The angular diameter, angular size, apparent diameter, or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, in optics, it is the angular aperture; the angular diameter can alternatively be thought of as the angle through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side. Angular radius equals half the angular diameter; the angular diameter of a circle whose plane is perpendicular to the displacement vector between the point of view and the centre of said circle can be calculated using the formula δ = 2 arctan , in which δ is the angular diameter, d is the actual diameter of the object, D is the distance to the object. When D ≫ d, we have δ ≈ d / D, the result obtained is in radians. For a spherical object whose actual diameter equals d a c t, where D is the distance to the centre of the sphere, the angular diameter can be found by the formula δ = 2 arcsin The difference is due to the fact that the apparent edges of a sphere are its tangent points, which are closer to the observer than the centre of the sphere.
For practical use, the distinction is only significant for spherical objects that are close, since the small-angle approximation holds for x ≪ 1: arcsin x ≈ arctan x ≈ x. Estimates of angular diameter may be obtained by holding the hand at right angles to a extended arm, as shown in the figure. In astronomy, the sizes of celestial objects are given in terms of their angular diameter as seen from Earth, rather than their actual sizes. Since these angular diameters are small, it is common to present them in arcseconds. An arcsecond is 1/3600th of one degree, a radian is 180/ π degrees, so one radian equals 3,600*180/ π arcseconds, about 206,265 arcseconds. Therefore, the angular diameter of an object with physical diameter d at a distance D, expressed in arcseconds, is given by: δ = d / D arcseconds; these objects have an angular diameter of 1″: an object of diameter 1 cm at a distance of 2.06 km an object of diameter 725.27 km at a distance of 1 astronomical unit an object of diameter 45 866 916 km at 1 light-year an object of diameter 1 AU at a distance of 1 parsec Thus, the angular diameter of Earth's orbit around the Sun as viewed from a distance of 1 pc is 2″, as 1 AU is the mean radius of Earth's orbit.
The angular diameter of the Sun, from a distance of one light-year, is 0.03″, that of Earth 0.0003″. The angular diameter 0.03″ of the Sun given above is the same as that of a person at a distance of the diameter of Earth. This table shows the angular sizes of noteworthy celestial bodies as seen from Earth: The table shows that the angular diameter of Sun, when seen from Earth is 32′, as illustrated above, thus the angular diameter of the Sun is about 250,000 times that of Sirius. The angular diameter of the Sun is about 250,000 times that of Alpha Centauri A; the angular diameter of the Sun is about the same as that of the Moon. Though Pluto is physically larger than Ceres, when viewed from Earth Ceres has a much larger apparent size. Angular sizes measured in degrees are useful for larger patches of sky. However, much finer units are needed to measure the angular sizes of galaxies, nebulae, or other objects of the night sky. Degrees, are subdivided as follows: 360 degrees in a full circle 60 arc-minutes in one degree 60 arc-seconds in one arc-minuteTo put this in perspective, the full Moon as viewed from Earth is about 1⁄2°, or 30′.
The Moon's motion across the sky can be measured in angular size: 15° every hour, or 15″ per second. A one-mile-long line painte
The Andromeda Galaxy known as Messier 31, M31, or NGC 224, is a spiral galaxy 780 kiloparsecs from Earth, the nearest major galaxy to the Milky Way. Its name stems from the area of the Earth's sky; the virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at a trillion solar masses. The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%; this has been called into question by a 2018 study which cited a lower estimate on the mass of the Andromeda Galaxy, combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way. The Andromeda Galaxy has a diameter of about 220,000 light-years, making it the largest member of the Local Group at least in terms of extension, if not mass; the number of stars contained in the Andromeda Galaxy is estimated at one trillion, or twice the number estimated for the Milky Way.
