Roger Samworth

Some musings on solar scopery

In order to see features on the sun in the presence of its extreme glare, Ha scopes and the like select out a very narrow band of frequencies with an (expensive) filter called an etalon.

In order to do this the etalons have to be “tuned” by various methods. To use them visually you need a very good contrast, and sometimes 2 etalons are used – the so called “double stacking” to narrow the bandwidth (and double the expense!) and improve the contrast. This can show breathtaking visual views.

However this only improves the contrast – not the spatial resolution, I believe. Resolution is controlled by the scope aperture.

Now, when imaging, you can readily improve contrast by signal processing with “Curves” and the like, as long as your camera has sufficient dynamic range. Tuning is therefore a lot less critical, and “double stacking” probably unnecessary.

Have I got this right? Any comments?

AR 2738 today – 13/04/2019

Quite a lot of activity this morning but AR2738 still dominates the show. The white light “split” is now quite clear.

SpaceWeather says:

“IS SUNSPOT AR2738 SPLITTING IN TWO? The primary core of sunspot AR2738 is divided by a brilliant canyon of light–also known as a “light bridge“–measuring some 20,000 km from end to end.  – – – – The light bridge is only about 800 km wide–less than the width of the state of Texas. His image captures not only that narrow divide, but also hundreds of surrounding granules on the sun’s boiling surface .

The nature of light bridges is not fully understood. They often herald the break-up of a sunspot. Some research suggests that magnetic fields at the base of a light bridge are busy cross-crossing and reconnecting–the same explosive process that sparks solar flares. Does this mean sunspot AR2738 will explode–or quietly fall apart? No one can say.”

Globular gazing 11/04/2019

I had another of my restless sleepless nights last night, but looking out of the window in the early hours it was clear. So, as a distraction, I went on a globular hunt in the Scorpius/Ophiuchus region.

Some of them were quite challenging from the window-sill for one reason or another, and results were a bit mixed.

First, M80 in Scorpius. This is small (10’ diameter) so I couldn’t really resolve any stars.

Then, on to M107 in Ophiuchus. This one is a bit bigger (13’) and brighter, so some stars were resolved.

Moving back to Scorpius NGC6144, near Antares,  again is small and faint (9’ diameter) and trends to get lost in the glare from Antares. So there is little more than a fuzzy blob. I have unsuccessfully searched for this before, so it was quite satisfying to get anything!

Then back in Ophiuchus, M19 is a bit better, with a diameter of 14’, although there is only a hint of resolution of stars.

Another small fuzzy blob next, NGC6284 in Ophiuchus has a diameter of only just over 6’.

Finally, M12 in Ophiuchus with a diameter of 14’ and some resolution into stars.


All these were acquired using a stack of 40X10-second images, stacked in Registax 5 and processed with GIMP.