45 Minutes in the life of a Quiescent Prominence - 8th September

Lovely clear blue skies this morning, only a couple of degrees above zero at dawn, won't be long till we have a frost I think... The sun was completely blank, nothing to see apart from the glorious proms. So, with deep blue skies and no sign of cloud imminent I decided to go for an animation with the Coronado SM90ii, 2x Cemax barlow and the GH3 IMX174 camera. The movement is subtle, but there is a lot going on when you look closely...

Promtastic Sunday - 8th September

The suns disk is blank, really blank!  not much at all is happening, but today all the action was around the limb in the form of prominences.  There were lovely sets on both limbs in the northern hemisphere.  This image has an inverted disk with a limb composite, taken with the Coronado SM90ii and the PGR Grasshopper camera.

Calcium Full Disk 25th August

It seems to have been a while since I imaged in calcium wavelengths, so on Sunday afternoon I decided to go for a full disk with the skywatcher ED80 stopped down to 60mm, coronado 2x cemax barlow and the Grasshopper camera with the homebrew calcium filter.  It was interesting to see the polar faculae are noticeably larger in size than plage bright points mid disk.  The polar faculae in calcium match up very well position wise with these features in the 2 disks prior to this post.

Sodium Full Disk 25th August

I was going for the trio of full disks on Sunday so had to shoot a sodium disk with the Daystar Quark.  There is little to see but around the poles the polar faculae synonymous with solar minimum conditions were visible.  Taken with the Tecnosky 60mm f6 scope.

Ha Full Disk - 25th August

The sun at first sight appears blank again, however a number of small filaments can be seen on the disk; at the south pole the diffuse filaments represent the proms in the previous 2 posts that I did an animation of.  Mid disk a filament and brighter plage are the remnants of the active region that first appeared at Easter time, now with a coronal hole also associated this region is now on it's 4th rotation of our star.  In the northern hemisphere the filaments are associated with the magnetic fields due to sub surface cycle 25 jet stream activity, with a small emphemeral region at the 2 o'clock position being cycle 25.  At the north pole polar faculae can be seen shining through the chromosphere as bright points.  Throw in a few proms too and there is more than meets the eye.  Taken with a Lunt 50C etalon double stacked with a Daystar Quark, Baader solar telecompressor and a FLIR Grasshopper 3 camera.

Still Raining on the Sun - 24th August

Saturday gave me some free time and with blue skies I decided to try another animation of the active prom region that has been rounding the limb.  I got 140 frames covering 45 minutes real time to produce this animation.  I included an Earth scale just so you can see how small we are in the bigger picture of things that happen on our star.  Taken with the Coronado SM90, 1.6x barlow and Grasshopper IMX174 camera.

Descending Prominence Knots and Coronal Rain - 23rd August

Friday started grey and misty for me which was frustrating given the forecast was for blue skies, however by early afternoon all the low cloud burnt off to reveal really quite blue skies without the usual haze. I went out and set up and also pleasantly surprised the SSM was coming in with seeing values in the region of 2-3 arc seconds:

I knew this was too much to bother with the HaT so got the SM90ii out. With nothing of note on the disk worth pursuing, I went hunting for the big prom that was visible; Starting off with a 3x barlow it quickly became clear that this scale was going to be too much, so dropped down to the 2x, again too much (I was running files through AS3 on the fly), however dropping down to a magnimax barlow nosepiece giving me a image scale of ~1.6x straight away it was obvious on firecapture this scale to image at was working with the seeing. I decided to opt with the smaller image scale knowing I would get something I could work with rather than waste time (and hard drive space) chasing an elusive super close up that might or might not work out.

Using the Grasshopper with the IMX174 chip I went in automated mode, using the Hinode solar guider to keep the scope squarely on the prom and the SSM and plugin in FC to set a threshold so I was only recording the sharpest of frames. Despite the prom looking pretty quiescent on GONG I could tell from looking visually through the SM90 there was quite a bit of subtle activity with it so decided just to blitz it, and get as much data as my diminutive hard disk would allow. A few passing fluffy clouds interrupted what would have been a perfect run but these have little effect on the result. I managed just shy of 40 minutes of observation from 14.57 to 15.36. I decided to leave the less sharp images in the sequence as they keep the continuity of the movement that was visible, only deleting the cloud sections. I ended up with an animation of 120 frames spanning nearly 40 minutes, so a cadence of about 3 frames a minute.

The result pleasantly surprised me. I aligned in ImPPG with several alignment iterations as Photoshop just locked up every time. I know the image is inverted to the norm, but is looks strange raining the wrong way. It then got me looking around as to whether coronal rain is the right terminology for it, as, traditionally coronal rain is associated with post flare loops, and there was definitely no flaring with this! Turns out there are different categories of coronal rain with the rain in this type being called 'descending prominence knots'. The rain part refers to the condensation of cooler material - plasma on the sun as opposed to water on Earth, however in post flare loops the rain is guided and forms along the magnetic field lines, whereas in this situation the field lines in a prominence are flat (compared to looped) so the rain forms due to temperature differences (instability) in the corona. As the environment is 'viscous' they fall back towards the sun at less than terminal velocity. Given all frames are timestamped and we know image scale it would be quite possible to work out a velocity for these 'descending prominence knots' (or raindrops), i've not done this but theory suggests a few tens of kilometres a second. The science in all this is really very new, this paper https://iopscience.iop.org/article/10.1 ... /1/21/meta from 2014 is perhaps the most comprehensive I found, and heavy going in parts still gives useful information.

The STEREO image suggests a couple of brighter points about to round the limb at these low southern latitudes (remember my ani is vertically inverted), given there latitude this means they are cycle 25, and this is also contemporaneous with the latitude of the prom, so, definitely the area to keep an eye on this weekend.

Hope you like my cinema, just about to head out and see what I can get this morning.