Monday 30 December 2013

Solar Shadow Rings - 29th December

The sun hangs low among the trees and rooftops around mid winter and this if often more of a hinderance than anything else, however today I noticed a very curious effect I have never seen before.  I could see a strange ring patter created by the branches rapidly appearing and disappearing on the laptop screen.  I initially thought this was similar to when there is an eclipse in progress and light shining through the leaves on the trees creates crescent shaped shadows, however I quickly dismissed this as there are no leaves this time of year, and if a pin hole projection effect was happening then there would be circles projected not annuli as in the animation above.  Then it dawned on me, the Coronado SM40 etalons I use have a central obstruction that project a shadow on the image of the projected circular disks through the trees.  Well, that's my theory anyway, if anyone knows any other possibilities please feel free to comment on this post.  Either way i'm happy with the result and have ended up photographing something i've never seen before! 

Sunday 29 December 2013

Ha Full Disk 29th December

Ha-Full-Disk-Colour1 by Mark Townley
Ha-Full-Disk-Colour1, a photo by Mark Townley on Flickr.

The sun was certainly low in the sky today, and in the crisp air and deep blue sky looked very picturesque. However looking in the wavelength of hydrogen light details on the sun just pop into view that can't be seen in normal light. This shot was taken with the Coronado DS40 at f10 with a DMK31 camera. It's easy to see all the activity is focused in the suns southern hemisphere corresponding to the this dual hemispherical peaking we seem to be having this solar maximum.

CaK triband Closeup 29th December

About as close as the low sun and turbulent seeing would let me get on a cold frosty winters morning. This image was taken with the triband ERF, DS CaK filter and 70mm frac at f10 with the DMK31 camera. A good result from a setup that shows much promise!

CaK Full Disk Triband ERF 29th December

CaK-triband-colour by Mark Townley
CaK-triband-colour, a photo by Mark Townley on Flickr.

This was the first outing for my new triband ERF from Oliver Smie at Beloptik; I installed it in the dew shield of my 70mm f6 refractor where it was a perfect fit. Using my using rear mounted homemade CaK filter setup the first thing that struck me was how much shorter the exposure time was probably due to the ERFs transmission of 70% compared to the usual 5% of the solar wedge I was using as a filter. Optical quality is spot on, and later in the year I plan to do a more thorough review at the 3 wavelengths it operates at. I'm pretty pleased with this image - even given the smudge at the bottom of the disk is the branch of a foreground tree.

CaK Sun - 29th December

caK sun bw by Mark Townley
caK sun bw, a photo by Mark Townley on Flickr.

After weeks of unfavourable conditions I was able to end the year on a solar high. After spending the day rebuilding the helical focus assembly on my Coronado SM40 tube assembly I switched the Ha filters for my homemade double stacked CaK filter, seeing was awful first thing on this frosty sunday morning so used a 0.5x focal reducer to try and tame the seeing a bit. It seems to have worked and i'm pretty pleased with this result!

Friday 27 December 2013

Sauðárkrókur Aurora - 31st October

During late october we visited Northern Iceland for the week, and naturally I was quite keen to photograph the aurora, especially as we are around solar maximum and any activity should be reasonably good.  On the 31st of October we stayed overnight in the small town of Sauðárkrókur on the North coast of Iceland.  With a population of only just over couple of thousand people this was a quiet town.  On sunset that evening I was watching the aurora and weather forecasts, and for once both seemed pretty good.  At nightfall I went for a walk around the town to try and find a dark corner free from lights, however for such a small town what it lacked in people it made up for in street lights - they were all over the place; big bright streetlights.  With the border of the town the mountains on one side and the Arctic ocean on the other there simply was nowhere to go.  I tried my usual dark sky tricks and went to the rocks at the top of the beach that formed sea defences (right hand side in the pictures above), however these rocks were there for a reason as big waves crashed over the top of them with an intimidating ferocity.  

I tried aiming the camera higher in the sky to cut out the foreground horizon, but this made no difference at all; the temperature was well below freezing and the crashing waves a hundred metres to the north of me were throwing mist up into the air at an annoying rate.  All the way through this imaging session I used my trusty Canon 350D at iso800, 30 second exposure with a Sigma 10-22mm lens, at 10mm f4 all mounted on my manfrotto tripod.  I tried reducing both the exposure and ISO, and while this reduced the brightness of the skyglow it also reduced the brightness of the aurora,  which is definitely not what we are trying to achieve.  
Turning the camera to the part of the town with the least number of streetlights had a marginal improvement on sky conditions, however the foreground was still too bright for my liking, and as was also pointing in a westerly direction it meant that auroral activity was also reduced.  Despite it being quite an active auroral display with curtains of green dancing all over the sky these just weren't happening where was needed for a good picture.  Taking the land rover out to a dark spot in the mountains wasn't an option either as we'd had a drink with our meal earlier on in the evening.  Then the answer came to me from the skies as I could see a huge auroral curtain was going to pass pretty much straight overhead - point the camera vertically upwards thus getting the darkest part of the sky with the least light pollution.  
It worked!  The above animation is made up from 24 30second exposures, spanning a time frame of just over 12 minutes in total.  The auroral curtain was moving across the sky from east to west at the zenith, and was shortly followed thereafter with clouds!  However to get this I was more than pleased as i'd pretty much written off any chances of recording anything that night.  Hopefully when we revisit in february there will be clear skies again and the aurora will put on a good show for us!

Sunday 22 December 2013

Some Late Solstice Sunshine 22nd December

I made this animation late this sunday afternoon, and it typifies to me my luck with solar imaging at winter time:  a low sun, behind the trees and passing clouds making the view hazy.  Still, it is significant image taken a day after the winter solstice, the nights are now getting shorter again, the days longer, and with each passing day the sun gets ever so slightly higher in the sky.  Here's hoping 2014 is a great year for solar astronomy!

Saturday 14 December 2013

December CMEs & UK Cloud

The cloudy weather continues here for me in the UK, with any sunshine normally when i'm at work and cloudy skies on a weekend - the only time I can observe with the low sun that we have in december.  Despite the weather here on Earth the Sun keeps putting on a show; on December 12th, a pair of magnetic filaments on the sun erupted in quick succession between 0300 UT and 0630 UT. The explosions hurled a pair of coronal mass ejections (CMEs) into space. SOHO recorded the clouds racing away from the sun at approximately 1.1 million mph (500 km/s).  Although neither explosion was squarely Earth-directed, the two clouds could deliver glancing blows to Earth's magnetic field on Dec. 14th or (more likely) the 15th. NOAA forecasters estimate a 40% chance of polar geomagnetic storms when the clouds arrive.