NASA Logo - Web Link to NASA.gov Vertical Line

+ Text Only Site
+ Non-Flash Version
+ Contact Glenn

Go
ABOUT NASA NEWS AND EVENTS MULTIMEDIA MISSIONS MyNASA WORK FOR NASA

A B C D E F G H I J K L M N O P R S T U V W Y Z


Words begining with "F"

FAA

Federal Aviation Administration.

facsimile (FAX)

A process by which graphic or photographic information is transmitted or recorded by electronic means.

False Color

See digital image.

Fahrenheit

Temperature scale designed by the German scientist Gabriel Fahrenheit in 1709, based upon water freezing at 32 degrees and water boiling at 212 degress under standard atmospheric pressure. Compare with centigrade.

Far Infrared

Electromagnetic radiation, longer than the thermal infrared, with wavelengths between about 25 and 1000 micrometers. See elctromagnetic spectrum.

Feedhorn

A metallic cylinder closed at one end, used to obtain and direct radio frequency (RF) energy reflected from a satellite dish. It acts as a wave guide at microwave frequencies. RF energy inside the horn is picked up by a small probe; once inside the horn, the wavelength (energy) of the microwave radiation changes to a guided wave.

FEMA

U.S. Federal Emergency Management Agency.

Feng Yun

Chinese geostationary environmental satellite that was destroyed by an explosion before launch in April 1994. The name Feng Yun, meaning Wind and Cloud, was originally applied to the Chinese polar-orbiting environmental satellite launched in September 1991 (Feng Yun 1-2), which offered direct readout services. The Chinese polar-orbiter program has since been abandoned.

Field

The set of influences (electricity, magnetism, gravity) that extend throughout space.

Field Of View

The range of angles that are scanned or sensed by a system or instrument, measured in degrees of arc.

Filter

Device that while selectively passing desired frequencies removes undesired ones.

FM

See frequency modulation.

Focal Length

  1. In optics, the distance usually expressed in millimeters - from the principal point of a lens or concave mirror to its focal point.
  2. The distance, measured from the center of the surface of a parabolic or spherical reflector (e.g., satellite dish) where RF energy is brought to essential point focus.

Focal Point

The area where weak signals collected by a satellite dish, concentrated into a smaller receiving area, converge.

Fog

A cloud on the ground.

Fossil

Hardened remains or traces of plant or animal life from a previous geological period preserved in the Earth's crust.

Fossil Fuel

Any hydrocarbon deposit that can be burned for heat or power, such as petroleum, coal, and natural gas.

Frame

A single image or picture. A single complete vertical scan of the cathode ray tube (CRT).

Free Radicals

Atomic or molecular species with unpaired electrons or an otherwise open shell configuration, usually very reactive. Specific to atmospheric chemistry, free radicals are: short-lived, highly reactive, intermediate species produced by dissociation of the source molecules by solar ultraviolet radiation or by reactions with other stratospheric constituents. Free radicals are the key to intermediate species in many important stratospheric chain reactions in which an ozone molecule is destroyed and the radical is regenerated. See ozone.

Frequency (F)

Number of cycles and parts of cycles completed per second. F = 1/T, where T is the length of one cycle in seconds.

Frequency Division Multiplexing

The combining of a number of signals to share a medium by dividing it into different frequency bands for each signal. See signal.

Frequency Modulation (FM)

The instantaneous variation of the frequency of a carrier wave in response to changes in the amplitude of a modulating signal. As applied to APT, the radio signal from the satellite is broadcast on an FM transmitter and received on the ground on an FM radio receiver. See frequency division multiplexing, signal.

Front

A boundary between two different air masses. The difference between two air masses sometimes is unnoticeable. But when the colliding air masses have very different temperatures and amounts of water in them, turbulent weather can erupt.

A cold front occurs when a cold air mass moves into an area occupied by a warmer air mass. Moving at an average speed of about 20 mph, the heavier cold air moves in a wedge shape along the ground. Cold fronts bring lower temperatures and can create narrow bands of violent thunderstorms. In North America, cold fronts form on the eastern edges of high pressure systems.

A warm front occurs when a warm air mass moves into an area occupied by a colder air mass. The warm air is lighter, so it flows up the slope of the cold air below it. Warm fronts usually form on the eastern sides of low pressure systems, create wide areas of clouds and rain, and move at an average speed of 15 mph.

When a cold front follows and then overtakes a warm front (warm fronts move more slowly than cold fronts) lifting the warm air off the ground, an occluded front forms.

Frost

Water condensation occurring on surfaces below freezing. Condensing water turns to ice.


A B C D E F G H I J K L M N O P R S T U V W Y Z




TRC Activities

 

     First Gov Image


+ Inspector General Hotline
+ Equal Employment Opportunity Data Posted Pursuant to the No Fear Act
+ Budgets, Strategic Plans and Accountability Reports
+ Freedom of Information Act
+ The President's Management Agenda
+ NASA Privacy Statement, Disclaimer,
and Accessibility Certification

 

NASA Logo   
Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Jun 12 2014

+ Contact Glenn