The Milky Way and Andromeda galaxies are expected to collide in ~4.5 billion years, merging to form a giant elliptical galaxy or a large disc galaxy. With an apparent magnitude of 3.4, the Andromeda Galaxy is among the brightest of the Messier objects making it visible to the naked eye from Earth on moonless nights when viewed from areas with moderate light pollution. Around the year 964, the Persian astronomer Abd al-Rahman al-Sufi described the Andromeda Galaxy, in his Book of Fixed Stars as a "nebulous smear". Star charts of that period labeled it as the Little Cloud. In 1612, the German astronomer Simon Marius gave an early description of the Andromeda Galaxy based on telescopic observations; the German philosopher Immanuel Kant in 1755 in his work Universal Natural History and Theory of the Heavens conjectured that the blurry spot was an island universe. In 1764, Charles Messier cataloged Andromeda as object M31 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye.
In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda. He believed Andromeda to be the nearest of all the "great nebulae", based on the color and magnitude of the nebula, he incorrectly guessed that it is no more than 2,000 times the distance of Sirius. In 1850, William Parsons, 3rd Earl of Rosse and made the first drawing of Andromeda's spiral structure. In 1864, William Huggins noted; the spectra of Andromeda displays a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. Andromeda's spectrum is similar to the spectra of individual stars, from this, it was deduced that Andromeda has a stellar nature. In 1885, a supernova was seen in the first and so far only one observed in that galaxy. At the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, was named accordingly. In 1887, Isaac Roberts took the first photographs of Andromeda, still thought to be a nebula within our galaxy.
Roberts mistook Andromeda and similar spiral nebulae as solar systems being formed. In 1912, Vesto Slipher used spectroscopy to measure the radial velocity of Andromeda with respect to our Solar System—the largest velocity yet measured, at 300 kilometres per second. In 1917, Heber Curtis observed a nova within Andromeda. Searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred elsewhere in the sky; as a result, he was able to come up with a distance estimate of 500,000 light-years. He became a proponent of the so-called "island universes" hypothesis, which held that spiral nebulae were independent galaxies. In 1920, the Great Debate between Harlow Shapley and Curtis took place concerning the nature of the Milky Way, spiral nebulae, the dimensions of the Universe. To support his claim of the Great Andromeda Nebula being, in fact, an external galaxy, Curtis noted the appearance of dark lanes within Andromeda which resembled the dust clouds in our own galaxy, as well as historical observations of Andromeda Galaxy's significant Doppler shift.
In 1922 Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars. His result placed the Andromeda Nebula far outside our galaxy at a distance of about 450,000 parsecs. Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of Andromeda; these were made using the 2.5-metre Hooker telescope, they enabled the distance of Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within our own galaxy, but an separate galaxy located a significant distance from the Milky Way. In 1943, Walter Baade was the first person to resolve stars in the central region of the Andromeda Galaxy. Baade identified two distinct populations of stars based on their metallicity, naming the young, high-velocity stars in the disk Type I and the older, red stars in the bulge Type II; this nomenclature was subsequently adopted for stars within the Milky Way, elsewhere.
Baade discovered that there were two types of Cepheid variables, which resulted in a doubling of the distance estimate to Andromeda, as well as the remainder o
Cosmic distance ladder
The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. A real direct distance measurement of an astronomical object is possible only for those objects that are "close enough" to Earth; the techniques for determining distances to more distant objects are all based on various measured correlations between methods that work at close distances and methods that work at larger distances. Several methods rely on a standard candle, an astronomical object that has a known luminosity; the ladder analogy arises because no single technique can measure distances at all ranges encountered in astronomy. Instead, one method can be used to measure nearby distances, a second can be used to measure nearby to intermediate distances, so on; each rung of the ladder provides information that can be used to determine the distances at the next higher rung. At the base of the ladder are fundamental distance measurements, in which distances are determined directly, with no physical assumptions about the nature of the object in question.
