Messier 33

For some reason I never thought I would be able to photograph this galaxy.  Wasn’t it supposed to be too faint, wasn’t the surface brightness too low, wasn’t it a target for much better systems than mine?  I’ve no idea why, but that barrier had stuck in my mind.

Looking for targets on my Sky Safari App, I noticed that the declination (the celestial version of latitude) of M33 gave it a very long track across the otherwise restricted view of the sky from my back yard.  It would rise above the trees to the east and then move quite high across the open space to fall below the roofline to the west some five and a half hours later.

Time for an experiment.  On a night when cloud-free skies cannot be guaranteed, set the system running and leave it to its own devices: choose an exposure length that is short enough to run unguided but take as many frames as can be captured in five and a half hours (that’s a longer session than I’ve ever attempted).

Why unguided?  Well, a guided system has to be attended all the time.  If a cloud passes across the field of view of the guide scope, the system loses the guide star and stops guiding.  All subsequent frames probably have to be thrown away, so a guided session needs a greater guarantee of clear skies if it is to be left running while the operator sleeps.

On the 2nd of October I set up the AZ-EQ6 mount and polar aligned to one arc minute.  All other things being equal,that should allow my system’s resolution of 1.41 arcseconds per pixel to take unguided exposures of 300 seconds without star trailing.  I set the timer to 150 seconds, giving a plentiful margin to absorb other imperfections in the tracking system.  With a 30-second pause between frames, allowing the sensor time to cool down, I’d be taking 20 frames per hour.

Next morning, all had gone as planned.  That doesn’t always happen!  Clouds had interfered as expected, so I took the best 58 frames from the session to stack and process.  Despite the relative humidity of 80-90% throughout the night, the result is a most pleasing rendition of Messier 33 “The Triangulum Galaxy”.  It is about 3 million light years away and is the third largest of the “Local Group” of galaxies which includes the Milky Way and the Andromeda Galaxy.

M33 The Triangulum Galaxy
58 frames of 150 sec, ISO 800, Nikon D90 through 805mm focal length telescope, f/7

Lunar eclipse 28 September 2015

Torn between astrophotography and sleep for this one!  Our walking holiday on the Amalfi coast had finished on Saturday with a beautifully long slow lunch among friends on the terrace at Leonardo’s in San Lazzaro, and our late flight out of Naples finally put us down at Gatwick at about 11.30pm.  Overnight hotel at the airport, train journey to have lunch with my mother-in-law (where we had left the car) then a five-hour drive home to Cumbria.  We arrived home in the early evening on Sunday, ready to drop.

The Moon was set to move into the Earth’s full shadow at about 2.15 Monday morning, so I set the alarm for 1.30, as you do.  The forecast was good, it had been improving steadily over the last couple of days, and I guessed that if I woke up and looked out just before the start of the action I would be able to decide whether it was worth setting up a session.

1.30 brought glorious clear sky and an added bonus: the Moon’s position meant that I could catch at least a couple of hours from my own back yard.  That was the deciding factor – just the trusty DSLR on a tripod with the 300mm telephoto lens.  This was the view at the start, reproduced actual size in the viewfinder:

2.06am. The shadow is just visible.
Nikon D90 through Nikkor Nikon 300mm f/4 AF.
1/1250 sec f/8, ISO 800.

I decided to take one shot every 30 seconds, with the intention of stitching them together as a time-lapse video.  Of course the Moon drifted fairly quickly across the frame so the tripod had to be adjusted every few shots.

2.45am: 40 minutes into shadow.

By the time the Moon was about to disappear behind the house, it was in full eclipse.

3.12am: exposure increased to see the illumination in full eclipse.
1 sec @f/5.6, ISO 1000.

Noticeably very red to the naked eye – and the camera – it was somewhat of a disappointment in binoculars as the brightness dropped so significantly.  This could be because the Moon was almost at perigee (the so-called “supermoon”), closer to the Earth than normal and therefore deeper into the cone of the Earth’s shadow.  The air went a little murky too, so the final shots lost some definition.

Each frame had to be cropped and realigned to make the video run smoothly.  Stitched together and reduced from 4288 x 2848 to 1000 x 1000 pixels, these make a reasonable time-lapse.

Spring galaxies

Not sure why I haven’t posted for a while, as there was a spell in April when we had a string of back-to-back clear nights.  There were opportunities galore to capture springtime galaxies, and I found new locations such as Elterwater carpark to take advantage of dark skies.

17 April, with some cloud in the east, I headed to the centre of the Lake District in pursuit of “Markarian’s Chain” using my new protocol of guided 10-minute exposures.   Elterwater is a small village in the Langdale valley, but has a good accessible hard standing carpark where I set up my system.  The netbook computer guides for only a couple of hours on its old battery, so once it’s up and running I have to get on with it.

The target was Markarian’s Chain of galaxies just east of Leo, and I managed six frames of 10 minutes each before the clouds chased me down.  One frame was a little hazy, so the result is a stack of 5×10 minutes.  Darkness was good, but disadvantages of Elterwater include some very bright outside lights on tourist rental properties, and large camper vans using the carpark for overnight stays.  Also it is low altitude and a bit of a bowl for mist and condensation.

That said, there are 25 or more galaxies easily seen in this photo, and the stats are mind-boggling.  Most objects in this frame are over 50 million light years away, and the galaxy in the bottom left corner (M87) is a million light years from M84 at the right hand end of the chain.  Galaxy NGC4388 at bottom right (the “smile” on the face at the front of the chain) is 11th magnitude, which makes it less than 1% of the brightness of the faintest object visible to the naked eye from a dark location.  The galaxies are gravitationally bound to one another, despite the incomprehensible distances involved.  All that with a Nikon D90!

