The Venetia Burney Student Dust Counter ( VBSDC ) is a scientific instrument aboard the uncrewed New Horizons space probe that is designed to detect dust impacts in outer space. VBSDC is the first planetary science instrument to be built by students. The dust counter was launched in 2006, and named later that year after Venetia Burney , the young girl who originally named Pluto. The detector works when dust strikes films of polarized polyvinylidene fluoride (PVDF), which generates an electrical charge. The space dust is then detected over the course of the New Horizons spacecraft flight out of the Solar System and past Pluto .
65-539: In 2010, VBSDC collected data on dust past 18 AU (1.67 billion miles), which is the distance the Pioneer 10 and Pioneer 11 dust counters stopped working. Five other spacecraft have carried dust detectors beyond the asteroid belt including Pioneer 10 , Pioneer 11 , Ulysses (heliocentric orbit out to the distance of Jupiter), Galileo (Jupiter Orbiter), and Cassini (Saturn orbiter). The Voyager 1 and Voyager 2 spacecraft did detect dust by using data from
130-613: A 4.35 ha (10.7-acre) site (originally 2.52 ha or 6.2 acres) granted to the Bureau by the French Government in 1876. Since 1969 the site has been considered international territory, and the BIPM has all the rights and privileges accorded to an intergovernmental organisation. This status was further clarified by the French decree No 70-820 of 9 September 1970. Several significant changes to
195-580: A collection of data called an ephemeris . NASA 's Jet Propulsion Laboratory HORIZONS System provides one of several ephemeris computation services. In 1976, to establish a more precise measure for the astronomical unit, the IAU formally adopted a new definition . Although directly based on the then-best available observational measurements, the definition was recast in terms of the then-best mathematical derivations from celestial mechanics and planetary ephemerides. It stated that "the astronomical unit of length
260-469: A considerable improvement in parallax measurement. Another international project to measure the parallax of 433 Eros was undertaken in 1930–1931. Direct radar measurements of the distances to Venus and Mars became available in the early 1960s. Along with improved measurements of the speed of light, these showed that Newcomb's values for the solar parallax and the constant of aberration were inconsistent with one another. The unit distance A (the value of
325-502: A distance within the Solar System without specifying the frame of reference for the measurement is problematic. The 1976 definition of the astronomical unit was incomplete because it did not specify the frame of reference in which to apply the measurement, but proved practical for the calculation of ephemerides: a fuller definition that is consistent with general relativity was proposed, and "vigorous debate" ensued until August 2012 when
390-466: A ratio of solar to lunar distance of approximately 19, matching Aristarchus's figure. Although Ptolemy's procedure is theoretically workable, it is very sensitive to small changes in the data, so much so that changing a measurement by a few per cent can make the solar distance infinite. After Greek astronomy was transmitted to the medieval Islamic world, astronomers made some changes to Ptolemy's cosmological model, but did not greatly change his estimate of
455-426: A solar parallax of 8.6″ . Although Huygens' estimate is remarkably close to modern values, it is often discounted by historians of astronomy because of the many unproven (and incorrect) assumptions he had to make for his method to work; the accuracy of his value seems to be based more on luck than good measurement, with his various errors cancelling each other out. Jean Richer and Giovanni Domenico Cassini measured
520-484: A star's shift enabled the star's distance to be calculated. But all measurements are subject to some degree of error or uncertainty, and the uncertainties in the length of the astronomical unit only increased uncertainties in the stellar distances. Improvements in precision have always been a key to improving astronomical understanding. Throughout the twentieth century, measurements became increasingly precise and sophisticated, and ever more dependent on accurate observation of
585-599: Is an intergovernmental organisation , through which its 59 member-states act on measurement standards in areas including chemistry , ionising radiation , physical metrology , as well as the International System of Units (SI) and Coordinated Universal Time (UTC). It is based in Saint-Cloud , near Paris , France . The organisation has been referred to as IBWM (from its name in English) in older literature. The BIPM
