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Flash Stuff:


Solar System


Q (10)






The indivisible unit in which waves may be emitted or absorbed.


Quantum Chronodynamics (QCD)

The theory that describes the interactions of quarks and gluons.


Quantum Efficiency
The ratio of the number of photons incident on a detector to the number actually detected.


Quantum Mechanics
The branch of physics that deals with the structure of atoms and their interactions with one another and with radiation.


Quantum Theory

General term for ideas based on microscopic world that human eyes can't see or feel with our hands. In this world, there is phenomenon, such as matter that is wave as well as being particles that you can't explain with the rules in the world that you can see.
This theory was made to explain these circumstances. Having the quantum hypothesis (Max Planck) in late 19th century as a beginning, many leading physicists of the time have continued studying. Famous examples are Heisenberg uncertainty principle, and Shroedinger's equation.



A (charged) elementary particle that feels the strong force; protons and neutrons are composed of three quarks each.



A quasi-stellar radio source. These peculiar objects emit radio waves with a large red shift. The red shift represents the fraction of the percentage in which the wavelengths are switched. Quasars are very far away, and very bright, and many astronomers agree that giant black holes are present within these objects.


Quasi-Stellar Source (QSS)
Sometimes also called quasi-stellar object (QSO); A stellar-appearing object of very large redshift that is a strong source of radio waves; presumed to be extragalactic and highly luminous.






R (39)



The technique of bouncing radio waves off an object to measure its distance or map its surface.


Radial Velocity

The movement of a celestial body toward or away from an observer.


Radial Velocity Curve
A plot of the variation of radial velocity with time for a binary or variable star.


Radian (rad)
The supplementary SI unit of angular measure, defined as the central angle of a circle whose subtended arc is equal to the radius of the circle. One radian is approximately 57o.


Radiant (of meteor shower)
The point in the sky from which the meteors belonging to a shower seem to radiate.



Electromagnetic wave which is emitted by a matter in order to emit light/heat. Example is Sun's rays.


Radiation Belt

Regions of charged particles in a magnetosphere.


Radiation Pressure
The transfer of momentum carried by electromagnetic radiation to a body that the radiation impinges upon.


Electromagnetic radiation which has the lowest frequency, the longest wavelength, and is produced by charged particles moving back and forth; the atmosphere of the Earth is transparent to radio waves with wavelengths from a few millimeters to about twenty meters.


Radioactive Dating
The technique of determining the ages of rocks or other specimens by the amount of radioactive decay of certain radioactive elements contained therein; something you do when you are desperate on Saturday night.



The property possessed by some elements (as uranium) of spontaneously emitting alpha or beta rays and sometimes also gamma rays by the disintegration of the nuclei of atoms.


Radio Galaxy

A radio-luminous galaxy. Radio galaxies are a part of a larger group of galaxies called active galaxies. The "active" refers to the fact that the observed radiation source is non-thermal: Glowing matter does not radiate this "active" luminous component. Furthermore, radio galaxies are named so because they are "louder" at radio wavelengths than at visible light wavelengths. This indicates tremendous activity within radio galaxies...something must be driving the non-thermal emission. Radio telescopes show lobes of radio emission extending millions of light years, centered at the nucleus of some radio galaxies, called extended radio galaxies. Centaurus A is a nearby example of an extended radio galaxy that features two outer lobes 650,000 and 1,350,000 light-years in diameter. Compact radio galaxies emit radio lobes not much larger that the galactic nucleus.


Radio Telescope

Instead of gathering and focusing visual wavelength light, a radio telescope collects radio wavelength light with a huge dish-shaped antenna. An array of radio telescopes called the Very Large Array lies 80 kilometers west of Soccoro, New Mexico. VLA radio telescopes are arranged in a "Y" pattern with each arm supporting nine 25-meter parabolic dishes. These radio telescopes probe the galaxy and universe where optical telescopes cannot. Astronomers have mapped the hydrogen content of our galaxy, and discovered enormous activity and structures in other galaxies invisible to optical telescopes.

Radio Waves

Electromagnetic radiation with very long wavelengths, produced by gas clouds and energetic objects.


Radius Vector

A straight line joining the center of an attracting body with that of a body describing an orbit around it; for example, a line joining the Sun and a planet.


Rayleigh Criterion
A criterion for how finely a set of optics may be able to distinguish the location of objects which are near each other. It begins with the assumption that the central ring of one image should fall on the first dark ring of another image; for an objective lens with diameter d and employing light with a wavelength lambda (usually taken to be 560 nm), the resolving power is approximately given by

1.22 x lambda/d

See also: Resolving Power.


Rayleigh-Taylor Instabilities
Rayleigh-Taylor instabilities occur when a heavy (more dense) fluid is pushed against a light fluid -- like trying to balance water on top of air by filling a glass 1/2 full and carefully turning it over. Rayleigh-Taylor instabilities are important in many astronomical objects, because the two fluids trade places by sticking "fingers" into each other. These "fingers" can drag the magnetic field lines along with them, thus both enhancing and aligning the magnetic field.


