ASTR 103 - Astronomy
Glossary - F
Latest Modification: March 5, 2003
- faculae
- Enhanced bright regions best observed near the Sun's edge.
- field of force
- Region of space of each point of which a given physical quantity (a force) has some definite value; for example, a gravitational or magnetic field.
- filament
- Slender wisp or drawn-out form of gaseous material moving outward from an object.
- fireball
- Exceptionally brilliant meteor.
- fission (nuclear)
- The spontaneous disintegration of the nucleus of the atom.
- flare
- Sudden energetic eruption of radiation in the Sun's chromosphere.
- flare star
- orange or red dwarf star that exhibits sudden, brief, unpredictable outbursts of radiation.
- flash spectrum
- bright-line spectrum of the Sun's chromospheric layer momentarily observed after the start and before the finish of the total phase of the eclipse.
- flux
- rate of flow of energy.
- focal length
- distance from a lens or mirror to the focus.
- focal ratio
- focal length of a lens or mirror divided by its aperture. The smaller the focal ratio, the greater the speed of the optical system.
- focus
- place where the light rays form an object in an optical system converge to form the image of the object.
- forbidden lines
- spectral lines originating in a gaseous medium of exceedingly low density, where the probability of their occurrence is high compared with that under ordinary laboratory conditions.
- force
- a push or pull that causes a body to change its state of motion.
- frame of reference
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- Fraunhofer lines
- the most prominent dark lines in the solar spectrum first mapped by J. Fraunhofer in 1814.
- free-free radiation
- radiation emitted by an electron as it approaches an atomic nucleus and is deflected by it without capture.
- Friedmann universe
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- frequency
- number of electromagnetic waves that pass by a given point each second.
- F star
- A star of spectral type F with a surface temperature of about 6000 to 7500 K in whose spectrum absorption lines of Ca II K of hydrogen are prominent.
- fusion (nuclear)
- Thermonuclear synthesis of heavier elements form lighter ones.
Physics & Astronomy Department, George Mason University
Maintained by J. C. Evans; jevans@gmu.edu