Ionize Calcium / Better Than H-alpha?

This post (

is entitled “Ionize Calcium / Better Than H-alpha?”

Not sure I’m convinced!

Compare with this a day earlier –

(same as this:

Need to see Ha and Ca-K at the same time. Pete? Andy?

Interestingly, although we have no sunspots, prominences are fairly abundant.

Some solar scope calculations

I have wondered about the resolution I get with my solar scope, so here are some fag-packet calculations:

Telescope diffraction limit (in radians)= 1.22 X wavelength in cm/scope dia. in cm

Telescope diffraction limit (in arcseconds)= 206265 X 1.22 X wavelength in cm/scope dia. in cm

Ha light  wavelength = 6562 angstroms = 6562 X 10^-8 cm

Lunt LS35 THa is 3.5 cm dia

Diffraction limit = (206265 X 1.22 X 6562 X 10^-8)/3.5

= 4.7 seconds, or about 5

Solar diameter is around 30 arcminutes, or about 1800 arcseconds

In this image the distance between the 2 spots is around 0.135 X the solar diameter, or around 250 arcseconds

The lines or striations around spot 2620 at their thinnest, are around 1/50th of this distance, or around 5 arcseconds.

So. my Lunt LS35THa images could, in fact be diffraction limited!

The GONG cameras have an aperture of 2.8cm, so they are similar.

Conclusion, to get images like this one (


  1. Win lottery
  2. Buy Lunt LS152 THa
  3. Get bigger window-sill

Of course, a Quark fitted to a 80mm scope should be pretty good! (Andy)