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Glossary of Astronomy Terms
beginning with letter R
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radar astronomy Tweet Definition of radar astronomy Like Definition of radar astronomy on Facebook
  1. (astronomy) a technique that uses radar echoes to examine bodies within the solar system, obtaining information about size, shape, topography, surface density, spin etc
radiant Tweet Definition of radiant Like Definition of radiant on Facebook
  1. A point source from which radiation is emitted.
  2. (astronomy) The apparent origin, in the night sky, of a meteor shower.
  1. Radiate, Radiating light and/or heat.
  2. Emitted as radiation.
  3. Bright, glowing or filled with light.
radio astronomy Tweet Definition of radio astronomy Like Definition of radio astronomy on Facebook
  1. The branch of astronomy which utilizes radio waves through the use of radio telescopes to study celestial bodies and occurances.
radio telescope Tweet Definition of radio telescope Like Definition of radio telescope on Facebook
  1. (astronomy) A device for observing astronomical sources of radio waves, normally having one or more large parabolic dishes.
Ray Tweet Definition of Ray Like Definition of Ray on Facebook
proper noun 
  1. (given name, male), a diminutive of Raymond.
red dwarf Tweet Definition of red dwarf Like Definition of red dwarf on Facebook
  1. (star) A small, relatively cool star of the main sequence; most stars in the Milky Way are red dwarfs.
red giant Tweet Definition of red giant Like Definition of red giant on Facebook
  1. (star) A large red coloured star with a lower surface temperature than many stars.
redshift Tweet Definition of redshift Like Definition of redshift on Facebook
  1. (context, physics) A change in the wavelength of light, in which the wavelength is longer than when it was emitted at the source.
rete Tweet Definition of rete Like Definition of rete on Facebook
noun (plural retia)
  1. (anatomy) a network of blood vessels or nerves
  2. an anatomical part resembling or including a network
retrograde Tweet Definition of retrograde Like Definition of retrograde on Facebook
  1. A degenerate person.
verb (retrograd, ing)
  1. (intransitive) To move backwards; to recede; to retire; to decline; to revert.
  2. (context, intransitive, astronomy) To show retrogradation.
  1. Directed backwards, retreating; reverting especially inferior state, declining; inverse, reverse; movement opposite to normal or intended motion, often circular motion.
  2. counterproductive, Counterproductive to a desired outcome.
Rhea Tweet Definition of Rhea Like Definition of Rhea on Facebook
proper noun 
  1. (greekmyth): A Titan, the daughter of Uranus and Gaia, the mother of Demeter, Hades, Hera, Hestia, Poseidon, and Zeus.
  2. (astronomy): One of the moons of Saturn.
Rigel Tweet Definition of Rigel Like Definition of Rigel on Facebook
proper noun 
  1. (star) A blue supergiant star in the constellation Orion; Beta (β) Orionis. The seventh brightest star in the night sky.
rise Tweet Definition of rise Like Definition of rise on Facebook
  1. The action of moving upwards
    1. An increase (in a quantity, price, etc)
  2. (UK, Ireland) A pay rise (rfv-sense)
verb (rises, rising, rose, risen)
  1. (intransitive) To move upwards.
We watched the balloon .
  1. (intransitive, of a celestial body) To appear to move upwards from behind the horizon of a planet as a result of the planet's rotation
The sun was rising in the East.
  1. (intransitive) To be resurrected
He rose from the grave.
He is risen!
  1. (intransitive) of a quantity, price, etc, To increase.
river Tweet Definition of river Like Definition of river on Facebook
  1. A large stream of water that alters the nearby landscape. Occasionally rivers overflow their banks and cause floods.
  2. Any large flow of a liquid in a single body (e.g., 'a river of blood').
  3. (poker) The last card received by a player in poker
  1. (poker) To improve one"s hand to beat another player on the final card in a poker game.
