continuum filter

Solar Images in H alpha, Calcium K and Visible

Most of my solar images have been taken in visible or H alpha , the Baader CaK filter in conjunction with a Herschel wedge provides a relatively “cheap” way of imaging in CaK.

Images in Visible light give detail of the photosphere , which we can consider as the Suns “surface”, above this is the chromosphere, the upper part of which is viewed in H alpha and mid section can be viewed in Ca K wavelengths. (Not quite this simple as there is some overlap, but broadly works this way) The Cak is sensitive to magnetic fields and the stronger the magnetic filed the brighter the image, this gives more detail of the plages around sunspots and more detail of how magnetic field varies in these areas.

After some time setting up a system to image in all 3 wavelengths a fine clear day arrived on Friday 22nd June and I imaged the sunspots and prominences , then went away, which is why I’ve only just finished processing images.

All images were taken using a mono CCD camera : Imaging Source DMK41, the H alpha images were taken using a Coronado PST, the Visual White light images with a Herschel wedge with a ND.3 filter and Baader continuum filter on the camera, using a Skywatcher Evostar 120 refractor. The Cak images were taken with a Baader Cak filter attached to DMK41 and using a Herschel wedge with either a ND.3 or ND 0.6 filter on Skywatcher  ST102 ( for full disc) and / or Skywatcher Evostar 120. All Images were 600 frame avi’s stacked in AutoStakkert, wavelets tweaked in Registax 6 and final processing in Photoshop CS6. Not having imaged for a while I soon realised that I needed to do some cleaning before the next session as the “dust bunnies”  were more numerous than usual, luckily I was either able to manipulate image to avoid most of them or eliminate them in processing.

I have left the images as mono as features show up better for comparison rather than processing in false colour.

Whole disc in CaK and H alpha, no prominences visible in CaK.














Main surface features in Cak in Evostar 120, left to right : faculae, AR2715, AR2713


















Faculae in Halpha x2 barlow



AR2715 In Cak, Vis,  H alpha (x2 Barlow)









AR2713 in Cak, Vis , H alpha (x2 Barlow)









Prominences x2 Barlow






Comparison of Visible and CaK images of sunspots. (6th Oct2017)

Below are 4 pairs of images of sunspots 2683 (large one) and 2682 ( smaller one , only in first two images) taken on 6/10/17. No H alpha was taken as at the end of this sequence high  cirrus stopped any further imaging, in fact last CaK shot is diminished by the entrance of the high cirrus. Experiences of using CaK so far suggests that it brings out more detail in the faculae (bright spots) around sunspots , these are linked to the intense magnetic fields associated with sunspots. The other noticeable effect with CaK is the longer exposure time required, discussion at the IAS suggested that since the filter is double stacked, it requires a Herschel wedge without a ND.3 neutral density filter as supplied by Astrograph ( it’s on my list for Santa!!) , also choice of barlows can be crucial depending on coatings, will see what happens when I’ve tried the new Herschel wedge.

The images are laterally inverted, I haven’t flipped them.

Images are below and are self explanatory.

Pete H