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.
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
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.
Duct tape turned out to be one of the darkest materials I could build into the spectroheliograph, to limit parasite light and scatter on the chromium-bright (visually black) focuser for example.
He I 10830
Even though there is a band pass filter, 1075/50 in front of the instrument, those 50 nanometers still cause trouble. Duct tape to the rescue. The slit also got a light trap in front of it, partly to limit the thermal load on the plastic, and mainly to trap light reflected off the slit. The trap is an aluminum radiator from an old circuit board (some might have noticed, I have quite a few circuit board related components in my setup) that I inspected and confirmed it is indeed black. I cut it in half and use the wings as light traps, to prevent that light from getting onto surfaces I have less control over. And duct tape, duct tape went into the focuser tube. And. It. Helps. A. Lot. Also, a second bandpass filter has been ordered, 1100/50, to further limit the parasite light. These are laser and fluorescence filters, so no helium wavelength available off the shelf. I may one day go for the not that cheap custom option. Or just say that He I D3 is much more feasible.
To the best of my knowledge, just like with the Fe II 5018 dark plages and visible prominences, this image is among the first in this wavelength (I know only about the proof of concept level precedent by Christian Buil), and the best quality to date, as far as amateur astronomy is concerned.
The disk I present here is the reconstruction of the wavelength, there is no local contrast enhancement, and there is no continuum subtraction. Direct wavelength image. A stack of 136 scans.
Heavily amplified oxygen signal, projected back onto the 7772Å disk
With this new spectroheliograph, still in the tuning, I observed the infrared oxygen triplet at 7772, 7774 and 7775 Å, on 2025-12-13. As an ERF, I used a Nantong Foric bandpass filter, OD2-ish with the CWL close enough.
To the best of my knowledge, this is the first full solar disk with (amplified) oxygen features and prominences.
A subjective impression is that this oxygen line is somewhat similar to a weak helium. The line is in clear absorption on the disk, but turns into emission as going off the limb. Prominences are readily visible if bright, or become visible after applying math. Continuum subtraction shows that spots seem to be less dark, and the plages are also a bit shaded, less overall contrast.
2025-12-13, He I 10830 disk. Direct wavelength reconstruction, stack of 50 scans. No continuum was subtracted. The signal is this strong.
Using a Sol’Ex type spectroheliograph[1], we imaged the full solar disk in the He I 10830 line. We obtained rich helium details on the direct disk reconstruction, without applying continuum subtraction, as it is the practice in He I D3. As a side note, the Paschen-gamma disk was also imaged. The original Sol’Ex design was modified and adapted to the near infrared / short wave infrared range, using off the shelf and DIY elements, as well as some high end custom components.
Reaching the Helium line at 10830Å, with the available instruments, seems challenging:
In spite of the challenges, there is some precedence. Christian Buil (Sol’Ex) recorded a proof of concept a while back [2]. So we reached out to Mr. Buil for his insights, and he was kind enough to point us into the right direction regarding the grating and lenses.
A bright one and then more quiescent prominences in the G-band
In this post I show a bright prominence in the G-band spectrum, and examples that I can routinely show brighter quiescent prominences in both the G-band 4308Å and in the Ca I 4227Å lines.
Various setup configurations are used, Sol’Ex and ML Astro SHG 700 spectroheliographs, 42/400 (62/400 stepped down) and 80/540 refractors, various filters used as ERF to reduce the thermal load on the delicate parts of the optics. Two cameras provided the images, the ZWO 678MM (IMX 678) and Altair Astro 26M (IMX 571).
On 2025-06-16, at around 0936Z there was a bright flare visible in both Na D1 and Na D2, but also in He I D3 as a bright flash. 27 scans were recorded between 0856Z and 0940Z, with the last couple having the flare. The presented disk image is a composition of stacks, one stack of the disk without the flare, and another stack that shows the flare (motion blurred over a few minutes). Curious dopplers are also present in the raw, as sample frames from the raw scan show.
I recorded 30 scans of the Sun, using the SHG 700 with a 678MM camera.
I used my solex setup to image the singly ionized iron right next to the forbidden oxygen. The signal is strong there. I cleaned up the image to remove most of the artefacts. Stack of 17 scans. 2025-04-21.
