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Glossary
FITS Flexible image transport system. The standard format for astronomical
images.
FITS Header The part of a FITS image containing image data but not imaging
data.
Flat Fielding A process to deal with nonuniformity of a CCD.
Flat Frame An image of the twilight sky or the inside of the dome. Used for
removing the flat field noise.
Flip Mirror A flat mirror that can be moved from a position in which the mirror
is parallel to the telescope to one in which it is inclined by 45
◦ to the telescope.
Flux The amount of energy transferred through an area in a set time.
Focal Length The distance between the first optical component and the first point
of focus. A main characteristic of a telescope.
Focal Reducer A device to decrease the effective focal length of a telescope.
Forbidden Line A spectral line that cannot be produced on Earth due to the low
gas densities needed.
Free-Bound Emission Emission caused by the capture of a free electron. This
contributes to continuum emission.
Full Well Capacity The number of electrons a pixel can hold.
FWHM The full width half maximum, a measure of the spread of a Gaussian
profile such as seen with a star.
Gain The ratio of photons to count in a pixel in a CCD.
Gravitational Reddening The general relativity effect that causes the light from
high-gravity environments to have an increased wavelength.
Great Circle A circle on a sphere whose diameter intersects the centre of the
sphere, so that the circle has the same circumference as the sphere.
Greenwich Mean Time The mean solar time at the Royal Observatory in Greenwich.
Hertzsprung–Russell (HR) diagram A plot of absolute magnitude against colour.
HR diagrams describe stellar evolution and are one of the foundations of modern
astrophysics.
Home The zeroing position of a telescope.
Hot Pixel A pixel reporting high at all times.
Hour Angle Local sidereal time minus the RA of the object.
Hour Circle Any great circle celestial sphere that passes through the celestial
poles perpendicular to the equator.
Hubble Palette The guidelines for how the narrow-band Hubble filter set is displayed in colour images.
Hydrogen-Alpha A Balmer series emission line at 656.28 nm, caused by an n = 3
to n = 2 hydrogen transition.
Image Processing The process of producing a high-quality image by manipulation
of the data.
Image Reduction The process of turning a light frame into a science frame.
Integrated Magnitude The total amount of radiation in a set band coming from
an object, expressed as a magnitude. Most often used for extended sources.
Glossary
FITS Flexible image transport system. The standard format for astronomical
images.
FITS Header The part of a FITS image containing image data but not imaging
data.
Flat Fielding A process to deal with nonuniformity of a CCD.
Flat Frame An image of the twilight sky or the inside of the dome. Used for
removing the flat field noise.
Flip Mirror A flat mirror that can be moved from a position in which the mirror
is parallel to the telescope to one in which it is inclined by 45
◦ to the telescope.
Flux The amount of energy transferred through an area in a set time.
Focal Length The distance between the first optical component and the first point
of focus. A main characteristic of a telescope.
Focal Reducer A device to decrease the effective focal length of a telescope.
Forbidden Line A spectral line that cannot be produced on Earth due to the low
gas densities needed.
Free-Bound Emission Emission caused by the capture of a free electron. This
contributes to continuum emission.
Full Well Capacity The number of electrons a pixel can hold.
FWHM The full width half maximum, a measure of the spread of a Gaussian
profile such as seen with a star.
Gain The ratio of photons to count in a pixel in a CCD.
Gravitational Reddening The general relativity effect that causes the light from
high-gravity environments to have an increased wavelength.
Great Circle A circle on a sphere whose diameter intersects the centre of the
sphere, so that the circle has the same circumference as the sphere.
Greenwich Mean Time The mean solar time at the Royal Observatory in Greenwich.
Hertzsprung–Russell (HR) diagram A plot of absolute magnitude against colour.
HR diagrams describe stellar evolution and are one of the foundations of modern
astrophysics.
Home The zeroing position of a telescope.
Hot Pixel A pixel reporting high at all times.
Hour Angle Local sidereal time minus the RA of the object.
Hour Circle Any great circle celestial sphere that passes through the celestial
poles perpendicular to the equator.
Hubble Palette The guidelines for how the narrow-band Hubble filter set is displayed in colour images.
Hydrogen-Alpha A Balmer series emission line at 656.28 nm, caused by an n = 3
to n = 2 hydrogen transition.
Image Processing The process of producing a high-quality image by manipulation
of the data.
Image Reduction The process of turning a light frame into a science frame.
Integrated Magnitude The total amount of radiation in a set band coming from
an object, expressed as a magnitude. Most often used for extended sources.