Lyra is a small constellation. It is one of 48 listed by the 2nd century astronomer Ptolemy, is one of the 88 constellations recognized by the International Astronomical Union. Lyra was represented on star maps as a vulture or an eagle carrying a lyre, hence is sometimes referred to as Vultur Cadens or Aquila Cadens, respectively. Beginning at the north, Lyra is bordered by Draco, Hercules and Cygnus. Lyra is visible from the northern hemisphere from spring through autumn, nearly overhead, in temperate latitudes, during the summer months. From the southern hemisphere, it is visible low in the northern sky during the winter months. Vega, Lyra's brightest star, is one of the brightest stars in the night sky, forms a corner of the famed Summer Triangle asterism. Beta Lyrae is the prototype of a class of stars known as Beta Lyrae variables; these binary stars are so close to each other that they become egg-shaped and material flows from one to the other. Epsilon Lyrae, known informally as the Double Double, is a complex multiple star system.
Lyra hosts the Ring Nebula, the second-discovered and best-known planetary nebula. In Greek mythology, Lyra represents the lyre of Orpheus. Made by Hermes from a tortoise shell, given to Apollo as a bargain, it was said to be the first lyre produced. Orpheus's music was said to be so great that inanimate objects such as trees and rocks could be charmed. Joining Jason and the Argonauts, his music was able to quell the voices of the dangerous Sirens, who sang tempting songs to the Argonauts. At one point, Orpheus married a nymph. While fleeing from an attack by Aristaeus, she stepped on a snake. To reclaim her, Orpheus entered the Underworld. Hades relented and let Orpheus bring Eurydice back, on the condition that he never once look back until outside. Near the end, Orpheus faltered and looked back, causing Eurydice to be left in the Underworld forever. Orpheus spent the rest of his life strumming his lyre while wandering aimlessly through the land, rejecting all marriage offers from women. There are two competing myths relating to the death of Orpheus.
According to Eratosthenes, Orpheus failed to make a necessary sacrifice to Dionysus due to his regard for Apollo as the supreme deity instead. Dionysus sent his followers to rip Orpheus apart. Ovid tells a rather different story, saying that women, in retribution for Orpheus's rejection of marriage offers, ganged up and threw stones and spears. At first, his music charmed them as well, but their numbers and clamor overwhelmed his music and he was hit by the spears. Both myths state that his lyre was placed in the sky by Zeus, Orpheus' bones buried by the muses. Vega and its surrounding stars are treated as a constellation in other cultures; the area corresponding to Lyra was seen by the Arabs as a vulture or an eagle carrying a lyre, either enclosed in its wings, or in its beak. In Wales, Lyra is known as King Arthur's Harp, King David's harp; the Persian Hafiz called it the Lyre of Zurah. It has been called the Manger of Praesepe Salvatoris. In Australian Aboriginal astronomy, Lyra is known by the Boorong people in Victoria as the Malleefowl constellation.
Lyra was worshipped as an animal deity. Lyra is bordered by Vulpecula to the south, Hercules to the east, Draco to the north, Cygnus to the west. Covering 286.5 square degrees, it ranks 52nd of the 88 modern constellations in size. It appears prominently in the northern sky during the Northern Hemisphere's summer, the whole constellation is visible for at least part of the year to observers north of latitude 42°S, its main asterism consists of six stars, 73 stars in total are brighter than magnitude 6.5. The constellation's boundaries, as set by Eugène Delporte in 1930, are defined by a 17-sided polygon. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 18h 14m and 19h 28m, while the declination coordinates are between +25.66° and +47.71°. The International Astronomical Union adopted the three-letter abbreviation "Lyr" for the constellation in 1922. German cartographer Johann Bayer used the Greek letters alpha through nu to label the most prominent stars in the constellation.
Flamsteed observed and labelled two stars each as delta, zeta and nu. He added pi and rho, not using xi and omicron as Bayer used hese letters to denote Cygnus and Hercules on his map; the brightest and far the most well-known star in the constellation is Vega, a main-sequence star of spectral type A0Va. Only 7.7 parsecs distant, is a Delta Scuti variable, varying between magnitudes −0.02 and 0.07 over 0.2 days. On average, it is the second-brightest star of a northern hemisphere and the fifth-brightest star in all, surpassed only by Arcturus, Alpha Centauri and Sirius. Vega was the pole star in the year 12,000 BCE, will again become the pole star around 14,000 CE. Vega is one of the most-magnificent of all stars, has been called "arguably the next most important star in the sky after the Sun". Vega was the first star other than the Sun to be photographed, as well as the first to have a clear spectrum recorded, showing absorption lines for the first time; the star was the first single main-sequence star other than the Sun to be known to emit X-rays, is surrounded by a circumstellar debris disk, similar to the Kuiper Belt.
