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The speed that light travels in a vacuum. It is about 3 x 108 m/s (186,000 miles/s). This is the fundamental maximum speed that any particle (including light) or information can travel.
- Browse Related Terms: c, speed of light, Elementary Particle Physics, Fundamental Interactions, Fundamental Particles, Gluon, Gravitational Attraction, Last Scattering Surface, Mass Defect, Meson, Particle Accelerators, Particle Physics, Photon, Quark, radiation, Strong Force
2,500 km thick (1,600 mi) layer of plasma above the Sun’s photosphere. Temperatures range from ~4500 K to 60,000 K (110,000 to 8,000°F). The word chromosphere means, literally, “color sphere” and refers to its reddish color when seen with the naked eye during a total solar eclipse.
The irregular layer of the solar atmosphere that is located above the photosphere and beneath the corona. The temperature in the chromosphere rises from 6000° C to about 20,000° C. It is hotter than the photosphere but not as hot as the corona. At these higher temperatures hydrogen emits light that gives off a reddish color (called H-alpha emission). This colorful emission can be seen in prominences that project above the surface of the Sun during total solar eclipses. This is what gives the chromosphere its name (color-sphere). The chromosphere also produces most of the UV light from the Sun.
- Browse Related Terms: Chromosphere, Corona, Coronagraph, Coronal Hole, Filament, Photosphere, Prominence, Prominences, Solar Eclipse, Transition Region
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A universe where the geometry of space closes upon itself like the surface of a sphere. For a universe containing only ordinary matter this means that it must have more than the critical desnity, Ω > 1.
- Browse Related Terms: Background Radiation, Closed Universe, COSMIC, Cosmic Microwave Backgroun (CMB), Cosmology, Flat Universe, Flatness Problem, Geocentric, Geometries, Heliocentric, Metastable Energy Density, Omega, Ω, Opaque to Radiation, Open Universe , Ω, Planck Time, Universe, Vacuum Energy
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A group of galaxies held together by gravitational pull.
- Browse Related Terms: Cluster, Density Fluctuations in Matter, Galaxy, Globular Clusters, Inhomogeneity, Large Scale Structure, local group, Structure, Super Cluster
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When scientists or theoreticians find a mathematical relationship between two quantities, they design an equation, so that, for example, if one quantity is known, the other can be solved for. However when a scientist wants to solve for a quantity, they have to make sure that the units work. A constant of proportionality is a number that is inserted in to the equation which performs this task.
For example, if you knew that force x distance was proportional to work, but you wanted a concrete equation, you could say force x distance equals a constant times work. The constant is the constant of proportionality. You could find it by plugging observed data into the equation and solving for it.
- Browse Related Terms: Angular Size, Apparent luminosities, Constant of Proportionality, Dark Matter, Flux, Heavenly Bodies, Intrinsic Luminosity, Inverse Square, Luminosity, Main Sequence Star, Observed Brightness, Parallax, Parsec, Relative Brightness, Standard Candle, Type Ia Supernova, Variable Stars
The movement of matter due to changes in temperature and density. Warm material rises because it is less dense (lighter) and cool material sinks because it is denser (heavier).
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The Sun is made up of different layers. From its center outward, the Sun’s layers include the core, the convective zone, the radiative zone, the photosphere, the chromosphere, and the corona. The convective zone extends from just below the photosphere to the radiative zone. In this region convection currents transport the Sun’s energy to the surface.
In the convective zone, rising and falling currents carry heat from the radiative zone to the surface. This nonstop churning is similar to what happens when you boil water on a stove.
- Browse Related Terms: Convective Zone, Granules, Irradiation, Solar Spectral Irradiance (SSI), Sunspot Cycle, Total Solar Irradiance
The innermost part of the Sun. The core produces colossal amounts of energy, including all of the Sun's light and heat. The temperature and pressure are so great in the Sun’s core that hydrogen atoms are squeezed together to form helium. This reaction is called nuclear fusion. The temperature at the center of the Sun is about 15,000,000 °C (27,000,000 °F) and the density is about 10 times that of gold or lead.
The innermost layer of the Sun, where energy is released by the fusing together of nuclei to form heavier nuclei (nuclear fusion).
- Browse Related Terms: Atmospheric Imaging Assembly (AIA), Convection, Core, Fission, Flare, Fusion, Radiative Zone
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The outermost layer of the Sun’s outer atmosphere. This halo of ions extends millions of miles into space and consists of a gas that is much thinner than Earth’s atmosphere. The temperature is greater than one million kelvin. The corona is visible to the naked eye only during a solar eclipse.
The very hot outer layer of the Sun's atmosphere, composed of highly diffused, superheated, ionized gases, and extending into interplanetary space. Some of the hot gasses in the solar corona escape the Sun to form the solar wind.
- Browse Related Terms: Chromosphere, Corona, Coronagraph, Coronal Hole, Filament, Photosphere, Prominence, Prominences, Solar Eclipse, Transition Region
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An instrument designed to study the Sun’s corona by covering the bright disk of the Sun. This instrument creates an artificial eclipse that allows us to see the Sun’s faint outer atmosphere. Each STEREO observatory has two coronagraphs.
