The optical microscope referred to as the light microscope, is a type of microscope that uses visible light and a system of lenses to magnify images of small objects. Optical microscopes are the oldest design of microscope and were invented in their present compound form in the 17th century. Basic optical microscopes can be simple, although many complex designs aim to improve resolution and sample contrast. Used in the classroom and at home unlike the electron microscope, used for closer viewing; the image from an optical microscope can be captured by normal, photosensitive cameras to generate a micrograph. Images were captured by photographic film, but modern developments in CMOS and charge-coupled device cameras allow the capture of digital images. Purely digital microscopes are now available which use a CCD camera to examine a sample, showing the resulting image directly on a computer screen without the need for eyepieces. Alternatives to optical microscopy which do not use visible light include scanning electron microscopy and transmission electron microscopy and scanning probe microscopy.
On 8 October 2014, the Nobel Prize in Chemistry was awarded to Eric Betzig, William Moerner and Stefan Hell for "the development of super-resolved fluorescence microscopy," which brings "optical microscopy into the nanodimension". There are two basic types of optical microscopes: compound microscopes. A simple microscope is one. A compound microscope uses several lenses to enhance the magnification of an object; the vast majority of modern research microscopes are compound microscopes while some cheaper commercial digital microscopes are simple single lens microscopes. Compound microscopes can be further divided into a variety of other types of microscopes which differ in their optical configurations and intended purposes. A regular microscope uses a lens or set of lenses to enlarge an object through angular magnification alone, giving the viewer an erect enlarged virtual image; the use of a single convex lens or groups of lenses are found in simple magnification devices such as the magnifying glass and eyepieces for telescopes and microscopes.
A compound microscope uses a lens close to the object being viewed to collect light which focuses a real image of the object inside the microscope. That image is magnified by a second lens or group of lenses that gives the viewer an enlarged inverted virtual image of the object; the use of a compound objective/eyepiece combination allows for much higher magnification. Common compound microscopes feature exchangeable objective lenses, allowing the user to adjust the magnification. A compound microscope enables more advanced illumination setups, such as phase contrast. There are many variants of the compound optical microscope design for specialized purposes; some of these are physical design differences allowing specialization for certain purposes: Stereo microscope, a low-powered microscope which provides a stereoscopic view of the sample used for dissection. Comparison microscope, which has two separate light paths allowing direct comparison of two samples via one image in each eye. Inverted microscope, for studying samples from below.
Fiber optic connector inspection microscope, designed for connector end-face inspection Traveling microscope, for studying samples of high optical resolution. Other microscope variants are designed for different illumination techniques: Petrographic microscope, whose design includes a polarizing filter, rotating stage and gypsum plate to facilitate the study of minerals or other crystalline materials whose optical properties can vary with orientation. Polarizing microscope, similar to the petrographic microscope. Phase contrast microscope, which applies the phase contrast illumination method. Epifluorescence microscope, designed for analysis of samples which include fluorophores. Confocal microscope, a used variant of epifluorescent illumination which uses a scanning laser to illuminate a sample for fluorescence. Two-photon microscope, used to image fluorescence deeper in scattering media and reduce photobleaching in living samples. Student microscope – an low-power microscope with simplified controls and sometimes low quality optics designed for school use or as a starter instrument for children.
