# C/2012 S1 (ISON) - 2013/2014 naked eye comet

## C/2012 S1 ISON is coming...

According to many astronomical sources comet C/2012 S1 ISON can give a spectacular show in the sky at the end of this year. Experts warn however, that this is ONLY THE POSSIBILITY. While it is to early to predict brightness of this comet near its perihelion passage it is also highly premature to calculate its definitive orbit.

However, over two thousand positional observations of C/2012 S1 have been already made, covering more than a year, and both professionals and amateurs make first attempts to calculate its accurate orbit.

Figure 1. Data structure of Comet C/2012 S1 ISON

Since the one of the main goals of our research is to study the past motion of long period comets and their possible origin and source regions we also attempted to calculate its orbit and to analyze its dynamical history.

Basing on 1662 positional observations made up to 2013 Jan. 24 we determined an orbit, which can give us first impressions on its origin.

In Figure 1 we plot the structure of the observational material, including geocentric and heliocentric comet distance at any given moment. In the top panel one can find the time distribution of positional observations with corresponding heliocentric and geocentric distance at which they were taken. Horizontal dotted line shows the perihelion distance from the Sun, the moment of perihelion passage is outside the right border of this plot. Please note the six prediscovery observations (three of them made on December 28, 2011, at Mt.Lemmon and three from PanSTARRS made on January 28) which are placed 8 months before the discovery on September 21, 2012.

In the middle and bottom panels we present the O-C diagrams for pure gravitational orbits derived from data shown in the upper panel, where the middle panel represent non-weighted data, and the bottom - weighted data (for more details on weighting method see our Paper 1). Residuals in right ascension are shown as magenta dots and in declination as blue circles.

## Updated orbit of C/2012 S1 ISON

### Pure gravitational nominal solution for weighted data (Solution A5-2):

   Observational arc:        2011 Dec.  28 - 2013 Mar. 17
Number of observations:   3189
RMS:                      0.32 arcsec (6284 residuals used, 1.5% rejected residuals )


### Heliocentric osculating orbit

  Epoch        Perihelion time              q                 e              ω                Ω             i
2012 11 28   20131128.794258130   0.012510739735     1.000003625662   345.502937001   295.747437843    61.804103410
± 0.000484676   0.000000271399     0.000000034762     0.000133664     0.000191930     0.001090774

NG parameters:
A1 = 0
A2 = 0
A3 = 0


### Barycentric nominal original orbit (at 250 AU from the Sun), obtained from the above elements

  Epoch        Perihelion time        q               e               ω              Ω              i
1717 11 15   20131128.70850676   0.01237960876   1.00000044647   345.52456942   295.76980842    61.80191841
±0.00050085   0.00000027717   0.00000005771     0.00013812     0.00019880     0.00112649
1/aori = (-36.06 ± 2.79)×10-6 AU-1