Vega forms one corner of the famous Summer Triangle asterism. Vega forms one vertex of a much s
A day is the period of time during which the Earth completes one rotation around its axis. A solar day is the length of time which elapses between the Sun reaching its highest point in the sky two consecutive times. In 1960, the second was redefined in terms of the orbital motion of the Earth in year 1900, was designated the SI base unit of time; the unit of measurement "day", was symbolized d. In 1967, the second and so the day were redefined by atomic electron transition. A civil day is 86,400 seconds, plus or minus a possible leap second in Coordinated Universal Time, plus or minus an hour in those locations that change from or to daylight saving time. Day can be defined as each of the twenty-four-hour periods, reckoned from one midnight to the next, into which a week, month, or year is divided, corresponding to a rotation of the earth on its axis; however its use depends on its context, for example when people say'day and night','day' will have a different meaning. It will mean the interval of light between two successive nights.
However, in order to be clear when using'day' in that sense, "daytime" should be used to distinguish it from "day" referring to a 24-hour period. The word day may refer to a day of the week or to a calendar date, as in answer to the question, "On which day?" The life patterns of humans and many other species are related to Earth's solar day and the day-night cycle. Several definitions of this universal human concept are used according to context and convenience. Besides the day of 24 hours, the word day is used for several different spans of time based on the rotation of the Earth around its axis. An important one is the solar day, defined as the time it takes for the Sun to return to its culmination point; because celestial orbits are not circular, thus objects travel at different speeds at various positions in their orbit, a solar day is not the same length of time throughout the orbital year. Because the Earth orbits the Sun elliptically as the Earth spins on an inclined axis, this period can be up to 7.9 seconds more than 24 hours.
In recent decades, the average length of a solar day on Earth has been about 86 400.002 seconds and there are about 365.2422 solar days in one mean tropical year. Ancient custom has a new day start at either the setting of the Sun on the local horizon; the exact moment of, the interval between, two sunrises or sunsets depends on the geographical position, the time of year. A more constant day can be defined by the Sun passing through the local meridian, which happens at local noon or midnight; the exact moment is dependent on the geographical longitude, to a lesser extent on the time of the year. The length of such a day is nearly constant; this is the time as indicated by modern sundials. A further improvement defines a fictitious mean Sun that moves with constant speed along the celestial equator. A day, understood as the span of time it takes for the Earth to make one entire rotation with respect to the celestial background or a distant star, is called a stellar day; this period of rotation is about 4 minutes less than 24 hours and there are about 366.2422 stellar days in one mean tropical year.
Other planets and moons have solar days of different lengths from Earth's. A day, in the sense of daytime, distinguished from night time, is defined as the period during which sunlight directly reaches the ground, assuming that there are no local obstacles; the length of daytime averages more than half of the 24-hour day. Two effects make daytime on average longer than nights; the Sun has an apparent size of about 32 minutes of arc. Additionally, the atmosphere refracts sunlight in such a way that some of it reaches the ground when the Sun is below the horizon by about 34 minutes of arc. So the first light reaches the ground when the centre of the Sun is still below the horizon by about 50 minutes of arc. Thus, daytime is on average around 7 minutes longer than 12 hours; the term comes from the Old English dæg, with its cognates such as dagur in Icelandic, Tag in German, dag in Norwegian, Danish and Dutch. All of them from the Indo-European root dyau which explains the similarity with Latin dies though the word is known to come from the Germanic branch.
As of October 17, 2015, day is the 205th most common word in US English, the 210th most common in UK English. A day, symbol d, defined as 86 400 seconds, is not an SI unit, but is accepted for use with SI; the Second is the base unit of time in SI units. In 1967–68, during the 13th CGPM, the International Bureau of Weights and Measures redefined a second as … the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium 133 atom; this makes the SI-based day last 794 243 384 928 000 of those periods. Due to tidal effects, the
Kepler-5b is one of the first five planets discovered by NASA's Kepler spacecraft. It is a Hot Jupiter that orbits a subgiant star, more massive and more diffuse than the Sun is. Kepler-5 was first flagged as the location of a transiting planet, was reclassified as a Kepler Object of Interest until follow-up observations confirmed the planet's existence and many of its characteristics; the planet's discovery was announced at a meeting of the American Astronomical Society on January 4, 2010. The planet has twice the mass of Jupiter, is about 1.5 times larger. It is fifteen times hotter than Jupiter. Kepler-5b orbits Kepler-5 every 3.5 days at a distance of 0.051 AU. The Kepler spacecraft's first days of science activity revealed a series of transit events, in which some body crosses in front of, therefore dims, its host star; such objects were taken from the Kepler Input Catalog and reclassified as Kepler Objects of Interest. Kepler-5 was one of these objects of interest, was given the designation KOI-18.