Ultramicroscope, an adapted light microscope that uses light scattering to allow viewing of tiny particles whose diameter is below or near the wavelength of visible light. Microscopes can be or wholly computer-controlled with various levels of automation. Digital microscopy allows greater analysis of a microscope image, for example measurements of distances and areas and quantitaton of a fluorescent or histological stain. Low-powered digital microscopes, USB microscopes, are commercially available; these are webcams with a high-powered macro lens and do not use transillumination. The camera attached directly to the USB port of a computer, so that the images are shown directly on the monitor, they offer modest magnifications without the need to use eyepieces, at low cost. High power illumination is provided by an LED source or sources adjacent to the camera lens. Digital microscopy with low light levels to avoid damage to vulnerable biological samples is available using sensitive photon-counting digital
Total internal reflection
Total internal reflection is the phenomenon that makes the water-to-air surface in a fish-tank look like a silvered mirror when viewed from below the water level. Technically, TIR is the total reflection of a wave incident at a sufficiently oblique angle on the interface between two media, of which the second medium is transparent to such waves but has a higher wave velocity than the first medium. TIR occurs not only with electromagnetic waves such as light waves and microwaves, but with other types of waves, including sound and water waves. In the case of a narrow train of waves, such as a laser beam, we tend to speak of the total internal reflection of a "ray". Refraction is accompanied by partial reflection; when a wavetrain is refracted from a medium of lower propagation speed to a medium of higher propagation speed, the angle of refraction is greater than the angle of incidence. Hence, as the angle of incidence approaches a certain limit, called the critical angle, the angle of refraction approaches 90°, at which the refracted ray becomes tangential to the interface.
As the angle of incidence increases beyond the critical angle, the conditions of refraction can no longer be satisfied. In an isotropic medium such as air, water, or glass, the ray direction is the direction normal to the wavefront. If the internal and external media are isotropic with refractive indices n1 and n2 the critical angle is given by θ c = arcsin , is defined if n2 ≤ n1. For example, for visible light, the critical angle is about 49° for incidence from water to air, about 42° for incidence from common glass to air. Details of the mechanism of TIR give rise to more subtle phenomena. Unlike partial reflection between transparent media, total internal reflection is accompanied by a non-trivial phase shift for each component of polarization, the shifts vary with the angle of incidence. While total reflection, by definition, involves no continuing transfer of power across the interface, the external medium carries a so-called evanescent wave, which travels along the interface with an amplitude that falls off exponentially with distance from the interface.
The "total" reflection is indeed total if the external medium is lossless, of infinite extent, but can be conspicuously less than total if the evanescent wave is absorbed by a lossy external medium, or diverted by the outer boundary of the external medium or by objects embedded in that medium. The phase shifts in TIR are utilized by a polarization-modifying device called the Fresnel rhomb; the efficiency of the reflection is exploited by optical fibers, by reflective prisms, such as erecting prisms for binoculars. Although total internal reflection can occur with any kind of wave that can be said to have oblique incidence, including microwaves and sound waves, it is most familiar in the case of light waves. Total internal reflection of light can be demonstrated using a semicircular-cylindrical block of common glass or acrylic glass. In Fig. 3, a "ray box" projects a narrow beam of light radially inward. The semicircular cross-section of the glass allows the incoming ray to remain perpendicular to the curved portion of the air/glass surface, thence to continue in a straight line towards the flat part of the surface, although its angle with the flat part varies.
Where the ray meets the flat glass-to-air interface, the angle between the ray and the normal to the interface is called the angle of incidence. If this angle is sufficiently small, the ray is reflected but transmitted, the transmitted portion is refracted away from the normal, so that the angle of refraction is greater than the angle of incidence. For the moment, let us call the angle of incidence θi and the angle of refraction θt; as θi increases and approaches a certain "critical angle", denoted by θc, the angle of refraction approaches 90°, the refracted ray becomes fainter while the reflected ray becomes brighter. As θi increases beyond θc, the refracted ray disappears and only the reflected ray remains, so that all of the energy of the incident ray is reflected. In brief: If θi < θc, the incident ray is split, being reflected and refracted. The critical angle is the smallest angle of incidence. For light waves and other electromagnetic waves in isotropic media, there is a well-known formula for the critical angle in terms of the refractive indices.
For some other types of waves, it is more convenient to think in terms of propagation velocities rather than refractive indices. The latter approach is more direct and more general, will therefore be discussed first; when a wavefront is refracted from one medium to another, the incident and refracted portions of the wavefront meet at a common line on the
A telescope is an optical instrument that makes distant objects appear magnified by using an arrangement of lenses or curved mirrors and lenses, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. The first known practical telescopes were refracting telescopes invented in the Netherlands at the beginning of the 17th century, by using glass lenses, they were used for both terrestrial applications and astronomy. 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; the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, in some cases other types of detectors. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei's instruments presented at a banquet at the Accademia dei Lincei.
