In particle physics, a lepton is an elementary particle of half-integer spin (spin 1⁄2) that does not undergo strong interactions.
Two main classes of leptons exist, charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos).
Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed.
Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium.
The first-generation leptons, also called electronic leptons, comprise the electron ( e− ) and the electron neutrino ( ν e);
The heavier muons and taus will rapidly change into electrons and neutrinos through a process of particle decay: the transformation from a higher mass state to a lower mass state.
Thus electrons are stable and the most common charged lepton in the universe, whereas muons and taus can only be produced in high energy collisions (such as those involving cosmic rays and those carried out in particle accelerators).
The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending on the relative spin states.
In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.
a helium atom in the ground state has spin 0 and behaves like a boson, even though the quarks and electrons which make it up are all fermions.
Unlike quarks, however, leptons are not subject to the strong interaction, but they are subject to the other three fundamental interactions: gravitation, the weak interaction, and to electromagnetism ...
electromagnetism ... is proportional to charge, and is thus zero for the electrically neutral neutrinos.
For every lepton flavor, there is a corresponding type of antiparticle, known as an antilepton, that differs from the lepton only in that some of its properties have equal magnitude but opposite sign.
According to certain theories, neutrinos may be their own antiparticle. It is not currently known whether this is the case.
In particle physics, every type of particle is associated with [an] antiparticle with the same mass but with opposite physical charges (such as electric charge).
For example, the antiparticle of the electron is the antielectron (which is often referred to as positron).
While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. The opposite is also true: the antiparticle of the positron is the electron.
In modern physics, antimatter is defined as matter which is composed of the antiparticles (or "partners") of the corresponding particles of 'ordinary' matter.
In theory, a particle and its anti-particle (for example, a proton and an antiproton) have the same mass, but opposite electric charge and other differences in quantum numbers. For example, a proton has positive charge while an antiproton has negative ...
The invariant mass of an electron is approximately 9.109×10−31 kilograms, or 5.489×10−4 atomic mass units. On the basis of Einstein's principle of mass–energy equivalence, this mass corresponds to a rest energy of 0.511 MeV.
Electrons have an electric charge of −1.602176634×10−19 coulombs, which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge.
Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign.
As the symbol e is used for the elementary charge, the electron is commonly symbolized by e−, where the minus sign indicates the negative charge.
The positron is symbolized by e+ because it has the same properties as the electron but with a positive rather than negative charge.
Leptons are spin 1/2 particles. The spin-statistics theorem thus implies that they are fermions and thus that they are subject to the Pauli exclusion principle: No two leptons of the same species can be in the same state at the same time.
there are only two possible values for a spin-1/2 particle: sz = +1/2 and sz = -1/2. These correspond to quantum states in which the spin component is pointing in the +z or −z directions respectively, and are often referred to as "spin up" and "spin down"
The Pauli exclusion principle is the quantum mechanical principle which states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously.
In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin 1/2, 3/2 etc. These particles obey the Pauli exclusion principle.
Fermions include all quarks and leptons, as well as all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei.
Some fermions are elementary particles, such as the electrons, and some are composite particles, such as the protons.
According to the spin-statistics theorem in any reasonable relativistic quantum field theory, particles with integer spin are bosons, while particles with half-integer spin are fermions.
In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3).
The most familiar baryons are protons and neutrons, both of which contain three quarks, and for this reason these particles are sometimes described as triquarks.
Protons are spin-1/2 fermions and are composed of three valence quarks, making them baryons (a sub-type of hadrons).
Because spin projections vary in increments of 1 (that is 1 ħ), a single quark has a spin vector of length 1/2, and has two spin projections (Sz = +1/2 and Sz = −1/2).
Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of length S = 1 and three spin projections (Sz = +1, Sz = 0, and Sz = −1).
If two quarks have unaligned spins, the spin vectors add up to make a vector of length S = 0 and has only one spin projection (Sz = 0), etc.
Since baryons are made of three quarks [DISPUTED], their spin vectors can add to make a vector of length S = 3/2, which has four spin projections (Sz = +3/2, Sz = +1/2, Sz = −1/2, and Sz = −3/2), or a vector of length S = 1/2 with two spin projections ...
Four closely related Δ baryons exist: Δ++ (constituent quarks: uuu), Δ+ (uud), Δ0 (udd), and Δ− (ddd), which respectively carry an electric charge of +2 e, +1 e, 0 e, and −1 e.
