C/2012 S1 From Wikipedia, the free encyclopedia Jump to: navigation, search Ambox currentevent.svg This article documents a current event. Information may change rapidly as the event progresses. (November 2013) C/2012 S1 Comet ISON (C-2012 S1) by TRAPPIST on 2013-11-15.jpg C/2012 S1 as captured by TRAPPIST Discovery Discovered by Vitaly Nevsky and Artyom Novichonok at ISON-Kislovodsk, Russia using a 0.4-m reflector (D00)[1] Discovery date 21 September 2012 Orbital characteristics A Epoch 14 December 2013 (JD 2456640.5)[2] Perihelion 0.01244 AU (q)[2] Eccentricity 0.9999947[2] 1.0002 (epoch 2050)[3] Orbital period Ejection trajectory (epoch 2050)[3] Inclination 62.4°[2] Last perihelion 28 November 2013[2] C/2012 S1, also known as Comet ISON or Comet Nevski–Novichonok, is a sungrazing comet discovered on 21 September 2012 by Vitali Nevski (Виталий Невский, Vitebsk, Belarus) and Artyom Novichonok (Артём Новичонок, Kondopoga, Russia).[4] The discovery was made using the 0.4-meter (16 in) reflector of the International Scientific Optical Network (ISON) near Kislovodsk, Russia.[1] Data processing was carried out by automated asteroid-discovery program CoLiTec.[5] Precovery images by the Mount Lemmon Survey from 28 December 2011 and by Pan-STARRS from 28 January 2012 were quickly located.[6] Follow-up observations were made on 22 September by a team from Remanzacco Observatory in Italy using the iTelescope network.[1][7] The discovery was announced by the Minor Planet Center on 24 September.[6] Observations by Swift in January 2013 suggested that C/2012 S1s nucleus was around 5 kilometers (3 mi) in diameter.[8] Later estimates were that the nucleus was only about 2 kilometers (1 mi) in diameter.[9] C/2012 S1 was at first suspected to have disintegrated near perihelion.[10][11] But CIOC members suspect some small fragment of C/2012 S1 has survived perihelion passage as a coma has been detected.[10][12][13] Contents [hide] * 1 Orbit * 2 Brightness, observations, and visibility * 3 Name * 4 Media coverage * 5 Notes * 6 References * 7 External links Orbit[edit] C/2012 S1 came to perihelion (closest approach to the Sun) on 28 November 2013 at a distance of 0.0124 AU (1,860,000 km; 1,150,000 mi) from the center point of the Sun.[2] Accounting for the solar radius of 695,500 km (432,200 mi), C/2012 S1 passed approximately 1,165,000 km (724,000 mi) above the Suns surface.[14] Its trajectory appeared to be hyperbolic, which suggested that it was a dynamically new comet coming freshly from the Oort cloud.[15][16] Near perihelion, a generic heliocentric two-body solution to the orbit suggests that the orbital period was around 400,000 years.[17] But for objects at such high eccentricity, the Suns barycentric coordinates are more stable than heliocentric coordinates.[18] The orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. Using JPL Horizons, the barycentric orbital elements for epoch 1 January 2050 generate a hyperbolic solution.[3] On its closest approach, C/2012 S1 passed about 0.07248 AU (10,843,000 km; 6,737,000 mi) from Mars on 1 October 2013, and the remnants of the comet will pass about 0.43 AU (64,000,000 km; 40,000,000 mi) from Earth on 26 December 2013.[19] Shortly after its discovery, similarities between the orbital elements of C/2012 S1 and the Great Comet of 1680 led to speculation that there might be a connection between them.[20] Further observations of ISON, however, showed that the two comets are not related.[21] Earth will pass near the orbit of C/2012 S1 on 14–15 January 2014, well after C/2012 S1 has passed, at which time micron-sized dust particles blown by the Suns radiation may cause a meteor shower or noctilucent clouds;[22][23] however, both events are unlikely. Because Earth only passes near C/2012 S1s orbit, not through the tail, the chances that a meteor shower will occur are slim.[24] In addition, meteor showers from long-period comets that make just one pass into the inner solar system are very rare, if ever recorded.[25] The possibility that small particles left behind on the orbital path—almost one hundred days after the nucleus has passed—could form noctilucent clouds is also slim. No such events are known to have taken place in the past under similar circumstances.[25] Orbital position of C/2012 S1 on 11 December 2013 after perihelion File:Comet ISON Approaches Perihelion.ogv Visualization of the orbit of comet ISON as it moves into the inner Solar System in 2013 Brightness, observations, and visibility[edit] The path of C/2012 S1 (ISON) from December 2012 through October 2013 as it passes through Gemini, Cancer, and Leo At the time of its discovery, C/2012 S1s apparent magnitude was approximately 18.8, far too dim to be seen with the naked eye, but bright enough to be imaged by amateurs with large telescopes.[26][27] It then followed the pattern of most comets and increased gradually in brightness on approach to the Sun. As of 15 November 2013 (2013-11-15)[update], ten spacecraft have detected C/2012 S1.