67P/Churyumov-Gerasimenko

This was a tough one from Cumbria.

My interest in astrophotography embraces several categories of night sky objects, but perhaps none more so than comets.  Having met some of the Rosetta Team at the EPSC last year, I have felt a real affinity with this mission and had determined to capture comet 67P/Churyumov-Gerasimenko when visible from the UK.  Opportunities have been very few, but one came along on the night of 10 September / morning of 11 September 2015.

The comet would be visible low in the very early morning sky, so I needed a clear view to the north east.  The obvious choice would be a dark location to the east of Kendal, looking across the Yorkshire Dales, but as there was some chance of cloud in the forecasts, I opted for my tried and tested lay-by on the A591 between Kendal and Windermere.  A little light pollution could be more easily eliminated than cloud cover.

I headed out about midnight, with another comet in my sights as a practice target – it’s been a while since I did this!  The mount setup went as smoothly as could be expected, and I achieved polar alignment accurate to less than one arc minute.  That means the axis of the rotating mount was less than one sixtieth of a degree out of alignment with the rotation of the Earth.  Good enough for 5-minute exposures, and to be on the safe side I kept it down to 3-minute exposures.

First up, a stack of six frames of comet C/2014 S2 (PANSTARRS), almost overhead.  This comet had apparently been in outburst – i.e. brightening unexpectedly – but brightening from Magnitude 15 is still pretty dim.

Comet C/2014 S2 Nikon D90 on Altair Wave 115/805 ISO 1600, 6 x 180 sec.

Comet C/2014 S2 (PANSTARRS)
Nikon D90 on Altair Wave 115/805
ISO 1600, 6 x 180 sec.

You can see the tremendous amount of noise in the background, much of it from the humidity in the Cumbrian air catching and scattering stray light from nearby – even though I am using a light pollution filter between the telescope and the camera.

Here’s the same view with a Photoshopped Moon to scale:

c2014S2_square_moon

And finally a magnified section of the comet “detail”:

C2014_S2

As night turned to morning, so arrived the time I had been waiting for: 67P/Churyumov-Gerasimenko came up over the horizon only 45° ahead of the Sun and 23° ahead of the crescent Moon.  At 4:13am, when I started shooting the first frame, the comet was only 18° above the horizon.  Not the best conditions for a true once-in-a-lifetime opportunity to photograph a comet that has the ESA Rosetta probe orbiting round it, and its lander, Philae, on the surface.  By the final frame at 5:02am, the sky had become noticeably lighter as we were well into nautical twilight.

All 15 frames are used here, stacked together on the comet so that the stars appear to trail:

67P/Churyumov-Gerasimenko Nikon D90 on Altair Wave 115/805 ISO 1600, 15 x 3min.

67P/Churyumov-Gerasimenko
Nikon D90 on Altair Wave 115/805
ISO 1600, 15 x 3min.

The magnification panel shows a square that is only 5.8 arc minutes on each side.

Yes, it’s just a smudge on a dark photo covered in short lines, but that smudge is 266 million kilometres away and completely invisible to the naked eye (it’s about one sixth of one percent of the faintest star visible unaided).  Inside that smudge is the nucleus of the comet where the ESA landed a probe after ten years flying through space.  The light photons took nearly 15 minutes to reach my camera, and I left the shutter open for 3 minutes at a time.  I sat in a picnic chair in a lay-by five minutes’ drive from home, and photographed it with a camera that is normally used for holiday snaps. Happy times!

Encounter with Lovejoy

Images have been pouring in from around the world of this most photogenic comet, which is already around 4th magnitude and visible in the night sky of the northern hemisphere.  After many frustrating evenings of cloud hopping, or being completely defeated by the inclement weather,  or having the comet’s delicate tail features drowned out by a full Moon, our turn came round on Monday the 12th of January.

The normal best options of Tebay Road and Shap Summit were forecasting winds gusting to 30 and 40 mph, and looked as though they would be clouded over earlier than more northerly locations.  Keswick, in the north of the Lake District, showed great promise on the forecast charts – and there is a beautiful location above the town which is home to the Castlerigg Stone Circle.  The forecast here was for gentle breeze and cloudless skies from twilight to about 9pm.

After about an hour’s drive it was pedestrian access only, through a narrow gate on a strong spring, so it took several trips from the parked car to set up the tripod, mount, telescope, camera and all the bits and bobs that make up an astrophotography session.  The sky looked clear as the light faded, and Lovejoy was clearly visible to the naked eye before full darkness at 18:36.

