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73-523: The Sciencenter's Sagan Planet Walk is a walkable scale model of the Solar System , located in Ithaca, New York . The model scales the entire Solar System—both planet size and distances between them—down to one five billionth of its actual size. The exhibition was originally created in 1997 in memory of Ithaca resident and Cornell Professor Carl Sagan . Consisting of eleven obelisks situated along

146-402: A binary component. The AB designation, or older A×B , denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system. AB-C refers to the component of Proxima Centauri in relation to the central binary, being the distance between the centre of mass and the outlying companion. Because the distance between Proxima (C) and either of Alpha Centauri A or B

219-667: A scale model of the Solar System a challenging task. As one example of the difficulty, the distance between the Earth and the Sun is almost 12,000 times the diameter of the Earth. If the smaller planets are to be easily visible to the naked eye, large outdoor spaces are generally necessary, as is some means for highlighting objects that might otherwise not be noticed from a distance. The Boston Museum of Science had placed bronze models of

292-583: A 1.18 km (0.73 mi) path through the streets of downtown Ithaca, the original Planet Walk leads from the Sun at Center Ithaca to Pluto at the Ithaca Sciencenter . In 2012, the model was expanded 7,630 kilometers (4,740 mi) to include a representation of Alpha Centauri , the Sun's closest neighboring star, at the ʻImiloa Astronomy Center at the University of Hawaii . The addition of

365-541: A 280 millimetres (11 in) semicircle under its chin to represent its scale size. This extension made the Sagan Planet Walk the world's largest exhibition. Television host and former student of Carl Sagan, Bill Nye , narrated a podcast tour of the Planet Walk in 2006 which can be accessed free by calling 703-637-6237 as you walk through the scale-model representation of the Solar System. The models of

438-555: A brilliant optical double star in the southern sky. It will then pass just north of the Southern Cross or Crux , before moving northwest and up towards the present celestial equator and away from the galactic plane . By about 26,700  CE , in the present-day constellation of Hydra , α Centauri will reach perihelion at 0.90  pc or 2.9  ly away, though later calculations suggest that this will occur in 27,000 AD. At its nearest approach, α Centauri will attain

511-588: A few minutes. Some amateur and professional astronomers regularly monitor for outbursts using either optical or radio telescopes. In August 2015, the largest recorded flares of the star occurred, with the star becoming 8.3 times brighter than normal on 13 August, in the B ;band (blue light region) . Alpha Centauri may be inside the G-cloud of the Local Bubble , and its nearest known system

584-492: A fraction of a degree since Ptolemy 's time due to proper motion .) In Ptolemy's time, Alpha Centauri was visible from Alexandria, Egypt , at 31° N, but, due to precession , its declination is now –60° 51′ South , and it can no longer be seen at that latitude. English explorer Robert Hues brought Alpha Centauri to the attention of European observers in his 1592 work Tractatus de Globis , along with Canopus and Achernar , noting: Now, therefore, there are but three Stars of

657-399: A high proper motion. In this case, the apparent stellar motion was found using Nicolas Louis de Lacaille 's astrometric observations of 1751–1752, by the observed differences between the two measured positions in different epochs. Calculated proper motion of the centre of mass for α Centauri AB is about 3620 mas/y (milliarcseconds per year) toward the west and 694 mas/y toward

730-877: A mass between that of Neptune and one-half that of Saturn, though it may be a dust disk or an artifact. The possibility of C1 being a background star has been ruled out. If this candidate is confirmed, the temporary name C1 will most likely be replaced with the scientific designation Alpha Centauri Ab in accordance with current naming conventions. GO Cycle 1 observations are planned for the James Webb Space Telescope (JWST) to search for planets around Alpha Centauri A, as well as observations of Epsilon Muscae . The coronographic observations, which occurred on July 26 and 27, 2023, were failures, though there are follow-up observations in March 2024. Pre-launch estimates predicted that JWST will be able to find planets with

803-459: A mass of roughly 7 M E and orbits about 1.49 AU from Proxima Centauri with a period of 1,928 days (5.28 yr). In June 2020, a possible direct imaging detection of the planet hinted at the presence of a large ring system. However, a 2022 study disputed the existence of this planet. A 2020 paper refining Proxima b's mass excludes the presence of extra companions with masses above 0.6  M E at periods shorter than 50 days, but