Red Giant
A state of stellar evolution beyond the main-sequence life of a star. A red giant core is degenerate ionized helium, surrounded by a shell of hydrogen fusion, that expands the outer atmosphere in response to higher core temperatures. The hydrogen fusing shell eats through the surrounding atmosphere and deposits helium onto the shrinking core. The ballooning atmosphere cools and glows red; hence red giant. The Sun will become a red giant the size of Earth's orbit in five to six billion years. Once the helium core reaches 100 million degrees, it explosively begins fusing helium. The birth of the active helium core is called the helium flash. The Sun as a red giant will fuse helium for about 2 billion years after the helium flash.



The Doppler effect shifting light wavelengths to the red end of the spectrum because of the motion of the source. A red shift indicates a receding source of light, with the magnitude of the shift corresponding to the velocity of the source. Astronomers relate red shifts to a calibrated distance in order to stretch their cosmic yard stick beyond the local realm of galaxies. Planetary astronomers observe small red shifts and blue shifts in stars that unseen planets orbit.


Reflection Law
For a wavefront intersecting a reflecting surface, the angle of incidence is equal to the angle of reflection, in the same plane defined by the ray of incidence and the normal.



A telescope that forms an image with mirrors.



A change in the direction of light that depends on incident angle, wavelength (color), and the material. Raindrops refract light into rainbows. Each color is a different wavelength that refracts at a unique angle, forming a band of color in order of wavelength: red, orange, yellow, green, blue, indigo, and violet. A prism behaves the same way using glass instead of water. The refraction happens at the boundary between two different, transparent materials.






The layer of rocky debris and dust made by meteoritic impact that forms the uppermost surface of planets, satellites and asteroids.


Relativity, General Theory of
A theory formulated by Einstein that describes the relations between measurements of physical phenomena by two different observers who are in relative motion at constant velocity (the special theory of relativity) or that describes how a gravitational field can be replaced by a curvature of space-time (the general theory of relativity).


Resolution (Spatial)
In astronomy, the ability of a telescope to differentiate between two objects in the sky which are separated by a small angular distance. The closer two objects can be while still allowing the telescope to see them as two distinct objects, the higher the resolution of the telescope.


Resolution (Spectral or Frequency)
Similar to spatial resolution except that it applies to frequency, spectral resolution is the ability of the telescope to differentiate two light signals which differ in frequency by a small amount. The closer the two signals are in frequency while still allowing the telescope to separate them as two distinct components, the higher the spectral resolution of the telescope.


Resolving Power

A measure of a telescope's ability to distinguish fine detail.



A relationship in which the orbital period of one body is related to that of another by a simple integer fraction, such as 1/2, 2/3, 3/5.



Reticular (net-like) pattern.



The rotation or orbital motion of an object in a clockwise direction when viewed from the north pole of the ecliptic; moving in the opposite sense from the great majority of solar system bodies.


Retrograde Motion

An apparent backward movement of a superior planet in the sky, as Earth overtakes it on its journey around the Sun.


Rift Valley

An elongated valley formed by the depression of a block of the planet's crust between two faults or groups of faults of approximately parallel strike.


Right Ascension

The position of a celestial object in the sky east of the vernal equinox along the celestial equator. Sidereal hours, minutes and seconds divide the celestial equator from 0 to 24 sidereal hours of right ascension. Keep in mind that the celestial equator is a projection of Earth's equator onto the sky, and Earth's rotation period is 24 sidereal hours (23.9345 solar mean hours). Thus dividing the celestial equator into sidereal hours, minutes and seconds instead of 360 degrees makes some intuitive sense. Set 1 sidereal hour equals 15 degrees to convert between right ascension and degrees.





Roche Limit

The closest a fluid body can orbit to its parent planet without being pulled apart by tidal forces. A solid body may survive within the Roche limit if the tidal forces do not exceed its structural strength. The Roche limit is calculated with the equation:


RL = 2.456*R*(p'/p)^(1/3)


Where p' is the density of the planet, p is the density of the moon, and R is the radius of the planet.


Roche Lobe
The volume around a star in a binary system in which, if you were to release a particle, it would fall back onto the surface of that star. A particle released above the Roche lobe of either star will, in general, occupy the `circumbinary' region that surrounds both stars. The point at which the Roche lobes of the two stars touch is called the inner Lagrangian or L1 point. If a star in a close binary system evolves to the point at which it `fills' its Roche lobe, theoretical calculations predict that material from this star will overflow both onto the companion star (via the L1 point) and into the environment around the binary system.


Turning of a body about an axis running through it.



The term applied to scarps on planetary surfaces; many scarps are thought to be the surface expression of faults within the crust of the planetary object.