In particle physics, mesons are hadronic subatomic particles composed of one quark and one antiquark, bound together by strong interactions.
The resulting attraction between different quarks causes the formation of composite particles known as hadrons
Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.
Due to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons (such as protons and neutrons) and mesons, or in quark–gluon plasmas.
Quarks ... are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation, strong interaction, and weak interaction).
Quarks ... are the only known particles whose electric charges are not integer multiples of the elementary charge.
A neutrino (denoted by the Greek letter ν) is a fermion (an elementary particle with spin of 1/2) that interacts only via the weak subatomic force and gravity.
The heavier quarks rapidly change into up and down quarks through a process of particle decay: the transformation from a higher mass state to a lower mass state.
Because of this, up and down quarks are generally stable and the most common in the universe, whereas strange, charm, bottom, and top quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators).
For every quark flavor there is a corresponding type of antiparticle, known as an antiquark, that differs from the quark only in that some of its properties (such as the electric charge) have equal magnitude but opposite sign.
The Standard Model is the theoretical framework describing all the currently known elementary particles. This model contains six flavors of quarks (q), named up (u), down (d), strange (s), charm (c), bottom (b), and top (t).
Antiparticles of quarks are called antiquarks, and are denoted by a bar over the symbol for the corresponding quark, such as ū for an up antiquark.
Elementary fermions are grouped into three generations, each comprising two leptons and two quarks. The first generation includes up and down quarks, the second strange and charm quarks, and the third bottom and top quarks.
Hadrons contain, along with the valence quarks that contribute to their quantum numbers, virtual quark–antiquark pairs known as sea quarks.
The quarks that determine the quantum numbers of hadrons are called valence quarks; apart from these, any hadron may contain an indefinite number of virtual "sea" quarks, antiquarks, and gluons, which do not influence its quantum numbers.
A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron.
The two up quarks and one down quark of a proton are held together by the strong force, mediated by gluons.
A modern perspective has a proton composed of the valence quarks (up, up, down), the gluons, and transitory pairs of sea quarks.
Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons" (particles present in atomic nuclei).
One or more protons are present in the nucleus of every atom; they are a necessary part of the nucleus.
The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z). Since each element has a unique number of protons, each element has its own unique atomic number.
Although protons were originally considered fundamental or elementary particles, in the modern Standard Model of particle physics, protons are classified as hadrons, like neutrons, the other nucleon.
Protons are composite particles composed of three valence quarks: two up quarks of charge + 2/3e and one down quark of charge –1/3e.
The remainder of a proton's mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together.
The neutron is a subatomic particle, symbol n or n0, with no electric charge and a mass slightly greater than that of a proton.
Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one atomic mass unit, they are both referred to as nucleons.
A free neutron is unstable, decaying to a proton, electron and antineutrino with a mean lifetime of just under 15 minutes (881.5±1.5 s).
This radioactive decay, known as beta decay, is possible because the mass of the neutron is slightly greater than the proton.
Neutrons or protons bound in a nucleus can be stable or unstable, however, depending on the nuclide.
Beta decay, in which neutrons decay to protons, or vice versa, is governed by the weak force, and it requires the emission or absorption of electrons and neutrinos, or their antiparticles.
The neutron has no measurable electric charge. With its positive electric charge, the proton is directly influenced by electric fields, whereas the neutron is unaffected by electric fields.
The neutron has a magnetic moment, however, so the neutron is influenced by magnetic fields. The neutron's magnetic moment has a negative value, because its orientation is opposite to the neutron's spin.
The neutron is classified as a hadron, because it is a composite particle made of quarks. The neutron is also classified as a baryon, because it is composed of three valence quarks.
The finite size of the neutron and its magnetic moment both indicate that the neutron is a composite, rather than elementary, particle.
Protons and neutrons are both nucleons, which may be bound together by the nuclear force to form atomic nuclei.
The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element.
A telescope is an optical instrument using lenses, curved mirrors [DISPUTED], or a combination of both to observe distant objects ...
The word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.
The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses.
All refracting telescopes use the same principles. The combination of an objective lens and some type of eyepiece is used to gather more light than the human eye is able to collect on its own, focus it, and present the viewer with a brighter, clearer, ...
An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device.
The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope.
In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s.
A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image.
Optical radiation is part of the electromagnetic spectrum. It is subdivided into ultraviolet radiation (UV), the spectrum of light visible for man (VIS) and infrared radiation (IR). It ranges between wavelengths of 100 nm to 1 mm [DISPUTED]
Infrared and optical astronomy are often practiced using the same telescopes, as the same mirrors or lenses are usually effective over a wavelength range that includes both visible and infrared light.
