Comet C/2012 S1 (ISON) could be the brightest object in December night sky

 21 September 2012  C/2012 S1 (ISON) was discovered on 21 September 2012.
 28 November 2013 In November 2013, comet ISON will pass the Sun at just 0.012AU (~1.1-million kilometres above the solar surface), classifying it as a Sun-grazing Comet, and potentially a spectacular one! It will come to perihelion (closest approach to the Sun) on 28 November 2013. The comet will pass approximately 1,100,000 kilometres (680,000 mi) above the Sun's surface. Its orbit is nearly parabolic, which suggests that it may be a dynamically new comet coming freshly from the Oort cloud
 6 December 2013  On closest approach, the comet will pass about 0.42 AU (63,000,000 km; 39,000,000 mi) from Earth on 26 December 2013 ...
 1 October 2013  ...and it will pass about 0.072 AU (10,800,000 km; 6,700,000 mi) from Mars on 1 October 2013
 14–15 January 2014 Earth is expected to pass through the orbit of the comet on 14–15 January 2014, which may result in the creation of a meteor shower
 Visibility  At the time of its discovery, the comet's 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.
 August 2013 During August 2013, it should become bright enough to be visible through small telescopes or binoculars, becoming visible to the naked eye by late October or early November and remaining so until mid-January 2014.
 October 2013 In October, the comet will pass through the constellation Leo, passing near Leo's brightest star Regulus and then passing near Mars in the night sky, and these brighter objects might make the comet easier to locate.
 November 2013 In November, when the comet is brighter, it will sweep another bright star in our sky, Spica in the constellation Virgo, and another planet, Saturn.
Around the time the comet reaches its perihelion on 28 November, it may become extremely bright if it remains intact, probably reaching a negative magnitude. It is expected to be brightest around the time it is closest to the Sun; however, it may be less than 1° from the Sun at its closest, making it difficult to see against the Sun's glare.
 December 2013  In December, the comet will be growing dimmer, but, assuming that it remains intact, it will be visible from both hemispheres of Earth, possibly with a long tail.
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. Comet Kohoutek and C/1999 S4 did not meet expectations, but if comet C/2012 S1 does not fragment, it could look similar to the Great Comet of 1680, the Great Comet of 2007, or C/2011 W3 (Lovejoy). The brightest comet since 1935 was Comet Ikeya–Seki in 1965 at magnitude −10. Comet C/2012 S1 (ISON) will be well placed for observers in the northern hemisphere during mid to late December 2013.