The precise measurement of stellar positions is part of the discipline of astrometry. Direct distance measurements are based upon the astronomical unit, the distance between the Earth and the Sun. Kepler's laws provide precise ratios of the sizes of the orbits of objects orbiting the Sun, but provides no measurement of the overall scale of the orbit system. Radar is used to measure the distance of a second body. From that measurement and the ratio of the two orbit sizes, the size of Earth's orbit is calculated; the Earth's orbit is known with an absolute precision of a few meters and a relative precision of a few 1×10−11. Observations of transits of Venus were crucial in determining the AU. Presently the orbit of Earth is determined with high precision using radar measurements of distances to Venus and other nearby planets and asteroids, by tracking interplanetary spacecraft in their orbits around the Sun through the Solar System; the most important fundamental distance measurements come from trigonometric parallax.
As the Earth orbits the Sun, the position of nearby stars will appear to shift against the more distant background. These shifts are angles in an isosceles triangle, with 2 AU making the base leg of the triangle and the distance to the star being the long equal length legs; the amount of shift is quite small, measuring 1 arcsecond for an object at 1 parsec's distance of the nearest stars, thereafter decreasing in angular amount as the distance increases. Astronomers express distances in units of parsecs; because parallax becomes smaller for a greater stellar distance, useful distances can be measured only for stars which are near enough to have a parallax larger than a few times the precision of the measurement. Parallax measurements have an accuracy measured in milliarcseconds. In the 1990s, for example, the Hipparcos mission obtained parallaxes for over a hundred thousand stars with a precision of about a milliarcsecond, providing useful distances for stars out to a few hundred parsecs; the Hubble telescope WFC3 now has the potential to provide a precision of 20 to 40 microarcseconds, enabling reliable distance measurements up to 5,000 parsecs for small numbers of stars.
In 2018, Data Release 2 from the Gaia space mission provides accurate distances to most stars brighter than 15th magnitude. Stars have a velocity relative to the Sun that causes radial velocity; the former is determined by plotting the changing position of the stars over many years, while the latter comes from measuring the Doppler shift of the star's spectrum caused by motion along the line of sight. For a group of stars with the same spectral class and a similar magnitude range, a mean parallax can be derived from statistical analysis of the proper motions relative to their radial velocities; this statistical parallax method is useful for measuring the distances of bright stars beyond 50 parsecs and giant variable stars, including Cepheids and the RR Lyrae variables. The motion of the Sun through space provides a longer baseline that will increase the accuracy of parallax measurements, known as secular parallax. For stars in the Milky Way disk, this corresponds to a mean baseline of 4 AU per year, while for halo stars the baseline is 40 AU per year.
After several decades, the baseline can be orders of magnitude greater than the Earth–Sun baseline used for traditional parallax. However, secular parallax introduces a higher level of uncertainty because the relative velocity of observed stars is an additional unknown; when applied to samples of multiple stars, the uncertainty can be reduced. Moving cluster parallax is a technique where the motions of individual stars in a nearby star cluster can be used to find the distance to the cluster. Only open clusters are near enough for this technique to be useful. In particular the distance obtained for the Hyades has been an important step in the distance ladder. Other individual objects can have fundamental distance estimates made for them under special circumstances. If the expansion of a gas cloud, like a supernova remnant or planetary nebula, can be observed over time an expansion parallax distance to that cloud can be estimated; those measurements however suf
Right ascension is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the point above the earth in question. When paired with declination, these astronomical coordinates specify the direction of a point on the celestial sphere in the equatorial coordinate system. An old term, right ascension refers to the ascension, or the point on the celestial equator that rises with any celestial object as seen from Earth's equator, where the celestial equator intersects the horizon at a right angle, it contrasts with oblique ascension, the point on the celestial equator that rises with any celestial object as seen from most latitudes on Earth, where the celestial equator intersects the horizon at an oblique angle. Right ascension is the celestial equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a primary direction on an equator. Right ascension is measured from the Sun at the March equinox i.e. the First Point of Aries, the place on the celestial sphere where the Sun crosses the celestial equator from south to north at the March equinox and is located in the constellation Pisces.