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared (IR) radiation.
The wavelength of infrared light ranges from 0.75 to 300 micrometers. Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves.
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz.
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency of approximately 30 PHz) to 400 nm (750 THz), shorter than that of visible light but longer than X-rays.
There are no precisely defined boundaries between the bands of the electromagnetic spectrum; rather they fade into each other like the bands in a rainbow (which is the sub-spectrum of visible light).
Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm
Infrared radiation with wavelengths just longer than visible light, known as near-infrared, behaves in a very similar way to visible light, and can be detected using similar solid state devices ...
For this reason, the near infrared region of the spectrum is commonly incorporated as part of the "optical" spectrum, along with the near ultraviolet.
Many optical telescopes, such as those at Keck Observatory, operate effectively in the near infrared as well as at visible wavelengths.
Near Infrared: 2.0 to 2.4: Wavelength (micrometres): K band: Most major optical telescopes and most dedicated infrared telescopes
The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is defined as 299792458 metres per second (approximately 300000 km/s, or 186000 mi/s)
It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 second.
Under ideal laboratory conditions, people can see infrared up to at least 1050 nm; children and young adults may perceive ultraviolet wavelengths down to about 310–313 nm.
An optical telescope is a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct view, or to make a photograph, or to collect data through electronic image sensors.
The basic scheme is that the primary light-gathering element, the objective (the convex lens or concave mirror used to gather the incoming light), focuses that light from the distant object to a focal plane where it forms a real image.
This image may be recorded or viewed through an eyepiece, which acts like a magnifying glass. The eye then sees an inverted [DISPUTED] magnified virtual image of the object.
Most telescope designs produce an inverted image at the focal plane; these are referred to as inverting telescopes.
There are telescope designs that do not present an inverted image such as the Galilean refractor and the Gregorian reflector. These are referred to as erecting telescopes.
A telescope's ability to resolve small detail is directly related to the diameter (or aperture) of its objective (the primary lens or mirror that collects and focuses the light), and its light gathering power is related to the area of the objective.
In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself.
For example, in a telescope, the aperture stop is typically the edges of the objective lens or mirror (or of the mount that holds it). One then speaks of a telescope as having, for example, a 100-centimeter aperture.
In optical engineering, the objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image.
The eyepiece is placed near the focal point of the objective to magnify this image. The amount of magnification depends on the focal length of the eyepiece.
In optics, an image is defined as the collection of focus points of light rays coming from an object.
A real image is the collection of focus points actually made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays.
a virtual image is found by tracing real rays that emerge from an optical device (lens, mirror, or some combination) backward to perceived or apparent origins of ray divergences.
Because the rays never really converge, a virtual image cannot be projected onto a screen. In contrast, a real image can be projected on the screen as it is formed by rays that converge on a real location.
A diverging lens (one that is thicker at the edges than the middle) or a convex mirror forms a virtual image. Such an image is reduced in size when compared to the original object.
A converging lens (one that is thicker in the middle than at the edges) or a concave mirror is also capable of producing a virtual image if the object is within the focal length. Such an image will be magnified.
A real image ... is an image which is located in the plane of convergence for the light rays that originate from a given object.
In ray diagrams ... real rays of light are always represented by full, solid lines; perceived or extrapolated rays of light are represented by dashed lines.
A real image occurs where rays converge, whereas a virtual image occurs where rays only appear to diverge.
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.
Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics.
The front and rear (or back) focal planes are defined as the planes, perpendicular to the optic axis, which pass through the front and rear focal points.
If the medium surrounding the optical system has a refractive index of 1 (e.g., air or vacuum), then the distance from the principal planes to their corresponding focal points is just the focal length of the system.
A principal focus or focal point is a special focus: For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused.
rays that enter the system parallel to the optical axis are focused such that they pass through the rear focal point
Schematic of a Keplerian refracting telescope. The arrow at (4) is a (notional) representation of the original image; the arrow at (5) is the inverted image at the focal plane; the arrow at (6) is the virtual image that forms in the viewer's visual sphere
This image may be ... viewed through an eyepiece, which acts like a magnifying glass. The eye then sees a ... magnified virtual image of the object.
This image may be ... viewed through an eyepiece, which acts like a magnifying glass. The eye then sees an inverted magnified virtual image of the object.