After the stellar parameters were established, the Kepler science team ran models and fits to ensure that Kepler-5's transit event was not a false positive, such as an eclipsing binary star. Once the planetary nature of Kepler-5b was established, the Kepler team searched for the planet's occultation behind its star, hoping to find the temperature on its day side, they found both, were able to set the equilibrium temperature of the planet. The use of speckle imaging using adaptive optics at the WIYN Observatory in Arizona and the Palomar Observatory in California isolated the starlight of Kepler-5 from background stars. Use of the Fibre-fed Echelle Spectrograph at the Nordic Optical Telescope on the Canary Islands on June 4, 2009 provided data, used to determine the star's stellar classification; the W. M. Keck Observatory's High Resolution Echelle Spectrometer, used on June 3–6, 2009, July 2–4, 2009, determined radial velocity measurements for the star, which helped to further define stellar parameters.
Kepler-5 has, as considered by the Kepler team, the potential for use in the study of planets in extreme conditions. The findings of the Kepler team, which included planets Kepler-4b, Kepler-6b, Kepler-7b, Kepler-8b, were announced at the 215th meeting of the American Astronomical Society of January 4, 2010. Kepler-5 is a subgiant in the Cygnus constellation, expected to soon deplete its hydrogen stores in the core and begin fusing hydrogen in the shell region surrounding the core; the star is 1.374 times the mass of the Sun, although it is more diffuse at 1.793 times the Sun's radius. The star's metallicity is measured to be at = 0.04, which means that Kepler-5 has 1.10 times the levels of iron as the Sun does. The star's apparent magnitude is 13.4. Kepler-5b is a Hot Jupiter with a mass, 2.114 times that of Jupiter and a radius of 1.431 times Jupiter's radius. This means that Kepler-5b is not dense; the planet's measured density is 0.894 grams/cm3, less than that of pure water and comparable only to the density of Saturn, 0.69 grams/cm3.
The planet has an equilibrium temperature of 1868 K, making it fifteen times hotter than Jupiter. Kepler-5b orbits its host star every 3.5485 days at a mean distance of 0.05064 AU. In addition, with an orbital inclination of 86.3º, Kepler-5b orbits Kepler-5 edge-on with respect to Earth. In comparison, planet Mercury orbits the Sun at a distance of 0.387 AU every 87.97 days. Discovery of the Transiting Planet Kepler-5b Media related to Kepler-5 b at Wikimedia Commons
W. M. Keck Observatory
The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of 4,145 meters near the summit of Mauna Kea in the U. S. state of Hawaii. Both telescopes feature 10 m primary mirrors among the largest astronomical telescopes in use. With a concept first proposed in 1977, telescope designers at the University of California and Lawrence Berkeley Labs had been developing the technology necessary to build a large, ground-based telescope. With a design in hand, a search for the funding began. In 1985, Howard B. Keck of the W. M. Keck Foundation gave $70 million to fund the construction of the Keck I telescope. Construction of Keck I began in September 1985, with first light occurring on 24 November 1990 using only nine of the eventual 36 segments. With construction of the first telescope well advanced, further donations allowed the construction of a second telescope starting in 1991; the Keck I telescope began science observations in May 1993, while first light for Keck II occurred on October 23, 1996.
The key advance that allowed the construction of the Keck Observatory's large telescopes was the ability to operate smaller mirror segments as a single, contiguous mirror. In the case of the Keck Observatory telescopes each of the primary mirrors is composed of 36 hexagonal segments that work together as a single unit; each segment is 1.8 meters wide, 7.5 centimeters thick, weighs half a ton. The mirrors were made from Zerodur glass-ceramic by the German company Schott AG. On the telescope, each segment is kept stable by a system of active optics, which uses rigid support structures in combination with three actuators under each segment. During observation, the computer-controlled system of sensors and actuators adjusts the position of each segment, relative to its neighbors, to an accuracy of four nanometers; this twice-per-second adjustment counters the effect of gravity as the telescope moves, in addition to other environmental and structural effects that can affect the mirror shape. Each Keck Observatory telescope sits on an altazimuth mount.