Right ascension is measured continuously in a full circle from that alignment of Earth and Sun in space, that equinox, the measurement increasing towards the east. As seen from Earth, objects noted to have 12h RA are longest visible at the March equinox. On those dates at midnight, such objects will reach their highest point. How high depends on their declination. Any units of angular measure could have been chosen for right ascension, but it is customarily measured in hours and seconds, with 24h being equivalent to a full circle. Astronomers have chosen this unit to measure right ascension because they measure a star's location by timing its passage through the highest point in the sky as the Earth rotates; the line which passes through the highest point in the sky, called the meridian, is the projection of a longitude line onto the celestial sphere. Since a complete circle contains 24h of right ascension or 360°, 1/24 of a circle is measured as 1h of right ascension, or 15°. A full circle, measured in right-ascension units, contains 24 × 60 × 60 = 86400s, or 24 × 60 = 1440m, or 24h.
Because right ascensions are measured in hours, they can be used to time the positions of objects in the sky. For example, if a star with RA = 1h 30m 00s is at its meridian a star with RA = 20h 00m 00s will be on the/at its meridian 18.5 sidereal hours later. Sidereal hour angle, used in celestial navigation, is similar to right ascension, but increases westward rather than eastward. Measured in degrees, it is the complement of right ascension with respect to 24h, it is important not to confuse sidereal hour angle with the astronomical concept of hour angle, which measures angular distance of an object westward from the local meridian. The Earth's axis rotates westward about the poles of the ecliptic, completing one cycle in about 26,000 years; this movement, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates are inherently relative to the year of their observation, astronomers specify them with reference to a particular year, known as an epoch.
Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. Right ascension for "fixed stars" near the ecliptic and equator increases by about 3.05 seconds per year on average, or 5.1 minutes per century, but for fixed stars further from the ecliptic the rate of change can be anything from negative infinity to positive infinity. The right ascension of Polaris is increasing quickly; the North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18h and 6h respectively. The used standard epoch is J2000.0, January 1, 2000 at 12:00 TT. The prefix "J" indicates. Prior to J2000.0, astronomers used the successive Besselian epochs B1875.0, B1900.0, B1950.0. The concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC, but Hipparchus and his successors made their star catalogs in ecliptic coordinates, the use of RA was limited to special cases.
With the invention of the telescope, it became possible for astronomers to observe celestial objects in greater detail, provided that the telescope could be kept pointed at the object for a period of time. The easiest way to do, to use an equatorial mount, which allows the telescope to be aligned with one of its two pivots parallel to the Earth's axis. A motorized clock drive is used with an equatorial mount to cancel out the Earth's rotation; as the equatorial mount became adopted for observation, the equatorial coordinate system, which includes right ascension, was adopted at the same time for simplicity. Equatorial mounts could be pointed at objects with known right ascension and declination by the use of setting circles; the first star catalog to use right ascen
Andromeda is one of the 48 constellations listed by the 2nd-century Greco-Roman astronomer Ptolemy and remains one of the 88 modern constellations. Located north of the celestial equator, it is named for Andromeda, daughter of Cassiopeia, in the Greek myth, chained to a rock to be eaten by the sea monster Cetus. Andromeda is most prominent during autumn evenings in the Northern Hemisphere, along with several other constellations named for characters in the Perseus myth; because of its northern declination, Andromeda is visible only north of 40° south latitude. It is one of the largest constellations, with an area of 722 square degrees; this is over 1,400 times the size of the full moon, 55% of the size of the largest constellation and over 10 times the size of the smallest constellation, Crux. Its brightest star, Alpha Andromedae, is a binary star, counted as a part of Pegasus, while Gamma Andromedae is a colorful binary and a popular target for amateur astronomers. Only marginally dimmer than Alpha, Beta Andromedae is a red giant, its color visible to the naked eye.