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876-467: A maximum apparent magnitude of −0.86, comparable to present-day magnitude of Canopus , but it will still not surpass that of Sirius , which will brighten incrementally over the next 60,000 years, and will continue to be the brightest star as seen from Earth (other than the Sun) for the next 210,000 years. Alpha Centauri is a triple star system, with its two main stars, A and B, together comprising

949-601: A passing comet from his station in Puducherry . Alpha Centauri was only the third binary star to be discovered, preceded by Mizar AB and Acrux . The large proper motion of Alpha Centauri AB was discovered by Manuel John Johnson , observing from Saint Helena , who informed Thomas Henderson at the Royal Observatory, Cape of Good Hope of it. The parallax of Alpha Centauri was subsequently determined by Henderson from many exacting positional observations of

1022-424: A radius of 5 R 🜨 at 1–3 AU . Multiple observations every 3–6 months could push the limit down to 3 R 🜨 . Post-launch estimates based on observations of HIP 65426 b find that JWST will be able to find planets even closer to Alpha Centauri A and could find a 5 R 🜨 planet at 0.5–2.5 AU . Candidate 1 has an estimated radius between 3.3–11 R 🜨 and orbits at 1.1 AU . It

1095-486: A terrestrial planet discovered in 2016 by astronomers at the European Southern Observatory (ESO). It has an estimated minimum mass of 1.17 M E ( Earth masses ) and orbits approximately 0.049 AU from Proxima Centauri, placing it in the star's habitable zone . The discovery of Proxima Centauri c was formally published in 2020 and could be a super-Earth or mini-Neptune . It has

1168-663: Is circumpolar and never sets below the horizon. North of about 29° N latitude, Alpha Centauri never rises. Alpha Centauri lies close to the southern horizon when viewed from the 29° North latitude to the equator (close to Hermosillo and Chihuahua City in Mexico ; Galveston, Texas ; Ocala, Florida ; and Lanzarote , the Canary Islands of Spain ), but only for a short time around its culmination . The star culminates each year at local midnight on 24 April and at local 9 p.m. on 8 June. As seen from Earth, Proxima Centauri

1241-638: Is 2.2° southwest from α Centauri AB ; this distance is about four times the angular diameter of the Moon . Proxima Centauri appears as a deep-red star of a typical apparent magnitude of 11.1 in a sparsely populated star field, requiring moderately sized telescopes to be seen. Listed as V645 Cen in the General Catalogue of Variable Stars , version 4.2, this UV Ceti star or "flare star" can unexpectedly brighten rapidly by as much as 0.6 magnitude at visual wavelengths, then fade after only

1314-651: Is 35.6 AU (5.33 × 10 ^  km), about the distance between the Sun and Pluto. The most recent periastron was in August 1955 and the next will occur in May ;2035; the most recent apastron was in May 1995 and will next occur in 2075. Viewed from Earth, the apparent orbit of A and B means that their separation and position angle (PA) are in continuous change throughout their projected orbit. Observed stellar positions in 2019 are separated by 4.92 arcsec through

1387-502: Is a first-magnitude star and is fainter only than Sirius and Canopus . It is the outer star of The Pointers or The Southern Pointers , so called because the line through Beta Centauri (Hadar/Agena), some 4.5° west, points to the constellation Crux —the Southern Cross. The Pointers easily distinguish the true Southern Cross from the fainter asterism known as the False Cross . South of about 29° South latitude, α Cen

1460-412: Is a triple star system in the southern constellation of Centaurus . It consists of three stars: Rigil Kentaurus ( α Centauri A ), Toliman ( α Centauri B ), and Proxima Centauri ( α Centauri C ). Proxima Centauri is the closest star to the Sun at 4.2465  light-years (1.3020  pc ). α Centauri A and B are Sun-like stars ( class G and K , respectively) that together form

1533-524: Is approximately 511 000 +41 000 −30 000 years, with an eccentricity of 0.5, much more eccentric than Mercury 's. Proxima Centauri comes within 4100 +700 −600   AU of AB at periastron, and its apastron occurs at 12 300 +200 −100   AU . Asteroseismic studies, chromospheric activity , and stellar rotation ( gyrochronology ) are all consistent with the Alpha Centauri system being similar in age to, or slightly older than,

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1606-414: Is comparable to that of the Sun, showing coronal variability due to star spots , as modulated by the rotation of the star. However, since 2005 the activity level has fallen into a deep minimum that might be similar to the Sun's historical Maunder Minimum . Alternatively, it may have a very long stellar activity cycle and is slowly recovering from a minimum phase. Alpha Centauri B, also known as Toliman,