- Browse Related Terms: Chromosphere, Corona, Coronagraph, Coronal Hole, Filament, Photosphere, Prominence, Prominences, Solar Eclipse, Transition Region
An area of the corona which appears dark in X-rays and ultraviolet light. They are usually located at the poles of the Sun, but can occur in other places as well. The magnetic field lines in a coronal hole extend out into the solar wind rather than coming back down to the Sun's surface as they do in other parts of the Sun.
An area of the corona that appears dark when viewed in ultraviolet light. They are usually located around the poles of the Sun, but can occur at other latitudes as well. The magnetic field lines in a coronal hole extend out into the solar wind rather than coming back down to the Sun’s surface. Because the magnetic field lines extend into space, they carry hot material with them and leave patches of the solar surface cooler.
- Browse Related Terms: Chromosphere, Corona, Coronagraph, Coronal Hole, Filament, Photosphere, Prominence, Prominences, Solar Eclipse, Transition Region
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A catastrophic expansion of a part of the coronal magnetic field that causes a huge bubble of plasma and magnetic field to erupt from the Sun. A CME can last for several hours and travels though space at a million miles per hour. CMEs are usually accompanied by a solar flare. The charged particles and magnetic fields associated with CMEs can cause power and communications outages, damage to satellites, and health problems for astronauts. They usually take about three days to reach Earth, but very fast ones can arrive in under a day.
High speed coronal mass ejections produce major disturbances in the solar wind. Often loop-like in appearance, coronal mass ejections rise as massive clouds of material from the solar atmosphere. Dangerous, high energy, charged particles are often produced in these disturbances and, when they are directed towards Earth, often produce large magnetic storms in the magnetosphere.
- Browse Related Terms: AURORA, Auroral Oval, Coronal Mass Ejection (CME), Geosynchronous, Heliosphere, Magnetic Field, Magnetic Field Lines, Magnetic Storms and Substorms, Magnetosphere, Magnetotail, Radiation Belt, Solar System, Solar Wind, Space Weather
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Having to do with the universe as a whole.
- Browse Related Terms: Background Radiation, Closed Universe, COSMIC, Cosmic Microwave Backgroun (CMB), Cosmology, Flat Universe, Flatness Problem, Geocentric, Geometries, Heliocentric, Metastable Energy Density, Omega, Ω, Opaque to Radiation, Open Universe , Ω, Planck Time, Universe, Vacuum Energy
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Radiation filling the universe, remaining from the early, hot phase. (It is sometimes called the "primal glow.") Today this radiation has cooled to 2.73 K and is strongest in the microwave part of the spectrum.
- Browse Related Terms: Background Radiation, Closed Universe, COSMIC, Cosmic Microwave Backgroun (CMB), Cosmology, Flat Universe, Flatness Problem, Geocentric, Geometries, Heliocentric, Metastable Energy Density, Omega, Ω, Opaque to Radiation, Open Universe , Ω, Planck Time, Universe, Vacuum Energy
High energy charged particles traveling through interstellar space at nearly the velocity of light. Most are produced in supernova explosions.
- Browse Related Terms: Auroral Substorms, Cosmic Ray, Electromagnetic Radiation, Electron, Energetic Particles, Ion, Ion, Ionize, Ionosphere, Magnetism, plasma, Proton
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The energy density of the smooth vacuum. Eisntein introduced it as a component of the universe but later withdrew it.
- Browse Related Terms: Cosmological Constant, Λ, Critical Density, Dark Energy, Deceleration, Energy Density, inflation, Lambda, Λ, Matter-Dominated Universe, model, Quantum Fluctuations, Radiation-Dominated Universe, scalar, Steady State Theory
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A principle invoked in cosmology that severely restricts the large variety of possible cosmological theories: On large scales, the Universe is homogeneous and isotropic.
The universe, when viewed on sufficiently large distance scales, has no preferred directions or preferred places. Or, in other words, on a large scale the Universe looks the same in all directions for an observer at any place. This principle is consistent with observations of the universe. If one assumes these two properties to be true about the Universe, then the only possible cosmic evolution is a global expansion or contraction. Exerpt from Wikipedia. Information held under GNU Free Documentation License.
- Browse Related Terms: Aberration, Big Bang, Cosmological Principle, Curvature of Spacetime, General Relativity, Hubble's Law, Milky Way, Quasar, Recede, Relativity, Spacetime, Supernova
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The study of the universe as a whole, of the contents, structure, and evolution of the universe from the beginning of time to the future.
- Browse Related Terms: Background Radiation, Closed Universe, COSMIC, Cosmic Microwave Backgroun (CMB), Cosmology, Flat Universe, Flatness Problem, Geocentric, Geometries, Heliocentric, Metastable Energy Density, Omega, Ω, Opaque to Radiation, Open Universe , Ω, Planck Time, Universe, Vacuum Energy
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Matter, such as charged particles, that is strongly affected by radiation.
- Browse Related Terms: Annihilated/annihilation, Antimatter, Antiparticle/antiquark/antielectron, Coupled to Radiation, Electromagnetic Force, Electron, Ion, Ionized, Muon, Neutrino, plasma, Positron, Radiation Gas
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The density of matter/energy that would just halt the expansion of the universe. The dividing line between a collapsing and an ever-expandinguniverse.
- Browse Related Terms: Cosmological Constant, Λ, Critical Density, Dark Energy, Deceleration, Energy Density, inflation, Lambda, Λ, Matter-Dominated Universe, model, Quantum Fluctuations, Radiation-Dominated Universe, scalar, Steady State Theory