The constellation's most obvious deep-sky object is the naked-eye Andromeda Galaxy, the closest spiral galaxy to the Milky Way and one of the brightest Messier objects. Several fainter galaxies, including M31's companions M110 and M32, as well as the more distant NGC 891, lie within Andromeda; the Blue Snowball Nebula, a planetary nebula, is visible in a telescope as a blue circular object. In Chinese astronomy, the stars that make up Andromeda were members of four different constellations that had astrological and mythological significance. Andromeda is the location of the radiant for the Andromedids, a weak meteor shower that occurs in November; the uranography of Andromeda has its roots most in the Greek tradition, though a female figure in Andromeda's location had appeared earlier in Babylonian astronomy. The stars that make up Pisces and the middle portion of modern Andromeda formed a constellation representing a fertility goddess, sometimes named as Anunitum or the Lady of the Heavens.
Andromeda is known as "the Chained Lady" or "the Chained Woman" in English. It was known as Mulier Catenata in al-Mar ` at al Musalsalah in Arabic, it has been called Persea or Cepheis, all names that refer to Andromeda's role in the Greco-Roman myth of Perseus, in which Cassiopeia, the queen of Ethiopia, bragged that her daughter was more beautiful than the Nereids, sea nymphs blessed with incredible beauty. Offended at her remark, the nymphs petitioned Poseidon to punish Cassiopeia for her insolence, which he did by commanding the sea monster Cetus to attack Ethiopia. Andromeda's panicked father, was told by the Oracle of Ammon that the only way to save his kingdom was to sacrifice his daughter to Cetus, she was chained to a rock by the sea but was saved by the hero Perseus, who in one version of the story used the head of Medusa to turn the monster into stone. Perseus and Andromeda married. After Andromeda's death Athena placed her in the sky as a constellation. Several of the neighboring constellations represent characters in the Perseus myth.
It is connected with the constellation Pegasus. Andromeda was one of the original 48 constellations formulated by Ptolemy in his 2nd-century Almagest, in which it was defined as a specific pattern of stars, she is depicted with α Andromedae as her head, ο and λ Andromedae as her chains, δ, π, μ, Β, γ Andromedae representing her body and legs. However, there is no universal depiction of Andromeda and the stars used to represent her body and chains. Arab astronomers were aware of Ptolemy's constellations, but they included a second constellation representing a fish at Andromeda's feet. Several stars from Andromeda and most of the stars in Lacerta were combined in 1787 by German astronomer Johann Bode to form Frederici Honores, it was designed to honor King Frederick II of Prussia, but fell into disuse. Since the time of Ptolemy, Andromeda has remained a constellation and is recognized by the International Astronomical Union, although like all modern constellations, it is now defined as a specific region of the sky that includes both Ptolemy's pattern and the surrounding stars.
In 1922, the IAU defined its recommended three-letter abbreviation, "And". The official boundaries of Andromeda were defined in 1930 by Eugène Delporte as a polygon of 36 segments, its right ascension is between 22h 57.5m and 2h 39.3m and its declination is between 53.19° and 21.68° in the equatorial coordinate system. In traditional Chinese astronomy, nine stars from Andromeda, along with seven stars from Pisces, formed an elliptical constellation called "Legs"; this constellation either represented the foot of a wild boar. Gamma Andromedae and its neighbors were called "Teen Ta Tseang Keun", representing honor in astrology and a great general in mythology. Alpha Andromedae and Gamma Pegasi together made "Wall", representing the eastern wall of the imperial palace and/or the emperor's personal library. For the Chinese, the northern swath of Andromeda formed a stable for changing horses and the fa
The horizontal branch is a stage of stellar evolution that follows the red giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core and by hydrogen fusion in a shell surrounding the core; the onset of core helium fusion at the tip of the red giant branch causes substantial changes in stellar structure, resulting in an overall reduction in luminosity, some contraction of the stellar envelope, the surface reaching higher temperatures. Horizontal branch stars were discovered with the first deep photographic photometric studies of globular clusters and were notable for being absent from all open clusters, studied up to that time; the horizontal branch is so named because in low-metallicity star collections like globular clusters, HB stars lie along a horizontal line in a Hertzsprung–Russell diagram. After exhausting their core hydrogen, stars leave the main sequence and begin fusion in a hydrogen shell around the helium core and become giants on the red giant branch.
