Add multi-wavelength spectroscopy tutorial by aditya-pandey-dev · Pull Request #203 · JuliaAstro/JuliaAstro.github.io

aditya-pandey-dev · 2026-03-20T13:24:41Z

Closes #202

What's included

A new tutorial at docs/src/tutorials/multi-wavelength-spectroscopy.md covering a realistic end-to-end spectroscopy workflow:

Loading a real SDSS DR14 spectrum from a FITS binary table (FITSIO.jl)
Attaching physical units — Å, erg/s/cm²/Å (Unitful + UnitfulAstro)
Fλ ↔ Fν conversion (Jansky)
Dust extinction with CCM89, OD94, CAL00 laws (DustExtinction.jl)
Spectral axis inspection via spectral_axis / flux_axis (Spectra.jl)
Automatic uncertainty propagation (Measurements.jl)
Synthetic blackbody spectra at 4 temperatures
Spectral arithmetic — sky subtraction, scaling
Cosmological redshift + luminosity distances (Cosmology.jl)

Testing

Includes test/test_tutorial.jl — a standalone verification script:

julia --project=docs/ test/test_tutorial.jl

All 5 dependency tests pass on Julia 1.12.5

Packages exercised

Spectra.jl, FITSIO.jl, DustExtinction.jl, UnitfulAstro.jl, Measurements.jl, Cosmology.jl, Plots.jl

Notes

Code blocks use plain julia fences (not @example) since Spectra.jl
is installed from GitHub and not yet in the General registry
continuum() is referenced as a planned future feature with a link to
Towards SpectrumBase.jl SpectrumBase.jl#41
[compat] bounds added for all new registered dependencies

Adds an end-to-end spectroscopy tutorial covering: - Loading real SDSS spectra from FITS files (FITSIO.jl) - Physical units and Fλ↔Fν conversions (Unitful + UnitfulAstro) - Dust extinction with CCM89, OD94, CAL00 laws (DustExtinction.jl) - Spectral axis inspection via spectral_axis/flux_axis (Spectra.jl) - Automatic uncertainty propagation (Measurements.jl) - Synthetic blackbody spectra generation (Spectra.jl) - Spectral arithmetic: sky subtraction and scaling - Cosmological redshift and luminosity distances (Cosmology.jl) Includes test/test_tutorial.jl — standalone verification script. Updates docs/Project.toml with [compat] bounds for all new deps. Closes JuliaAstro#202

DustExtinction='0.6, 1' excluded v0.11.x (current release), creating an unsolvable constraint with FITSIO 0.17 in CI.

@example

Tutorial uses plain julia code blocks (not @example), so docs build environment does not need to install tutorial dependencies. Extra packages were causing CI resolution failures in the JuliaAstroDocs test suite.

The CI test runner picks up all .jl files in test/ and tries to execute them. test_tutorial.jl requires packages not present in the test environment, causing JuliaAstroDocs to error. Users can run the tutorial locally by installing the packages listed in the tutorial's Packages section.

aditya-pandey-dev · 2026-03-21T09:33:36Z

@icweaver can you check the PR. What changes should I do?

cgarling

Interesting example, thanks for the PR. I made some specific comments/suggestions below, here is some high-level feedback:

It would be nice to have this run on CI so the output can be displayed. Could you expand on why you can't use @example here? I thought that if you setup the doc build environment correctly there shouldn't be a problem with importing Spectra.jl even if it isn't in the General registry yet (i.e., using [sources] to set the url in the Project.toml).
Mostly you are dealing with flux density units in this example so we should make the associated plot labels "Flux Density" rather than "Flux" for clarity
I would try to be more consistent with using units when constructing the wavelength / flux density vectors, some places where you are constructing blackbody spectra you are not putting units on the wavelengths/temperatures and I think we want to encourage the use of units
I think that blackbody returns radiance units so you may need to calculate the luminosity density as L_lam(lambda) = 4 \pi^2 R^2 B(lambda,T) where R is the radius of the spherical blackbody (say 1 solar radius) and B(lambda, T) is what blackbody returns. It would be good to check this and amend the blackbody docstring to be more descriptive.
We are mostly using Makie.jl for plotting in our documentation now, idk if anyone has strong feelings on this. I don't mind using Plots.jl but would probably prefer makie

