take
calibration frames. If you have been recently observing with this telescope and
camera and have bias, dark, and flats for the binning, and the exposure times
and filters you intend to use, then you can most likely use them instead of taking
new ones, although they may limit your exposure times. If your flats are more
than a week old, it is normally worth taking new ones. Dark and bias frames are