Calcium K Solar Image

....and here is the second image instead of getting to bed. Slightly different composition and processing.

Calcium-K Quarter by astrograph ltd, on Flickr

Wow !! Fantastic images. Well worth burning that midnight oil.

Thanks for sharing them.

These are wonderful images, Rupert.

I have coloured this the normal blue but am experimenting with other colours to see what will bring out the contrast more.

I've always been intrigued by these colour choices. There does seem to be a convention that images in certain wavelengths are coloured in a particular way. However, it seems to only loosely relate to where the frequency of that colour choice is on the visible spectrum.

For instance, H-alpha at 656.3nm is firmly in the red part of the visible spectrum, but most solar images that I see published at this wavelength are coloured orange. And here, again, Ca-K at 393.3nm is in the violet part of the spectrum, but I've normally seen published images coloured blue.

I suppose our perception of colour is very different from purely looking at it from a wavelength or frequency perspective. All colours can be described by 3 variables: hue, saturation and brightness, but light wavelengths only relate to hue. You can convert a colour with hue, saturation and brightness variables to a specific light wavelength, but you can't convert a light wavelength to a specific colour with these variables.

Sorry... gone off on a tangent here... but these choice of colours just triggered my thoughts.

Rupert, you'll be waking up this morning to a bunch of praise for those photos!

In No 2, what's the long bright streak right at  the edge of the limb?

what’s the long bright streak right at  the edge of the limb?

Look like solar prominences to me, but I'm sure Rupert will confirm.

Nascent, given we're looking at them in profile?

This looks like a big active area that's currently rotating into view, so the prominences may just be starting to become visible.

See http://www.solarham.net/regions/2172.htm for more views.

It looks like this could be a productive area for solar flare activity over the coming days. One to watch, I think.

rotating into view

For 50-odd years I've known the difference between left and right, east and west - and now I have to unlearn all that for scope viewing 🙁

For 50-odd years I’ve known the difference between left and right, east and west – and now I have to unlearn all that for scope viewing

It's often a good idea to mark images with a basic compass so that you can communicate the orientation. It's not always obvious!

In this case, I happen to know that this active area is on the "eastern" limb of the Sun (by that, I mean to the left... yes, I know this is confusing... but if you were looking towards the Sun, it would be the part closest to the eastern horizon). As it's on the eastern limb, it is currently rotating into view.

Mike - Colouring Solar or any Deep Sky Objects falls, I think into two categories. Art and Practicality. The Art bit is really the main one. Is an DSO object imaged actually visible as pictures display them? Answer, no! We mainly enhance them to see what they are composed of and make pretty pictures.

The Sun is one of those bizzare objects that people insist is yellow! I don't know about you but have you had a good hard look at the Sun with the naked eye recently and been able to confirm that for me! (There was an older lady at Herstmonceux who informed us this was how she observed the Sun! We were all wondering where her cane and dog were!)

As people 'expect' the Sun to be yellow then I think this is why most H-Aplpha images tend to be that colour. If coloured red, they don't look that natural and red is very hard for the eye to deal with so you don't see much contrast or detail in a red coloured imaged. The goldish type tint seems to bring out the most detail but its quite an Alien view for most but yellow / gold tints are recognised for enhancing constrast. I may try the effect on Cak once I get the hang of imaging with it a bit more.

Cak and blue just seems to send the message 'I am CaK'. Again blue / violet is not an easy colour for the eye to deal with. I intend to experiment with colour, but I find it quite hard to produce the colour I want in PS!

Andy - That streak is a prominence. In H-Alpha these two areas are much bigger. You really have to search for them in the K-Line but they are there. See this link from our guest last Friday that explains a lot about Cak.

ftp://ftp.ngdc.noaa.gov/STP/space-weather/solar-data/solar-imagery/composites/documentation/observations-in-caii.pdf

Fixed your link above.

The Sun is one of those bizzare objects that people insist is yellow!

I suppose that's because most people only take notice of it when it's low on the horizon, and therefore has most of the blue and violet light scattered. In Japan, of course, most children colour the Sun as red!

Interestingly, the Sun has its peak visible output in the green part of the spectrum. But, because the Sun emits in all visible wavelengths, sunlight is white.

sunlight is white

As my white light filter solar shot confirms 😉

Great link, Rupert. Thank you. I'll put it in the 'Useful stuff' section!

Wow, those are stunning photos of the sun! Thank you for sharing! Amazing.