Reference
Data, calculations and accuracy
Sky Map 2000 combines established public catalogues with browser-side astronomical calculations, and stays explicit about the limits that come with an online reference.
What the map draws from
The star field uses the HYG Database, version 44, with more than 99,000 records down to about magnitude 9.5. Selected Messier, NGC and IC objects come from the open OpenNGC catalogue. Constellation outlines, boundaries and the Milky Way reference layer are derived from data used by d3-celestial.
Local place names come from a bundled GeoNames dataset. Meteor-shower reference data draws on the International Astronomical Union Meteor Data Center and the International Meteor Organization. All of these ship with the app, so the map can work without sending an observer’s saved location anywhere.
What is calculated for your view
For the chosen location, date and time, the app derives the local orientation of the sky: altitude, azimuth, horizon, sidereal context and the positions used by the selected coordinate mode. The Sun, Moon and planets use low-precision orbital calculations that are enough for a sky-atlas view. Physical reference values are cross-checked against sources such as NASA JPL’s planetary fact sheets.
That makes the map well suited to orientation, identifying a target and preparing an observing session. It is not a replacement for ephemeris software designed for precision astrometry, telescope pointing or navigation.
Where the limits live
A calculated horizon is a geometric horizon. Trees, buildings, hills and haze at your site can hide objects the map draws above it. Weather, transparency, moonlight, light pollution, eyesight and equipment shape what is actually visible.
Set the location and time carefully before you rely on the display. If the map does not match the sky, check the observer location, time zone, selected date and whether a live or simulated time mode is active.
For the meaning of a catalogue field or a local calculation, see object cards and map key, the meteor-shower guide and the frequently asked questions.