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

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


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:


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


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.

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!