In the Starry Messenger, Galileo had used the term perspicillum. The earliest existing record of a telescope was a 1608 patent submitted to the government in the Netherlands by Middelburg spectacle maker Hans Lippershey for a refracting telescope; the actual inventor is unknown but word of it spread through Europe. Galileo heard about it and, in 1609, built his own version, made his telescopic observations of celestial objects; the idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs and several attempts to build reflecting telescopes. In 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector; the invention of the achromatic lens in 1733 corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes.
Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by the introduction of silver coated glass mirrors in 1857, aluminized mirrors in 1932. The maximum physical size limit for refracting telescopes is about 1 meter, dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors; the largest reflecting telescopes have objectives larger than 10 m, work is underway on several 30-40m designs. The 20th century saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays; the first purpose built radio telescope went into operation in 1937. Since a large variety of complex astronomical instruments have been developed; the name "telescope" covers a wide range of instruments. Most detect electromagnetic radiation, but there are major differences in how astronomers must go about collecting light in different frequency bands.
Telescopes may be classified by the wavelengths of light they detect: X-ray telescopes, using shorter wavelengths than ultraviolet light Ultraviolet telescopes, using shorter wavelengths than visible light Optical telescopes, using visible light Infrared telescopes, using longer wavelengths than visible light Submillimetre telescopes, using longer wavelengths than infrared light Fresnel Imager, an optical lens technology X-ray optics, optics for certain X-ray wavelengthsAs wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation. The near-infrared can be collected much like visible light, however in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm to 2000 μm, but uses a parabolic aluminum antenna. On the other hand, the Spitzer Space Telescope, observing from about 3 μm to 180 μm uses a mirror. Using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the frequency range from about 0.2 μm to 1.7 μm.
With photons of the shorter wavelengths, with the higher frequencies, glancing-incident optics, rather than reflecting optics are used. Telescopes such as TRACE and SOHO use special mirrors to reflect Extreme ultraviolet, producing higher resolution and brighter images than are otherwise possible. A larger aperture does not just mean that more light is collected, it enables a finer angular resolution. Telescopes may be classified by location: ground telescope, space telescope, or flying telescope, they may be classified by whether they are operated by professional astronomers or amateur astronomers. A vehicle or permanent campus containing one or more telescopes or other instruments is called an observatory. An optical telescope gathers and focuses light from the visible part of the electromagnetic spectrum. Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness. In order for the image to be observed, photographed and sent to a computer, telescopes work by employing one or
Magnetic declination, or magnetic variation, is the angle on the horizontal plane between magnetic north and true north. This angle varies depending on changes over time. Somewhat more formally, Bowditch defines variation as “the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north; the angle between magnetic and grid meridians is called grid magnetic angle, grid variation, or grivation.”By convention, declination is positive when magnetic north is east of true north, negative when it is to the west. Isogonic lines are lines on the Earth's surface along which the declination has the same constant value, lines along which the declination is zero are called agonic lines; the lowercase Greek letter δ is used as the symbol for magnetic declination. The term magnetic deviation is sometimes used loosely to mean the same as magnetic declination, but more it refers to the error in a compass reading induced by nearby metallic objects, such as iron on board a ship or aircraft.
Magnetic declination should not be confused with magnetic inclination known as magnetic dip, the angle that the Earth's magnetic field lines make with the downward side of the horizontal plane. Magnetic declination varies both with the passage of time; as a traveller cruises the east coast of the United States, for example, the declination varies from 16 degrees west in Maine, to 6 in Florida, to 0 degrees in Louisiana, to 4 degrees east. The declination at London, UK was one degree 7 minutes west, reducing to 5' as of early 2019, as the country is quite small that figure is good for the whole, it is reducing, scientists predict that in about 2050 it will be zero. In most areas, the spatial variation reflects the irregularities of the flows deep in the Earth. Secular changes to these flows result in slow changes to the field strength and direction at the same point on the Earth; the magnetic declination in a given area may change over time as little as 2–2.5 degrees every hundred years or so, depending upon how far from the magnetic poles it is.
