THANKS as ISON keeps GIVING!

UPDATE: 10:00 UT

It is clear that a part (reduced or fragment) of the nucleus of Comet ISON made it round the sun and is now moving away from the sun. After initally brightening and reforming a dust tail derived from its momentum as it swung around the sun, it seems to be fading now as it moves towards the outer FOV of the Lasco C3 camera of the SOHO observatory. The tail is gradually swinging around to the outbound direction. It will be interesting to see what the mission scientists can gleen from this from the multitude of data sets.

For now my rule of thumb, is really not very sciency, but if a naked eye comet reaches the Lasco C3 FOV - its going round! Not a lot of math in that, but its two from two in 3 years! Seriously though for the real science - read NASA's Comet ISON observing campaign blog which is being regularly updated by respected comet supremo Karl Battams.

UPDATE: 05:30 UT

ISON continues to brighten and a new dust tail appears to be swinging around from its transit path towards its outbound trajectory.

Image Credit: Solar and Heliospheric Observatory - Lasco C3 23:30 UT 28/11/2013

What we know about comets is alot more than we used to know, but not everything there is to know!

Like most people with a passing interest in astronomy I have been following the passage of Comet ISON as it approached perihelion. I have followed the intense debates about what might constitute a "secular light curve" and observed daily predictions and alerts about what was about to happen.

Today it has been hilarious to see people pronounce ISON dead on arrival at perihelion and wander off to their thanksgiving dinner thinking its all over red rover!

Currently twitter is ablaze with witty retorts and updates as some sort of remenant has re-emerged and continues to brighten. Most of the wise observers are doing the appropriate thing and "waiting for more information". So far on twitter it has been re-named Schrodinger's Comet, Schwartzneger's "I'll be back" comet.

Image Credit: Solar and Heliospheric Observatory - Lasco C2

As for me, I am reminded of Comet Lovejoy (2011) which surprised everyone and made it past perihelion and broke up outbound after a spectacular display at Christmas 2011. I couldn't help remembering that the tail didn't really return immediately after perhelion, until the Comet moved away from the immediate vicintiy of the Sun. In fact in 2011 Lovejoy's tail didn't really reform until it was even further out than it is now.

One thing to consider here is that the perspective from which we view these images is only two dimentional, ie whats in the image, and its very hard to tell from that perspective what at the front or behind.

Image credit: Comet Lovejoy (2011) Solar and Heliospheric Observatory - Lasco C3

Whilst comets are not made of sugar, think of creme brulee, the sugar gets heated up, some smoke comes off, it suffers intense heat, changes its composition and comes out the otherside a crunchy piece of toffee with roughly its same mass but slightly different texture. Now this is a bit of a stretch scientifically as I said, as comets are not made of sugar, but with the heat, the increase in speed, the change of direction, the resultant slowing and cooling after perihelion, there is alot going on there that we really just don't know enough about.

Which is why comets are, always have been, and always will be, incredibly undpredicatable.

Garradd Lights Up!

Comet Garradd C/2009 P1 is making nice progress towards its perihelion (closest approach to the sun) on Dec 23rd. Its a lovely comet and should brighten further of the coming months and has the best chance of becoming our next "naked eye" comet. I hope to have some better images soon.

It had a nice little double tail going about a week ago, but that seems to have swung away from us a little. My attempt to get a nice full color version was foiled by cloud knocking out the blue channel on the 24th, so I added some shorter luminance into the Blue channel. [Below]

This image, is 600sec Red, 600 secs Green and 360 secs Lum ....with comets you kind of need to get it all in one night to match it up with the background stars. I am playing with a new technique to process the stars and the comet seperately in two different layers and this can be quite tricky....and when you are missing the blue channel - I'll reset and try again another night.


However for now the image is stacked for movement of the comet against the background stars, which appear in each color channel. Comet Garradd is currently around magnitude 8.5 (according to other observers, as I haven't done any photometery on it).

UPDATE:29th July.

I finally got back to try and grab the blue channel that I missed the other night.
You actually have to start again, as the stars of course, will be in a different place. The Weather foiled me again so I jumped on board our Scope in Nerpio Spain, G17, and grabbed another color run. Here I have 40 Mins of RGB stacked for movement of the comet. G17 also has a tighter FOV so the Coma is larger here.

Image: Comet Garradd from Nerpio, Spain. 29th July 2011. (c)P.Lake

Now, thats where the fun really starts. Once you have good color you have to then create a superb image by seperating out the background stars from the Comet itself. So you do two stacks 1) a color combine in Maxim DL stacked for the coma of the comet and 2) another color combine stack of the same frames but stacked to the stars (with the comet trailed.



Then you use Photoshop>Filter>Noise>Dust and scratches (increase the Pixels to suit) and remove the trailed stars from the Comet Stack, Then use Photoshop>Select>color range to pick out (only) the Stars (and the Comet Coma) and copy to another layer, erase the Coma then add the two separate layers back together. I put the Stars on top (as they are the only thing in that layer, the comet next in its starless sky and then add a solid black background underneath and back the the opacity of the comet layer off by about 5-8% just to soften it up a little, and assist the layers to blend.

If you have done well you should have a stunning comet, and individual star colors that give real depth to the photo.

Its an amazing result, you can then treat each layer with curves and levels to make sure you have it just right.

Enjoy!

You can take your own photo here.