@example

- @example blocks for CI + Spectra via [sources] in Project.toml - Flux -> Flux Density in all plot ylabels - Units on wave_bb, wave_synth (.* u"angstrom"), temperatures (u"K") - L_lam = 4pi^2 * R^2 * B(lambda,T) correct luminosity formula - SDSS ivar column for real Measurements uncertainties - F_obs = L*(1+z)/(4pi*d_L^2) correct cosmological formula - Plots.jl -> CairoMakie throughout - SFD98Map with ICRSCoords -> GalCoords conversion

…o extra deps

…fixes applied

- Replace synthetic galaxy spectrum with real SDSS plate 1323 data - Use FITS ivar column for real per-pixel σ = 1/√ivar uncertainties - Addresses mentor comment: use Measurements with actual SDSS error column

aditya-pandey-dev · 2026-04-01T15:15:27Z

@cgarling I've added Spectra.jl to docs/Project.toml via
[sources]. However, @example blocks still can't run on CI
because the tutorial makes network calls:

Downloads a real SDSS FITS file (~50 MB)
SFD98Map() downloads dust map tiles (~120 MB)
So i think there are two suitable options : (a) Keep plain julia blocks with a note explaining network
dependency (b) Split into @example (synthetic/offline parts) + plain
julia (network parts)
Which approach would you prefer?

cgarling · 2026-04-08T02:13:38Z

I do Github Actions with network dependencies pretty frequently (e.g., through DataDeps.jl) and can't recall any issues. What exactly is the problem CI is creating, are you hitting a firewall (Github won't let you access external URLs)?

cgarling

Thanks for the update, good progress! More comments below

cgarling · 2026-04-08T03:02:49Z

+fig4, ax4 = lines(ustrip.(wave_rest), ustrip.(bb_rest.flux);
+    label = "z = 0", color = :black,
+    axis  = (xlabel = "Wavelength (Å)",
+             ylabel = "Flux Density (erg s⁻¹ cm⁻² Å⁻¹)",
+             title  = "Cosmological Surface-Brightness Dimming"))
+
+for (z, col) in zip([0.5, 1.0, 2.0], [:blue, :green, :red])
+    d_L   = uconvert(u"cm", luminosity_dist(cosmo, z))
+    w_obs = wave_rest .* (1 + z)
+    F_obs = L_lam .* (1 + z) ./ (4π .* d_L.^2)
+    lines!(ax4, ustrip.(w_obs), ustrip.(F_obs); label = "z = $z", color = col)
+end
+axislegend(ax4, position = :rt)
+fig4


Suggested change

fig4, ax4 = lines(ustrip.(wave_rest), ustrip.(bb_rest.flux);

label = "z = 0", color = :black,

axis = (xlabel = "Wavelength (Å)",

ylabel = "Flux Density (erg s⁻¹ cm⁻² Å⁻¹)",

title = "Cosmological Surface-Brightness Dimming"))

for (z, col) in zip([0.5, 1.0, 2.0], [:blue, :green, :red])

d_L = uconvert(u"cm", luminosity_dist(cosmo, z))

w_obs = wave_rest .* (1 + z)

F_obs = L_lam .* (1 + z) ./ (4π .* d_L.^2)

lines!(ax4, ustrip.(w_obs), ustrip.(F_obs); label = "z = $z", color = col)

end

axislegend(ax4, position = :rt)

fig4

fig4, ax4 = lines(ustrip.(wave_rest), ustrip.(bb_rest.flux);

label = "z = 0", color = :black,

axis = (xlabel = "Wavelength (Å)",

ylabel = "Flux Density (erg s⁻¹ cm⁻² Å⁻¹)",

yscale = log10, yticks=LogTicks(LinearTicks(5)),

title = "Cosmological Surface-Brightness Dimming"))

for (z, col) in zip([0.1, 0.5, 1.0], [:blue, :green, :red])

d_L = uconvert(u"cm", luminosity_dist(cosmo, z))

w_obs = wave_rest .* (1 + z)

F_obs = L_lam .* (1 + z) ./ (4π .* d_L.^2)

lines!(ax4, ustrip.(w_obs), ustrip.(F_obs); label = "z = $z", color = col)

end

axislegend(ax4, position = :rt)

fig4

Changed to display a little better

icweaver · 2026-05-12T21:03:23Z

I've been thinking about re-homing our tutorials section under our learn.JuliaAstro site that is currently in the works. My thinking is that this would help reduce duplication of efforts and also help make things more discoverable. I'd be happy to help migrate things over if this sounds like a reasonable organizational step to y'all. I think I am already seeing a good bit of overlap with our Dust extinction notebook, which could probably absorb the changes proposed here

barrettp · 2026-05-13T17:44:14Z

Replace FITSIO.jl with FITSFile.jl.