The new alignment routine for the mount was really straightforward, and the handset reported alignment to within ten arc minutes in altitude and azimuth.  That’s enough for the exposure needed, so I hooked up the camera and started.

First off, a series of frames through the 300mm lens, which stacked nicely to reveal some good detail in the comet’s tail.

Comet C/2014 Q2 (Lovejoy), 12 January 2015 Nikkor 300mm f/5.6, ISO 800, 22 minutes. 22 frames of 1 minute.

Comet C/2014 Q2 (Lovejoy), 12 January 2015
Nikkor 300mm f/5.6, ISO 800, 22 minutes.
22 frames of 1 minute.

To be really critical, there are some major defects in this photo.  The ambient light from the nearby town caught the humidity in the air and presented a layer of faint light – invisible to the eye – that blurred in the wind across the long exposures.   It can be seen as a scratchy effect right across this photo.  I last saw this phenomenon when I took summer photos of Comet C/2011 L4 (PANSTARRS) passing Yildun from my back yard in June 2013.  At the time I thought this might be a combination of light, moisture and wind, and now I’m sure of it.  This defect also made replacement of the stars – eliminated by the comet processing – less satisfactory.

By the time I have collected enough of these frames the clouds are creeping in, so I switch to using the Nikon straight through the telescope, effectively an 805mm lens.  Some of the effect of the ambient light is eliminated by this move, but the result is still less than totally satisfying.  Several of the frames had to be discarded as they were degraded by cloud interference.

Comet C/2014 Q2 (Lovejoy), 12 January 2015 Altair Wave 115/805 f/7, ISO 800, 16 minutes. 16 frames of 1 minute.

Comet C/2014 Q2 (Lovejoy), 12 January 2015
Altair Wave 115/805 f/7, ISO 800, 16 minutes.
16 frames of 1 minute.

It is interesting to think that a couple of years ago, I would have been blown away by the thought that I could take photos like these.  Now, with greater experience and understanding of the techniques, I cannot help but see the imperfections.  That falls somewhere between a disappointment and a really exciting challenge!

Some you win…

Not sure if this constitutes a win or a loss, on balance.  It was a rare clear night on Saturday, after the weather system of the last week had passed, and it left in its wake a crystal clear arctic air mass with low humidity – low for Cumbria, that is, of which more later.

I took the gear up to the Shap Road lay-by and set about capturing comet C/2014 Q2 (Lovejoy).  Once the mount was aligned, I dialled in the location of the comet, listened to the wheels and belts of the mount humming away and heard the handset beep to indicate the comet was in the viewfinder.

The 300mm lens was already attached to the telescope so I took a sequence of shots using this setup first.  The light level of the full Moon was ridiculous, and Lovejoy was only 30º from the Moon.   No trouble seeing the comet, of course, but I know there is a subtle tail streaking across the field of view and I wanted to catch it.

Stacking and processing was immensely trying.  The tail is there, but it is so completely lost in the moonlight scattering off the moisture in the air that it is an impossible task to isolate it.  The more I stretch the processing of these images, the more frustrating it becomes.

300mm telephoto lens ISO 800, 70 x 20sec exposures

300mm telephoto lens
ISO 800, 70 x 20sec exposures

Against a dark sky, this would be a stunning shot.  In the “low” Cumbrian humidity of around 80%,  catching the moonlight and spreading it across the frame, it is a nightmare.

Through the telescope at 805mm focal length, it’s the same story.

Comet C/2014 Q2 (Lovejoy)  Nikon D90 on Altair Wave 115/805 ISO 800, 100 x 20sec

Comet C/2014 Q2 (Lovejoy)
Nikon D90 on Altair Wave 115/805 ISO 800, 100 x 20sec

There’s a wonderful hint of comet tails here, but they are drowned in moonlight.

Maybe I should have stuck to the “context shot”, the wide angle image that shows the brightness of the sky and the fuzzy blob of the comet.  Oh well, we get what we get, and live to get some more next time.

moon

For those that like the Moon (and yes that includes me!) here it is from that night.  I’ve toned it down a little, to show some surface detail and the tiny crescent of shadow on the edge that indicates it’s not quite full.  Once it’s safely out of the way in about a week, I’ll be back for more comet action.

Autumn targets

Another clear sky forecast tempted me out to the Tebay road again last night.  I have a list of zenith targets that will keep me going for a few sessions.

It is important to understand the limitations of your setup in astrophotography.  I avoid nebulae, as the red light they emit is mostly filtered out before it reaches my camera sensor: that’s one of the disadvantages of a standard DSLR.  Star clusters and galaxies are much more appropriate targets for me – along with comets, of course!

