ISON outburst

ISON observers had begun to report an “outburst” that might have increased  the comet’s brightness by up to two orders of magnitude.  While it is advisable to temper one’s enthusiasm with the knowledge that Cumbrian skies don’t always play ball with astrophotography, my trusty forecaster App indicated that there might be a short window this morning between ISON’s rising at 04:04 and the development of an overcast dawn from twilight at 05:34.

Alarm set for 03:30, swap texts with Stuart Atkinson at 03:40, load the kit in the car and off we go towards Farleton, east of Kendal, to get away from urban lights.

Remember that Cumbrian skies don’t play ball?  Well, there was a stubborn bank of low cloud on the eastern horizon (Stuart’s wider angle photos give a much better context of our session) but suddenly, in the gaps…

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 800, 30 sec. Single frame.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 800, 30 sec.
Single frame.

Amazing for a single shot, compared with the stack of 20 frames from the previous outing.  Note also that this is 30 seconds at ISO 800 whereas the previous outing was 20 x 60 seconds at ISO 1600.  I have stretched the histogram in PixInsight, and rebalanced the colour to get rid of the more extreme red glow in the clouds.

The 12MP frame can even stand cropping to enlarge it to 6x the original…

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 800, 30 sec. Single frame, cropped.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 800, 30 sec.
Single frame, cropped.

Eddington and comets

Members of the Eddington Astronomical Society met at Kendal Castle early on Sunday morning (was that really only yesterday?), to have a look for comet ISON.  There was a good turnout, which meant my photography session wasn’t quite the lonely vigil it usually is. I guess that was down to the presence of the Discovery Channel who are making a documentary about comet hunting, organised through our society Secretary the tireless astronomy outreacher Stuart Atkinson.  To be honest, I was really only there to boost the numbers, as I didn’t think the seeing would be too good – the forecast was well over 90% humidity.

But the humidity wasn’t too bad, especially in our elevated position up Castle Hill, and it was great fun to be staring at the sky with friends for a change!

For the most part, it made sense to stick with the 6 x 60-seconds at ISO 1600 on the new 300mm lens at f/5.6.  I have the dark frames and flat frames for this combination already on file.

First up, comet Lovejoy, very easy to find at an elevation of 54 degrees, well above the mist, and just north of the Beehive Cluster in Cancer.

Comet C/2011 W3 (Lovejoy) 300mm f/5.6, ISO 1600, 6 x 60 sec.

Comet C/2011 W3 (Lovejoy)
300mm f/5.6, ISO 1600, 6 x 60 sec.

 PixInsight allows stacking on the comet centre, so the starts are slightly trailed.

Then on to ISON, by star-hopping from Regulus through Mars straight down the ecliptic.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 1600, 6 x 60 sec.

ISON doesn’t present as well as Lovejoy, owing to its position nearer the horizon.

That went well, so a quick trip over to LINEAR, rising next to Arcturus.

Comet C/2012 X1 (LINEAR) 300mm f/5.6, ISO 1600, 6 x 60 sec.

Comet C/2012 X1 (LINEAR)
300mm f/5.6, ISO 1600, 6 x 60 sec.

LINEAR doesn’t look anywhere near as good as last week’s capture.

After that, I left the camera running, for twenty more frames of ISON.

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 1600, 20 x 60 sec.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 1600, 20 x 60 sec.

These have processed quite well in PixInsight to remove most of the sky glow. I might return to these frames and see if I can’t eliminate more of that background colour. I’d also like to try putting the comet back onto a set of frames stacked on the stars.

ISON, finally!

After all the fuss and hyperbole and general excitement in the astronomy press, I finally managed to get a 5am clear sky and have a go at comet C/2012 S1 (ISON), using my newly-acquired (but about fifteen years old) Nikkor ED 300mm f/4. This lens is autofocus, so no reassuring “thunk” as the focus ring hits the infinity stop. On the other hand, it fixes focus on first-magnitude Altair!

The standard for this session was six frames of 60 seconds for all shots. I also took a set of dark frames, flat frames and bias frames, and had a play with the processing suite PixInsight, which I’ve downloaded for a 45-day trial. More of that later.