1679-417: Is controversial. α Centauri A may have a Neptune-sized planet in the habitable zone, though it is not yet known with certainty to be planetary in nature and could be an artifact of the discovery mechanism. α Centauri B has no known planets: Planet α Cen Bb , purportedly discovered in 2012, was later disproven, and no other planet has yet been confirmed. α Centauri ( Latinised to Alpha Centauri )

1752-481: Is more magnetically active than Alpha Centauri A, showing a cycle of 8.2 ± 0.2 yr compared to 11 years for the Sun, and has about half the minimum-to-peak variation in coronal luminosity of the Sun. Alpha Centauri B has an apparent magnitude of +1.35, slightly dimmer than Mimosa . Alpha Centauri C, better known as Proxima Centauri, is a small main-sequence red dwarf of spectral class M6-Ve. It has an absolute magnitude of +15.60, over 20,000 times fainter than

1825-415: Is part of the α Centauri system and slightly closer to Earth than α Centauri AB . As such, Innes concluded that Proxima Centauri was the closest star to Earth yet discovered. All components of α Centauri display significant proper motion against the background sky. Over centuries, this causes their apparent positions to slowly change. Proper motion was unknown to ancient astronomers. Most assumed that

1898-483: Is similar, the AB binary system is sometimes treated as a single gravitational object. The A and B components of Alpha Centauri have an orbital period of 79.762 years. Their orbit is moderately eccentric , as it has an eccentricity of almost 0.52; their closest approach or periastron is 11.2 AU (1.68 × 10 ^  km), or about the distance between the Sun and Saturn; and their furthest separation or apastron

1971-408: Is smaller and cooler, at 0.9 solar mass and less than 0.5 solar luminosity. The pair orbit around a common centre with an orbital period of 79 years. Their elliptical orbit is eccentric , so that the distance between A and B varies from 35.6  astronomical units ( AU ), or about the distance between Pluto and the Sun, to 11.2 AU , or about the distance between Saturn and

2044-419: Is the binary brown dwarf system Luhman 16 , at 3.6 light-years (1.1 parsecs ) from Alpha Centauri. Alpha Centauri is listed in the 2nd century the star catalog appended to Ptolemy 's Almagest . He gave its ecliptic coordinates , but texts differ as to whether the ecliptic latitude reads 44° 10′ South or 41° 10′ South . (Presently the ecliptic latitude is 43.5° South , but it has decreased by

2117-532: Is the principal member, or primary, of the binary system. It is a solar-like main-sequence star with a similar yellowish colour, whose stellar classification is spectral type G2-V; it is about 10% more massive than the Sun, with a radius about 22% larger. When considered among the individual brightest stars in the night sky, it is the fourth-brightest at an apparent magnitude of +0.01, being slightly fainter than Arcturus at an apparent magnitude of −0.05. The type of magnetic activity on Alpha Centauri A

2190-471: Is the secondary star of the binary system. It is a main-sequence star of spectral type K1-V, making it more an orange colour than Alpha Centauri A; it has around 90% of the mass of the Sun and a 14% smaller diameter. Although it has a lower luminosity than A, Alpha Centauri B emits more energy in the X-ray band. Its light curve varies on a short time scale, and there has been at least one observed flare . It

2263-662: Is the system's designation given by J. Bayer in 1603. It belongs to the constellation Centaurus , named after the half human, half horse creature in Greek mythology. Hercules accidentally wounded the centaur and placed him in the sky after his death. Alpha Centauri marks the right front hoof of the Centaur . The common name Rigil Kentaurus is a Latinisation of the Arabic translation رجل القنطورس Rijl al-Qinṭūrus, meaning "the Foot of

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2336-412: Is therefore likely within the reach of JWST observations. The first claim of a planet around Alpha Centauri B was that of Alpha Centauri Bb in 2012, which was proposed to be an Earth-mass planet in a 3.2-day orbit. This was refuted in 2015 when the apparent planet was shown to be an artifact of the way the radial velocity data was processed. A search for transits of planet Bb was conducted with

