Space and Solar Definitions - R

Radian - Unit of angular measurement equal to the angle at the center of a circle subtended by an arc equal in length to the radius. Equals about 57.296 degrees.

Radio Emission - Emissions of the sun in radio wavelengths from centimeters to dekameters, under both quiet and disturbed conditions. Type i. A noise storm composed of many short, narrow-band bursts in the metric range (300 - 50 mhz). Type ii. Narrow-band emission that begins in the meter range (300 mhz) and sweeps slowly (tens of minutes) toward deka- meter wavelengths (10 mhz). Type ii emissions occur in loose association with major flares and are indicative of a shock wave moving through the solar atmosphere. Type iii. Narrow-band bursts that sweep rapidly (seconds) from decimeter to dekameter wavelengths (500 - 0.5 mhz). They often occur in groups and are an occasional feature of complex solar active regions. Type iv. A smooth continuum of broad-band bursts primarily in the meter range (300 - 30 mhz). These bursts are associated with some major flare events beginning 10 to 20 minutes after the flare maximum, and can last for hours. A smooth continuum of broad-band bursts primarily in the meter range (300 - 30 mhz). These bursts are associated with some major flare events beginning 10 to 20 minutes after the flare maximum, and can last for hours.

Radio Event - Flares with centimetric bursts and/or definite ionospheric event (sid).

RAM - Random Access Memory.

RCP - Right-hand circular polarization.

Recurrence - Used especially in reference to the recurrence of physical parameters every 27 days (the rotation period of the sun).

Red dwarf - A small star, on the order of 100 times the mass of Jupiter.

Reflection - The deflection or bouncing of electromagnetic waves when they encounter a surface.

Refraction - The deflection or bending of electromagnetic waves when they pass from one kind of transparent medium into another.

Retrograde - Orbit in which the spacecraft moves in the opposite direction from the planet's rotation.

RF - Radio Frequency.

RFI - Radio Frequency Interference.

Right Ascension - The angular distance of a celestial object measured in hours, minutes, and seconds along the celestial equator eastward from the vernal equinox.

Riometer (Relative Ionospheric Opacity Meter - A specially designed radio receiver for continuous monitoring of cosmic noise. The absorption of cosmic noise in the polar regions is very sensitive to the solar low-energy cosmic ray flux.

RNS - GCF reliable network service.

ROM - Read Only Memory.

RPIF - Regional Planetary Imaging Data Facilities.

RS - DSN Radio Science System. Also, radio science data

RTG - Radioisotope Thermo-Electric Generator onboard a spacecraft.

RTLT - Round-Trip Light Time, elapsed time roughly equal to 2 x OWLT.