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Reaumur scale

The Reaumur scale is a way of measuring temperature. The unit associated with the scale is called Reaumur, named after the physicist Rene-Antoine Ferchault de Reaumur who created it in 1731. The unit is usually abbreviated "Re", sometimes "r". Th ...

                                               

Reception theory

Reception theory is a theory proposed by Stuart Hall. Its main principal is that a text can have different meanings to different audiences. It is also called "reader response theory". The reader contributes to a text by interpreting it to what th ...

                                               

Recloser

A recloser is a circuit breaker which can be closed automatically after the breaker has been opened because of electric fault. Because many faults in power systems fix themselves after they happen, the installation of recloser ensures more contin ...

                                               

Red dwarf

A red dwarf is a kind of star. Red dwarf stars are smaller than half the size of the Sun. They are also cooler than most stars. Red dwarfs burn their fuel slowly, so they shine with less light than hot stars. Red dwarf stars are the most common i ...

                                               

Red supergiant star

A red supergiant star is a larger and brighter type of red giant star. Red supergiants are often variable stars and are between 200 to 2.200 times bigger than the Sun. An example of a red supergiant star is Antares. 119 Tauri, Betelgeuse, Mu Ceph ...

                                               

Reef

A reef is a rock, sandbar, or other feature below the water surface. The best-known reefs are the coral reefs in tropical waters. They are built by corals and calcareous algae. Artificial reefs such as shipwrecks are sometimes created to attract ...

                                               

Reference ellipsoid

A reference ellipsoid is an ellipsoid which is used as a frame of reference for geodetic calculations. It is a figure like the shape of the Earth. It is easier to work with than the geoid, which is another shape like that of the Earth. It is rela ...

                                               

Reflex

A reflex or reflex action is an automatic and fast movement in response to a stimulus. A true reflex is a behaviour done by the reflex arc. This is the path the signal of a reflex takes. That path is from the outside stimulus to the central nervo ...

                                               

Refractory

A refractory is a material that can stand high temperature. It is used in furnaces, kilns, incinerators and reactors. Materials to make refractory must be chemically and physically stable at high temperature, such as alumina, silica, magnesia and ...

                                               

Regression (psychology)

Regression is a word used in psychology on defense mechanism. It means the act of reversing the ego into an earlier state which allows one to avoid dealing with impulses in a mature manner. A common example of regression is" curling up into a bal ...

                                               

Regurgitation

Regurgitation is the process of a human or animal letting out the food it had been digesting. Sometimes, blood can come out as well. Regurgitation can be very important to some animals, such as birds for example. It is used by a number of species ...

                                               

Relative dating

Relative dating is the kind of geochronology that determines the relative order of past events. The idea is to find the age of an object or event by comparing it to another object or event, or by using clues from the environment or circumstances ...

                                               

Renewable resource

A renewable resource is a resource which can be used repeatedly and replaced naturally. Renewable energy almost never runs out, for example: solar energy is powered by heat from the sun and never runs out. Examples include oxygen, fresh water, so ...

                                               

Resultant force

A resultant force, also called a net force, is a force equal to the sum of all forces applied to an object. If 30N and 60N are applied to the right, then the resultant force is 90N to the right. If 40N is applied to the left and 30N applied to th ...

                                               

Reticulum

                                               

Retrograde and direct motion

Direct motion is the motion of a planetary body in a direction similar to that of other bodies within its system, and is sometimes called prograde motion. Retrograde motion is motion in the opposite direction. In the case of celestial bodies such ...

                                               

Rhea (moon)

Rhea, does known as Tomatoosaurus, a portmanteau of tomato + Tyrannosaurus, is Saturns second largest moon. It is made of ice and rock.

                                               

Rheology

                                               

Rho Cassiopeiae

Rho Cassiopeiae is a yellow hypergiant star, the brightest one in the night sky. It is located in the constellation Cassiopeia. It is also one of the largest, with a size 450 times larger than the Sun.

                                               

Rhyacian

The Rhyacian is the second geological period in the Palaeoproterozoic that began 2.3 billion years ago, and ended at 2.05 billion years ago. Before it was the Siderian It is followed by the Orosirian. The Huronian Makganyene global glaciation beg ...

                                               

Rhyolite

                                               

Rift (geology)

In geology, a rift is caused by tectonic plates in the Earths lithosphere moving apart. Rifts are usually accompanied by orogeny, volcanoes and earthquakes. Rifting often makes a rift valley, which may hold a rift lake. The Great Rift Valley in E ...

                                               

Right ascension

Right ascension is the astronomical word for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. It is the celestial counterpart to longitude. The other coordinate is the declination. The moo ...

                                               

Ring galaxy

A ring galaxy is a kind of galaxy that has a ring shape. Hoags Object and NGC 1291 are two examples. The ring is made up of many massive, young blue stars, which are extremely bright. The middle of the galaxy contains far less luminous matter. So ...

                                               

Rings of Saturn

The rings of Saturn are the planetary rings around the planet Saturn, which can be seen with a small telescope. They consist of many small particles, ranging in size from microscopic to the size of a bus that form clumps that move around Saturn. ...

                                               

Rings of Uranus

The rings of Uranus are planetary rings that go around the planet Uranus. There are 11 rings in total. In order of increasing distance from Uranus, they are: 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν and μ. Nine rings were found on 10 March 1977 ...