Most current 8–10 m class telescopes use altazimuth designs due to the reduced structural requirements compared to older equatorial designs. This mounting style provides the greatest strength and stiffness for the least amount of steel, for Keck Observatory, totals about 270 tons per telescope; the total weight of each telescope is more than 300 tons. Two of the proposed designs for the next generation 30 and 40 m telescopes use the same basic technology pioneered at Keck Observatory, a hexagonal mirror array coupled with an altazimuth mounting; the primary mirrors of each of the two telescopes are 10 meters in diameter smaller than the Gran Telescopio Canarias. However, all of the light collected by the Keck Observatory primary mirrors is sent to the secondary mirror and the instruments, compared to GTC's primary mirror, which has an effective light-collection area of 73.4 m2, or 2.36 m2 less than each of the Keck Observatory primary mirrors. Because of this fundamental difference in design, Keck Observatory's telescopes arguably remain the largest steerable, optical/infrared telescopes on Earth.
The telescopes are equipped with a suite of instruments, both cameras and spectrometers that allow observations across much of the visible and near infrared spectrum. The Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501 organization whose board of directors includes representatives from Caltech and the University of California. Construction of the telescopes was made possible through private grants totaling more than $140 million provided by the W. M. Keck Foundation; the National Aeronautics and Space Administration joined the partnership in October 1996, at the time Keck II commenced observations. Telescope time is allocated by the partner institutions. Caltech, the University of Hawaii System, the University of California accept proposals from their own researchers. NASA accepts proposals from researchers based in the United States. Jerry Nelson was the project scientist for the Keck Telescope, he contributed to multi-mirror projects until he died in June 2017.
Nelson was behind one of the key innovations of the Keck telescope, the use of multiple thin segments acting as one mirror to provide the reflecting surface. MOSFIRE MOSFIRE is a third generation instrument for the W. M. Keck Observatory. MOSFIRE was delivered to Keck Observatory on February 8, 2012 and first light on the Keck I telescope was obtained on April 4, 2012. A Multi-Object Spectrograph For Infra-Red Exploration and wide-field camera for the near-infrared, MOSFIRE's special feature is the cryogenic Configurable Slit Unit, reconfigurable under remote control in less than 6 minutes without any thermal cycling. Bars move in from each side to form up to 46 short slits; when the bars are removed MOSFIRE becomes a wide-field imager. The instrument was developed by teams from the University of California, Los Angeles, the California Institute of Technology and the University of California, Santa Cruz; the Co- Principal Investigators are Ian S. McLean and Charles C. Steidel, the project was managed by WMKO Instrument Program Manager, Sean Adkins.
MOSFIRE was funded in part by the Telescope System Instrumentation Program, operated by AURA and funded by the National Science Foundation, by a private donation to WMKO by Gordon and Betty Moore. DEIMOS The Deep Extragalactic Imaging Multi-Object Spectrograph is capable of gathering spectra from 130 galaxies or more in a single exposure. In "Mega Mask" mode, DEIMOS
Astronomy is a monthly American magazine about astronomy. Targeting amateur astronomers for its readers, it contains columns on sky viewing, reader-submitted astrophotographs, articles on astronomy and astrophysics that are readable by nonscientists. Astronomy is a magazine about the hobby of astronomy. Based near Milwaukee in Waukesha, Wisconsin, it is produced by Kalmbach Publishing. Astronomy’s readers include those interested in astronomy, those who want to know about sky events, observing techniques and amateur astronomy in general. Astronomy was founded in 1973 by Stephen A. Walther, a graduate of the University of Wisconsin–Stevens Point and amateur astronomer; the first issue, August 1973, consisted of 48 pages with five feature articles and information about what to see in the sky that month. Issues contained illustrations created by astronomical artists. Walther had worked part time as a planetarium lecturer at the University of Wisconsin–Milwaukee and developed an interest in photographing constellations at an early age.
