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C/2009 R1 (McNaught)
Comet C/2009 R1 McNaught, image taken from Slovenia, Europe on June 9, 2010
Discovered byRobert H. McNaught
Discovery dateSeptember 9, 2009
Orbital characteristics
(June 13, 2010)
1.00029 (epoch 2020+)[2]
Last perihelionJuly 2, 2010[1]
Next perihelionejection[3]

C/2009 R1 (McNaught), one of more than fifty comets known as Comet McNaught,[4] is a non-periodic comet discovered by British-Australian astronomer Robert H. McNaught on September 9, 2009, using the Uppsala Southern Schmidt Telescope at Siding Spring Observatory in New South Wales, Australia.[5] The discovery was confirmed the same day at the Optical Ground Station telescope at Tenerife.[5] After the discovery, earlier images of the comet were found from July 20, August 1, and August 18, 2009.[5] It is believed that C/2009 R1 has left the Solar System permanently.[3]


In early June 2010, C/2009 R1 was visible with binoculars in the constellations Andromeda and Perseus, and by June 8 it was visible to the unaided eye in a dark sky with little light pollution.[6] Astronomers predicted the comet to grow brighter and become widely visible in the northern hemisphere to the unaided eye by mid-[6] or late-June,[7] at which time it appeared between the constellations Auriga and Gemini.[8] Because the new 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,[9] and it was expected to be "an easy skywatching target for most people."[6] Late the following week, the comet remained "easy to spot in binoculars".[10]

Cometary brightness is difficult to predict, especially when, as in this case, it is the first known appearance of the comet.[4] C/2009 R1 proved to be brighter than expected, so much so that Sky and Telescope retitled an online article from "Faint Comet in the June dawn" to "Comet in the June dawn".[11] Predictions expected C/2009 R1 to eventually reach a brightness as high as magnitude 2 from June 30 to July 2, 2010,[8] the latter date marking perihelion. 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.[5] The exception to this was the total solar eclipse on July 11 in the Southern Hemisphere (visible in the South Pacific, touching land at Mangaia, Easter Island, and far southern Chile and Argentina[12]), which allowed the comet to be seen during the day. The comet was notable for its "impressive green coma and long ion tail", which spanned 5 degrees as of June 6, 2010,[7] and its appearance was likened to an "apple on a stick."[6] By June 13, a second tail created by dust from the comet, was also visible, sharing the same green hue of the coma.[10] The green colors in the coma were caused by the presence of cyanogen and diatomic carbon, while bluish hues in the ion tail were produced by positively charged carbon monoxide and carbon dioxide ions.[11]


  1. ^ a b c d "C/2009 R1 (McNaught)". Minor Planet Center. Archived from the original on 2016-01-31. Retrieved 2011-05-26.
  2. ^ Horizons output. "Barycentric Osculating Orbital Elements for Comet C/2009 R1 (McNaught)". Retrieved 2011-03-12. (Solution using the Solar System Barycenter and barycentric coordinates. Select Ephemeris Type:Elements and Center:@0)
  3. ^ a b See "future 1/a" value on Kazuo Kinoshita home page Archived 2010-03-25 at the Wayback Machine
  4. ^ a b "Comet in the June dawn". Sky and Telescope. New Track Media. 2010-06-09. Archived from the original on 2010-05-22. Retrieved 2010-06-09.
  5. ^ a b c d "C/2009 R1 (McNaught)". Retrieved 2010-06-08.
  6. ^ a b c d Rao, Joe (2010-06-08). "New Comet Visible in Early Morning Sky". Retrieved 2010-06-09.
  7. ^ a b Nemiroff, R.; Bonnell, J., eds. (7 June 2010). "Comet McNaught Becoming Visible to the Unaided Eye". Astronomy Picture of the Day. NASA. Retrieved 2010-06-08.
  8. ^ a b "C/2009 R1 ( McNaught )". Multitudinous Image-based Sky-survey and Accumulative Observations. Retrieved 2010-06-09.
  9. ^ Bakich, Michael (2010-06-04). "A comet flies through June's sky". Astronomy Magazine. Kalmbach Publishing. Retrieved 2010-06-09.
  10. ^ a b Nemiroff, R.; Bonnell, J., eds. (2010-06-17). "Comet McNaught Passes NGC 1245". Astronomy Picture of the Day. NASA. Retrieved 2010-06-18.
  11. ^ a b Faint Comet in the June Dawn (Google cache of the original article); Comet in the June Dawn (updated and retitled article) Archived 2010-05-22 at the Wayback Machine
  12. ^ "Total Solar Eclipse of 11 July 2010". NASA. Retrieved 2010-06-09.