In stars with masses up to 2.3 times the mass of the Sun the helium core becomes a region of degenerate matter that does not contribute to the generation of energy. It continues to grow and increase in temperature as the hydrogen fusion in the shell contributes more helium. If the star has more than about 0.5 solar masses, the core reaches the temperature necessary for the fusion of helium into carbon through the triple-alpha process. The initiation of helium fusion begins across the core region, which will cause an immediate temperature rise and a rapid increase in the rate of fusion. Within a few seconds the core becomes non-degenerate and expands, producing an event called helium flash. Non-degenerate cores initiate fusion more smoothly, without a flash; the output of this event is absorbed by the layers of plasma above, so the effects are not seen from the exterior of the star. The star now changes to a new equilibrium state, its evolutionary path switches from the red giant branch onto the horizontal branch of the Hertzsprung–Russell diagram.
Stars between about 2.3 M☉ and 8 M☉ have larger helium cores that do not become degenerate. Instead their cores reach the Schoenberg-Chandrasekhar mass at which they are no longer in hydrostatic or thermal equilibrium, they contract and heat up, which triggers helium fusion before the core becomes degenerate. These stars become hotter during core helium fusion, but they have different core masses and hence different luminosities from HB stars, they vary in temperature during core helium fusion and perform a blue loop before moving to the asymptotic giant branch. Stars more massive than about 8 M☉ ignite their core helium smoothly, go on to burn heavier elements as a red supergiant. Stars remain on the horizontal branch for around 100 million years, becoming more luminous in the same way that main sequence stars increase luminosity as the virial theorem shows; when their core helium is exhausted, they progress to helium shell burning on the asymptotic giant branch. On the AGB they become cooler and much more luminous.
Stars on the horizontal branch all have similar core masses, following the helium flash. This means that they have similar luminosities, on a Hertzsprung–Russell diagram plotted by visual magnitude the branch is horizontal; the size and temperature of an HB star depends on the mass of the hydrogen envelope remaining around the helium core. Stars with larger hydrogen envelopes are cooler; this creates the spread of stars along the horizontal branch at constant luminosity. The temperature variation effect is much stronger at lower metallicity, so old clusters have more pronounced horizontal branches. Although the horizontal branch is named because it consists of stars with the same absolute magnitude across a range of temperatures, lying in a horizontal bar on a color–magnitude diagrams, the branch is far from horizontal at the blue end; the horizontal branch ends in a "blue tail" with hotter stars having lower luminosity with a "blue hook" of hot stars. It is not horizontal when plotted by bolometric luminosity, with hotter horizontal branch stars being less luminous than cooler ones.
The hottest horizontal-branch stars, referred to as extreme horizontal branch, have temperatures of 20,000–30,000K. This is far beyond. Theories to explain these stars include binary interactions, "late thermal pulses", where a thermal pulse that Asymptotic giant branch stars experience occurs after fusion has ceased and the star has entered the superwind phase; these stars are "born again" with unusual properties. Despite the bizarre-sounding process, this is expected to occur for 10% or more of post-AGB stars, although it is thought that only late thermal pulses create extreme horizontal-branch stars, after the planetary nebular phase and when the central star is cooling towards a white dwarf. Globular cluster CMDs show horizontal branches that have a prominent gap in the HB; this gap in the CMD incorrectly suggests that the cluster has no stars in this region of its CMD. The gap occurs at the instability strip, so many stars in this region pulsate; these pulsating horizontal-branch stars are known as RR Lyrae variable stars and they are variable in brightness with periods of up to 1.2 days.