Polar alignment went like a dream this time, after the nightmare of the previous outing.  The handset reported both azimuth and altitude correct to 1 arc minute, so I felt comfortable taking exposures of 60 seconds plus.  With a telescope focal length of 805mm, I still think I should be able to take longer exposures than this without guiding, but further refinement will have to wait – probably when the clocks go back at the end of the month.

First up, a star cluster in Cygnus, designated NGC6910.  Not large, at 10 arc minutes, it is set against the background of the Gamma Cygni Nebula at the centre of the constellation of Cygnus.  That’s Sadr, the central star of Cygnus, just to the right of centre at the bottom of the frame:

NGC6910 with Sadr Nikon D90 on Altair Wave 115/805 ISO 800, 10x57 sec

NGC6910 with Sadr
Nikon D90 on Altair Wave 115/805
ISO 800, 10×57 sec

Next in line is another star cluster in Cygnus, catalogued by Messier as M39.  A very loose arrangement of stars covering 29 arc minutes, about the same visual size as the moon:

M39 Open Cluster in Cygnus Nikon D90 on Altair Wave 115/805 ISO800, 10x57sec.

M39 Open Cluster in Cygnus
Nikon D90 on Altair Wave 115/805
ISO800, 10x57sec.

Very slightly west of straight up overhead, seventy stars forming the faint cluster NGC 6939 (mag 7.8), conveniently located right next to spiral galaxy NGC6946 (mag 8.8):

NGC6946 and NGC6939 Nikon D90 on Altair Wave 115/805 ISO 800, 20 x 57sec.

NGC6946 and NGC6939
Nikon D90 on Altair Wave 115/805
ISO 800, 20 x 57sec.

After the Moon sets at about half past eleven, I have a go at Comet C/2011 J2 (LINEAR) which has been reported recently as having split into two parts.  At magnitude 14, it is only about 1% of the brightness of the spiral galaxy in the last photo, so it’s about as ambitious as it can be for my setup.

I catch the comet (just), but no possible trace of the split.

Comet C/2011 J2 LINEAR at Mag 13.9 Nikon D90 on Altair Wave 115/805 ISO 1250, 20x57 sec.

Comet C/2011 J2 LINEAR at Mag 13.9
Nikon D90 on Altair Wave 115/805
ISO 1250, 20×57 sec.

Patience and perseverance…

The forecast for the night of the 26th of September looked very promising, so I packed the car and set off for my Tebay Road site about at about 7.30 pm.  Full darkness was due at 9pm, so that would give me half an hour to drive and set up, plus a full hour for fine tuning the polar alignment.  It still needs practice.

Sadly the clouds had other ideas, and after a frustrating couple of hours trying to polar align through cloud gaps – in anticipation of clearing skies later – I decided to cut my losses and pack up shortly after 10pm.  Of course, that’s when the skies started to clear, in a tempting, optimistic kind of way, so I unpacked and started again from scratch.

From 11pm onwards, there followed about three hours of good conditions, occasionally excellent, in which I took about a hundred and twenty frames of various objects.  Afterwards, while the camera sat in the back of the car taking dark frames for calibration, I sat at the telescope eyepiece and manually calibrated the mount’s Periodic Error Correction system.

Good to be out under a clear dark sky!

First up, an attempt at Comet C/2014 E2 (Jacques), discovered in early March this year and now moving away from the Sun at about 32 kilometres per second (71,461 mph) at the time of writing.  Elevated 40º above the southern horizon, it makes a challenging target at Mag 10.0, given its distance of 175 million kilometres from Earth.  That part of the sky “moves” fastest, accentuating the slightest misalignment of the mount, so I restrict the exposure of each frame to just 45 seconds and push the ISO to 3200.  Here is the comet against half an hour of star movement:

C/2014 E2 (Jacques)  Nikon D90 on Altair Wave 115/805, 38x45 sec, ISO 3200

C/2014 E2 (Jacques)
Nikon D90 on Altair Wave 115/805, 38×45 sec, ISO 3200

Not my best comet photo to date, but it’s something.  Processing out the star movement:

Comet C/2014 E2 (Jacques) Nikon D90 on Altair Wave 115/805, 38 x 45 sec, ISO 3200

Comet C/2014 E2 (Jacques)
Nikon D90 on Altair Wave 115/805, 38 x 45 sec, ISO 3200

With the comet in the bag, I look to the zenith for promising targets.  NGC7789_WideThere have been a few to look forward to recently, and I am tempted by NGC 7789, a beautiful looking star cluster in Cassiopeia known as “Caroline’s Rose”.  It was discovered by William Herschel’s sister Caroline in 1783, and I have only seen it before in my wide-field photos of Cassiopeia.