2409-586: The Centaur ". Qinṭūrus is the Arabic transliteration of the Greek Κένταυρος (Kentaurus). The name is frequently abbreviated to Rigil Kent ( / ˈ r aɪ dʒ əl ˈ k ɛ n t / ) or even Rigil , though the latter name is better known for Rigel ( β Orionis). An alternative name found in European sources, Toliman , is an approximation of the Arabic الظليمان aẓ-Ẓalīmān (in older transcription, aṭ-Ṭhalīmān ), meaning 'the (two male) Ostriches', an appellation Zakariya al-Qazwini had applied to

2482-845: The Chinese name for Alpha Centauri itself is 南門二 Nán Mén Èr , the Second Star of the Southern Gate. To the Indigenous Boorong people of northwestern Victoria in Australia, Alpha Centauri and Beta Centauri are Bermbermgle , two brothers noted for their courage and destructiveness, who speared and killed Tchingal "The Emu" (the Coalsack Nebula ). The form in Wotjobaluk is Bram-bram-bult . To

2555-713: The Hubble Space Telescope from 2013 to 2014. This search detected one potential transit-like event, which could be associated with a different planet with a radius around 0.92  R 🜨 . This planet would most likely orbit Alpha Centauri B with an orbital period of 20.4 days or less, with only a 5% chance of it having a longer orbit. The median of the likely orbits is 12.4 days. Its orbit would likely have an eccentricity of 0.24 or less. It could have lakes of molten lava and would be far too close to Alpha Centauri B to harbour life . If confirmed, this planet might be called Alpha Centauri Bc . However,

2628-632: The IAU approved the name Toliman ( / ˈ t ɒ l ɪ m æ n / ) for α Centauri B . During the 19th century, the northern amateur popularist E.H. Burritt used the now-obscure name Bungula ( / ˈ b ʌ ŋ ɡ juː l ə / ). Its origin is not known, but it may have been coined from the Greek letter beta ( β ) and Latin ungula 'hoof', originally for Beta Centauri (the other hoof). In Chinese astronomy , 南門 Nán Mén , meaning Southern Gate , refers to an asterism consisting of Alpha Centauri and Epsilon Centauri . Consequently,

2701-619: The Solar System , in order: The Sagan Planet Walk has inspired the creation of other scale-model Solar Systems in the United States. Solar System model Solar System models , especially mechanical models, called orreries , that illustrate the relative positions and motions of the planets and moons in the Solar System have been built for centuries. While they often showed relative sizes, these models were usually not built to scale. The enormous ratio of interplanetary distances to planetary diameters makes constructing

2774-535: The Working Group on Star Names of the IAU, having decided to attribute proper names to individual component stars rather than to multiple systems , approved the name Rigil Kentaurus ( / ˈ r aɪ dʒ əl k ɛ n ˈ t ɔːr ə s / ) as being restricted to α Centauri A and the name Proxima Centauri ( / ˈ p r ɒ k s ɪ m ə s ɛ n ˈ t ɔːr aɪ / ) for α Centauri C . On 10 August 2018,

2847-430: The asteroid belt . The obelisk representing the asteroid belt was added several years after the initial installation. Its display contains the only public, unguarded meteorite in the world. The Jupiter Obelisk sits at the corner of Seneca and Cayuga streets, outside the downtown Dewitt Mall, and not far from the famed Moosewood Restaurant . The model of Jupiter within the glass window is the first planet representation on

2920-439: The binary star system α Centauri AB . To the naked eye , these two main components appear to be a single star with an apparent magnitude of −0.27 . It is the brightest star in the constellation and the third-brightest in the night sky , outshone by only Sirius and Canopus . α Centauri A (Rigil Kentaurus) has 1.1 times the mass and 1.5 times the luminosity of the Sun , while α Centauri B (Toliman)

2993-401: The AB system between April 1832 and May 1833. He withheld his results, however, because he suspected they were too large to be true, but eventually published them in 1839 after Bessel released his own accurately determined parallax for 61 Cygni in 1838. For this reason, Alpha Centauri is sometimes considered as the second star to have its distance measured because Henderson's work

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3066-627: The Alpha Centauri Obelisk made it the world's largest exhibition, until the Akaa Solar System Scale Model added Proxima Centauri in 2018 at a distance of 13,370 kilometres (8,310 mi) away from Akaa. In 2014, the inner planets and Sun were removed as part of extensive construction being done to the Ithaca Commons , but have since been replaced. In 2015, a grant was approved to further expand

3139-463: The Alpha Centauri system. Several established planet-hunting teams have used various radial velocity or star transit methods in their searches around these two bright stars. All the observational studies have so far failed to find evidence for brown dwarfs or gas giants . In 2009, computer simulations showed that a planet might have been able to form near the inner edge of Alpha Centauri B's habitable zone, which extends from 0.5–0.9 AU from