It requires an extended observing program to establish the star's true apparent color. Such a program is beyond the scope of an investigation of a cluster's color
A camera is an optical instrument to capture still images or to record moving images, which are stored in a physical medium such as in a digital system or on photographic film. A camera consists of a lens which focuses light from the scene, a camera body which holds the image capture mechanism; the still image camera is the main instrument in the art of photography and captured images may be reproduced as a part of the process of photography, digital imaging, photographic printing. The similar artistic fields in the moving image camera domain are film and cinematography; the word camera comes from camera obscura, which means "dark chamber" and is the Latin name of the original device for projecting an image of external reality onto a flat surface. The modern photographic camera evolved from the camera obscura; the functioning of the camera is similar to the functioning of the human eye. The first permanent photograph was made in 1825 by Joseph Nicéphore Niépce. A camera works with the light of the visible spectrum or with other portions of the electromagnetic spectrum.
A still camera is an optical device which creates a single image of an object or scene and records it on an electronic sensor or photographic film. All cameras use the same basic design: light enters an enclosed box through a converging/convex lens and an image is recorded on a light-sensitive medium. A shutter mechanism controls the length of time. Most photographic cameras have functions that allow a person to view the scene to be recorded, allow for a desired part of the scene to be in focus, to control the exposure so that it is not too bright or too dim. On most digital cameras a display a liquid crystal display, permits the user to view the scene to be recorded and settings such as ISO speed and shutter speed. A movie camera or a video camera operates to a still camera, except it records a series of static images in rapid succession at a rate of 24 frames per second; when the images are combined and displayed in order, the illusion of motion is achieved. Traditional cameras capture light onto photographic film.
Video and digital cameras use an electronic image sensor a charge coupled device or a CMOS sensor to capture images which can be transferred or stored in a memory card or other storage inside the camera for playback or processing. Cameras that capture many images in sequence are known as movie cameras or as ciné cameras in Europe; however these categories overlap as still cameras are used to capture moving images in special effects work and many modern cameras can switch between still and motion recording modes. A wide range of film and plate formats have been used by cameras. In the early history plate sizes were specific for the make and model of camera although there developed some standardisation for the more popular cameras; the introduction of roll film drove the standardization process still further so that by the 1950s only a few standard roll films were in use. These included 120 film providing 8, 12 or 16 exposures, 220 film providing 16 or 24 exposures, 127 film providing 8 or 12 exposures and 135 providing 12, 20 or 36 exposures – or up to 72 exposures in the half-frame format or in bulk cassettes for the Leica Camera range.
For cine cameras, film 35 mm wide and perforated with sprocket holes was established as the standard format in the 1890s. It was used for nearly all film-based professional motion picture production. For amateur use, several smaller and therefore less expensive formats were introduced. 17.5 mm film, created by splitting 35 mm film, was one early amateur format, but 9.5 mm film, introduced in Europe in 1922, 16 mm film, introduced in the US in 1923, soon became the standards for "home movies" in their respective hemispheres. In 1932, the more economical 8 mm format was created by doubling the number of perforations in 16 mm film splitting it after exposure and processing; the Super 8 format, still 8 mm wide but with smaller perforations to make room for larger film frames, was introduced in 1965. Traditionally used to "tell the camera" the film speed of the selected film on film cameras, film speed numbers are employed on modern digital cameras as an indication of the system's gain from light to numerical output and to control the automatic exposure system.
Film speed is measured via the ISO system. The higher the film speed number the greater the film sensitivity to light, whereas with a lower number, the film is less sensitive to light. On digital cameras, electronic compensation for the color temperature associated with a given set of lighting conditions, ensuring that white light is registered as such on the imaging chip and therefore that the colors in the frame will appear natural. On mechanical, film-based cameras, this function is served by the operator's choice of film stock or with color correction filters. In addition to using white balance to register natural coloration of the image, photographers may employ white balance to aesthetic end, for example, white balancing to a blue object in order to obtain a warm color temperature; the lens of a camera brings it to a focus on the sensor. The design and manufacture of the lens is critical to the quality of the photograph being taken; the technological revolution in camera design in the 19th century revolutionized optical glass manufacture and lens design with great benefits for modern lens manufacture in a wide range of optical instruments from reading glasses to microscopes.
Pioneers included Leitz. Camera lenses are