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 C/2009 R1 (McNaught) photographed fromSlovenia on 9 June 2010 | |
| Discovery | |
|---|---|
| Discovered by | Robert H. McNaught |
| Discovery site | Siding Spring Observatory |
| Discovery date | 9 September 2009 |
| Designations | |
| CK09R010 | |
| Orbital characteristics[2][3][4] | |
| Epoch | 18 April 2013 (JD 2456400.5) |
| Observation arc | 344 days |
| Number of observations | 800 |
| Perihelion | 0.405 AU |
| Eccentricity | 1.00041 |
| Inclination | 77.031° |
| 322.62° | |
| Argument of periapsis | 130.69° |
| Last perihelion | 2 July 2010 |
| Next perihelion | ejection[1] |
| EarthMOID | 0.446 AU |
| JupiterMOID | 1.221 AU |
| Comet total magnitude (M1) | 9.9 |
C/2009 R1 (McNaught), one of more than fiftycomets known asComet McNaught,[5] is anon-periodiccomet discovered by British-AustralianastronomerRobert H. McNaught on 9 September 2009, using theUppsala Southern Schmidt Telescope atSiding Spring Observatory inNew South Wales,Australia.[6] The discovery was confirmed the same day at theOptical Ground Station telescope atTenerife.[6] After the discovery, earlier images of the comet were found from July 20, August 1, and August 18, 2009.[6] It is believed that C/2009 R1 has left theSolar System permanently.[1]
In early June 2010, C/2009 R1 was visible with binoculars in theconstellationsAndromeda andPerseus, and by June 8 it was visible to the unaided eye in a dark sky with littlelight pollution.[7] Astronomers predicted the comet to grow brighter and become widely visible in the northern hemisphere to the unaided eye by mid-[7] or late-June,[8] at which time it appeared between the constellationsAuriga andGemini.[9] Because thenew moon on June 12 provided a particularly dark night sky, the weekend of Friday, June 11 to Sunday, June 13 was expected to be the best time to view the comet,[10] and it was expected to be "an easy skywatching target for most people."[7] Late the following week, the comet remained "easy to spot in binoculars".[11]
Cometary brightness is difficult to predict, especially when, as in this case, it is the first known appearance of the comet.[5] C/2009 R1 proved to be brighter than expected, so much so thatSky and Telescope retitled an online article from "Faint Comet in the June dawn" to "Comet in the June dawn".[12] Predictions expected C/2009 R1 to eventually reach a brightness as high as magnitude 2 from June 30 to July 2, 2010,[9] the latter date markingperihelion. However, as it grew brighter, its proximity to the Sun made it difficult to see, and would make it likely only visible near the horizon at dawn and dusk.[6] The exception to this was thetotal solar eclipse on July 11 in the Southern Hemisphere (visible in theSouth Pacific, touching land atMangaia,Easter Island, and far southernChile andArgentina[13]), which allowed the comet to be seen during the day. The comet was notable for its "impressive greencoma and longiontail", which spanned 5 degrees as of 6 June 2010,[8] and its appearance was likened to an "apple on a stick."[7] By June 13, a second tail created by dust from the comet, was also visible, sharing the same green hue of the coma.[11] The green colors in the coma were caused by the presence ofcyanogen anddiatomic carbon, while bluish hues in the ion tail were produced by positively chargedcarbon monoxide andcarbon dioxide ions.[12]
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