Crescent Moonset

On Tuesday evening 1 April the forecast looked pretty good.  As I packed the car in an optimistic mood for another go at the constellation of Leo, I glanced towards the west and saw the thin crescent Moon about 90 minutes from the horizon.  All plans changed, and I headed out to Helsington church, south-west of Kendal, with good views to the hills of the Lake District on the western horizon.

The Moon looked okay through the new combination of Nikon D90 and Altair Wave 115/805 ED Triplet (hereafter “my telescope”), but only okay.  The humidity was higher than expected, as was the wind speed, and the atmosphere low to the horizon was not going to cooperate.

This was about the best on offer:

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805mm f/7, ISO 800 1/30 sec

Of course this location and composition are one of my favourite combinations, so I switched to the 300mm lens as the Moon approached the horizon.  ISO 800 with the lens wide open at f/4, this is the series of 30-second exposures as the Moon set behind the skyline of the National Park:

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I stopped the mount motor to take one frame with the horizon stationary, which shows how much the Moon was moving over the 30 seconds:

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Clipping that horizon in Photoshop, I can use it to take the blur out of the earlier shots. I’ll leave it to you to decide whether this is an improvement.

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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.

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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.

M31 and PANSTARRS

When the Cumbrian skies cleared on 1 April we had the opportunity for several nights of catching PANSTARRS in glorious juxtaposition with the Andromeda Galaxy M31.

First up, some test frames on 1 April which turned into a nice capture that I’d had in mind for some time.

50mm f/5.6, ISO1600, 2min 4 x 30-sec frames stacked in DSS

50mm f/5.6, ISO1600, 2min
4 x 30-sec frames stacked in DSS

With a standard 50mm lens and some judicious cropping, this letterbox format shows Mirach (one of the guide stars used when finding M31: “from Mirach, hop right one star, then again, then down to the fuzzy blob”) with M33 faintly visible on the left, M31 on the right and PANSTARRS making its way in from the bottom.

Quite a windy evening, so I cranked up the ISO to 1600 and took just four good frames at 30 seconds.

On to the following night…

200mm f/5.6, ISO 1600, 15 min. 30 x 30 sec. frames stacked in DSS.

200mm f/5.6, ISO 1600, 15 min.
30 x 30 sec. frames stacked in DSS.

Quite breezy again, so I kept the exposures down at 30 seconds, but on the 200mm lens.  30 frames stacked for a 15 minute total exposure.

PANSTARRS is only about 7 degrees above the horizon here.  That presents a whole new set of problems.  At this angle, the line of sight goes through about ten times as much atmosphere as at zenith, multiplying the effect of water vapour on the incoming light.  From this location, Helsington Church, the view North-West also passes over the lights of Windermere and Ambleside, giving a street light skyglow to the bottom of the frame.  One of the beautiful features of PANSTARRS is its fan tail, glowing by reflected sunlight, so any attempt to process out the skyglow tends to eliminate the tail too.

300mm f/5.6, ISO 400, 40 min. 20 x 120 sec. frames stacked in DSS.

300mm f/5.6, ISO 400, 40 min.
20 x 120 sec. frames stacked in DSS.

Another shot I had framed in my mind, estimating there would be just enough room in the 300mm frame to put both M31 and PANSTARRS.  As the wind had dropped, I could get exposure up to 2 minutes, and grabbed 23 frames of which 20 were acceptable.

Finally on 3 April…

200mm f/6.3, ISO 200, 60 min 12 x 5 min. frames stacked in DSS

200mm f/6.3, ISO 200, 60 min
12 x 5 min. frames stacked in DSS

The birthday fairy brought me a polarscope this year, which dramatically reduces the time taken to polar-align the EQ3-2 equatorial mount.  In  a couple of minutes I can align more accurately than I used to get from 30 to 40 minutes of drift alignment using the camera.  Certainly it is good enough for 5 minute exposures at up to 300mm.  I must find time to test the alignment with longer focal length.  Anyway, this stack of 12 frames at 5 minutes each has cropped nicely.  M31 is not as clear as I would have liked (see M31: up to 200mm) but it was too low in the sky for that.

There was another very pleasing alignment on 5 April but the Cumbrian clouds had closed in.

PANSTARRS @ 300mm

A quick outing last night to catch PANSTARRS through a gap in the clouds.

300mm f/5.6, ISO 3200, 2 sec.

300mm f/5.6, ISO 3200, 2 sec.

300mm from a fixed tripod will produce short star trails very quickly, so I used the EQ3-2 mount, RA driven.  It only needs a vague polar alignment for this – as the latitude is already set, I just place the tripod with the RA axis pointing roughly to where I already know is North.  That’s it.  No sighting, no levelling, no adjustment.  Good enough for a few seconds at 300mm.

Prizewinner!

The Eddington Astronomical Society runs a photography competition for members, and the 2012 submissions were judged by astronomy journalist, author and lecturer Dr Stuart Clark.

Prime focus through Evostar 102: 1000mm f/9.8, ISO 800, 1/40 sec.

Prime focus through Evostar 102: 1000mm f/9.8, ISO 800, 1/40 sec.

Dr Clark judged this one of mine to be best in the “Through the telescope” category.  I’ll thank him in person after his lectures at the International Astronomy Show on 17th/18th May 2013.

M31 Andromeda first attempt: fixed tripod

The moment of revelation that turned me on to the possibilities of amateur astrophotography occurred on the evening of 5th March 2012, when Jeremy Hunt (not that one) came from Cockermouth Astronomical Society to present some examples of his work in Kendal.  All his slides included a note in the corner, giving details of the focal length of the lens used.  In the Q&A, I commented that there must be something amiss – if only with my understanding of the process.  If he had taken that photo with, say, the 300mm lens as noted, then he must have enlarged or cropped it because I knew the object in the sky simply wasn’t that big.  Jeremy’s answer turned my understanding on its head: “It is that big, it just isn’t that bright”.

Some of the night sky objects are visually enormous.  The reason that we cannot see them is not that they are small, but that they are faint.  Next time you look at the full Moon, imagine 12 of them arranged six by two like eggs in a dozen box.  That’s the visual size of M31, the “Andromeda” galaxy.

The key to photographing faint objects in the night sky is not magnification, but exposure.  You don’t need a long lens, but you do need to hold the shutter open for a long time.  Unfortunately for the astrophotographer, the sky moves (the Earth rotates) so long exposures of stars appear as lines rather than dots.  Holding the camera stationary for long exposure against the rotating Earth requires technology which I didn’t have for my first attempt at M31.  However, using a 50mm lens and 5-second exposures meant I could get satisfactory results from a fixed tripod.

50mm f/1.8, ISO 3200 5 sec.

50mm f/1.8, ISO 3200 5 sec.

This is a 5-second frame using a standard 50mm manual lens at full aperture.  There is nowhere for lens defects to hide in astrophotography, and the distorted shape of the stars towards the edge of the frame is a fine example of coma.  Coma is most noticeable at wide apertures, and can be fixed by stopping the lens down.  I took 40 frames of 5 seconds and stacked them using the free software “Deep Sky Stacker“.

50mm f/1.8, ISO 3200 5-sec40 frames stacked in DSS

50mm f/1.8, ISO 3200 5-sec
40 frames stacked in DSS

This is the stacked result, cropped to pick out the galaxy.  It’s not brilliant, but it is:

  • an object that is almost invisible to the naked eye
  • photographed with a standard lens from a fixed tripod
  • stacked using free software

From here, as the song says, the only way is up.