The meteor that grazed the skies above Russia earlier yesterday (15Feb13) is not the biggest Solar system news for this year (2013). That one, though expected was not expected to have created such a visible commotion. Scientific eyes were more focused on the Asteroid that passed close to Earth. The big news is Comet ISON (Comet C/2012 S1) which is paying it’s first visit to the inner-Solar system this year.
Why is it called Comet ISON? Well, It was discovered by two Russian astronomers at `International Scientific Optical Network’ (ISON) and the media has incorrectly called it Comet ISON. The formal name (by a catalog system) is C/2012 S1 (and if they had discovered another comet on the same day that would have been called S2.. ie C.2012 S2).
Where is a Comet coming from: It’s one of many millions of far-earth objects that exit in the outer Solar system – mainly the Oort cloud (rocks, dust gases that are part of the Oort cloud, which is a giant spherical cloud of icy bodies surrounding our solar system so far away its outer edge is about a third of the way to the nearest star). Every once in a while, one of these objects gets nudged from its established orbit out there, and as a result get drawn in by Sun’s gravity inwards – into the inner solar system. As the object gets closer to the Sun (and its heat) the ice of dust and gases melt and vaporise …and thus we see a `tail of light’ (burning gas). The tail of a comet is always pointing away from the Sun.. (Solar winds.. ie particles and radiation from the Sun are pushing it outwards).
Important dates for Comet ISON C/2012 S1
- Comet ISON (C/2012 S1) will be heading closer to the Sun and passes very close to Mars on 1st October 2013.
- Comet ISON (C/2012 S1) will graze the Sun – that is to say – travel past the Sun very very close on 28th November 2013 – (very much like a Meteor grazing past Earth’s atmosphere with a streak of burning gas).
- Comet ISON (C/2012 S1) will be closest to Earth (40 millions miles!) on 26th December 2013.
About Comet ISON (C/2012 S1): According to NASA blogs,
“..ISON was discovered on Sept. 21, 2012, by two Russian astronomers using the International Scientific Optical Network’s 16-inch (40-centimeter) telescope near Kislovodsk. NASA’s Near-Earth Object Program Office, based at JPL, has plotted its orbit and determined that the comet is more than likely making it first-ever sweep through the inner solar system. Having not come this way before means the comet’s pristine surface has a higher probability of being laden with volatile material just spoiling for some of the sun’s energy to heat it up and help it escape. With the exodus of these clean ices could come a boatload of dust, held in check since the beginnings of our solar system. This released gas and dust is what is seen on Earth as comprising a comet’s atmosphere (coma) and tail. ISON will not be a threat to Earth – getting no closer to Earth than about 40 million miles on Dec. 26, 2013. But stargazers will have an opportunity to view the comet’s head and tail before and after its closest approach to the sun — if the comet doesn’t fade early or break up before reaching the sun..”.
Orbit Graphics for Comet ISON (C/2012 S1)
Below are some graphics I have generated using the Java applet provided by NASA for working out Comet positions and view angles. (I used the 3 dates (today, 26th Nov & 26th Dec) for this graphics.
The light-blue parabolic arc in these diagrams shows the path of the Comet. It is an `anti-clockwise’ path .. that is above the ecliptic plane of the Earth’s orbit. However the path of the Comet `dips’ below the orbital plane, sling-shots past the Sun and up again..and leaves the inner Solar system (top light blue line).
[Note from NASA: Additional Notes: the orbits shown in the applet are color coded. The planets are white lines, and the asteroid/comet is a blue line. The bright white line indicates the portion of the orbit that is above the ecliptic plane, and the darker portion is below the ecliptic plane. Likewise for the asteroid/comet orbit, the light blue indicates the portion above the ecliptic plane, and the dark blue the portion below the ecliptic plane. Orbit Viewer applet originally written and kindly provided by Osamu Ajiki (AstroArts), and further modified by Ron Baalke (JPL).]
..On 1st October, 2013 (figure 2 below) , this Comet will be closest to Mars. (graphics below shows this. )
On 28th November 2013, the Comet C/2012 S1 will graze past the Sun (fig 3b below).
On 26th Dec’13, comet ISON (C/2012 S1) moving further away from the Sun will be at its closest to Earth at some 40 millions miles!
Well, that’s all the basics. I’ll be dong more research and exploration on this one.. as the date of closest approach to Sun is quite an important one for me personally.. Even the date of closest approach to Mars is of interest to me…so much so..I think I may have to give this Comet a special magical name of my own. Thor’s Hammer? Centaur’s Arrow? Hern’s Spear? 🙂
More on those aspects in another blog 🙂
-Main Navasothy
(blog updated on 18Feb13 with Fig 3b above, and previous fig 3 removed. Explanation for name Comet ISON added).
QuantumPhoenix 
Hopefully will be a spectacular bright comet, even better than Hyakutake in 1996 and Hale-Bopp the following year, but I remember in 1973 when comet Kohutek was pedicted to be a daylight comet but turned out to be relatively faint and only visible from a dark site. Would be lovely to see a really bright comet with tail right across the sky as described for great comets in the distant past.