650-399: Is composed of 12 panels, each 14.2 centimetres (5.6 in) long and 6.5 centimetres (2.6 in) wide, meaning it has a width of 28.4 centimetres (11.2 in) and length of 39 centimetres (15 in). The instrument is designed to detect dust between 10 ng and 10 pg in mass and between 0.5 and 10 μm in size. By December 2008 it had taken dust measurements between 1.2 and 11.0 AU from
715-504: Is constant for all observers, the terrestrial metre appears to change in length compared with the "planetary metre" on a periodic basis. The metre is defined to be a unit of proper length . Indeed, the International Committee for Weights and Measures (CIPM) notes that "its definition applies only within a spatial extent sufficiently small that the effects of the non-uniformity of the gravitational field can be ignored". As such,
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#1732851903367780-418: Is increasingly becoming the norm. A 2004 analysis of radiometric measurements in the inner Solar System suggested that the secular increase in the unit distance was much larger than can be accounted for by solar radiation, + 15 ± 4 metres per century. The measurements of the secular variations of the astronomical unit are not confirmed by other authors and are quite controversial. Furthermore, since 2010,
845-539: Is overseen by the International Committee for Weights and Measures ( French : Comité international des poids et mesures, CIPM ), a committee of eighteen members that meet normally in two sessions per year, which is in turn overseen by the General Conference on Weights and Measures ( French : Conférence générale des poids et mesures, CGPM ) that meets in Paris usually once every four years, consisting of delegates of
910-821: Is presented at each meeting of the General Conference for consideration with the BIPM budget. The final programme of work is determined by the CIPM in accordance with the budget agreed to by the CGPM. Currently, the BIPM's main work includes: The BIPM is one of the twelve member organisations of the International Network on Quality Infrastructure (INetQI), which promotes and implements QI activities in metrology , accreditation, standardisation and conformity assessment. The BIPM has an important role in maintaining accurate worldwide time of day. It combines, analyses, and averages
975-576: Is related to the Earth–Sun distance as measured in Earth radii by The smaller the solar parallax, the greater the distance between the Sun and Earth: a solar parallax of 15″ is equivalent to an Earth–Sun distance of 13,750 Earth radii. Christiaan Huygens believed that the distance was even greater: by comparing the apparent sizes of Venus and Mars , he estimated a value of about 24,000 Earth radii, equivalent to
1040-526: Is that length ( A ) for which the Gaussian gravitational constant ( k ) takes the value 0.017 202 098 95 when the units of measurement are the astronomical units of length, mass and time". Equivalently, by this definition, one au is "the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass, moving with an angular frequency of 0.017 202 098 95 radians per day "; or alternatively that length for which
1105-456: Is the first time this has happened since the creation of the BIPM. These changes were made official on World Metrology Day in 2019. Beginning in 1970, the BIPM began publishing the SI Brochure, a document detailing an up-to-date version of the International System of Units . As of November 2024, the most recent version of the SI Brochure was the 9th edition published in 2019. The BIPM has
1170-613: The Zhoubi Suanjing ( c. 1st century BCE ), shows how the distance to the Sun can be computed geometrically, using the different lengths of the noontime shadows observed at three places 1,000 li apart and the assumption that Earth is flat. According to Eusebius in the Praeparatio evangelica (Book XV, Chapter 53), Eratosthenes found the distance to the Sun to be "σταδιων μυριαδας τετρακοσιας και οκτωκισμυριας" (literally "of stadia myriads 400 and 80,000″ ) but with
1235-571: The Seven Years' War , dozens of astronomers were dispatched to observing points around the world at great expense and personal danger: several of them died in the endeavour. The various results were collated by Jérôme Lalande to give a figure for the solar parallax of 8.6″ . Karl Rudolph Powalky had made an estimate of 8.83″ in 1864. Another method involved determining the constant of aberration . Simon Newcomb gave great weight to this method when deriving his widely accepted value of 8.80″ for
1300-480: The heliocentric gravitational constant (the product G M ☉ ) is equal to ( 0.017 202 098 95 ) au /d , when the length is used to describe the positions of objects in the Solar System. Subsequent explorations of the Solar System by space probes made it possible to obtain precise measurements of the relative positions of the inner planets and other objects by means of radar and telemetry . As with all radar measurements, these rely on measuring