3212-658: The PA of 337.1°, increasing to 5.49 arcsec through 345.3° in 2020. The closest recent approach was in February 2016, at 4.0 arcsec through the PA of 300°. The observed maximum separation of these stars is about 22 arcsec, while the minimum distance is 1.7 arcsec. The widest separation occurred during February 1976, and the next will be in January 2056. Alpha Centauri C is about 13,000 AU (0.21 ly; 1.9 × 10 ^  km) from Alpha Centauri AB, equivalent to about 5% of

3285-554: The Solar System. This gives a speed with respect to the Sun of 32.4 km/s (20.1 mi/s), very close to the peak in the distribution of speeds of nearby stars. Since α Centauri AB is almost exactly in the plane of the Milky Way as viewed from Earth, many stars appear behind it. In early May 2028, α Centauri A will pass between the Earth and a distant red star, when there is a 45% probability that an Einstein ring will be observed. Other conjunctions will also occur in

3358-663: The Sun at 5 to 6 billion years, as derived by their mass and spectral characteristics. From the orbital elements , the total mass of Alpha Centauri AB is about 2.0  M ☉ – or twice that of the Sun. The average individual stellar masses are about 1.08  M ☉ and 0.91  M ☉ , respectively, though slightly different masses have also been quoted in recent years, such as 1.14  M ☉ and 0.92  M ☉ , totaling 2.06  M ☉ . Alpha Centauri A and B have absolute magnitudes of +4.38 and +5.71, respectively. Alpha Centauri A, also known as Rigil Kentaurus,

3431-427: The Sun. α Centauri C , or more commonly, Proxima Centauri , is a small faint red dwarf ( class M ). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 ly (1.30 pc), slightly closer than α Centauri AB . Currently, the distance between Proxima Centauri and α Centauri AB is about 13,000  AU (0.21 ly), equivalent to about 430 times

3504-484: The Sun. Asteroseismic analyses that incorporate tight observational constraints on the stellar parameters for the Alpha Centauri stars have yielded age estimates of 4.85 ± 0.5 Gyr, 5.0 ± 0.5 Gyr, 5.2 ± 1.9 Gyr, 6.4 Gyr, and 6.52 ± 0.3 Gyr. Age estimates for the stars based on chromospheric activity (Calcium H & K emission) yield 4.4 ± 2.1 Gyr, whereas gyrochronology yields 5.0 ± 0.3 Gyr. Stellar evolution theory implies both stars are slightly older than

3577-400: The Sun. Its mass is calculated to be 0.1221   M ☉ . It is the closest star to the Sun but is too faint to be visible to the naked eye. The Alpha Centauri system as a whole has two confirmed planets, both of them around Proxima Centauri. While other planets have been claimed to exist around all of the stars, none of the discoveries have been confirmed. Proxima Centauri b is

3650-400: The authors detected a radial-velocity curve with a periodicity of 5.15 days, suggesting the presence of a planet with a mass of about 0.29  M E . This planet, Proxima Centauri d, was confirmed in 2022. In 2021, a candidate planet named Candidate 1 (or C1) was detected around Alpha Centauri A, thought to orbit at approximately 1.1 AU with a period of about one year, and to have

3723-445: The coming decades, allowing accurate measurement of proper motions and possibly giving information on planets. Based on the system's common proper motion and radial velocities, α Centauri will continue to change its position in the sky significantly and will gradually brighten. For example, in about 6,200  CE , α Centauri's true motion will cause an extremely rare first-magnitude stellar conjunction with Beta Centauri , forming

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3796-418: The distance between Alpha Centauri AB and the Sun. Until 2017, measurements of its small speed and its trajectory were of too little accuracy and duration in years to determine whether it is bound to Alpha Centauri AB or unrelated. Radial velocity measurements made in 2017 were precise enough to show that Proxima Centauri and Alpha Centauri AB are gravitationally bound. The orbital period of Proxima Centauri

3869-470: The exhibition by installing an exoplanet Kepler-37d station on the Moon 384,500 kilometers (238,900 mi) away. The scaled size of the Sun is given by a 27.8 cm (10.9 in) diameter circular frame repeated at the top of each 6 ft (1.8 m) tall obelisk. Centered within each sun-sized frame, the proportional size of each planet is represented by a small sphere affixed in a glass window. All of