SITL ISON 6x60

Comet C/2012 S1 (ISON)with Mars
300mm f/5.6, ISO 1600, 6x60sec.

ISON is in Leo, next to Mars, and still invisible to the naked eye. I couldn’t resist a little cheer when I saw this in the camera display. The stars are trailed because the six frames are stacked by aligning on the comet.

1ISON

Comet C/2012 S1 (ISON) with Mars, cropped.
300mm f/5.6, ISO 1600, 6x60sec.

Most pictures benefit from a little cropping, and this is no exception.

ISON agg

Comet C/2012 S1 (ISON) with Mars, cropped.
300mm f/5.6, ISO 1600, 6x60sec.

A bit more crop and slightly more aggressive processing, still looks okay. The tail is tinged with green as the icy comet sublimates and releases cyanogen, emphasised by Mars’s red hue.

2Encke

Comet 2P/Encke
300mm f/5.6, ISO 1600, 6x60sec.

Still in Leo, Comet 2P/Encke is a few degrees to the north.

3LINEAR

Comet C/2012 X1 (LINEAR)
300mm f/5.6, ISO 1600, 6x60sec.

Comet C/2012 X1 (LINEAR) is only a few degrees away too, in the constellation Coma Berenices.

Nova Delphini 2013

The news of this star’s change to a nova about two weeks ago has highlighted the frustrations of Cumbria-based amateur astrophotography. Work commitments, late evening sunsets, early evening moonrises, waxing gibbous / full / waning gibbous moon phases and Cumbria’s generally cloudy night time conditions have combined on this occasion to make this discovery more “internet” than “actual” for me.

Nova1

This crop from a wide angle shot taken from Shap on a “clear” night illustrates the vagaries of Cumbrian weather forecasting. I stayed for another hour after this, waiting for the clouds to pass by, but they just got thicker and thicker. Nova Delphini 2013 is there, in the top left of the frame, but it was a hurried single-frame capture.

Last night, 25th August, promised clear skies and a sunset about 90 minutes before moonrise. Off to Helsington Church, set up to catch a view to the south in the gap between sunset in the north west and moonrise in the east. As the light faded, I was joined by a family who had come to look for shooting stars, so we swapped tales of stargazing as the darkness fell. I think at least one of them has decided to come and try the Eddington Astronomical Society meetings (if you don’t already know, they are on the first Monday of the month, 7-9pm at Kendal Museum, all welcome)!

50mm 4x30 sec  5.6 1600 paths8

50mm f/5.6, ISO 1600 2 min.
4 frames of 30 sec, stacked in DSS.

Once the background light had faded, conditions were pretty good. The air felt humid, but the sky was clear. Clockwise from the bottom, Altair, Delphinus the Dolphin, “the wonky H”, Nova Delphini 2013, Sagitta the Arrow, Brocchi’s Cluster – the “Coathanger” asterism.

50mm f/5.6, ISO 1600 2 min.
4 frames of 30 sec, stacked in DSS.

Again, without the lines. Photoshop has been used to take out some of the background glow. The sky never became fully dark as the Moon rose when the Sun was only about 12 degrees below the north-western horizon.

300mm f/5.6, ISO 1600 6 min.
6 frames of 60 sec, stacked in DSS.

The contrast and the magnification are increased with a 300mm lens.

300mm f/5.6, ISO 1600 6 min.
6 frames of 60 sec, stacked in DSS.

So I caught Nova Delphini 2013 at last, although it is now below its peak magnitude of about 4. Invisible to the naked eye last night (probably due to the never-quite-dark sky), in binoculars I estimated it at about Mag 5.5 – 6.0.  The “wonky H” asterism is made up of stars that are all below Mag 6.

PANSTARRS one more last time… (actually two)

The night after my encounter with the noctilucent clouds, we were again presented with a clear sky in Cumbria.  I decided to have a last go at the increasingly remote target of PANSTARRS from my back yard, not exactly the darkest of sites.  Next door is a small hotel, and the all-night corridor light is behind a window with no curtain.  There is some intrusion from the street lights, and when the council staff in the offices behind the house leave for the night, they often leave the lights on.  Finally, if the Fire Station or Ambulance Station do their night test drill, there can be every kind of light pouring into the yard.