Through the telescope, the camera’s field of view is only 1.68º x 1.12º and the cluster is indeed a beauty.  This shot is slightly cropped from full frame:

NGC 7789 "Caroline's Rose" Nikon D90 on Altair Wave 115/805, 20x45 sec, ISO 3200.

NGC 7789 “Caroline’s Rose”
Nikon D90 on Altair Wave 115/805, 20×45 sec, ISO 3200.

Between Cassiopeia and Perseus, the “double cluster” is next, NGC 869 and NGC 884:

Double Cluster in Perseus Nikon D90 on Altair Wave 115/805, 20x45sec, ISO 3200

Double Cluster in Perseus
Nikon D90 on Altair Wave 115/805, 20x45sec, ISO 3200

Then a very challenging edge-on spiral galaxy in Andromeda, NGC 891, showing angular size of only 11.7 x 1.6 arc minutes and Mag 9.9.  This galaxy is about 30 million light years away:

NGC 891 Nikon D90 on Altair Wave 115/805, 20x45sec, ISO3200

NGC 891
Nikon D90 on Altair Wave 115/805, 20x45sec, ISO3200

With the telescope in the region of Andromeda, it would be wrong not to take a peek, wouldn’t it?  Even with minimal processing, the Andromeda galaxy M31 makes a very big impression through the telescope and deserves a full session to itself on another night.

Andromeda Galaxy through the telescope Just 6 frames of 45 sec @ ISO 3200

Andromeda Galaxy through the telescope
Just 6 frames of 45 sec @ ISO 3200

Chasing ISON through the clouds – the full story of early morning 15 November 2013

To say that astrophotography in Cumbria is “hit and miss” would be an understatement.  It is mostly miss.  Cumbria, home to The English Lake District, is probably the wettest county in the UK.  When we are not catching the wet weather fronts coming in every few days from the Atlantic, the terrain tends to generate its own weather system, which is likewise cloudy and wet.  This forecast is not untypical:

0010 forecast

Against this backdrop, my astrophotography is based on a simple (EQ3-2) equatorial mount, an RA motor with rechargeable batteries, and my trusty Nikon D90 with a small collection of reasonably good lenses.  My favourite piece of kit at the moment is the WiFi SD card, which means I can review shots immediately on the iPad rather than on the back screen of the camera.  The temptation of further investment in hi-tech astrophotography kit is a constant companion, but yielding would only serve to heighten the frustration (by increasing the sunk cost) of all those cloudy nights.

0020 mysetup

I guess it follows that every outing is tempered with fairly low expectations, as conditions can appear good, then change at a moment’s notice.  On this particular night, my expectations were on the low side – the forecast of “clear intervals” and humidity around 90%, were not very encouraging for a target low on the horizon.  However, my good friend Stuart Atkinson from the Eddington Astronomical Society had texted the previous evening and persuaded me to set my alarm for 3.30am, so I set about planning for our excursion.

My plan for all sessions follows the same rules: (i) examine the star chart to plan the frame and check the timetable, (ii) go to the chosen location and set up whatever the prospects, (iii) don’t be disappointed if the forecast is wrong.

Get the idea?  How I envy those with reliable clear skies!

Rule number one, check the star chart.  On the morning of 15 November, ISON would rise at 04:05 and astronomical twilight would begin at 05:34.  That meant a window of 89 minutes, but for the first 40 of those ISON would be below 5 degrees.  Okay, set up and be ready by half past four, leaving an hour for capture.

At 03:30 the alarm goes off and a quick glance through the curtains suggests a “reasonable” sky.  Load the car, drive past Stuart’s to collect him, then off we go to the east of town where there is a good view to the eastern horizon across open countryside.  There is a small hill which, viewed from my observing spot, is perfectly shaped and positioned so that the ecliptic glides up above the left-hand slope.  I have used this location several times over the last month or so.

When we arrive and take a look, I realise to my embarrassment that the ecliptic has moved south since my last excursion, and is now behind the hill.  Oops!  Stuart politely mutters something about “a mistake anyone could make” as we jump back in the car and head for the next best situation, a small car park about a mile further north.  Unfortunately this car park is on the western side of the main road, so by looking east we will have to put up with the headlights from any pre-dawn traffic.