Although in childhood he was interested to obsession in Astronomy, he did so poorly in mathematics that his mother despaired that he would be able to earn a living. However he graduated in Journalism from the University of Wisconsin Stevens Point, as a senior class project he created a business plan for a magazine for amateur astronomers. With the help of his brother David, he was able to bring the magazine to fruition.. He died in 1977. AstroMedia Corp. the company Walther had founded to publish Astronomy, brought in Richard Berry as editor. Berry created the offshoot Odyssey, aimed at young readers, the specialized Telescope Making. In 1985, Milwaukee hobby publisher Kalmbach bought Astronomy. In 1992, Richard Berry left Robert Burnham took over as chief editor. Kalmbach discontinued Deep Sky and Telescope Making magazines and sold Odyssey. In 1996 Bonnie Gordon, now a professor at Central Arizona College, assumed the editorship. David J. Eicher, the creator of "Deep Sky," became chief editor in 2002.
The Astronomy staff produces other publications. These have included Explore the Universe. There was, for a time in the mid-2000s, a Brazilian edition – published by Duetto Editora – called Astronomy Brasil. However, due to low circulation numbers, Duetto ceased its publication in September 2007. Astronomy publishes articles about the science of astronomy; the front half of the magazine reports on professional science, while the back half of the magazine presents items of interest to hobbyists. Science articles cover such topics as cosmology, space exploration, research conducted by professional-class observatories, individual professional astronomers; each issue of Astronomy contains a foldout star map showing the evening sky for the current month and the positions of planets, some comets. The magazine has regular columnists, they include science writer Bob Berman, who writes a column called “Bob Berman’s Strange Universe”. Stephen James O’Meara writes “Stephen James O’Meara’s Secret Sky,” which covers observing tips and stories relating to deep-sky objects and comets.
Glenn Chaple writes "a beginner's column. Phil Harrington writes "Phil Harrington’s Binocular Universe", about observing with binoculars. "Telescope Insider" interviews people. In each issue of Astronomy magazine, readers will find star and planet charts, telescope observing tips and techniques, advice on taking photography of the night sky; the magazine publishes reader-submitted photos in a gallery, lists astronomy-related events, letters from readers and announcements of new products. Astronomy may include special sections bound into the magazine, such as posters. Recent examples have included a Messier Catalog booklet, poster showing comet C/2006 P1 and historical comets, a Skyguide listing upcoming sky events, a Telescope Buyer's Guide. Astronomy is the largest circulation astronomy magazine, with monthly circulation of 114,080; the majority of its readers are in the United States, but it is circulated in Canada and internationally. Its major competitor is Sky & Telescope magazine with a circulation of 80,023.
Amateur astronomy Amateur telescope making Official website
Methods of detecting exoplanets
Any planet is an faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons few of the extrasolar planets reported as of April 2014 have been observed directly, with fewer being resolved from their host star. Instead, astronomers have had to resort to indirect methods to detect extrasolar planets; as of 2016, several different indirect methods have yielded success. The following methods have at least once proved successful for discovering a new planet or detecting an discovered planet: A star with a planet will move in its own small orbit in response to the planet's gravity; this leads to variations in the speed with which the star moves toward or away from Earth, i.e. the variations are in the radial velocity of the star with respect to Earth.
The radial velocity can be deduced from the displacement in the parent star's spectral lines due to the Doppler effect. The radial-velocity method measures these variations in order to confirm the presence of the planet using the binary mass function; the speed of the star around the system's center of mass is much smaller than that of the planet, because the radius of its orbit around the center of mass is so small.. However, velocity variations down to 3 m/s or somewhat less can be detected with modern spectrometers, such as the HARPS spectrometer at the ESO 3.6 meter telescope in La Silla Observatory, Chile, or the HIRES spectrometer at the Keck telescopes. An simple and inexpensive method for measuring radial velocity is "externally dispersed interferometry"; until around 2012, the radial-velocity method was by far the most productive technique used by planet hunters. The radial velocity signal is distance independent, but requires high signal-to-noise ratio spectra to achieve high precision, so is used only for nearby stars, out to about 160 light-years from Earth, to find lower-mass planets.
It is not possible to observe many target stars at a time with a single telescope. Planets of Jovian mass can be detectable around stars up to a few thousand light years away; this method finds massive planets that are close to stars. Modern spectrographs can easily detect Jupiter-mass planets orbiting 10 astronomical units away from the parent star, but detection of those planets requires many years of observation. Earth-mass planets are detectable only in small orbits around low-mass stars, e.g. Proxima b, it is easier to detect planets around low-mass stars, for two reasons: First, these stars are more affected by gravitational tug from planets. The second reason is that low-mass main-sequence stars rotate slowly. Fast rotation makes spectral-line data less clear because half of the star rotates away from observer's viewpoint while the other half approaches. Detecting planets around more massive stars is easier if the star has left the main sequence, because leaving the main sequence slows down the star's rotation.