However, a clear forecast tempted me to try setting up the system and leaving it running all night.  A guarantee of no rain convinced me this would be okay.  Of course, only the middle part of the night would be even vaguely dark (the Sun would never be more than 13 degrees below the horizon), but at least I would fill that darkish hour with frames and not have to stay up all night.

Balancing the RA axis of the mount took on a new importance.  Remember, this is a second hand EQ3-2, tracking but unguided.  Normally I would set the counter weight in an optimum position and ensure it was slightly heavy against the turn of the motor, using a ball & socket mount to retain flexibility in camera direction and orientation.  One of the advantages of sitting by the system while gathering shots, is that the RA axis can be moved back to the optimum position.  Leaving it running all night meant that the optimum had to survive about six hours or more.

300mm f/5.6, ISO 3200 5 min.

300mm f/5.6, ISO 3200 5 min.

This is a JPEG of the unprocessed RAW frame from about 1am.  You can see how much background light needs to be eliminated.  The level of humidity in the air made this an extremely difficult task.

300mm f/5.6, ISO 3200, 15 x 5 min.

300mm f/5.6, ISO 3200, 15 x 5 min.
15 frames stacked in DSS on both stars and comet.

Deep Sky Stacker (“DSS”) lets you stack the frames by reference to the stars, or the comet, or both.  In stacking for both, DSS makes two separate stacks.  It then selects the stacked comet (eliminating the accompanying star trails) and inserts it in the reference frame for the stacked stars (eliminating the accompanying trailed comet).  A significant loss of quality results, probably not helped by the humidity in the air.

Picture saved with settings applied.

300mm f/5.6, ISO 3200, 15 x 5 min.
15 frames stacked in DSS on the comet.

Stacking only on the comet avoids this loss of quality – and retains a more dynamic feel to the picture, in my view, showing clearly that the comet is moving against the star background.  This is my preferred setting, and my favourite shot of this page.  The tail is slicing past Yildun (Mag 4.3), some 2 degrees 33 minutes of arc away.  Given that PANSTARRS is 1.86 AU away from Earth in this photo, that angle represents about 12.4 million kilometres, and the visible tail must therefore be about 15 million kilometres long.  Visible, that is, at 5 minutes exposure.  At Mag 9.5, PANSTARRS is invisible to the naked eye.

I wondered whether the choice of ISO 3200 was excessive.  The comet’s core is burned out on the screen, and there is little dynamic range in the picture.  Three nights later, I got a second chance at the same experiment.  This time I reduced the ISO to 400, and the humidity in the night air was a little lower anyway.

300mm f/5.6, ISO 400, 5 min.

300mm f/5.6, ISO 400, 5 min.

This is a sample unprocessed frame from about 1am again.  This time, I stacked only the 11 frames from the darkest hour.

300mm f/5.6, ISO 400, 11 x 5 min. Stacked on stars and comet.

300mm f/5.6, ISO 400, 11 x 5 min.
11 frames stacked in DSS on stars and comet.

The quality of the result is still very hard to control when stacking on both stars and comet, but there is a definite improvement in dynamic range compared with the ISO 3200 version.  That’s Urodelus (Mag 4.2) in the bottom right corner, by the way.

300mm f/5.6, ISO 400, 11 x 5 min. 11 frames stacked in DSS on the stars alone.

300mm f/5.6, ISO 400, 11 x 5 min.
11 frames stacked in DSS on the stars alone.

Stacking on the stars shows the comet’s movement, but blurs its important detail.

300mm f/5.6, ISO 400, 11 x 5 min. 11 frames stacked in DSS on the comet alone.

300mm f/5.6, ISO 400, 11 x 5 min.
11 frames stacked in DSS on the comet alone.

