Astroblog: Comet C/2012 S1 ISON in STEREO H1A, great tail action (21 November 2013)

Monday, November 25, 2013

Comet C/2012 S1 ISON in STEREO H1A, great tail action (21 November 2013)


Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 21 November. 2P/Enke is to the top right and ISON is the big bright thing to the bottom left. Single frame of 26 images stacked in ImageJ and aligned then the images differenced to cancel out stars. The vertical lines are imaging artefacts from Earth being too bright (off screen).Click to embiggen	All 26 Images stacked in ImageJ, then the images differenced to cancel out stars and assembled into an animation. You will need to click on the image to embiggen it.

Comet ISON has moved further into the field of view of the STEREO H1 inager, and it looks quite stunning.

In the images above I have used Comet Al's ImageJ macro for using image differencing to really pull out the detail in the comet. Comet ISON shows amazing detail in it's tail, there may be some tail rotation, and you can see knots of material moving down the comets tail. In contrast Enke's tail is quite thin, but whips around a fair bit.

In the images below I have taken a differnt approach, using a log transform to try and bring out some of the detail in the comets tail. It gives a somewhat differnt view of the knots moving down the tail.

It tried estimating the magnitude of the comet using the reference stars Rho Ari (5.56), 38 Ari (5.18), Lambda Ceti (4.69), Mu ceti (4.28) and O Tau (3.61). It get the comet starting at magnitude 5 at the begining of the day, and magnitude 4.5 by the end of the day. This is probably an underestimate due to the spectral response of the H1A CCD camera. My estimate of the magnitude of Enke was 5.5, a full magnitude less than predicted.

However, the key point is irrepective of the absolute magnitude, the comet is steadily brightening. An analysis of the brightening of images from the 23rd.

Certainly, whatever happens in the next few days, ISON is giving us a pretty good show.


Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 21 November. 2P/Enke is to the right and ISON is the big bright thing to the bottom left. Single frame of 26 images stacked in ImageJ and aligned then LOG processed to enhance dim details. Click to embiggen	All 26 Images stacked in ImageJ, then the images LOGed to enhance detail and assembled into an animation. You will need to click on the image to embiggen it.