Today I managed to gather the best data so far in support of having visible filaments in oxygen, over the solar disk. Nota bene, they have to be dark and dense filaments, as seen in hydrogen alpha, but they are there. A nice addition to the smudges.

I used the a customized SolEx spectroheliograph, with an 1800 ln/mm holographic grating, an EO in-cone prefilter centered to 775nm, ML Astro’s slit, and Altair Astro’s IMX 678M camera implementation. The assembly was mounted to a 72/430 doublet.

Because oxygen darkens over plages, filament observation is extra hard. But blink comparing against AIA 1600 and the iron from below the oxygen triplet reveals no candidate plages.

The flare’s dark imprint is at the bottom left corner of the „bright” sunspot, on this continuum subtracted image

On 2026-06-24, I observed the flare that occurred and peaked at around 0710Z, in the neutral carbon lines C I 9095 and C I 9112. Both darken subtly when the flare is present, just like oxygen does. But unlike with oxygen, which has an obvious chromosphere, I failed so far to identify anything meaningful for these carbon lines.

Also much like the oxygen, sunspots show excess light, while plages show a deficit, the disk being overall rather dull in comparison to neighboring continuum lines.

An interesting factor when processing these pictures is that the reference lines land on tellurics, and hence the solar lines doppler visibly as we scan from solar west to east.

The flare is at the big „bright” sunspot, bottom left.

(tovább…)

I observed the Sun in multiple wavelengths, recording spectroheliograms in Sr II 4077, Fe I 4383, and spectra in the UV — no disks, because of the clouds. Always the mandatory clouds.

Fe I 4383

If I identified the lines correctly

Sr II 4077 delta1

Sr II 4077 division

Sr II 4077 delta2

Sr II 4077 continuum at 11 pixels distance

Sr II 4077 line reconstruction

O I 7772 ~ continuum, dark smudge at center-top-left

On 2026-04-05, I imaged the Sun across multiple wavelengths, and found that areas that are dark smudges in oxygen are:

• rather unassuming bright-ish plages in:
  • Hα
  • Ca II 8542
  • Na I D2
• nothing obvious, small sunspot aside, in:
  • continuum
  • Fe I 7781
• dark in:
  • (O I 7772, hence smudge)
  • He I D3
  • He I 10830
  • H Paschen gamma

The images presented below are from scans recorded across several hours, each wavelength is the result of several scans stacked together. During acquisition, no major flares were reported. More about oxygen smudges here, here and here.

(tovább…)