About NowSky

NowSky is an interactive sky and solar-system simulator that recreates tonight's sky from your location and the motion of the solar system with real orbital calculations. Find constellations, planets, satellites and eclipses in the sky above you, and run probes and comets along their orbits through time. Alongside that, it puts everything from a proton (10⁻¹⁵ m) to the observable universe (10²⁷ m) on one ruler for size and speed comparisons.

Why it exists

There is plenty of astronomy content, but few tools show "how big Jupiter is" and "where Jupiter is right now" in one place, with an honest sense of proportion. Textbook diagrams exaggerate scale, and professional planetarium software has a steep learning curve. NowSky aims for the middle: numerically grounded, but instantly usable in a browser with your fingers. It is a reference and learning aid — for precision work such as observation planning, please cross-check professional sources.

Data sources

• Planet & moon orbits — mean orbital elements (J2000) with Kepler-equation solutions. Moon and Sun positions use abridged series from Meeus' Astronomical Algorithms (60 longitude/distance and 60 latitude terms for the Moon).
• Star catalog — bright stars and constellation figures are approximations (J2000) based on public catalogs such as HYG.
• Satellite orbits — public TLE data from Celestrak.
• Object photos & write-ups — public material from Wikimedia Commons/Wikipedia, shown with attribution.
• Event times — eclipse times are computed from our own new/full-moon solutions and match published values within a few minutes; pages note that they are approximate.

On accuracy

On-screen positions are approximations. Stars use J2000 places without precession or proper motion; planet positions come from mean elements and can be off by arcminutes. Magnification features intentionally break true scale. Each view's footer explains its specific approximations under "How it's computed".

Who runs this

NowSky is an independent project built and run by a single developer. Suggestions and bug reports are welcome on the contact page. Terms and the privacy policy are linked in the footer.