On 2025-01-12, I imaged the Sun in He I D3. Using my scripts to extract the weak signal, I got able to show features otherwise characteristic of the corona. I stacked a total of 72 scans, spanning between 2025-01-12-0741Z and 2025-01-12-0933Z. Basically, I imaged the fingerprint of the giant coronal hole.
The Helium I D3 line, unless one knows exactly what to look for, is elusive to put it mildly. Hence the secret. And the poet, Attila JÓZSEF warned us: a titkokat ne lesd meg. So let’s take the spectroheliograph and image the Sun ostinatamente. 78 scans went into this image on 2024-11-02.
Using the spectroheliograph and the ~30nm wide sodium ERF filter, I imaged the Sun in the He I D3 spectral line. Recordings processed with JSol’Ex, and details enhanced by the script below. For the final images, about forty individual frames (reconstructed scans) were stacked.
Fun fact, the light triangle in the lower half of the image corresponds to a dark feature in the corona, as seen on the SDO AIA 211 image.
One day after the X1.8 flare, business as usual on the Sun. I collected 40 scans in the Helium I D3 line, spanning about 40 minutes — so if there were any small scale details to begin with, they are probably lost.
He I D3 enhanced, heavy wizardry
The Sun on 2024-09-13, around the CaH line, also touching Hydrogen epsilon. Pixel shifts range from -36 pixels (blue wing) to +40 pixels (red wing), meaning somewhere around -2..+2 Å in total, give or take.
Hydrogen Epsilon-Prime, extracted from the Epsilon-Raw and an adjacent context for continuum
Since Google is no longer our friend[1], thus finding the things we are looking for has become harder and harder[2], I decided to assemble a few things that help me tame JSol’Ex.
JSol’Ex Repo: https://github.com/melix/astro4j
JSol’Ex downloads: https://melix.github.io/astro4j/latest/en/jsolex.html
Help/Docs (at ImageMath): https://melix.github.io/astro4j/latest/fr/jsolex.html#imagemath
Extracting the Hydrogen Epsilon line, like it was He I D3, simple version (where, relative to CaH, epsilon is at +25px)
A verbose and more complex version of the epsilon script:
I combined some spectroheliograph data with the etalon, Sol’Ex at 62/400 with Lunt CaK B1800 at 102/1100.
The Sun in Helium D3, He I D3
This really feels like standing on the shoulders of giants. I got my Sol’Ex spectroheliograph, and started using it with INTI and JSol’Ex (links below). Long story short, while the Sol’Ex in the plastic feels like a toy, it bends, sags and kinks and twists and vibrates and all, I find it an excellent introduction, and beyond, to solargraphy and spectroscopy. The software? It blows my mind.
I’ve been photographing the Sun for more than two years now almost each and every day, in a bit of a hackish way: using all kinds of filters beyond the 540nm continuum – hydrogen alpha – near UV calcium triad. However, as I advanced, I discovered that this knowledge is simply not common in the community, and not just that, it’s also a bit hard to come by while googling around. Also, to better explain double stacking, off banding and similar stuff, articles like this one Altair Astro’s 3nm CaK Ultra filter: testing, comparison, review are maybe rare.
So I put together an interactive tool to play around with spectra, in a way amateur astronomers find it interesting. The Spectral Composer.
