What this is

A first-person view of the sky as it would look standing on the Moon, at any date you choose. Nothing here is decorative: the Sun and Moon come from Meeus's Astronomical Algorithms, the librations place your feet on the real lunar surface, and the planets come from JPL's orbital elements.

Three things that surprise people

• A day lasts a month. Sunrise to sunset is about 14.8 Earth days.
• Earth never moves. It hangs in one patch of sky forever, turning on its axis and cycling through phases — the Moon is tidally locked, so Earth never rises or sets the way the Sun does. On the far side you never see it at all, and right on the limb libration alone can lift it in and out of view.
• Earth is bigger than the Sun from here — about 3.7× wider. The sky stays black at noon, because there is no air to scatter the light.

Controls

Drag to look around, pinch or scroll to zoom. The speed row runs from real time to a week a second. The dial in the corner is a sky map — zenith at the centre, horizon at the rim; tap it to look that way.

The ◎ button in the top bar is Lock to Earth. While it is on, nothing can pan the view away — you can zoom right in, hide the panels, and Earth stays where it is. Press it again to let go.

Drag to look around and pinch to zoom. Tap the speed to choose how quickly time passes. Lock to Earth follows Earth as it moves. Jump to takes you to the next sunrise, eclipse and more.

Tap empty sky to hide or restore all controls. If a menu is open, tap outside it to close only that menu. Swipe inside a menu to scroll.

Keyboard: space play or pause · ←→↑↓ look around · +− zoom · E face Earth · L lock to Earth · S face the Sun · N face north · H hide the panels · Esc close this.