Astrophysics (index)about

photon

(quantum of light, i.e., light as a particle)

A photon is a particle of light (or of any electromagnetic radiation), i.e., a name for such a particle, when light is considered a stream of particles. It is the quantum of light, the minimum possible amount. The photon theory, i.e., the modern particle theory of light, posits the minimum possible amount of light depends upon the light's wave frequency. Dating from prior to photon theory, there has been a very successful theory that EMR consists of waves, as summarized by Maxwell's equations. Photon theory coexists because it is successful in modeling some light/matter interactions that the wave theory does not.

According to current particle physics, photons are elementary particles (a type of boson) that interact with other particles. They naturally travel "the speed of light", always. As implied above, a photon has an associated "light-wave frequency" and carries an amount of energy proportional to that frequency.

Phenomena successfully modeled with photon theory include the interactions of light with atoms and electrons, such as absorption, emission and scattering. The first such instance explained by photon theory was the photoelectric effect, i.e., that the emission of electrons which can occur when EMR strikes a metal surface ("metal" as in copper, silver, etc.) does not depend upon the total light energy striking the surface, which only happens with a sufficient EMR frequency, can be explained if light arrives in quanta based upon frequency, and only frequencies associated with sufficient energy to free an such an electron succeed in doing so. Einstein suggested this in one of his 1905 papers.


(physics,quantum mechanics)
http://en.wikipedia.org/wiki/Photon

Referenced by:
absorption
ACIS
advection dominated accretion flow (ADAF)
antimatter
astronomical quantities
atmospheric escape
atomic excitation
Auger effect
Balmer jump
baryon acoustic oscillations (BAO)
baryon
biofluorescence
Bohr model
Bose-Einstein statistics
bremsstrahlung
Cherenkov detector
cosmic microwave background (CMB)
CMB lensing
CMB polarization
CNO cycle
column density
Compton reflection
Compton scattering
continuous absorption
continuum emission
cooling function
cosmic rays (CR)
Cherenkov Telescope Array (CTA)
dark matter
dark matter annihilation
de Broglie wavelength
Doppler broadening
electron degeneracy
electron orbital
electron scattering
emission
epoch of reionization (EOR)
escape fraction
fluorescence
frequency
gamma rays
giant star
High-altitude Water Cherenkov Observatory (HAWC)
ionized hydrogen (HII)
HII region (HII)
hydrodynamic escape
hydrogen (H)
integration time
K-line
line blanketing
Lyman series
Lyman-Werner photon
mean free path
Milagro
neutrino (ν)
optical depth (τ)
oscillator strength
pair production
particle
photodissociation region (PDR)
photochemistry
photodissociation
photoionization
photometer
photon counting
photon noise
photosphere
Planck constant (h)
planetary nebula (PN)
power law
Poynting-Robertson effect
Poynting vector (S)
pressure integral
pulsar (PSR)
quantum
quantum mechanics (QM)
quantum number
random walk
Rayleigh scattering
recombination
equation of radiative transfer (RTE)
spectral energy distribution (SED)
superluminous supernova (SLSN)
spectral power distribution (SPD)
spin (ms)
synchrotron self-Compton (SSC)
standard model
state of excitation
Strömgren sphere
supersymmetry
synchrotron radiation
Sunyaev-Zel'dovich effect (SZ effect)
thermodynamic equilibrium (TE)
Thomson scattering
ultra-high-energy gamma rays (UHEGR)
VHE
very-high-energy gamma rays (VHEGR)
vegetation red edge (VRE)
wavelength
wave-particle duality
XMM-Newton

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