3942-592: The first magnitude that I could perceive in all those parts which are never seene here in England . The first of these is that bright Star in the sterne of Argo which they call Canobus [Canopus]. The second [Achernar] is in the end of Eridanus . The third [Alpha Centauri] is in the right foote of the Centaure . The binary nature of Alpha Centauri AB was recognized in December 1689 by Jean Richaud, while observing

4015-497: The four inner planets within eyesight of the Sun, yet the representations of each planet appear quite small within their glass windows, and can even be somewhat hard to see. The contrast between the size of the Sun and the size of the inner planets coupled with the visible distance between them illustrate the vastness and emptiness of space. Once leaving the inner planets, a visitor to the Planet Walk turns west along Seneca Street to continue towards Jupiter. Between Mars and Jupiter lies

4088-503: The main star. α Centauri C was discovered in 1915 by Robert T. A. Innes , who suggested that it be named Proxima Centaurus , from Latin  'the nearest [star] of Centaurus '. The name Proxima Centauri later became more widely used and is now listed by the International Astronomical Union (IAU) as the approved proper name; commonly, it is frequently abbreviated to Proxima . In 2016,

4161-491: The naked eye, α Centauri AB appears to be a single star, the brightest in the southern constellation of Centaurus . Their apparent angular separation varies over about 80 years between 2 and 22 arcseconds (the naked eye has a resolution of 60 arcsec), but through much of the orbit, both are easily resolved in binoculars or small telescopes. At −0.27 apparent magnitude (combined for A and B magnitudes (see Apparent magnitude § Magnitude addition ) ), Alpha Centauri

4234-429: The name has not been used in the literature, as it is not a claimed discovery. Additional planets may exist in the Alpha Centauri system, either orbiting Alpha Centauri A or Alpha Centauri B individually, or in large orbits around Alpha Centauri AB. Because both stars are fairly similar to the Sun (for example, in age and metallicity ), astronomers have been especially interested in making detailed searches for planets in

4307-443: The north, giving an overall motion of 3686 mas/y in a direction 11° north of west. The motion of the centre of mass is about 6.1  arcmin each century, or 1.02 ° each millennium. The speed in the western direction is 23.0 km/s (14.3 mi/s) and in the northerly direction 4.4 km/s (2.7 mi/s). Using spectroscopy the mean radial velocity has been determined to be around 22.4 km/s (13.9 mi/s) towards

4380-607: The obelisk for Uranus just across Cascadilla Creek at the entrance to Thompson Park. From Uranus, visitors follow Willow Avenue northwest and cross the Carl Sagan bridge at Adams street to reach the Neptune Obelisk. The Carl Sagan Bridge, built in 2000, features nine circular windows adorned with the signs of the nine planets. The obelisk for Neptune is located just across the bridge in Conley Park. The Planet Walk

4453-488: The original planet locations were chosen not only for accuracy to scale but also to highlight local landmarks and public spaces within Ithaca. However, since the original installation of the Planet Walk the public library has moved to a new location, leaving Saturn no longer attached to a local landmark. Additionally, as of 2016-2017, the original planets in plexiglass at each station have been replaced by simple yellow disks with

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4526-433: The pair of stars Lambda and Mu Sagittarii ; it was often not clear on old star maps which name was intended to go with which star (or stars), and the referents changed over time. The name Toliman originates with Jacobus Golius ' 1669 edition of Al-Farghani 's Compendium . Tolimân is Golius' latinisation of the Arabic name الظلمان al-Ẓulmān "the ostriches", the name of an asterism of which Alpha Centauri formed

4599-407: The planet simply represented by a relatively-sized hole. Some attendant moons are now represented by tiny holes in the disks. The Sun Obelisk is located in the center of the Ithaca Commons , a pedestrian shopping area in the heart of downtown Ithaca. The round window representing the size of the Sun at this station is roughly the size of a basketball and, in this obelisk only, contains no glass. All

4672-493: The planets in major public buildings, all on similar stands with interpretive labels. For example, the model of Jupiter was located in the cavernous South Station waiting area. The properly-scaled, basket-ball-sized model is 1.3 miles (2.14 km) from the model Sun which is located at the museum, graphically illustrating the immense empty space in the Solar System. The objects in such large models do not move. Traditional orreries often did move, and some used clockworks to display

