Events are moving rapidly in the story of C/2013 A1 Siding Spring and its close approach to Mars in 2014.
Leonid Elenin and the ISON team have made new measurements of the comets position, the refined orbit brings it to within 41,000 Km from Mars (we still can't exclude an impact yet though).
Talk about luck, Astroswanny notes that the Mars atmospheric analysis orbiter MAVEN arrives a few days before the comets closest approach.
While the close approach can be seen with telescopes, if you don't have a telescope then you can watch the event in the STEREO H2A instrument.
Hopefully I can get some images of the comet over the next few days and contribute to the effort of making its orbit more accurate.