Comet ISON, C/2012 S1 & 2P/Encke Will Perihelion A Week Apart, Encke Passing Earth At 0.48 AU On October 17, 2013.
.by Anura Guruge
Prior related post:
>> ISON & Encke close together — Apr. 11, 2013.
It is due to this conjunction that we are likely to see Comet ISON, C/2012 S1, and 2P/Encke in the night sky together as shown in the picture by Dave West below.
November 21, 2013 is when Encke perihelions. The above diagram shows quite dramatically the difference in orbital path of a common or garden periodic comet, à la Encke, and that of a sungrazer such as ISON. Notice how close ISON gets to the Sun compared to Encke.
Encke at perihelion is 0.33 AU from the Sun. ISON, in contrast, will be at 0.12 – both these distances from the center of the Sun rather than the Solar Surface. To get the Solar surface reading subtract 0.00465 AU.
In terms of separation ISON and Encke never get close enough to get in each others way or cause any perturbations.
Unlike C/2012 S1 which could be making its maiden voyage around the Sun, Encke is a routine periodic. Moreover, it has the shortest orbital period, i.e., 3.3 years, of any known comet. So it is a regular visitor, on occasions coming quite close to Earth. On October 17, 2013 it will be 0.48 AU, 44.3 million miles, away from Earth as it heads towards the Sun. That is a bit further out than the 39.9 million mile flyby expected from ISON if it survives perihelion.