# Your night sky companion

> A night sky companion with five sections: Tonight (cloud forecast, darkness, the Moon), Sky map (a planetarium for any place and time, with survey photographs of nebulae and galaxies, and a 3D universe to fly through), Targets (what to look at or photograph on any night, computed for your place, equipment and sky), Tools (ten tools, including a modelled light-pollution map and quick calculators) and a Buying guide (497 products across 9 categories, ranked by fit). All data is static JSON.

The buying guide asks a few questions (for telescopes: visual or imaging, targets, design, aperture, portability, pointing, budget) and ranks every product by fit and popularity. Prices are approximate US street prices.

## Sections
- Home: `/`
- Tonight: `/tonight?lat={deg}&lon={deg}&name={place}`
- Events: `/events?year={YYYY}` (eclipses with local circumstances, Moon phases, seasons, planet events, close approaches, meteor showers; computed with Meeus's algorithms)
- Cloud map: `/clouds` (model cloud forecasts over your saved place, hour by hour for about five days: Met Office UKV, DWD ICON-EU or ECMWF IFS via Open-Meteo open data)
- Space weather: `/space` (live NOAA SWPC data and the OVATION aurora forecast)
- The universe in 3D: `/universe?target={id}` (the Solar System with real positions, rotations and NASA/USGS surface maps, Hipparcos stars placed by parallax, the Milky Way and nearby galaxies)
- Sky map: `/sky?target={id}&t={UTC time}` (stars from Hipparcos, names from the IAU, photographs from the Digitized Sky Survey via CDS, comets from the Minor Planet Center's orbits, satellites from CelesTrak with visible passes, and a simulated view through the visitor's own telescope and eyepiece or camera)
- Assistant: every sky map and 3D universe card has "Ask about it" with questions suited to the object; answers come from an AI model the site owner connects
- Targets: `/targets?lat={deg}&lon={deg}&name={place}&mode=look|photo&gear=small` (ranked from the sky catalogue for that place and night; not a fixed list)
- Tools: `/tools` (light pollution map, field of view, telescope power, double stars, dark skies, camera match, sub length, sharp stars, polar alignment, calculators)
- Buying guide: `/{category}`

## Data
- [Manifest](data/index.json): categories, counts, every question with its allowed values, URL formats and formulas
- [Field reference](data/SCHEMA.md): units, enums and meaning of every field
- [Telescopes](data/telescopes.json): 244 products, JSON array
- [Mounts](data/mounts.json): 72 products, JSON array
- [Tripods and piers](data/tripods.json): 32 products, JSON array
- [Astro cameras](data/cameras.json): 38 products, JSON array
- [Guide scopes and off-axis guiders](data/guiding.json): 18 products, JSON array
- [Filters](data/filters.json): 50 products, JSON array
- [Focusers](data/focusers.json): 12 products, JSON array
- [Rotators](data/rotators.json): 6 products, JSON array
- [Eyepiece lines](data/eyepieces.json): 25 products, JSON array
- [Full catalogue as text](llms-full.txt): one line per product with key specs
- [Sky objects](data/objects.json): 212 deep-sky objects, double and coloured stars (J2000 degrees, sizes in arcminutes)
- Sky map data in data/sky/: stars-a.bin and stars-b.bin (117955 Hipparcos stars), sky.json (names and constellation figures), stars-info.json, bounds.json and milkyway.png; formats are in data/index.json

## Pages without JavaScript
- [Telescopes](catalog/telescopes.html)
- [Mounts](catalog/mounts.html)
- [Tripods and piers](catalog/tripods.html)
- [Astro cameras](catalog/cameras.html)
- [Guide scopes and off-axis guiders](catalog/guiding.html)
- [Filters](catalog/filters.html)
- [Focusers](catalog/focusers.html)
- [Rotators](catalog/rotators.html)
- [Eyepiece lines](catalog/eyepieces.html)

## Deep links (for sending people to a result)
- Guided finder with answers: `/telescopes?use=visual&see=planets,deepsky&budget=600` (question ids and values are in data/index.json; multi-select values are comma-separated)
- A product: `/{category}?p={productId}`
- Field of view: `/tools/fov?t=sky-watcher-skyliner-200p&ef=25&afov=52&target=moon`
- Telescope power: `/tools/scope?t={telescopeId}`
- Double stars: `/tools/doubles?t={telescopeId}&ef=9&seeing=avg`
- Dark skies: `/tools/sky?bortle=5`
- Camera match: `/tools/camera?t={telescopeId}&c={cameraId}&seeing=avg`
- Sub length: `/tools/subs?t={telescopeId}&c={cameraId}&filt=duo&bortle=6`
- Sharp stars (untracked exposure): `/tools/exposure?pcam=ff24&lens=24&fno=2.8&dec=-29`
- Polar alignment: `/tools/polar?lat=51.5&lon=-0.13&name=London&view=scope`
- Tonight's forecast: `/tonight?lat=50.7&lon=-3.52&name=Exeter`
- Targets to photograph with a 135 mm lens: `/targets?lat=50.7&lon=-3.52&name=Exeter&mode=photo&gear=lens&lens=135`
- Light pollution map: `/tools/map?lat=50.7&lon=-3.52&z=9`
- The Orion Nebula in the sky map at 11 pm UTC: `/sky?target=m42&t=2026-12-01T23:00Z`
- Saturn in 3D: `/universe?target=saturn`; Sirius: `/universe?target=hip:32349`
- Field of view for any catalogue object: `/tools/fov?t=sky-watcher-skyliner-200p&ef=25&afov=52&target=ngc7000`

All URL parameters and formulas are listed in data/index.json.

## Notes
- Forecasts come from Open-Meteo; the site computes darkness, the Moon, planet positions, moonlight and target rankings locally.
- Light pollution is modelled from NASA Black Marble night-lights imagery (GIBS); it is an estimate, typically within half a Bortle class.
- Product illustrations are drawn from the specs, not photographs.
- Updated 2026-10-24.