For a location closer to the pole like Ivujivik, the declination may change by 1 degree every three years. This may be insignificant to most travellers, but can be important if using magnetic bearings from old charts or metes in old deeds for locating places with any precision; as an example of how variation changes over time, see the two charts of the same area, surveyed 124 years apart. The 1884 chart shows a variation of 8 degrees, 20 minutes West; the 2008 chart shows 13 degrees, 15 minutes West. The magnetic declination at any particular place can be measured directly by reference to the celestial poles—the points in the heavens around which the stars appear to revolve, which mark the direction of true north and true south; the instrument used to perform this measurement is known as a declinometer. The approximate position of the north celestial pole is indicated by Polaris. In the northern hemisphere, declination can therefore be determined as the difference between the magnetic bearing and a visual bearing on Polaris.
Polaris traces a circle 0.73° in radius around the north celestial pole, so this technique is accurate to within a degree. At high latitudes a plumb-bob is helpful to sight Polaris against a reference object close to the horizon, from which its bearing can be taken. A rough estimate of the local declination can be determined from a general isogonic chart of the world or a continent, such as those illustrated above. Isogonic lines are shown on aeronautical and nautical charts. Larger-scale local maps may indicate current local declination with the aid of a schematic diagram. Unless the area depicted is small, declination may vary measurably over the extent of the map, so the data may be referred to a specific location on the map; the current rate and direction of change may be shown, for example in arcminutes per year. The same diagram may show the angle of grid north. On the topographic maps of the U. S. Geological Survey, for example, a diagram shows the relationship between magnetic north in the area concerned and true north, with a label near the angle between the MN arrow and the vertical line, stating the size of the declination and of that angle, in degrees, mils, or both.
A prediction of the current magnetic declination for a given location can be obtained online from a web page operated by the National Geophysical Data Center, a division of the National Oceanic and Atmospheric Administration of the United States. This model is built with all the information available to the map-makers at the start of the five-year period it is prepared for, it reflects a predictable rate of change, is more accurate than a map—which is months or years out of date—and never less accurate. The National Geospatial-Intelligence Agency provides source code written in C, based on the World Magnetic Model; the source code is fr
Electroplating is a process that uses an electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode. The term is used for electrical oxidation of anions on to a solid substrate, as in the formation of silver chloride on silver wire to make silver/silver-chloride electrodes. Electroplating is used to change the surface properties of an object, but may be used to build up thickness on undersized parts or to form objects by electroforming; the process used in electroplating is called electrodeposition. It is analogous to a concentration cell acting in reverse; the part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that it comprises and allowing them to dissolve in the solution.
At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated and thus the ions in the electrolyte bath are continuously replenished by the anode. Other electroplating processes may use a non-consumable anode such as carbon. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution; the most common form of electroplating is used for creating coins, such as US pennies, which are made of zinc covered in a layer of copper. The cations associate with the anions in the solution; this cations are reduced at the cathode to deposit in zero valence state. For example, for copper plating, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons; the Cu2+ associates with the anion SO2−4 in the solution to form copper sulfate.
At the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the effective transfer of copper from the anode source to a plate covering the cathode; the plating is most a single metallic element, not an alloy. However, some alloys can be electrodeposited, notably solder. Plated "alloys" are not true alloys, i.e. solid solutions, but rather discrete tiny crystals of the metals being plated. In the case of plated solder, it is sometimes deemed necessary to have a "true alloy", the plated solder is melted to allow the Tin and Lead to combine to form a true alloy; the true alloy is more corrosion resistant than the as-plated alloy. Many plating baths include cyanides of other metals in addition to cyanides of the metal to be deposited; these free cyanides facilitate anode corrosion, help to maintain a constant metal ion level and contribute to conductivity. Additionally, non-metal chemicals such as carbonates and phosphates may be added to increase conductivity; when plating is not desired on certain areas of the substrate, stop-offs are applied to prevent the bath from coming in contact with the substrate.