1365-540: The parsec and light-year are widely used. The parsec (parallax arcsecond ) is defined in terms of the astronomical unit, being the distance of an object with a parallax of 1″ . The light-year is often used in popular works, but is not an approved non-SI unit and is rarely used by professional astronomers. When simulating a numerical model of the Solar System , the astronomical unit provides an appropriate scale that minimizes ( overflow , underflow and truncation ) errors in floating point calculations. The book On
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#17328519033671430-456: The "planetary second" (conventionally measured in TDB). This is because the distance between Earth and the Sun is not fixed (it varies between 0.983 289 8912 and 1.016 710 3335 au ) and, when Earth is closer to the Sun ( perihelion ), the Sun's gravitational field is stronger and Earth is moving faster along its orbital path. As the metre is defined in terms of the second and the speed of light
1495-425: The 16th century. Johannes Kepler was the first to realize that Ptolemy's estimate must be significantly too low (according to Kepler, at least by a factor of three) in his Rudolphine Tables (1627). Kepler's laws of planetary motion allowed astronomers to calculate the relative distances of the planets from the Sun, and rekindled interest in measuring the absolute value for Earth (which could then be applied to
1560-496: The 2009 estimate. With the definitions used before 2012, the astronomical unit was dependent on the heliocentric gravitational constant , that is the product of the gravitational constant , G , and the solar mass , M ☉ . Neither G nor M ☉ can be measured to high accuracy separately, but the value of their product is known very precisely from observing the relative positions of planets ( Kepler's third law expressed in terms of Newtonian gravitation). Only
1625-502: The BIPM have been made throughout its history during the meetings overseen by the CGPM. An example of this would be how in the 12th general council meeting (held in 1964), the BIPM's budget was increased from $ 300,000 to $ 600,000 per year. A historic moment for the BIPM occurred during the 26th CGPM in 2018. At this council, it was decided that world standard for the units of kilograms, seconds, amperes, Kelvins, moles, candelas, and meters would be redefined to reflect constants in nature. This
1690-526: The Earth–Sun distance. For example, in his introduction to Ptolemaic astronomy, al-Farghānī gave a mean solar distance of 1,170 Earth radii, whereas in his zij , al-Battānī used a mean solar distance of 1,108 Earth radii. Subsequent astronomers, such as al-Bīrūnī , used similar values. Later in Europe, Copernicus and Tycho Brahe also used comparable figures ( 1,142 and 1,150 Earth radii), and so Ptolemy's approximate Earth–Sun distance survived through
1755-447: The Greek stadium of 185 to 190 metres, the former translation comes to 754,800 km to 775,200 km , which is far too low, whereas the second translation comes to 148.7 to 152.8 billion metres (accurate within 2%). In the 2nd century CE, Ptolemy estimated the mean distance of the Sun as 1,210 times Earth's radius . To determine this value, Ptolemy started by measuring
1820-409: The IAU adopted the current definition of 1 astronomical unit = 149,597,870,700 metres . The astronomical unit is typically used for stellar system scale distances, such as the size of a protostellar disk or the heliocentric distance of an asteroid, whereas other units are used for other distances in astronomy . The astronomical unit is too small to be convenient for interstellar distances, where
1885-492: The Moon and concluded that the apparent diameter of the Sun was equal to the apparent diameter of the Moon at the Moon's greatest distance, and from records of lunar eclipses, he estimated this apparent diameter, as well as the apparent diameter of the shadow cone of Earth traversed by the Moon during a lunar eclipse. Given these data, the distance of the Sun from Earth can be trigonometrically computed to be 1,210 Earth radii. This gives
1950-401: The Moon's parallax, finding what amounted to a horizontal lunar parallax of 1° 26′, which was much too large. He then derived a maximum lunar distance of 64 + 1 / 6 Earth radii. Because of cancelling errors in his parallax figure, his theory of the Moon's orbit, and other factors, this figure was approximately correct. He then measured the apparent sizes of the Sun and
2015-617: The NH Principal Investigator was able to present Venetia with a plaque about the naming of the Venetia Burney Student Dust Counter after her. Previously the instrument was called the Student Dust Counter . Astronomical unit The astronomical unit (symbol: au or AU ) is a unit of length defined to be exactly equal to 149,597,870,700 m . Historically, the astronomical unit
Venetia Burney Student Dust Counter - Misplaced Pages Continue
