Ca II K, stack of 30 scans, centered around 2026-08-01, 0805Z
Ca II 8542, stack of 10 scans, centered around 2026-08-01, 0950Z
Neutral Carbon – flares, proms, chromosphere?
Making carbon bright: dividing the disk edge frame with a nearby frame towards the disk center
With a spectroheliograph, I keep observing two carbon lines in the infrared, C I 9095 and 9112. Generally speaking, in both lines, the signal is weak. What I have seen so far: excess light over sunspots, a deficit of light over active regions, dark features that resemble the oxygen smudges and flares that look like darken on the disk.
While stray light could be the culprit for observing excess light in a dark line’s dark areas, as in light bleeds in, the deficit is another question, especially when it is visible against the continuum in blink compare, as a darkening, while the continuum shows no change. Then there are the disk edge phenomena, a surging-flaring prominence on 2026-07-05, at around 10:25UT, that are visible in the raw capture, without enhancement.
To enhance some frames, I decided to divide a frame close to the disk edge by a frame somewhat towards the disk center. Carbon, and only carbon, lights up. (tovább…)
A new Helium script
I wrote a new He I D3 script, now that I understand a bit better the quirks of the scripting.
A solar flare in neutral carbon
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.
Prominences in neutral iron
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
The Spectrum of the Sun’s Light
This collated spectrum, showing the light of the Sun between ~360-920 nm, marks that, from two years of work, I have amassed 122k solar disks, into the atlas.
This spectrum, made continuous and colorized, smoothed out gradients etc, is a sort of a byproduct of the individual cubes of the atlas. A sidenote: JSol’Ex marks the anchor line with lime, so that’s a bit of an information loss, resulting in an already dark spectral line’s uncertainty once every five-ten nanometers. Still, nice to look at.
Download versions:
mono, ~2500 x 10k pixels, ~2.5 MiB
colorized, pink infrared, magenta ultraviolet, ~2500 x 10k pixels, ~2.5 MiB
Oxygen Smudges Across The Wavelengths
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.
Oxygen Smudge, 2026-04-01
Using the familiar setup, I recorded four frames and stacked them together. The smudge appears somewhat embering-glowing in SDO AIA 1600, but as a bright spot in AIA/SUVI 304.
The smudge predictor is an attempt to estimate where a smudge could be expected:
stretch(someMath(AIA 1600) – someMath(AIA 1700)),
flares and smudges might appear bright in the image.
Oxygen Smudge, 2026-03-21
As I explained here, I keep seeing >>smudges<< in oxygen O I 7772. Smudges, ie regions that are darker than expected based solely on the location of flares and plages, yet seem to be related to whatever is happening in extreme UV. Here’s this day’s smudge.
2026-03-21-1244 solar disk, oxygen divided by continuum (and some other math), showing a smudge
2026-03-21-1244 smudge marked
Prominences and other observations across the spectrum
WIP/DRAFT
The first light of my spectroheliograph was in the summer of 2024. It was a stock Sol’Ex, with a modified setup, using full aperture bandpass filters as an energy rejection method, instead of the recommended full spectrum ND filter or Herschel prism, flooding the instrument with the right kind of wavelength, while also managing the thermal load and keeping the zero order and any internal spectral fog at bay. I quickly left the comfort of the Fraunhofer lines, and stumbled into prominences in „unknown” wavelengths[1], a frustrating experience that lead me towards literature, and also propelled me to create the atlas of spectroheliograms[2].
In the meanwhile, almost as a side project, dedicating telescope time to this in an on and off manner, I started to hunt down prominences in various spectral regions and lines, some known and expected, some not so much. Thus today I know that the ultraviolet „unknown” wavelengths showing prominences were most likely the magnesium triplet around 383nm, that Paschen hydrogens are dwarfed by not just Balmer hydrogens but also by the helium at 1083nm, which shows coronal holes, just like the yellow and the deep red helium do. I’ve seen the hydrogen ladder almost up till the Balmer break, and seen that neutral calcium is something worthy to at least check for prominences, that the infrared oxygen triplet can do very funny stuff, with obvious prominences, and that ionized metals show dark plages and often times prominences that are easier to see than some helium lines.
