Our nearest neighbour

The Moon Tonight

Nothing here is downloaded — the phase is worked out from the length of the lunar cycle. Pick any date, forwards or backwards, and you'll see the shape the Moon had on that night.

—
—
    Why does it change shape? The Moon doesn't glow — it reflects sunlight, and exactly half of it is always lit. What changes is how much of that lit half faces us as it orbits. A full moon means we're looking straight at the sunlit side; a new moon means we're looking at the night side.
    The whole cycle

    This month

    Every night of the month at a glance. Click any day to jump to it.

    Phases are calculated from a synodic month of 29.530589 days. Accurate to within a few hours — good enough for the naked eye, not for a spacecraft.

    Moon facts

    Things worth knowing about it

    You've never seen its back

    The Moon rotates exactly once per orbit, so the same face always points at us. This is called tidal locking, and Earth's gravity caused it. The far side was first photographed by the Soviet Luna 3 probe in 1959.

    It pulls the oceans

    The Moon's gravity drags water toward it, creating a bulge — and another on the opposite side of Earth. As the planet rotates through those bulges, coastlines get roughly two high tides a day.

    It's drifting away

    About 3.8 cm further from Earth every year — measured by bouncing lasers off mirrors the Apollo astronauts left behind. In the age of the dinosaurs, the Moon looked noticeably bigger.

    It was probably a collision

    The leading theory says a Mars-sized body called Theia struck the young Earth about 4.5 billion years ago. The debris thrown into orbit clumped together and became the Moon.

    No air, huge extremes

    With almost no atmosphere to hold heat, the surface swings from about 127 °C in sunlight to −173 °C in shadow. And the sky there is black even at noon.

    It fits the Sun exactly

    The Sun is about 400 times wider than the Moon — and about 400 times further away. That coincidence is why total solar eclipses work at all. No other planet in the solar system gets this.