[28][29][30] C/2012 S1 was first imaged by the Swift and Deep Impact spacecraft in January and February 2013, and shown to be active with an extended tail. In April and May 2013 the Hubble Space Telescope (HST) measured C/2012 S1s size, and the color, extent, and polarization of its emitted dust. The Spitzer Space Telescope (SST) observed C/2012 S1 on 13 June and estimated carbon dioxide production at about 1 million kilograms (2.2 million pounds) per day.[31] From 5 June to 29 August 2013, C/2012 S1 had an elongation less than 30 degrees from the Sun.[32] No obvious rotational variability was detected by either Deep Impact, HST, or Spitzer. Amateur astronomer Bruce Gary recovered it on 12 August 2013 when it was 6 degrees above the horizon and 19 degrees from the Sun.[33] Due to it brightening more slowly than predicted, C/2012 S1 only became visible through small telescopes during early October 2013.[34] On 1 October 2013, C/2012 S1 passed within 0.07 AU (10,000,000 km; 6,500,000 mi) of Mars. Between 29 September and 2 October, the Mars Reconnaissance Orbiter (MRO) detected C/2012 S1.[35] The twin STEREO spacecraft began detecting C/2012 S1 in the second week of October.[36] October 2013 images of C/2012 S1 displayed a greenish tint, probably attributable to the release of cyanogen and diatomic carbon.[37] On 31 October 2013, C/2012 S1 was detected with 10×50 binoculars.[38] Comet C/2012 S1 (ISON) seen from the Mount Lemmon SkyCenter on 8 October 2013, as it passes through the constellation of Leo On 14 November 2013, C/2012 S1 was reported to be visible to the naked eye by experienced observers located at dark sites.[39] ISON had an appearance similar to comet C/2013 R1 that is also visible to the naked eye. C/2012 S1 was not expected to reach the naked eye magnitude of 6 until mid-November,[32][40] and may not be observable by the general public until it brightens to about magnitude 4.[34] On 17–18 November, when C/2012 S1 was brighter and much closer to the morning twilight, it passed the bright star Spica in the constellation Virgo.[41] But due to the full moon and glow of twilight, C/2012 S1 had not become bright enough to be seen without optical aid by the general public. On 22 November C/2012 S1 started to drop below Mercury in the bright twilight.[42] SOHO started to view C/2012 S1 on 27 November first with the LASCO coronograph.[43][36] On 27 November ISON brightened to magnitude −2[note 1][44] and passed Delta Scorpii.[45] Around the time it reached perihelion on 28 November, it may have become extremely bright if it remained fully intact. Predicting the brightness of a comet is difficult, especially one that will pass so close to the Sun and be affected by the forward scattering of light. Originally media sources predicted it might become brighter than the full Moon,[15][16] but based on more recent observations, it was only expected to reach around apparent magnitude −3 to −5, about the same brightness as Venus.[40][46] In comparison, the brightest comet since 1935 was Comet Ikeya–Seki in 1965 at magnitude −10, which was much brighter than Venus.[47] Comet ISON, imaged by the Hubble Space Telescope on 10 April 2013—near Jupiters orbit;[48] also, enhanced (coma model ratio) version In a February 2013 study, 1,897 observations were used to create a light curve. The resulting plot showed C/2012 S1 increasing its brightness relatively quickly at R+4.35.[Unit?][49] If this had continued to perihelion, C/2012 S1 would have reached magnitude −17, brighter than the full moon. It had since exhibited a slowdown event, however, similar to the ones exhibited by many other Oort cloud comets, among them C/2011 L4. Therefore, C/2012 S1s brightness increased less quickly than predicted and it did not become as bright as expected. Recent observations of C/2012 S1 suggested that, even if it remained intact, it may only brighten to about magnitude −6.[46] It had been determined that this is a baby comet (i.e. an object with a photometric age less than four comet years).[49] The temperature at perihelion had been calculated to reach 2,700 °C (4,890 °F), sufficient to melt iron. Additionally, it was within the Roche limit, meaning it might disintegrate due to the Suns gravity. C/2012 S1 was expected to be brightest around the time it was closest to the Sun; but since it was less than 1° from the Sun at its closest, it would have been difficult to see against the Suns glare.[50] In December, C/2012 S1 will grow dimmer, and it might visible from both hemispheres of Earth. [26] C/2012 S1 will be well placed for observers in the northern hemisphere during mid to late December 2013.[51] After perihelion, it will move north on the celestial sphere, passing within two degrees of Polaris on 8 January.[27] ISON may be visible to the naked eye until early January 2014.[15][27] Name[edit] For more details on this topic, see Naming of comets.
Posted on: Fri, 29 Nov 2013 16:03:06 +0000
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