                                               

Rip current

A rip current is a strong surface flow of water returning outward from near the shore. It is often mistakenly called a rip tide or riptide ", which is a flow of water out of an inland lagoon or channel during an ebb tide. Colloquially a rip curre ...

                                               

RLC circuit

A circuit containing resistance, inductance, and capacitance is called an RLC circuit. A simple circuit only has one RLC series. With a resistance R present, the total electromagnetic energy U of the circuit the sum of the electric energy and mag ...

                                               

Rod cell

Rod cells are one of two types of photoreceptor cells that can be found in the retina of the eyes of humans and other mammals. Rod cells are very sensitive to light. They allow night vision. They are concentrated at the edge of the retina, where ...

                                               

Role

A role or a social role can be described as an expected behaviour of an individual. More precisely one could say it is a set of connected behaviours, rights and duties that a person has to follow in a social situation. It depends on social status ...

                                               

Rosalind (moon)

Rosalind is a closer moon to Uranus. It was found from the images taken by Voyager 2 on January 13, 1986, and was given the designation S/1986 U 4. It was named after the daughter of the banished Duke in William Shakespeares play As You Like It. ...

                                               

Rosenhan experiment

The Rosenhan experiment is a test in psychiatry. It wants to see how good a psychiatric diagnosis really is. The first person to do the test was David Rosenhan. The test is named after him. It was first conducted in 1972. Rosenhan published the r ...

                                               

Ross 248

Ross 248 is a small star about 10.30 light-years from Earth. It is in the direction of the northern constellation of Andromeda. Despite its proximity to the Earth, this star is too dim to be seen with the naked eye. Ross 248 was first catalogued ...

                                               

Rotation period

In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis relative to the background stars. For the Earth this is a sidereal day. It is different from a solar day, which is measur ...

                                               

Rover (space exploration)

A rover is a vehicle that travels on the ground of a planet, moon, or other astronomical object. Some rovers carry people that drive them. Most are robots that can drive themselves for short distances, but humans on Earth give them directions eac ...

                                               

Rubella

Rubella is a disease caused by the Rubella virus. It is often mild and an attack can pass unnoticed. However, this can make the virus very difficult to diagnose. The disease can last 1–5 days. Children recover more quickly than adults. The virus ...

                                               

Ruby

A ruby is a kind of precious stone. It is often associated with emerald, sapphire and topaz. It is usually red, but can sometimes be other colors. It is formed of aluminum and oxygen, and that means its a kind of corundum. A small amount of chrom ...

                                               

Russells paradox

Russells Paradox is the theory that states: If you have a list of lists that do not list themselves, then that list must list itself, because it doesnt contain itself. However, if it lists itself, it then contains itself, meaning it cannot list i ...

                                               

RW Cephei

RW Cephei is an orange hypergiant star in the Cepheus constellation. It is among the largest known stars with a diameter between 981 to 1.758 tmes larger than the Sun.

                                               

Rydberg constant

In spectroscopy, the Rydberg constant is a physical constant relating to the electromagnetic spectra of an atom. Its symbol is R ∞ {\displaystyle R_{\infty }} for heavy atoms or R H {\displaystyle R_{\text{H}}} for hydrogen. The constant is named ...

                                               

S/2007 S 2

S/2007 S 2 is an unnamed moon of Saturn. Its discovery was announced by Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden on May 1, 2007, from observations taken between January 18 and April 19, 2007. Telescope used is the Suba ...

                                               

S Doradus

S Doradus is a blue hypergiant star found in the large magellanic cloud. Its temperature can fall to lower than 7.000 degrees Kelvin in big eruptions. S Doradus can be more than a million times brighter than our Sun and 380 times larger in these ...

                                               

S Orionis

                                               

S Persei

                                               

S/2003 J 10

S/2003 J 10 is a non-spherical moon of Jupiter. It was found by a team of astronomers from the University of Hawaii led by Scott S. Sheppard et al. in 2003. S/2003 J 10 is about 2 kilometres in diameter, and orbits Jupiter at an average distance ...

                                               

S/2003 J 12

S/2003 J 12 is a moon of Jupiter, and is the smallest known. It was found by a team of astronomers from the University of Hawaii led by Scott S. Sheppard in 2003. S/2003 J 12 is about 1 kilometre in diameter, and orbits Jupiter at an average dist ...

                                               

S/2003 J 15

S/2003 J 15 is a moon of Jupiter. It was found by a team of astronomers from the University of Hawaii led by Scott S. Sheppard, et al. in 2003. S/2003 J 15 is about 2 kilometres in diameter, and orbits Jupiter at an average distance of 22.721.000 ...

                                               

S/2003 J 16

S/2003 J 16 is a moon of Jupiter. It was found by a team of astronomers led by Brett J. Gladman in 2003. S/2003 J 16 is about 2 kilometres in diameter, and orbits Jupiter at an average distance of 20.744.000 km in 610.362 days, at an inclination ...

                                               

S/2003 J 18

S/2003 J 18 is a moon of Jupiter. It was found by a team of astronomers led by Brett J. Gladman in 2003. S/2003 J 18 is about 2 kilometres in diameter, and orbits Jupiter at an average distance of 19.813.000 km in 569.728 days, at an inclination ...

                                               

S/2003 J 19

S/2003 J 19 is a moon of Jupiter. It was found by a team of astronomers led by Brett J. Gladman, et al. in 2003. S/2003 J 19 is about 2 kilometres in diameter, and orbits Jupiter at an average distance of 22.709.000 km in 699.125 days, at an incl ...

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