A curved primary mirror is the reflector telescope's basic optical element that creates an image at the focal plane [OF THE PRIMARY IF THERE IS NO SECONDARY]. The distance from the mirror to the focal plane is called the focal length.
Film or a digital sensor may be located here to record the image, or a secondary mirror may be added to modify the optical characteristics and/or redirect the light to film, digital sensors, or an eyepiece for visual observation.
The Gregorian telescope ... employs a concave secondary mirror that reflects the image back through a hole in the primary mirror. This produces an upright image
There are several large modern telescopes that use a Gregorian configuration such as the Vatican Advanced Technology Telescope, the Magellan telescopes, the Large Binocular Telescope, and the Giant Magellan Telescope.
The Newtonian telescope ... usually has a paraboloid primary mirror but at focal ratios of f/8 or longer a spherical primary mirror can be sufficient for high visual resolution.
A flat secondary mirror reflects the light to a focal plane at the side of the top of the telescope tube.
The cassegrain telescope (sometimes called the "Classic Cassegrain") ... has a parabolic primary mirror, and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary.
The Ritchey–Chrétien telescope ... is a specialized Cassegrain reflector which has two hyperbolic mirrors (instead of a parabolic primary).
It is free of coma and spherical aberration at a nearly flat focal plane if the primary and secondary curvature are properly figured.
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. ... They are used as objectives for large reflecting telescopes.
The Gregorian telescope consists of two concave mirrors; the primary mirror (a concave paraboloid) collects the light and brings it to a focus before the secondary mirror (a concave ellipsoid) where it is reflected back through a hole in the centre ...
In a prime focus design no secondary optics are used, the image is accessed at the focal point of the primary mirror.
The overall focal ratio of the complete telescope will be f/8 and the optical prescription is an aplanatic Gregorian telescope.
In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture"). It is also known as the focal ratio, f-ratio, or f-stop
Collapsible "truss tube" Dobsonians appeared in the amateur telescope making community as early as 1982 and allow the optical tube assembly, the largest component, to be broken down.
As the name implies, the "tube" of this design is actually composed of an upper 'cage assembly', which contains the secondary mirror, and focuser, held in place by several rigid poles over a ‘mirror box’ which contains the objective mirror.
In the Gregorian design, the primary mirror creates a real image before the secondary mirror. This allows for a field stop to be placed at this location, so that the light from outside the field of view does not reach the secondary mirror.
This is a major advantage for solar telescopes, where a field stop (Gregorian stop) can reduce the amount of heat reaching the secondary mirror and subsequent optical components.
In an imperfect lens L, all the rays do not pass through a focal point. The smallest circle that they pass through C is called the circle of least confusion.
Top: The formation of a real image using a convex lens. Bottom: The formation of a real image using a concave mirror. In both diagrams, f is the focal point, O is the object, and I is the image.
Top: The formation of a virtual image using a diverging lens. Bottom: The formation of a virtual image using a convex mirror. In both diagrams, f is the focal point, O is the object and I is the image, shown in grey ...
A trade study or trade-off study, also known as a figure of merit analysis or a factor of merit analysis, is the activity of a multidisciplinary team to identify the most balanced technical solutions among a set of proposed viable solutions (FAA 2006).
These viable solutions are judged by their satisfaction of a series of measures or cost functions. These measures describe the desirable characteristics of a solution. They may be conflicting or even mutually exclusive.
Trade studies are commonly used in the design of aerospace and automotive vehicles and the software selection process ... to find the configuration that best meets conflicting performance requirements.
In software engineering, dependency injection is a technique in which an object receives other objects that it depends on. These other objects are called dependencies.
In the typical "using" relationship the receiving object is called a client and the passed (that is, "injected") object is called a service. The code that passes the service to the client can be many kinds of things and is called the injector.
Instead of the client specifying which service it will use, the injector tells the client what service to use. The "injection" refers to the passing of a dependency (a service) into the object (a client) that would use it.
Validation can be expressed by the query "Are you building the right thing?" and verification by "Are you building it right?"
A sensor is a transducer that receives and responds to a signal or stimulus from a physical system. It produces a signal, which represents information about the system
An actuator is a device that is responsible for moving or controlling a mechanism or system. It is controlled by a signal from a control system or manual control.
René François Ghislain Magritte was a Belgian surrealist artist. He became well known for creating a number of witty and thought-provoking images.
Often depicting ordinary objects in an unusual context, his work is known for challenging observers' preconditioned perceptions of reality.