What CVAN actually computes

CVAN is a static web app: every astronomical calculation runs in your browser from public, free data feeds. Nothing about your location is sent to a server we run. The forecast pipeline has six stages:

• Site fix — IP geolocation, GPS, manual coords, or map pick.
• Sky state — sun and moon altitude, twilight class, Galactic Centre position, planet positions, all using Meeus algorithms and JPL Keplerian elements.
• Light pollution — NOAA NCEI VIIRS Day-Night Band radiance for the chosen pixel, converted via Falchi-style empirical fit to artificial sky brightness, SQM, then a Bortle class (1–9).
• Moon contribution — Krisciunas-Schaefer (1991) model: how much the moon brightens the local sky at your zenith, given its current altitude and phase.
• Weather — Open-Meteo cloud cover and visibility for the next 16 days, interpolated to the slider's previewed instant.
• Aurora — NOAA SWPC planetary Kp index and the geomagnetic auroral oval, scored against your geomagnetic latitude using the IGRF-13 dipole.

The Solar System tab

Planet positions come from JPL's Keplerian elements (Standish, valid 1800–2050 to ~1 arc-minute). The orrery has heliocentric and geocentric toggles plus an inner-planets zoom. Per-planet detail pages show altitude, azimuth, distance, magnitude, illumination, phase, and a 7-night altitude scrubber alongside the sun and moon. Jupiter's page surfaces the Galilean moon configuration and Great Red Spot transit times; Saturn's shows the live ring-tilt B angle.

The events panel finds the next opposition for each outer planet, the next greatest east / west elongations for Mercury and Venus, every conjunction within 3° over the next year, and the next Mercury or Venus transit of the Sun (Mercury 2032-11-13, Venus 2117-12-11). All verified against published ephemerides to the day.

NEOs, comets, Mars rovers, and the outer Solar System

NEOs come live from NASA NeoWs (close approaches over 1, 3, or 7 days, with a PHA filter). Comets are computed in-browser from JPL Keplerian elements — elliptic, near-parabolic (Barker's equation), and hyperbolic orbits all supported, so the catalog spans periodic comets and interstellar objects like 3I/ATLAS. The Mars page embeds a cylindrical- projection surface map with live status fetches for Perseverance, Curiosity, Zhurong, Opportunity, and Spirit, plus on-demand latest sol photos via the NASA Mars Photo API.

The Dwarfs / Outer sub-tabs cover Ceres, Pluto, Haumea, Makemake, Eris, the named centaurs (Chiron, Chariklo, Pholus), and the major TNOs (Sedna, Quaoar, Orcus, Gonggong). A log-scale axis stretches from Mercury's orbit out to Proxima Centauri — 6+ orders of magnitude.

Deep Sky catalogs

The complete Messier catalog (110 objects), a curated bright-end Caldwell (Omega Cen, 47 Tuc, Eta Carinae, SMC, Coalsack), 16 iconic NGC / IC additions (Horsehead, Heart, Soul, Flame, Bubble, Pacman, Double Cluster, Centaurus A, Sculptor), and the brightest Barnard dark nebulae. Filter by type, magnitude, minimum size, and scope aperture — the limiting magnitude updates as you slide the aperture from naked eye to 16-inch SCT. The Best Tonight tab ranks objects by maximum altitude tonight, headroom over your magnitude limit, and a Bortle-aware surface-brightness penalty.

A separate Hubble / JWST sub-tab is a press-image gallery — 12 iconic releases including the Hubble Ultra Deep Field, both takes on the Pillars of Creation, SMACS 0723, the Cosmic Cliffs, Stephan's Quintet, and the Phantom Galaxy — each linked to the official press page on ESA Hubble or STScI.

Exotica and transients

Curated catalogs of the historically and observationally important pulsars (Crab, Vela, Hulse-Taylor, B1937+21, J0740+6620), black holes spanning Cygnus X-1 through TON 618's 66-billion-solar-mass core, and a rotatable 3D view of the Local Group out to ~3 Mly. The Transients tab brings together recent supernovae (SN 2023ixf, SN 2024ggi), gravitational-wave events (GW150914, GW170817, GW190521, GW230529), fast radio bursts, and gamma-ray bursts including the BOAT (GRB 221009A), each linked to the live source feed (TNS, GraceDB, CHIME, NASA GCN).

Data sources

NOAA SWPC

Planetary Kp index, auroral oval position, K-index forecast (5-min refresh)

NOAA NCEI VIIRS

Day-Night Band radiance for light-pollution calculations

Open-Meteo

Cloud cover, visibility, temperature, dew point (16-day forecast)

NASA NeoWs

Near-Earth object close approaches and PHA flags

NASA Mars Photo API

Rover status, sol counts, and latest photos

JPL SSD

Approximate planetary positions (Standish Keplerian elements)

ESA Hubble

Press-release imagery and metadata

STScI

JWST press-release imagery

Nominatim

Geocoding for the location search field

OpenStreetMap

Base tiles for the location map picker

Methodology references

• Meeus, J. Astronomical Algorithms, 2nd edition (1998) — sun, moon, planet positions; eclipses; conjunctions.
• Krisciunas & Schaefer 1991, PASP 103, 1033 — moon-induced sky brightness model.
• Bortle 2001, Sky & Telescope — the Bortle dark-sky scale class definitions.
• Standish 2009, JPL Solar System Dynamics — Keplerian Elements for Approximate Positions of the Major Planets.
• NOAA SWPC operational documentation — Kp index, geomagnetic forecasts, auroral oval modelling.
• IGRF-13 (Alken et al. 2021) — geomagnetic-field model for the dipole approximation.

Open source & credits

CVAN is open source. The full codebase lives at github.com/LukasJT/cvan; every astronomy calculation, catalog, and verdict heuristic is in the repo. Pull requests welcome.

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