Co-authored-by: Chris Garling <chris.t.garling@gmail.com>

icweaver · 2026-05-16T17:24:44Z

Ok, I think I incorporated the above comments here and tried to clean things up a bit. Can add more if this seems like the right direction to go for this PR

Follow-up to JuliaAstro/JuliaAstro.github.io#203 Trying it out in notebook format Doc preview: https://learn.juliaastro.org/previews/PR28/tutorials/spectroscopy-sdss/ --------- Co-authored-by: Chris Garling <chris.t.garling@gmail.com>

icweaver · 2026-05-18T09:17:54Z

Thanks @aditya-pandey-dev for your contribution! We have merged things here over on our learn.JuliaAstro site that is currently under construction

aditya-pandey-dev added 7 commits March 20, 2026 18:29

Fix: add newline at end of Project.toml

c20e924

Fix: remove strict compat bounds causing DustExtinction conflict

f15060a

DustExtinction='0.6, 1' excluded v0.11.x (current release), creating an unsolvable constraint with FITSIO 0.17 in CI.

Fix: remove Spectra.jl from docs/Project.toml

699466e

Fix: revert docs/Project.toml to original deps

b7ea6ad

Tutorial uses plain julia code blocks (not @example), so docs build environment does not need to install tutorial dependencies. Extra packages were causing CI resolution failures in the JuliaAstroDocs test suite.

Fix: restore all required deps in docs/Project.toml

6830528

aditya-pandey-dev mentioned this pull request Mar 23, 2026

GSoC 2026 Proposals: Integrate a modern lazy-loading alternative for large-scale spectroscopic database processing (Aditya Kumar Pandey) OpenAstronomy/gsoc-proposals#21

Merged

5 tasks

cgarling reviewed Mar 29, 2026

View reviewed changes

aditya-pandey-dev added 7 commits March 31, 2026 14:51

Fix: address all cgarling review comments

cdea606

Fix: use plain julia blocks (Spectra.jl not in General registry yet)

e7c0108

Fix: correct Cosmology.jl UUID in docs/Project.toml

734911c

Fix: revert docs/Project.toml to original - plain julia blocks need n…

ffe896c

…o extra deps

Fix: complete tutorial rewrite - CairoMakie, no Plots.jl, all mentor …

fa112c1

…fixes applied

Fix: use real SDSS DR14 spectrum with ivar-based uncertainties in Part 1

8b26c8e

- Replace synthetic galaxy spectrum with real SDSS plate 1323 data - Use FITS ivar column for real per-pixel σ = 1/√ivar uncertainties - Addresses mentor comment: use Measurements with actual SDSS error column

This was referenced Apr 2, 2026

JuliaAstro: Spectra.jl across the electromagnetic spectrum (Aditya Kumar Pandey) aditya-pandey-dev/gsoc-proposals#1

Closed

JuliaAstro: Spectra.jl across the electromagnetic spectrum (Aditya Kumar Pandey) OpenAstronomy/gsoc-proposals#49

Merged

cgarling reviewed Apr 8, 2026

View reviewed changes

icweaver and others added 5 commits May 15, 2026 15:07

Update docs/src/tutorials/multi-wavelength-spectroscopy.md

56c3006

Co-authored-by: Chris Garling <chris.t.garling@gmail.com>

Update docs/src/tutorials/multi-wavelength-spectroscopy.md

d00ac88

Co-authored-by: Chris Garling <chris.t.garling@gmail.com>

Update docs/src/tutorials/multi-wavelength-spectroscopy.md

528b74f

Co-authored-by: Chris Garling <chris.t.garling@gmail.com>

Update docs/src/tutorials/multi-wavelength-spectroscopy.md

3a651be

Co-authored-by: Chris Garling <chris.t.garling@gmail.com>

Merge branch 'main' into add-spectroscopy-tutorial

5ba3cab

icweaver mentioned this pull request May 16, 2026

feat: Spectroscopy with SDSS tutorial JuliaAstro/learn-JuliaAstro#28

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icweaver closed this May 18, 2026

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What's included

Testing

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Notes

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aditya-pandey-dev commented Mar 20, 2026 •

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