Glossary
AB System A photometric standard based on instrumentation.
Absolute Magnitude The magnitude of a body at a distance of 10 pc for a nonsolar-system object and a distance of 1 AU for an object inside the solar system.
Absorption Lines Dark lines in a spectrum caused by the absorption of light by
atoms and molecules between the emitting source and the observer.
Achromatic A two-component lens designed to reduce chromatic aberration.
ADU Bit Number The number of bits that the processor of an ADU uses. This
limits the maximum number it can work with.
Airy Disc The pattern produced by the diffraction of light within the optics of a
telescope or other such device.
All-Sky Photometry A photometric technique that does not use reference stars.
Angular Resolution The telescope’s ability to separate two objects, given by the
average wavelength of the light being observed divided by the aperture of the
telescope.
Aperture Either the diameter of an optical system such as a telescope, or the size
of the region being measured in photometry.
Aperture Photometer Tool A freeware multiplatform application designed to
perform aperture photometry.
Aperture Photometry Photometry using an aperture around an image of a star
with the count within the aperture being integrated.
Apochromatic A three-component lens designed to reduce chromatic aberration.
Apogee For an object in an orbit, this is the point at which it is farthest from the
object it is orbiting.
Apparent Brightness The brightness of a source as viewed from Earth.
Apparent Magnitude The magnitude of a source as viewed from Earth.
Apparent Solar Time The local solar time based the observation of the Sun.
Arc Minute A measure of angle. One 60th of a degree.
Arc Second A measure of angle. One 60th of an arc minute.
© 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
223
AB System A photometric standard based on instrumentation.
Absolute Magnitude The magnitude of a body at a distance of 10 pc for a nonsolar-system object and a distance of 1 AU for an object inside the solar system.
Absorption Lines Dark lines in a spectrum caused by the absorption of light by
atoms and molecules between the emitting source and the observer.
Achromatic A two-component lens designed to reduce chromatic aberration.
ADU Bit Number The number of bits that the processor of an ADU uses. This
limits the maximum number it can work with.
Airy Disc The pattern produced by the diffraction of light within the optics of a
telescope or other such device.
All-Sky Photometry A photometric technique that does not use reference stars.
Angular Resolution The telescope’s ability to separate two objects, given by the
average wavelength of the light being observed divided by the aperture of the
telescope.
Aperture Either the diameter of an optical system such as a telescope, or the size
of the region being measured in photometry.
Aperture Photometer Tool A freeware multiplatform application designed to
perform aperture photometry.
Aperture Photometry Photometry using an aperture around an image of a star
with the count within the aperture being integrated.
Apochromatic A three-component lens designed to reduce chromatic aberration.
Apogee For an object in an orbit, this is the point at which it is farthest from the
object it is orbiting.
Apparent Brightness The brightness of a source as viewed from Earth.
Apparent Magnitude The magnitude of a source as viewed from Earth.
Apparent Solar Time The local solar time based the observation of the Sun.
Arc Minute A measure of angle. One 60th of a degree.
Arc Second A measure of angle. One 60th of an arc minute.
© 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
223