4745-424: The radius of Neptune's orbit. Proxima Centauri has two confirmed planets: Proxima b or α Centauri Cb , an Earth-sized planet in the habitable zone discovered in 2016, and Proxima d ( α Centauri Cd ) , a candidate sub-Earth which orbits very closely to the star, announced in 2022. The existence of Proxima c ( α Centauri Cc ) , a mini-Neptune 1.5  AU away discovered in 2019,

4818-470: The relative places of the stars from a binary star ephemeris . Others, like D. Pourbaix (2002), have regularly refined the precision of new published orbital elements. Robert T. A. Innes discovered Proxima Centauri in 1915 by blinking photographic plates taken at different times during a proper motion survey. These showed large proper motion and parallax similar in both size and direction to those of α Centauri AB, which suggested that Proxima Centauri

4891-1354: The relative speeds of objects accurately. These can be thought of as being correctly scaled in time , instead of distance . Many towns and institutions have built outdoor scale models of the Solar System. Here is a table comparing these models with the actual system. Belgium An Exploration of Scale National Mall, Washington, D.C. (2001) Kansas City, Missouri (2008) Space Center Houston, Texas (2008) Corpus Christi, Texas (2009) Boulder, Colorado (2021) Palo Alto, California (2022) Broken Arrow, Oklahoma (2022) Ocala, Florida (2022) Calcasieu Parish, Louisiana (2022) Dover, New Hampshire (2023) Spokane, Washington (2022) Memphis, Tennessee (2023) Chalmette, Louisiana (2023) Jonesboro, Arkansas (2023) Troy, New York (2024) Several sets of geocaching caches have been laid out as Solar System models. Solar System   → Local Interstellar Cloud   → Local Bubble   → Gould Belt   → Orion Arm   → Milky Way   → Milky Way subgroup   → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster   → Local Hole   → Observable universe   → Universe Each arrow ( → ) may be read as "within" or "part of". Alpha Centauri Alpha Centauri ( α Centauri , α Cen , or Alpha Cen )

4964-436: The star. Certain special assumptions, such as considering that the Alpha Centauri pair may have initially formed with a wider separation and later moved closer to each other (as might be possible if they formed in a dense star cluster ), would permit an accretion-friendly environment farther from the star. Bodies around Alpha Centauri A would be able to orbit at slightly farther distances due to its stronger gravity. In addition,

5037-417: The stars were permanently fixed on the celestial sphere , as stated in the works of the philosopher Aristotle. In 1718, Edmond Halley found that some stars had significantly moved from their ancient astrometric positions. In the 1830s, Thomas Henderson discovered the true distance to α Centauri by analysing his many astrometric mural circle observations. He then realised this system also likely had

5110-489: The subsequent obelisks in the Solar System model have Sun-sized glass windows containing their respective planets for the sake of comparison. The obelisks for the four inner planets are all contained within the commons area stretching north towards Seneca Street. Mercury is situated to scale about 12.7 yards (11.6 meters) away from the Sun, Venus another 10 yards (9.1 meters) away, Earth another 9.3 yards (8.5 meters) away, and Mars another 17.1 yards (15.6 meters) away. This keeps

5183-598: The walk that is easily visible, demonstrating how much bigger than the inner planets it is. To reach the Saturn Obelisk, visitors turn north and continue along Cayuga street. At the corner of Cayuga and Court street, Saturn's obelisk sits outside the former location of the Tompkins County Public Library . The rings of Saturn are clearly visible within the circular window. Visitors continue northward along Cayuga street from Saturn, reaching

5256-688: Was conceived and built prior to Pluto losing its planetary status in 2006, and the model includes the Pluto Obelisk, which is located just outside the Sciencenter on First street. The model was expanded 7,630 kilometers (4,740 mi) in 2012 to include Alpha Centauri , the star system closest to the Sun. The Alpha Centauri Obelisk is exhibited at the ʻImiloa Astronomy Center at the University of Hawaii in Hilo, Hawaii. The volcanic stone Hawaiian figure representing Alpha Centauri in female form has

5329-526: Was not fully acknowledged at first. (The distance of Alpha Centauri from the Earth is now reckoned at 4.396  light-years or 4.159 × 10  km.) Later, John Herschel made the first micrometrical observations in 1834. Since the early 20th century, measures have been made with photographic plates . By 1926, William Stephen Finsen calculated the approximate orbit elements close to those now accepted for this system. All future positions are now sufficiently accurate for visual observers to determine

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