Markarian’s Chain: M84, M86 and others, plus M87 in the lower left corner, all in the Virgo Cluster
Nikon D90 on Altair Wave 115/805 (f/7), ISO 400
50 minutes: 5 frames of 10 minutes each.

On the night of 18 April, M101 was at zenith, captured here in 9 frames guided at 10 minutes each.  That’s a total of an hour and a half on one galaxy, which is a lot for me (until now!).  10 minutes is fantastic for light gathering, but pushes the boundaries of long exposure v potential for disturbance.  If a car drives past, or if a strong gust of wind nudges the system – or even if the guiding software momentarily loses sight of the guide star – then the whole 10-minute frame is spoiled.  These were taken in the long layby on the A591 outside Staveley, which is sheltered but by no means unused, and I was fortunate that there was almost no traffic that night.

M101
Nikon D90 on Altair Wave 115/805 (f/7), ISO 400
90 minutes: 9 frames of 10 minutes each.

On 21 April, I was back on the Shap Road with fellow members of the Eddington Astronomical Society, and my target this time was M106, again at zenith.  Thirteen frames of 10 minutes were reduced to nine on closer inspection (gusts of wind spoiled four), so this is also a stack of 9×10 minutes.  In calm conditions I seriously wonder whether the DSLR could cope with 15 minutes per frame; with the ISO at a comfortable 400, there is very little by way of glow from the sensor.  What level of detail might be possible with three or four hours total exposure?

Nikon D90 on Altair Wave 115/805 (f/7), ISO 400
90 minutes: 9 frames of 10 minutes each.

Finally, on 26 April, a quick experiment from my own back yard.  With high buildings and trees obstructing a clear view of the sky, it’s not possible to go through the star alignment process on the GOTO handset, so I’m restricted to polar-aligning the mount by eye.  I hoped that with 5-minute frames, the guiding system might smooth out the alignment error.  Here’s 20×5 minutes on M51, with the ISO wound up to 800, suggesting this has some promise.  There’s light pollution from next door’s uncurtained landing window, so a light pollution filter might be a useful addition to the armoury.

Nikon D90 on Altair Wave 115/805 (f/7), ISO 800
100 minutes: 20 frames of 5 minutes each.

Moon and Saturn

The chart said these would be due south at 3.30am on 21 March, elevated 18° above the horizon.  A quick check the previous evening showed that the gap between the tree and the neighbour’s house, viewed across the top of my shed, would just give me an unobstructed view.

I was still awake at 1am, kept getting up to see whether the clouds had cleared, and was surprised when the alarm woke me at 3.00.  I opened the west-facing bedroom window to stick my head out, and saw clear sky to the south – with the Moon exactly as predicted.

Set up the tripod, mount the new Altair Wave 115 – with the Nikon attached as if to an 805mm f/7 lens.  After years of SLR photography, I still think in terms of focal length rather than objective lens diameter.  The field of view with this combination is 1.68° x 1.12°, perfect for this shot as Saturn was just 1.2° from the Moon.

Focusing was very easy with the Bahtinov mask and the dual speed focuser, especially with the Nikon’s LiveView screen zoomed right in on Saturn.  Even though Saturn is a ringed disk rather than a point of light, the changing shape of the view through the mask was obvious.

At ISO 400, trial and error gave 1/250th of a second exposure for the Moon, and 1/30th for Saturn.  By 4am I was quickly layering these together in Photoshop…

The Moon and Saturn separated by one degree
805mm f/7 ISO 400 1/250 sec (Moon) 1/30 sec (Saturn)

…and back in bed at 4.15, just as the clouds returned.

Supernova SN 2014J in M82

This is one of those quite gratifying occasions when a major discovery in the sky falls within the relatively easy reach of the amateur astrophotographer.

On 21 January, astronomy news feeds were reporting a supernova becoming visible in galaxy M82, close to the constellation of Ursa Major. Here in Kendal, we hadn’t seen much of the night sky since November, but on the night of 22 January, I looked out of the back door just before bedtime and saw clear skies with only the occasional cloud blowing over. An hour invested here would probably bring rich rewards.

In about five minutes I had managed to set up the mount, polar align, balance and focus the 300mm AF-Nikkor (on a conveniently placed Jupiter – that autofocus is a gem!). The next 20 minutes were spent in all sorts of contortions trying to find M82 in the viewfinder. I had set the tripod very low, to minimise vibration, and M82 was very high in the sky. That’s easy with a right-angle viewer on a telescope, less easy in a camera viewfinder. M82 is invisible to the naked eye, so each reframe needed a fresh exposure of about a minute to confirm, but the more frustrating problem was that M82 is so close to the celestial pole that minor adjustments of the mount go off in unexpected directions.

Once found and centered, I managed four reasonable frames of two minutes each before the clouds closed back in. Rather than stack using the usual software, I combined these as simple layers in Photoshop, boosted the contrast a little and tuned out the worst of the background glow of Kendal’s street lights.

About a year ago, I had shot M82 and its more circular companion M81 as a short experiment to mark a galaxy pair that I’d like to image later in more detail. Here is last year’s image, without the supernova (using the old manual 300mm lens):

M81 and M82, 1 March 2013
300mm f/5.6, ISO 400 30 minutes.
10 frames of 3 minutes.

Then the current image with the brand new dot in M82 (new lens, same focal length, better glass):

M81 and M82, 22 January 2014
300mm f/5.6, ISO 400 8minutes.
4 frames of 2 minutes.

I say brand new, but this galaxy is about 11 million light years away, so this event happened a long time ago and the news has taken a while to reach us.

Before, and after. Not bad for an hour in the back yard between the clouds.

…and for those who couldn’t spot the difference, here it is!

 

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.

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.
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.

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.

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.
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.

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.

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.