Sometimes Doppler spectrography produces false signals in multi-planet and multi-star systems. Magnetic fields and certain types of stellar activity can give false signals; when the host star has multiple planets, false signals can arise from having insufficient data, so that multiple solutions can fit the data, as stars are not observed continuously. Some of the false signals can be eliminated by analyzing the stability of the planetary system, conducting photometry analysis on the host star and knowing its rotation period and stellar activity cycle periods. Planets with orbits inclined to the line of sight from Earth produce smaller visible wobbles, are thus more difficult to detect. One of the advantages of the radial velocity method is that eccentricity of the planet's orbit can be measured directly. One of the main disadvantages of the radial-velocity method is that it can only estimate a planet's minimum mass; the posterior distribution of the inclination angle i depends on the true mass distribution of the planets.
However, when there are multiple planets in the system that orbit close to each other and have sufficient mass, orbital stability analysis allows one to constrain the maximum mass of these planets. The radial-velocity method can be used to confirm findings made by the transit method; when both methods are used in combination the planet's true mass can be estimated. Although radial velocity of the star only gives a planet's minimum mass, if the planet's spectral lines can be distinguished from the star's spectral lines the radial velocity of the planet itself can be found, this gives the inclination of the planet's orbit; this enables measurement of the planet's actual mass. This rules out false positives, provides data about the composition of the planet; the main issue is that such detection is possible only if the planet orbits around a bright star and if the planet reflects or emits a lot of light. While the radial velocity method provides information about a planet's mass, the photometric method can determine the planet's radius.
If a planet crosses in front of its parent star's disk the observed
The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the radial velocity is the component of the object's velocity that points in the direction of the radius connecting the object and the point. In astronomy, the point is taken to be the observer on Earth, so the radial velocity denotes the speed with which the object moves away from or approaches the Earth. In astronomy, radial velocity is measured to the first order of approximation by Doppler spectroscopy; the quantity obtained by this method may be called the barycentric radial-velocity measure or spectroscopic radial velocity. However, due to relativistic and cosmological effects over the great distances that light travels to reach the observer from an astronomical object, this measure cannot be transformed to a geometric radial velocity without additional assumptions about the object and the space between it and the observer. By contrast, astrometric radial velocity is determined by astrometric observations.
Light from an object with a substantial relative radial velocity at emission will be subject to the Doppler effect, so the frequency of the light decreases for objects that were receding and increases for objects that were approaching. The radial velocity of a star or other luminous distant objects can be measured by taking a high-resolution spectrum and comparing the measured wavelengths of known spectral lines to wavelengths from laboratory measurements. A positive radial velocity indicates the distance between the objects was increasing. In many binary stars, the orbital motion causes radial velocity variations of several kilometers per second; as the spectra of these stars vary due to the Doppler effect, they are called spectroscopic binaries. Radial velocity can be used to estimate the ratio of the masses of the stars, some orbital elements, such as eccentricity and semimajor axis; the same method has been used to detect planets around stars, in the way that the movement's measurement determines the planet's orbital period, while the resulting radial-velocity amplitude allows the calculation of the lower bound on a planet's mass using the binary mass function.
Radial velocity methods alone may only reveal a lower bound, since a large planet orbiting at a high angle to the line of sight will perturb its star radially as much as a much smaller planet with an orbital plane on the line of sight. It has been suggested that planets with high eccentricities calculated by this method may in fact be two-planet systems of circular or near-circular resonant orbit; the radial velocity method to detect exoplanets is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an exoplanet as it orbits the star. When the star moves towards us, its spectrum is blueshifted, while it is redshifted when it moves away from us. By looking at the spectrum of a star—and so, measuring its velocity—it can be determined if it moves periodically due to the influence of an exoplanet companion. From the instrumental perspective, velocities are measured relative to the telescope's motion. So an important first step of the data reduction is to remove the contributions of the Earth's elliptic motion around the sun at ± 30 km/s, a monthly rotation of ± 13 m/s of the Earth around the center of gravity of the Earth-Moon system, the daily rotation of the telescope with the Earth crust around the Earth axis, up to ±460 m/s at the equator and proportional to the cosine of the telescope's geographic latitude, small contributions from the Earth polar motion at the level of mm/s, contributions of 230 km/s from the motion around the Galactic center and associated proper motions.
In the case of spectroscopic measurements corrections of the order of ±20 cm/s with respect to aberration. Proper motion Peculiar velocity Relative velocity Space velocity The Radial Velocity Equation in the Search for Exoplanets