Stacking on the comet reveals its movement against the stars in a more dynamic way.  As for the reduced ISO, I think the dynamic range might be better, but there is less information overall.  On balance I prefer the ISO 3200, which is not surprising for a Mag 9.5 object using 5-minute subframes.

Anyway, the kit survived being left out all night, for two nights, which bodes well for when the nights get longer again.  That is definitely my last attempt at PANSTARRS.  It has been great fun, with cloud dodging, high humidity and low altitude at the key stage of passing M31, followed by increasingly light nights as it climbed towards the celestial pole.  It best, it has been a joy to watch and to capture.  Even at its most frustrating, it has given me bags of practice and experience to fall back on when ISON arrives this autumn.

PANSTARRS through floodlights in the sky

Inspired by several astrophotographers around the world posting images of the amazing tail developing on PANSTARRS, I decided to have another go at this comet.  There is a minor road / very long layby running parallel to the A591 on the hill between Kendal and Staveley, with unimpeded views to the north.  I reckoned it would be almost as good as driving into the Kentmere valley.

En route, I dropped by Helsington Church again, to see how the planetary alignment was changing over the Langdales.  Jupiter, Venus and Mercury were now in a straight line and all clearly visible.  I met a delightful family who had come to look at the sunset after spending the day in Kendal, and we passed such an enjoyable half hour with my binoculars spotting planets that I forgot to take photos.

On to the layby, and quite easy to set up with Polaris visible in almost enough twilight to see the mount dials.  Hold on though, that northern sky is getting brighter, not darker!

18mm f/3.5, ISO 1600 1 sec.

18mm f/3.5, ISO 1600 1 sec.

Yes the noctilucent cloud season is under way.  I can’t make up my mind about these clouds that are only visible at night – is this astronomy or meteorology?  Yes, they are really pretty to look at, with amazing variation and complexity in their structure, but that’s Cassiopeia up there, and my dark sky location is ruined.

18mm f/3.5, ISO 1600 1 sec. Two High Pass filters: 40 pixels and 4 pixels.

18mm f/3.5, ISO 1600 1 sec.
Two High Pass filters: 40 pixels and 4 pixels.

Sharpened in Photoshop, the structure resembles waves on a beach.

Prompted by a comment on Noctilucent Clouds 2013, I have experimented with sharpening these images using two Photoshop techniques: Unsharp Mask and High Pass Filter.

NLC plain

50mm f/8, ISO 1600, 3 sec.

The unsharpened image.

NLC USM 200% 4P

50mm f/8, ISO 1600, 3 sec.
Unsharp mask 200%, 4 pixels.

Unsharp mask – Photoshop’s main choice of sharpening tool, but the effect can be seen across the whole image.

NLC HP40SL HP4HL

50mm f/8, ISO 1600, 3 sec.
High pass filter 1: 40 pixels, soft light blend.
High pass filter 2: 4 pixels, hard light blend.

High pass filter – this sharpens only regions of higher contrast ie edges, that benefit from sharpening but leaves the rest of the image untouched.  I picked up this tip from Nik Szymanek in a workshop at the International Astronomy Show in Leamington.  Nik was using it to enhance detail in galaxy images, but the principle applies just as well to noctilucent clouds.  I prefer this sharpening effect which doesn’t introduce the “sharpened feel” artefact to the whole canvas.

Anyway, eventually the light fades and I catch seven reasonable frames of PANSTARRS.

PANSTARRS passing Mag 4.3 Yildun and its Mag 5.8 partner "24 Ursa Minor". Yildun is the next star to Polaris in the tail of Ursa Minor. 200mm f/5.6, ISO 3200 7x3min.

PANSTARRS passing Mag 4.3 Yildun and its Mag 5.8 partner “24 Ursa Minor”.
200mm f/5.6, ISO 3200 7x3min.

Yildun is the next star to Polaris in the tail of Ursa Minor.

North is to the lower left of the shot, and the glow from the pesky noctilucent clouds can be seen in the comet’s tail – which is pointing pretty much towards the Sun.  I shouldn’t really moan about the cloud, as the Sun is only 13 degrees below the horizon so it’s not exactly dark anyway (from an astronomical point of view).