Reading the scene
green = harder spectrum → emission ~110 km
red = softer spectrum → higher, redder emission — cell heights anchored to the photo-MEASURED border altitudes for each epoch (110–360 km)
ray tops turn blue-violet where they rise into sunlight above Earth's shadow (N₂⁺ resonance — the Gannon signature)
SAR arc = smooth thermal red glow @ ~400 km, detached equatorward of the oval — drawn only over the longitude sectors with SAR-classified reports; night side only
equatorward bnd. poleward bnd.
pink ring = AMPERE field-aligned-current oval — CONTINUOUS 10-min measurement (Iridium constellation), alive between satellite passes
Pins: camera SAR SAR+visible unclassified
cyan markers = 486 star-calibrated cameras with recovered capture times (bright within ±30 min of their moment; tick shows pointing)
emerald arcs = photo-MEASURED auroral border/top heights (ensemble fits, e.g. border 360 km @ maglat 51.7° over N.America 05:30 UT)
amber = light pollution: city lights on the night side (globe) and horizon light-domes near cities (ground view) — NASA Black Marble
pale drape = actual VIIRS night photo (aurora + city lights), near its overpass time
animated W-Canada patch = TREx RGB + THEMIS ground cameras: each circle is one camera's field of view, projected at an assumed 110 km (product limitation — red aurora above 110 km smears toward footprint edges); 5-min steps, rims feathered by view-elevation confidence
Measured vs. derived: flux, boundaries & timing are SSUSI measurements (per ~101-min orbit, no interpolation between passes). The
Modeled aurora layer is the fused normalization of every source into the sun-fixed magnetic frame: oval
position from AMPERE's measured 10-min field-aligned-current boundaries;
brightness/energy fused from DMSP/SSUSI FUV imaging and POES+MetOp TED electron precipitation (5 satellites in different local-time planes, cross-calibrated to FUV-equivalent flux — measured median ratio ≈8: TED's 50 eV–20 keV band misses the storm-time hard tail SSUSI sees), carried between samples in the sun-fixed frame with AE-indexed substorm scaling. In Source mode, brightness dims with per-cell
confidence — how directly that sector & moment was sampled; the Simulation renders the best estimate at near-full brightness and reports confidence in the HUD instead. F18's pre-midnight blind sector and between-pass gaps are constrained by POES crossings where they exist. Dayside precipitation is real (imagers measure it in sunlight) but invisible to the eye — so all auroral layers fade with ground daylight using the same sun position as the terminator: the model fades out fully, measured snapshots dim to a ghost. Where the photo ensemble measured the visible red border & column tops (green lines), the reconstruction extends soft red emission equatorward to that measured border and lifts red-column tops to the measured heights. Sub-boundary soft red renders as SAR-regime diffuse glow — smooth, structureless, pure 630 nm (Kozyra+ 1997) — rather than curtains. In Simulation mode, fine ray structure inside the curtains is
procedural — real auroral rays are 0.1–10 km, below every instrument's resolution here — while position, brightness, extent and heights stay measured. Column tops vary per cell: the photo-measured epoch envelope scaled by each cell's own measured flux & energy (Rees range–energy curve), so bright soft cells reach the measured maximum while weaker cells stand shorter. Where a column top rises above Earth's shadow (same sun geometry as the terminator), it turns
N₂⁺ blue-violet — deep-night sectors self-gate because the shadow there sits above every measured top. In ground view, cells near the observer resolve into
3D field-aligned columns at the dipole inclination, so looking straight up produces the true
corona convergence at the magnetic zenith — column placement, heights and brightness are the measured field; only sub-cell ray multiplicity is procedural.
Substorm flags (amber ▼ on the timeline, ⚡ badge while active) are detected from the AE index: onset = ≥150 nT rise within 20 min from a non-rising baseline, expansion until AE stops making new highs. Arc
dynamics follow published morphology: omega-band brightness waves ride the poleward edge eastward at ~0.9 km/s during substorm-active hours (Opgenoorth+ 1983), giant-undulation waves ride the equatorward diffuse edge westward when SYM-H drops below −150 nT (Lui+ 1982, K-H of the SAID shear), and the procedural fine structure drifts along the arc (curl/fold scales, Hallinan 1976; Partamies+ 2001) — all brightness-led, mean-neutral, with any displacement bounded inside one grid cell (sub-resolution). During flagged expansions the simulation brightens a bulge using the published statistical template (Gjerloev+ 2007) with westward/eastward expansion speeds of 8.8/5.3 km/s (Ogasawara+ 2011; Craven+ 1989) — timing & amplitude come from our measured AE, onset location from the model's own brightest near-midnight sector. Emission colors follow the Rees & Luckey (1974) energy–ratio relation; peak altitudes follow the Fang et al. (2008) Maxwellian energy-deposition parameterization (P
ij verified against three independent sources), epoch-scaled by our photo-measured heights (storm-time thermospheric expansion, cf. Kataoka+ 2024, who measured Gannon red to ~1000 km — consistent with our independent 790–870 km ensemble tops); ray structure fades with altitude per the 630 nm ~110 s radiative lifetime; the sunlit-blue gate matches the −24° solar-elevation threshold (Grandin+ 2024). The
👁 naked-eye view applies scotopic/mesopic vision to the simulation: rod sensitivity peaks at 507 nm and vanishes toward 630 nm (Purkinje), so faint aurora renders dim gray-green and red appears only where bright enough to engage cone vision — matching the naked-eye vs photograph color reports collected by Grandin+ 2024. Default 📷 long-exposure shows what cameras record.
Photo-POV: click any calibrated camera dot to stand at its exact spot & time with the plate-solved frame outlined on the sky; gold dots blend the actual photograph over the render for direct validation. Frames are auto-leveled using the photo's own horizon (the level-camera assumption that also powers the star clock) — untick "level" to see the raw solved orientation at the assumed exposure time; the residual tilt there mostly measures clock error (parallactic rotation), not camera tilt. Emission altitudes: hard/green cells at ~110 km; soft/red cells lifted to the photo-ensemble MEASURED border heights per epoch (110–360 km across the storms). Tall-ray
placement follows the observed soft-precipitation flank (illustrative until photo triangulation replaces it) — but ray
altitudes (500–1100 km) and the red→blue sunlight transition use real shadow geometry per location & time. SAR band: latitude fitted to SAR-classified reports in Chris Wicklund's sightings map, drawn only over reported longitude sectors; alt. ~400 km per FRIPON Europe obs. Sighting pins are event-integrated.
In memory of Jennifer Gannon. The May 2024 superstorm carries her name — this observatory began as its reconstruction.
Data: NASA SPDF (SSUSI, OMNI) · NASA GIBS (VIIRS DNB · Blue Marble globe) · AMPERE Science Data Center (JHU/APL, NSF; PI B. Anderson) · UCalgary AuroraX (TREx RGB + THEMIS ASI grid mosaics) · sightings: Chris Wicklund's maps (Wicklund et al. 2024, OSF e87cs) · ground view: map © OpenStreetMap contributors © CARTO, terrain Mapzen/AWS Terrain Tiles.