There is a bank of cloud on the eastern horizon, but it looks to be quite mobile.  Rule number two kicks in – always set up the mount and point the camera in the right direction.  If conditions improve, there might not be time to set up later.  My routine is sufficiently well practised that I can unload the mount from the back of the car and be polar aligned well enough for five-minute exposures at 300mm focal length in just a few minutes.  As always, I use the tripod unextended for stability, which means kneeling down to squint up through the polarscope while holding a small red torch to illuminate the reticle.  In a couple of minutes, Polaris is sitting nicely in the hole and I can clamp the camera to the mount.

So where’s ISON then?  I have memorised this grab from the star chart:

0030 star chart

That’s my camera frame on Porrima, in the constellation of Virgo, set at 4.5 x 3.0 degrees for the 300mm lens.  If I place Porrima in the top right corner of the frame, then slide exactly one frame down the declination axis, ISON will be in the bottom left corner.  So where’s Porrima?  Here’s the first test shot:

0040 Porrima

Porrima top right, then slide one frame down and…

0050 Where?

Cloud.  My eye is drawn to the smudge dead centre.  I now know this to be elliptical galaxy NGC 4697, but in my mind ISON will look like a smudge, and there’s a smudge dead centre.  I start to doubt my calculation and my preparation to such an extent that I miss the comet lurking behind the cloud at bottom left – exactly where it should be.

Back to Porrima, slide down the Dec axis again, that didn’t feel right, do it again, nudge it a little bit further (why did I do that?), wait a moment for the clouds to move, and grab another test shot.  All this while chatting with Stuart about clouds, traffic, whether our luck will change, whether it was worth it anyway, and suddenly…

0060 First sight

What on Earth is THAT???  I stop chatting while my brain struggles to reorganise all my expectations in the light of this capture.  It takes several seconds for the realisation to hit home – on all previous occasions ISON has been invisible in the viewfinder, invisible in binoculars, invisible even in small telescopes.  The best so far has been a faint smear in the camera frame, gathered at high ISO and long exposure.  I let out a long whispering sigh of “Ooooooooohhhhhh Gotcha!” and walk the few steps in silent anticipation to show Stuart the iPad image.  What the …..? Take a look at that, my friend, we’ve got ourselves a comet.  Suddenly we are like excited schoolboys, chuckling, giggling, I even dance a little soft shoe shuffle in celebration.  Now we start shouting at the clouds, there must be a gap coming soon?  I hurry to realign the camera very slightly and catch ISON mid frame…

0070 C:2012_S1_20131115_0511

Dead centre.  Perfect.  Only the one frame, then the clouds fill the gap.  For a moment I rejoice in my good fortune to be in the right place, at the right time, camera mounted and pointing in the right direction, mount aligned well enough for this 30 second exposure (yes, this version has been calibrated with dark and flat frames in PixInsight, and histogram stretched to improve contrast and minimise the urban glow on the clouds, but it’s still a single frame).  Then I remind myself it’s not good fortune, is it?  It’s thinking, planning, preparing and practising.  It’s taking notes of every previous comet shot and thinking how the camera, lens and exposure settings influenced the final picture.  Let’s not forget all the nights of going out and coming home disappointed.  It’s setting that alarm clock again and actually getting up, loading up, going out, setting up, being ready, waiting for the moment, and pressing the shutter.  Yes, pressing the shutter!  I hadn’t even set up the remote trigger when this gap appeared in the cloud.  This one, I took by hand.

There must have been hundreds of photos taken of ISON around the world that night, and many more in the weeks surrounding perihelion.  Some of these have revealed exquisite detail in this visitor to our skies, not to mention the contribution they make to scientific data gathering.  Anyone stumbling upon this photo in that context, will probably give it no more than a few seconds then click on by.  It’s really not that good, but… it’s mine.  I took it with my trusty Nikon and an old 300mm lens.  I can even see some detail in the tail.  All those nights of practice and rehearsal chasing PANSTARRS paid off.  After ISON had its outburst on 14 November, we were mostly clouded over.  Then the full Moon filled the night sky with light, and a few days later, ISON had its fateful rendezvous with the Sun.  This particular photo opportunity will never come round again.  From where I live, this might have been the one gap in the clouds that allowed one good shot of ISON between outburst and perihelion.  One chance, one shot, and I got it.

PS. More practice with PixInsight and stacking the other frames I took that morning, has culminated in this version, which I don’t expect to improve.  The embedded credit was added, if I might be permitted a name-dropping little boast, at NASA’s request so that they could circulate it in their outreach work.  That’s the cherry on the icing on the cake.

2013Nov15_SWhite_Adler