2080-628: The Plasma Wave instrument, but did not have dedicated dust detection instruments. The Pioneer dust detectors stopped working at 18 AU. The impacts of the dust is calculated to provide the mass and the velocity of the dust. One of the natural structures of the Solar System the VBSDC is designed to detect, is the Zodiacal cloud . The instrument is 1 centimetre (0.39 in) thick and has a total collecting area of less than 0.1 square metres (1.1 sq ft) and
2145-475: The Sizes and Distances of the Sun and Moon , which is ascribed to Aristarchus , says the distance to the Sun is 18 to 20 times the distance to the Moon , whereas the true ratio is about 389.174 . The latter estimate was based on the angle between the half-moon and the Sun, which he estimated as 87° (the true value being close to 89.853° ). Depending on the distance that van Helden assumes Aristarchus used for
2210-429: The Sun. By April 2012, the dust counter had produced data up to 23 AU. The direction of the dust impact is calculated by noting what direction the instrument is facing due to the orientation of the spacecraft. The instrument has very low power consumption. Examples of periods of Measurements: Data collected in the inner Solar System was compared to similar data from Galileo and Ulysses spacecraft. VBSDC recorded
2275-541: The Sun. This has led to calls to abandon the astronomical unit as a unit of measurement. As the speed of light has an exact defined value in SI units and the Gaussian gravitational constant k is fixed in the astronomical system of units , measuring the light time per unit distance is exactly equivalent to measuring the product G × M ☉ in SI units. Hence, it is possible to construct ephemerides entirely in SI units, which
2340-569: The additional note that in the Greek text the grammatical agreement is between myriads (not stadia ) on the one hand and both 400 and 80,000 on the other: all three are accusative plural, while σταδιων is genitive plural ("of stadia") . All three words (or all four including stadia ) are inflected . This has been translated either as 4 080 000 stadia (1903 translation by Edwin Hamilton Gifford ), or as 804,000,000 stadia (edition of Édouard des Places , dated 1974–1991). Using
2405-454: The astronomical unit by John Flamsteed , which accomplished it alone by measuring the martian diurnal parallax . Another colleague, Ole Rømer , discovered the finite speed of light in 1676: the speed was so great that it was usually quoted as the time required for light to travel from the Sun to the Earth, or "light time per unit distance", a convention that is still followed by astronomers today. A better method for observing Venus transits
2470-550: The astronomical unit has not been estimated by the planetary ephemerides. The following table contains some distances given in astronomical units. It includes some examples with distances that are normally not given in astronomical units, because they are either too short or far too long. Distances normally change over time. Examples are listed by increasing distance. International Bureau of Weights and Measures The International Bureau of Weights and Measures ( French : Bureau International des Poids et Mesures , BIPM )
2535-463: The astronomical unit in metres) can be expressed in terms of other astronomical constants: where G is the Newtonian constant of gravitation , M ☉ is the solar mass, k is the numerical value of Gaussian gravitational constant and D is the time period of one day. The Sun is constantly losing mass by radiating away energy, so the orbits of the planets are steadily expanding outward from
2600-591: The astronomical unit. In a 1976 resolution, the International Astronomical Union (IAU) had used the symbol A to denote a length equal to the astronomical unit. In the astronomical literature, the symbol AU is common. In 2006, the International Bureau of Weights and Measures (BIPM) had recommended ua as the symbol for the unit, from the French "unité astronomique". In the non-normative Annex C to ISO 80000-3 :2006 (later withdrawn),
2665-497: The best IAU 2009 estimate was A = c 0 τ A = 149,597,870,700 ± 3 m , based on a comparison of Jet Propulsion Laboratory and IAA–RAS ephemerides. In 2006, the BIPM reported a value of the astronomical unit as 1.495 978 706 91 (6) × 10 m . In the 2014 revision of the SI ;Brochure, the BIPM recognised the IAU's 2012 redefinition of the astronomical unit as 149,597,870,700 m . This estimate
Venetia Burney Student Dust Counter - Misplaced Pages Continue
2730-513: The change was an improved method of measuring the speed of light.) The speed of light could then be expressed exactly as c 0 = 299,792,458 m/s , a standard also adopted by the IERS numerical standards. From this definition and the 2009 IAU standard, the time for light to traverse an astronomical unit is found to be τ A = 499.004 783 8061 ± 0.000 000 01 s , which is slightly more than 8 minutes 19 seconds. By multiplication,
