Inside the app
A closer look.
About this app
Made for a clear purpose.
Sidereal is a serious, offline sky atlas and observation planner built for amateur astronomers and astrophotographers — not another horoscope or AR toy. Every star position, rise time, and planetary coordinate is computed on your device from bundled professional catalogs, so it works perfectly at a dark site with no cell signal.
A REAL CATALOG IN YOUR POCKET • 328,000 stars down to magnitude 10 (Hipparcos / ATHYG), with proper names, Bayer and Flamsteed designations, spectral types, distances and luminosities • 13,000+ deep-sky objects — the complete NGC and IC catalogs • The full Messier catalog and the Caldwell catalog, curated for observers • Constellation stick figures, IAU boundaries and full constellation reference • Everything is bundled and offline — no account, no cloud, no tracking
INTERACTIVE SKY CHART • Pan and pinch a live planetarium view of the sky from your exact location and time • Stars sized by magnitude and tinted by colour index; deep-sky objects drawn by type • Constellation lines and labels, the ecliptic, an alt-azimuth grid and a true horizon with cardinal points • Planets, the Sun and the Moon plotted from real ephemerides • Tap anything to identify it and open a full data sheet • Scrub time forward or back to see how the sky moves
PRECISE POSITIONAL ASTRONOMY • Rise, transit and set times, plus an altitude curve for any object across the night • Astronomical, nautical and civil twilight, and hours of true darkness • Precession, nutation, sidereal time and apparent (of-date) coordinates • Planetary and solar positions from the VSOP87 theory; lunar position, phase and illumination from an ELP-2000 series — all evaluated on device
PLAN YOUR NIGHT • Tonight view: sunset to sunrise, moon phase and interference, planet visibility • The best Messier and Caldwell targets tonight, ranked by altitude during darkness and distance from the Moon • Observing lists you build yourself, and a session log for seeing, transparency, equipment and notes
TOOLS FOR THE FIELD • Imaging field-of-view and image-scale calculator for any telescope and camera • Visual field-of-view, magnification and exit-pupil calculator for eyepieces • Polar-alignment helper with a live Polaris reticle clock position • Local and Greenwich sidereal time, Julian date and obliquity
BUILT FOR THE DARK • Red-light night mode preserves your dark adaptation • Choose your site by GPS or enter coordinates for anywhere on Earth
Sidereal keeps your observing entirely private and entirely on your device. Own it — no login, no subscription round-trips, no light pollution of your data.