Johnny rivered me by drawing that Ace of spades
roll Tweet Definition of roll Like Definition of roll on Facebook
  1. The act of rolling, or state of being rolled.
the roll of a ball
the roll of waves
  1. That which rolls; a roller
  2. Specifically, a heavy cylinder used to break clods.
  3. Specifically, one of a set of revolving cylinders, or rollers, between which metal is pressed, formed, or smoothed, as in a rolling mill; as, to pass rails through the rolls.
  4. That which is rolled up; as, a roll of fat, of wool, paper, cloth, etc.
  5. Specifically, a document written on a piece of parchment, paper, or other materials which may be rolled up; a scroll.
  6. Hence, an official or public document; a register; a record; also, a catalogue; a list.
  7. Specifically, a quantity of cloth wound into a cylindrical form; as, a roll of carpeting; a roll of ribbon.
  8. Specifically, A cylindrical twist of tobacco.
  9. A kind of shortened raised biscuit or bread, often rolled or doubled upon itself.
  10. (nautical) The oscillating movement of a vessel from side to side, in sea way, as distinguished from the alternate rise and fall of bow and stern called pitching.
  11. A heavy, reverberatory sound.
the roll of cannon
the roll of thunder
  1. The uniform beating of a drum with strokes so rapid as scarcely to be distinguished by the ear.
  2. (obsolete) Part; office; duty; rí´le.
  3. A measure of parchments, containing five dozen.
  • 1882: Parchement is sold by the dozen, and by the roll of five dozens. — James Edwin Thorold Rogers, A History of Agriculture and Prices in England, Volume 4, p. 594.
    1. the rotation angle about the longitudinal axis
the roll of an aircraft
  1. The act of, or total resulting from, rolling one or more dice.
Make your roll.
Whoever gets the highest moves first.
  1. (nautical) The measure of extent to which a nautical vessel rotates on its fore-and-aft axis, causing its sides to go up and down. Compare with pitch.
  1. (ergative) To cause to revolve by turning over and over; to move by turning on an axis; to impel forward by causing to turn over and over on a supporting surface.
roll a wheel, a ball, or a barrel
  1. To wrap round on itself; to form into a spherical or cylindrical body by causing to turn over and over.
roll a sheet of paper
roll clay or putty into a ball''
  1. To bind or involve by winding, as in a bandage; to inwrap; often with up
roll up a parcel
  1. (ergative) To drive or impel forward with an easy motion, as of rolling.
a river rolls its waters to the ocean
  1. (ergative) To utter copiously, especially with sounding words; to utter with a deep sound; -- often with forth, or out.
roll forth someone's praises
roll out sentences
  1. To press or level with a roller; to spread or form with a roll, roller, or rollers.
roll a field
roll paste
roll steel rails
  1. (ergative) To move, or cause to be moved, upon, or by means of, rollers or small wheels.
  2. To beat with rapid, continuous strokes, as a drum; to sound a roll upon.
  3. (geometry) To apply (one line or surface) to another without slipping; to bring all the parts of (one line or surface) into successive contact with another, in such a manner that at every instant the parts that have been in contact are equal.
  4. To turn over in one's mind; to revolve.
  5. (US slang) A manner of behaving or a way of doing certain things; a general disposition toward a situation.
I was going to kick his ass, but he wasn't worth getting all worked up over, I don't like that.
2006, Times Herald-Record, Tuesday, November 21, by Chris McKenna?. At
:"This is how we in Spring Valley," one teen reportedly boasted.
  1. (transitive or intransitive) To throw dice.
  2. (transitive) To roll dice such that they form a given pattern or total.
If you doubles, you get an extra turn.
With two dice, you're more likely to seven than ten.
  1. To turn over and over.
The child rolled on the floor.
  1. To tumble in gymnastics.
  2. (nautical) when a nautical vessel rotates on its fore-and-aft axis, causing its sides to go up and down. Compare with pitch.
rule Tweet Definition of rule Like Definition of rule on Facebook
  1. A regulation, law, guideline.
  2. A ruler; device for measuring, a straightedge, a measure.
  3. Something to keep order.
verb (rul, ing)
  1. To regulate, be in charge of, make decisions for, reign over.

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