Typical stop-offs include tape, foil and waxes. The ability of a plating to cover uniformly is called throwing power. A special plating deposit called a strike or flash may be used to form a thin plating with high quality and good adherence to the substrate; this serves as a foundation for subsequent plating processes. A strike uses a bath with a low ion concentration; the process is slow, so more efficient plating processes are used once the desired strike thickness is obtained. The striking method is used in combination with the plating of different metals. If it is desirable to plate one type of deposit onto a metal to improve corrosion resistance but this metal has inherently poor adhesion to the substrate, a strike can be first deposited, compatible with both. One example of this situation is the poor adhesion of electrolytic nickel on zinc alloys, in which case a copper strike is used, which has good adherence to both. Electrochemical deposition is used for the growth of metals and conducting metal oxides because of the following advantages: the thickness and morphology of the nanostructure can be controlled by adjusting the electrochemical parameters.
A simple modification in electroplating is pulse electroplating. This process involves the swift alternating of the potential or current between two different values resulting in a series of pulses of equal amplitude and polarity, separated by zero current. By changing the pulse amplitude and width, it is possible to change the deposited film's composition and thickness; the experimental parameters of pulse electroplating consist of peak current/potential, duty cycle and effective current/potential. Peak current/potential is the maximum setting of electroplating potential. Duty cycle is the effective portion of time in certain electroplating period with the current or potential applied; the effective current/potential is calculated by multiplying the duty cycle and peak value of current or potential. Pulse electroplating could help to improve the quality of electroplated film and release the in
Jet is a type of lignite, a precursor to coal, is a gemstone. Jet is not a mineral, but rather a mineraloid, it has an organic origin, being derived from wood. The English noun "jet" derives from the French word for the same material, jaiet referring to the ancient town of Gagae. Jet is either black or dark brown, but may contain pyrite inclusions, which are of brassy colour and metallic lustre; the adjective "jet-black", meaning as dark a black as possible, derives from this material. Jet is a product of high-pressure decomposition of wood from millions of years ago the wood of trees of the family Araucariaceae. Jet is found in two forms and soft. Hard jet is the result of salt water; the jet found at Whitby, in England, is of early Jurassic age 182 million years old. Whitby Jet is the fossilized wood from species similar to the extant Chile pine or Monkey Puzzle tree. Jet is found in Poland and Santiago de Compostela in northern Spain and near Erzurum in Turkey, where it is used to make prayer beads.
Native American Navajo and Pueblo tribes of New Mexico were using regionally mined jet for jewellery and the ornamentation of weapons when early Spanish explorers reached the area in the 1500s. Today these jet deposits are known for the Acoma Pueblo. Enormous coal deposits characterize the San Juan Basin of New Mexico and this geology is related to jet deposits mined in the Henry Mountains of Utah and the Front Range of El Paso County, Colorado. Jet has been used in Britain since the Neolithic period, but the earliest known object is a 10,000 BC model of a botfly larva, from Baden-Württemberg, found among the Venuses of Petersfels, it continued in use in Britain through the Bronze Age. During the Iron Age jet went out of fashion until the early-3rd century AD in Roman Britain; the end of Roman Britain marked the end of jet's ancient popularity, despite sporadic use in the Anglo-Saxon and Viking periods and the Medieval period. Jet regained popularity with a massive resurgence during the Victorian era.
Whitby jet was a popular material for jewellery in Roman Britain from the 3rd century onward. It was used in rings, hair pins, bracelets, bangles and pendants, many of which are visible in the Yorkshire Museum. There is no evidence for Roman jet working in Whitby itself, rather it was transferred to Eboracum where considerable evidence for jet production has been found; the collection of jet at this time was based on beachcombing rather than quarrying. In the Roman period it saw use as a magical material used in amulets and pendants because of its supposed protective qualities and ability to deflect the gaze of the evil eye. Pliny the Elder suggests that "the kindling of jet drives off snakes and relieves suffocation of the uterus, its fumes detect attempts to simulate a disabling illness or a state of virginity." It has been referenced by other ancient writers including Galen. Jet objects were exported from Eboracum all into Europe. Around the Rhine some jet bracelets from the period have been found that feature grooves with gold inserts.
