Subject:
All Disciplines Arts & Humanities Biology & Life Sciences Business & Economics Chemistry & Materials Science Computer Science & Mathematics Engineering Environmental & Earth Sciences Medicine & Pharmacology Physical Sciences Public Health & Healthcare Social Sciences
Sort:
Hottest Latest Alphabetical (A-Z) Alphabetical (Z-A)
Type:
All Topic Review Biography
Topic Review
Stellar Magnetic Field
A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively increasing the pressure without a comparable gain in density. As a result, the magnetized region rises relative to the remainder of the plasma, until it reaches the star's photosphere. This creates starspots on the surface, and the related phenomenon of coronal loops.
  • 268
  • 08 Oct 2022
Topic Review
Stellar Constellations in Fiction
Some stellar constellations have been featured in fictional works.
  • 781
  • 31 Oct 2022
Topic Review
Stellar Chromospheric Variability
Chromospheric (magnetic) activity is evidence of the presence of strong and variable magnetic fields. Magnetically active chromospheres are predominantly found in cool stars with convective envelopes of spectral types F and later. Day- to year-long variability is associated with the evolution and rotational modulation of individual magnetically active regions.
  • 822
  • 12 Jan 2022
Topic Review
Stellar Astronomy
Astronomy (from grc ἀστρονομία (Script error: No such module "Ancient Greek".) 'science that studies the laws of the stars') is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates beyond Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole. Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Babylonians, Greeks, Indians, Egyptians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. Nowadays, professional astronomy is often said to be the same as astrophysics. Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs play an active role. This is especially true for the discovery and observation of transient events. Amateur astronomers have helped with many important discoveries, such as finding new comets.
  • 877
  • 17 Oct 2022
Topic Review
Stellar Aberration (Derivation from Lorentz Transformation)
Stellar aberration is an astronomical phenomenon "which produces an apparent motion of celestial objects". It can be proven mathematically that stellar aberration is due to the change of the astronomer's inertial frame of reference. The formula is derived with the use of Lorentz transformation of the star's coordinates. As the astronomer John Herschel has already explained in 1844, the stellar aberration does not depend on the relative velocity of the star towards Earth. Otherwise eclipsing binary stars would appear to be separated, in stark contrast to observation: both stars are rotating with high speed —and ever changing and different velocity vectors— around each other, but they appear as one spot all the time.
  • 1.8K
  • 27 Oct 2022
Topic Review
Steady State Model
In cosmology, the steady state model is an alternative to the Big Bang theory of the evolution of our universe. In the steady state model, the density of matter in the expanding universe remains unchanged due to a continuous creation of matter, thus adhering to the perfect cosmological principle, a principle that asserts that the observable universe is basically the same at any time as well as at any place. While the steady state model enjoyed some popularity in the mid-20th century (though less popularity than the Big Bang theory), it is now rejected by the vast majority of cosmologists, astrophysicists and astronomers, as the observational evidence points to a hot Big Bang cosmology with a finite age of the universe, which the steady state model does not predict.
  • 2.3K
  • 14 Oct 2022
Topic Review
Statistical Ensemble (Mathematical Physics)
In physics, specifically statistical mechanics, an ensemble (also statistical ensemble) is an idealization consisting of a large number of virtual copies (sometimes infinitely many) of a system, considered all at once, each of which represents a possible state that the real system might be in. In other words, a statistical ensemble is a probability distribution for the state of the system. The concept of an ensemble was introduced by J. Willard Gibbs in 1902. A thermodynamic ensemble is a specific variety of statistical ensemble that, among other properties, is in statistical equilibrium (defined below), and is used to derive the properties of thermodynamic systems from the laws of classical or quantum mechanics.
  • 660
  • 07 Nov 2022
Topic Review
Stationary Action Principle
The stationary action principle – also known as the principle of least action – is a variational principle that, when applied to the action of a mechanical system, yields the equations of motion for that system. The principle states that the trajectories (i.e. the solutions of the equations of motion) are stationary points (a.k.a. critical points) of the system's action functional. The term "least action" is a historical misnomer since the principle has no minimality requirement: the value of the action functional need not be minimal (even locally) on the trajectories. The principle can be used to derive Newtonian, Lagrangian and Hamiltonian equations of motion, and even general relativity (see Einstein–Hilbert action). In relativity, a different action must be minimized or maximized. The classical mechanics and electromagnetic expressions are a consequence of quantum mechanics. The stationary action method helped in the development of quantum mechanics. In 1933, the physicist Paul Dirac demonstrated how this principle can be used in quantum calculations by discerning the quantum mechanical underpinning of the principle in the quantum interference of amplitudes. Subsequently Julian Schwinger and Richard Feynman independently applied this principle in quantum electrodynamics. The principle remains central in modern physics and mathematics, being applied in thermodynamics, fluid mechanics, the theory of relativity, quantum mechanics, particle physics, and string theory and is a focus of modern mathematical investigation in Morse theory. Maupertuis' principle and Hamilton's principle exemplify the principle of stationary action. The action principle is preceded by earlier ideas in optics. In Ancient Greece , Euclid wrote in his Catoptrica that, for the path of light reflecting from a mirror, the angle of incidence equals the angle of reflection. Hero of Alexandria later showed that this path was the shortest length and least time. Scholars often credit Pierre Louis Maupertuis for formulating the principle of least action because he wrote about it in 1744 and 1746. However, Leonhard Euler discussed the principle in 1744, and evidence shows that Gottfried Leibniz preceded both by 39 years.
  • 806
  • 14 Oct 2022
Topic Review
Standard Electrode Potential
In electrochemistry, standard electrode potential [math]\displaystyle{ E^\ominus }[/math], or [math]\displaystyle{ E^\ominus_{red} }[/math], is a measure of the reducing power of any element or compound. The IUPAC "Gold Book" defines it as: "the value of the standard emf (electromotive force) of a cell in which molecular hydrogen under standard pressure is oxidized to solvated protons at the left-hand electrode".
  • 492
  • 06 Oct 2022
Topic Review
Standard and Alternative Cosmology
The Standard and The Alternative Cosmological Models, Distances Calculation to Galaxies without Hubble Constant For the alternative cosmological models considered in the extended version of this entry, the distances  are calculated for galaxies without using the Hubble constant. This process is mentioned in the second narrative, and described in detail in the third narration. According to the third narrative, as the density of the relativistic mass of the universe decreases while the universe expands, new matter is created by a phase transition process which results in a continuously constant ordinary density of matter. While the universe develops on the basis of this postulate of the emergence of new matter, it is "assumed that matter arises as a result of such a phase transition of dark energy into both new dark and visible matter. It is somewhat irrelevant how we describe dark energy, calling it aether, or vice versa, the changing of aether into dark energy. It should be clear to everyone that this renaming does not change the essence of this phase transition phenomena. It should be noted that, unlike all well‐known geometric models of the Euclidean space of our existence, this phase transition of dark energy into matter would accordingly be a stereographic projection of a three‐dimensional surface on to a four‐dimensional globe.
  • 1.4K
  • 29 Oct 2020
  • Page
  • of
  • 118
Featured Entry Collections
>>

Featured Books

>>
Encyclopedia of Social Sciences
Encyclopedia of COVID-19
Encyclopedia of Fungi
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Video Production Service
Feedback