8.6 Stacking and Dithering
123
images from a 16-bit camera can be stacked to form a 32-Bit FITS, solving the
problem of very bright objects in the field.
Images need to be aligned before they can be stacked unless your telescope has
perfect tracking. However, the alignment process enables us to deal with a number
of issues. Variations within the CCD (for example bad pixels) can be evened out over
the chip by nodding or dithering the telescope. Dithering is performed by moving
the telescope a few arc seconds between exposures. Faults move with the telescope,
and so they appear in a different location in each frame. This can be used to minimise
their effects.
So we see that when we make our observations, we must be aware of the image
postprocessing that will be needed and take a number of exposures at an exposure
time appropriate to what is needed, both for the initial image and for later processing.
8.7 Practical 6: The Messier Marathon
The practicals in this chapter are designed to give you the skills to take science grade
astronomical images in an efficient manner so that you can utilise your precious clear
sky time to the maximum. You will be imaging a wide range of targets that require
the implementation of different imaging approaches. You will gain experience not
only on the telescope, but also with a range of astronomical software packages.
A common challenge amongst amateur astronomers is the Messier marathon—
seeing how many Messier objects one can image in a single night. A successful
Messier marathon requires careful planning and preparation, exactly the skills a
good observational astronomer needs. If you are a southern hemisphere observer, the
Messier marathon can be quite challenging, due to the limited number of southern
objects and the low altitude of many of those that are visible. If this is the case,
we suggest you use the Caldwell catalogue instead or as an addition. As noted in
Chap. 6, the Caldwell catalogue contains a further 109 bright objects that are not in
the Messier catalogue.
8.7.1 Aims
In this practical you will attempt to image as many Messier objects as possible in
a single observing session. Not only that, you will make colour composite images,
meaning that you will need to image in at least three filters. This practical will take
careful planning and teamwork if you are to execute it successfully. You will be
familiarising yourself with the use of the telescope and the camera to image a wide
range of object types, from bright clusters to faint galaxies.
123
images from a 16-bit camera can be stacked to form a 32-Bit FITS, solving the
problem of very bright objects in the field.
Images need to be aligned before they can be stacked unless your telescope has
perfect tracking. However, the alignment process enables us to deal with a number
of issues. Variations within the CCD (for example bad pixels) can be evened out over
the chip by nodding or dithering the telescope. Dithering is performed by moving
the telescope a few arc seconds between exposures. Faults move with the telescope,
and so they appear in a different location in each frame. This can be used to minimise
their effects.
So we see that when we make our observations, we must be aware of the image
postprocessing that will be needed and take a number of exposures at an exposure
time appropriate to what is needed, both for the initial image and for later processing.
8.7 Practical 6: The Messier Marathon
The practicals in this chapter are designed to give you the skills to take science grade
astronomical images in an efficient manner so that you can utilise your precious clear
sky time to the maximum. You will be imaging a wide range of targets that require
the implementation of different imaging approaches. You will gain experience not
only on the telescope, but also with a range of astronomical software packages.
A common challenge amongst amateur astronomers is the Messier marathon—
seeing how many Messier objects one can image in a single night. A successful
Messier marathon requires careful planning and preparation, exactly the skills a
good observational astronomer needs. If you are a southern hemisphere observer, the
Messier marathon can be quite challenging, due to the limited number of southern
objects and the low altitude of many of those that are visible. If this is the case,
we suggest you use the Caldwell catalogue instead or as an addition. As noted in
Chap. 6, the Caldwell catalogue contains a further 109 bright objects that are not in
the Messier catalogue.
8.7.1 Aims
In this practical you will attempt to image as many Messier objects as possible in
a single observing session. Not only that, you will make colour composite images,
meaning that you will need to image in at least three filters. This practical will take
careful planning and teamwork if you are to execute it successfully. You will be
familiarising yourself with the use of the telescope and the camera to image a wide
range of object types, from bright clusters to faint galaxies.