Jet as a gemstone was fashionable during the reign of Queen Victoria, during which the Queen wore Whitby jet as part of her mourning dress, mourning the death of Prince Albert. Jet was associated with mourning jewellery in the 19th century because of its sombre colour and modest appearance, it has been traditionally fashioned into rosaries for monks. In some jewellery designs of the period jet was combined with cut steel. In the United States, long necklaces of jet beads were popular during the Roaring Twenties, when women and young flappers would wear multiple strands of jet beads stretching from the neckline to the waistline. In these necklaces, the jet was strung using heavy cotton thread. Jet has been known as black amber, as it may induce an electric charge like that of amber when rubbed. Jet is easy to carve, but it is difficult to create fine details without breaking so it takes an experienced lapidary to execute more elaborate carvings. Jet has a Mohs hardness ranging between 2.5 and 4 and a specific gravity of 1.30 to 1.34.
The refractive index of jet is 1.66. The touch of a red-hot needle should cause jet to emit an odour similar to coal. Although now much less popular than in the past, authentic jet jewels are valued by collectors. Unlike black glass, cool to the touch, jet is not cool, due to its lower thermal conductivity. Glass was used as a jet substitute during the peak of jet's popularity; when it was used in this way it was known as French Vauxhall glass. Ebonite was used as a jet substitute and looks similar to jet, but it fades over time. In some cases jet offcuts were molded into jewellery. Anthracite is superficially similar to fine jet, has been used to imitate it; this imitation is not always easy to distinguish from real jet. When rubbed against unglazed porcelain, true jet will leave a chocolate brown streak; the microstructure of jet, which resembles the original wood, can be seen under 120× or greater magnification. Petrified wood Oltu stone Eliseo Nicolás Alonso – Asturian sculptor and wood carver Gemstone Guide: Jet Roman Objects in the Yorkshire Museum
A timeline is a display of a list of events in chronological order. It is a graphic design showing a long bar labelled with dates paralleling it, contemporaneous events. Timelines can use any suitable scale representing time, suiting data; this timescale is dependent on the events in the timeline. A timeline of evolution can be over millions of years, whereas a timeline for the day of the September 11 attacks can take place over minutes, that of an explosion over milliseconds. While many timelines use a linear timescale -- where large or small timespans are relevant -- logarithmic timelines entail a logarithmic scale of time. There are different types of timelines Text timelines, labeled as text Number timelines, the labels are numbers line graphs Interactive, zoomableThere are many methods of visualizations for timelines. Timelines were static images and drawn or printed on paper. Timelines relied on graphic design, the ability of the artist to visualize the data. Timelines, no longer constrained by previous space and functional limitations, are now digital and interactive created with computer software.
ChronoZoom is an example of computer-aided interactive timeline software. Timelines are used in education to help students and researchers with understanding the order or chronology of historical events and trends for a subject; when showing time on a specific scale on an axis, a timeline can be used to visualize time lapses between events and the simultaneity or overlap of spans and events. Timelines are useful for studying history, as they convey a sense of change over time. Wars and social movements are shown as timelines. Timelines are useful for biographies. Examples include: Timeline of the civil rights movement Timeline of European exploration Timeline of imperialism Timeline of Solar System exploration Timeline of United States history Timeline of World War I Timeline of religion Timelines are used in the natural world and sciences, for subjects such as astronomy and geology: 2009 flu pandemic timeline Chronology of the universe Geologic time scale Timeline of evolutionary history of life Another type of timeline is used for project management.
In these cases, timelines are used to help team members to know what milestones need to be achieved and under what time schedule. For example, in the case of establishing a project timeline in the implementation phase of the life cycle of a computer system. British Library interactive timeline Port Royal des Champs museum timeline