Astroblog: Comet C/2012 S1 ISON in STEREO H1A (23 November 2013)

Tuesday, November 26, 2013

Comet C/2012 S1 ISON in STEREO H1A (23 November 2013)

Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 23 November. 2P/Enke is to the top right and ISON is the big bright thing to the centre. 13 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

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. 26 Images stacked in ImageJ, then the images differenced to cancel out stars and assembled into an animation. The vertical lines are imaging artefacts from Earth being too bright (off screen).Click to embiggenYou will need to click on the image to embiggen it.

Comparison of Comet ISON on the 21st and 23rd in high resolution stereo H1A fits images. While there is a lot of debate over ISON's fate, I think these images show the comet is still in play.

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.

Although to the same scale comet ISON looks a trace dimmer on the 23rd vs the 21st, however this is basically image brightness scaling issues. You can see the comet apparently change significantly in brightness, but comet 2P Enke does the same in parallel. ISON has an extensive tail with what looks like knots of material moving down it, just as in the 21st.

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

I have not had a chance to do calibrated estimates of the comets. However, I think the imminent demise of ISON is less likely from these images and the medium resolution images from the 25th.


Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 23 November. 2P/Enke is to the right and ISON is the big bright thing in the centre. 13 images stacked in ImageJ and aligned then LOG processed to enhance dim details. Click to embiggen. Asteroid Kleopatra is towards the bottom of the image.	Comet C/2012 S1 ISON imaged in the STEREO satellites H1A instrument on 21 November. 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.