2795-438: The distance to the Moon, his calculated distance to the Sun would fall between 380 and 1,520 Earth radii. Hipparchus gave an estimate of the distance of Earth from the Sun, quoted by Pappus as equal to 490 Earth radii. According to the conjectural reconstructions of Noel Swerdlow and G. J. Toomer , this was derived from his assumption of a "least perceptible" solar parallax of 7 ′ . A Chinese mathematical treatise,
2860-418: The effects described by Einstein 's theory of relativity and upon the mathematical tools it used. Improving measurements were continually checked and cross-checked by means of improved understanding of the laws of celestial mechanics , which govern the motions of objects in space. The expected positions and distances of objects at an established time are calculated (in au) from these laws, and assembled into
2925-462: The first measurements of sub-micron space dust in the outer Solar System. In the outer Solar System VBSDC recorded an average flux of dust of grain size larger than 2 × 10 grams of 2.5 × 10 m s. The dust detection within the orbit of Jupiter registered by the VBSDC were compared to previous observations by dust detectors on the Ulysses and Galileo spacecraft. The results from VBSDC were consistent with
2990-623: The governments of the Member States and observers from the Associates of the CGPM. These organs are also commonly referred to by their French initialisms. The BIPM was created on 20 May 1875, following the signing of the Metre Convention , a treaty among 17 Member States (as of November 2018 there are now 59 members). It is based at the Pavillon de Breteuil in Saint-Cloud , France,
3055-478: The mandate to provide the basis for a single, coherent system of measurements throughout the world, traceable to the International System of Units (SI) . This task takes many forms, from direct dissemination of units to coordination through international comparisons of national measurement standards (as in electricity and ionising radiation). Following consultation, a draft version of the BIPM Work Programme
3120-486: The measurement of the time itself must be translated to a standard scale that accounts for relativistic time dilation . Comparison of the ephemeris positions with time measurements expressed in Barycentric Dynamical Time (TDB) leads to a value for the speed of light in astronomical units per day (of 86,400 s ). By 2009, the IAU had updated its standard measures to reflect improvements, and calculated
3185-453: The metre (exactly 149,597,870,700 m ). The new definition recognizes as a consequence that the astronomical unit has reduced importance, limited in use to a convenience in some applications. This definition makes the speed of light, defined as exactly 299,792,458 m/s , equal to exactly 299,792,458 × 86,400 ÷ 149,597,870,700 or about 173.144 632 674 240 au/d, some 60 parts per trillion less than
3250-399: The other planets). The invention of the telescope allowed far more accurate measurements of angles than is possible with the naked eye. Flemish astronomer Godefroy Wendelin repeated Aristarchus’ measurements in 1635, and found that Ptolemy's value was too low by a factor of at least eleven. A somewhat more accurate estimate can be obtained by observing the transit of Venus . By measuring
3315-540: The parallax of Mars between Paris and Cayenne in French Guiana when Mars was at its closest to Earth in 1672. They arrived at a figure for the solar parallax of 9.5″ , equivalent to an Earth–Sun distance of about 22,000 Earth radii. They were also the first astronomers to have access to an accurate and reliable value for the radius of Earth, which had been measured by their colleague Jean Picard in 1669 as 3,269,000 toises . This same year saw another estimate for
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#17328519033673380-417: The points of its extremes defined the exact shape mathematically, and made possible calculations for the entire orbit as well as predictions based on observation. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, defining times and places for observing the largest parallax (apparent shifts of position) in nearby stars. Knowing Earth's shift and
3445-428: The previously recorded data. The VBSDC was designed and is operated by students. Between 2002 and 2010 there were 32 students that worked on the project. By 2010 there was team of about a half-dozen students working on the mission, but the team was as large as 20 students at its start. The students were typically undergraduate or graduate level, with participants rotated in and out of the project over time. In June 2006
3510-500: The product is required to calculate planetary positions for an ephemeris, so ephemerides are calculated in astronomical units and not in SI units. The calculation of ephemerides also requires a consideration of the effects of general relativity . In particular, time intervals measured on Earth's surface ( Terrestrial Time , TT) are not constant when compared with the motions of the planets: the terrestrial second (TT) appears to be longer near January and shorter near July when compared with
