Chapter 8
Imaging
Abstract Astronomical imaging using a telescope and CCD camera is the foundation of modern astronomy. We show through practical examples how to plan, take,
and calibrate astronomical images for use in science. We work through the operation
of the telescope, including pointing, focusing, and camera operation. We discuss
problems associated with nonstellar sources such as galaxies, nebulae, and planets.
8.1 Introduction
Imaging is one of the four cornerstones of observational astronomy. The others
are photometry, astrometry, and spectrography. We can consider these practices to
answer the following questions: What does it look like? How bright is it? Where is
it? What is it made of? Imaging is an important part of photometry, astrometry, and
spectrography, as it is the collection of photons that makes these aspects possible.
When undertaking imaging, we need to understand what we are trying to achieve.
If we wish to perform photometry, then we need to keep the camera within its
linear range, which is not so important with astrometry, although we should avoid
saturating the target. With spectrography, we will be using a spectrograph rather
than an imaging camera, and while we are unlikely to overexpose, we will need to
undertake careful guiding to keep the target within the spectrograph’s slit. If we are
imaging to determine the morphology of a target, then a long integration time may be
needed whilst avoiding saturation and taking multiple images, which are combined
and manipulated to improve the visualisation of the target.
First light is the term used for the point where a telescope takes its first image,
the commissioning image. Although it is unlikely that you will be the first to use the
telescope, this might be the very first time you have used a telescope to gather photons
from an astronomical target. The previous chapters should have prepared you for your
first observations, and this chapter will guide you through that first observation from
planning to data reduction. The chapters that follow this one assume that you have
successfully completed the practicals that follow in this chapter, or at the very least
have experience in using astronomical telescopes and CCDs.
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_8
103
Imaging
Abstract Astronomical imaging using a telescope and CCD camera is the foundation of modern astronomy. We show through practical examples how to plan, take,
and calibrate astronomical images for use in science. We work through the operation
of the telescope, including pointing, focusing, and camera operation. We discuss
problems associated with nonstellar sources such as galaxies, nebulae, and planets.
8.1 Introduction
Imaging is one of the four cornerstones of observational astronomy. The others
are photometry, astrometry, and spectrography. We can consider these practices to
answer the following questions: What does it look like? How bright is it? Where is
it? What is it made of? Imaging is an important part of photometry, astrometry, and
spectrography, as it is the collection of photons that makes these aspects possible.
When undertaking imaging, we need to understand what we are trying to achieve.
If we wish to perform photometry, then we need to keep the camera within its
linear range, which is not so important with astrometry, although we should avoid
saturating the target. With spectrography, we will be using a spectrograph rather
than an imaging camera, and while we are unlikely to overexpose, we will need to
undertake careful guiding to keep the target within the spectrograph’s slit. If we are
imaging to determine the morphology of a target, then a long integration time may be
needed whilst avoiding saturation and taking multiple images, which are combined
and manipulated to improve the visualisation of the target.
First light is the term used for the point where a telescope takes its first image,
the commissioning image. Although it is unlikely that you will be the first to use the
telescope, this might be the very first time you have used a telescope to gather photons
from an astronomical target. The previous chapters should have prepared you for your
first observations, and this chapter will guide you through that first observation from
planning to data reduction. The chapters that follow this one assume that you have
successfully completed the practicals that follow in this chapter, or at the very least
have experience in using astronomical telescopes and CCDs.
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_8
103