3575-435: The solar parallax (and for the constant of aberration and the Gaussian gravitational constant) were incorporated into the first international system of astronomical constants in 1896, which remained in place for the calculation of ephemerides until 1964. The name "astronomical unit" appears first to have been used in 1903. The discovery of the near-Earth asteroid 433 Eros and its passage near Earth in 1900–1901 allowed
3640-424: The solar parallax (close to the modern value of 8.794 143 ″ ), although Newcomb also used data from the transits of Venus. Newcomb also collaborated with A. A. Michelson to measure the speed of light with Earth-based equipment; combined with the constant of aberration (which is related to the light time per unit distance), this gave the first direct measurement of the Earth–Sun distance in metres. Newcomb's value for
3705-433: The speed of light at 173.144 632 6847 (69) au/d (TDB). In 1983, the CIPM modified the International System of Units (SI) to make the metre defined as the distance travelled in a vacuum by light in 1 / 299,792,458 s. This replaced the previous definition, valid between 1960 and 1983, which was that the metre equalled a certain number of wavelengths of a certain emission line of krypton-86. (The reason for
3770-458: The student dust counter was named in honor of Venetia Phair (née Burney) who came up with the name Pluto in the 1930s as a girl, and she was given a plaque related to this naming in December, 2006. Venetia suggested the name Pluto after the discovery of the new planet by Clyde Tombaugh in 1930 at Lowell Observatory . The name Pluto was selected in a vote by the observatory's astronomers. In 2006,
3835-546: The symbol of the astronomical unit was also ua. In 2012, the IAU, noting "that various symbols are presently in use for the astronomical unit", recommended the use of the symbol "au". The scientific journals published by the American Astronomical Society and the Royal Astronomical Society subsequently adopted this symbol. In the 2014 revision and 2019 edition of the SI Brochure, the BIPM used
3900-436: The time taken for photons to be reflected from an object. Because all photons move at the speed of light in vacuum, a fundamental constant of the universe, the distance of an object from the probe is calculated as the product of the speed of light and the measured time. However, for precision the calculations require adjustment for things such as the motions of the probe and object while the photons are transiting. In addition,
3965-460: The transit in two different locations, one can accurately calculate the parallax of Venus and from the relative distance of Earth and Venus from the Sun, the solar parallax α (which cannot be measured directly due to the brightness of the Sun ). Jeremiah Horrocks had attempted to produce an estimate based on his observation of the 1639 transit (published in 1662), giving a solar parallax of 15 ″ , similar to Wendelin's figure. The solar parallax
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#17328519033674030-456: The unit symbol "au". ISO 80000-3:2019, which replaces ISO 80000-3:2006, does not mention the astronomical unit. Earth's orbit around the Sun is an ellipse . The semi-major axis of this elliptic orbit is defined to be half of the straight line segment that joins the perihelion and aphelion . The centre of the Sun lies on this straight line segment, but not at its midpoint. Because ellipses are well-understood shapes, measuring
4095-563: Was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion ), before its modern redefinition in 2012. The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec . One au is equivalent to 499 light-seconds to within 10 parts per million . A variety of unit symbols and abbreviations have been in use for
4160-473: Was devised by James Gregory and published in his Optica Promata (1663). It was strongly advocated by Edmond Halley and was applied to the transits of Venus observed in 1761 and 1769, and then again in 1874 and 1882. Transits of Venus occur in pairs, but less than one pair every century, and observing the transits in 1761 and 1769 was an unprecedented international scientific operation including observations by James Cook and Charles Green from Tahiti. Despite
4225-417: Was still derived from observation and measurements subject to error, and based on techniques that did not yet standardize all relativistic effects, and thus were not constant for all observers. In 2012, finding that the equalization of relativity alone would make the definition overly complex, the IAU simply used the 2009 estimate to redefine the astronomical unit as a conventional unit of length directly tied to
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