A visual explainer
Sunlight always illuminates exactly half the Moon. As the Moon orbits Earth over 29.5 days, our viewing angle of that lit half changes — creating the phases. Earth's shadow plays no role; that only occurs during a lunar eclipse.
The Moon is between Earth and Sun. Its sunlit hemisphere faces away from us entirely — we see only darkness. The Moon rises and sets with the Sun and is not visible from Earth.
The Moon has moved 90° around Earth. We see exactly half its sunlit face — a crisp half-disk. It rises around noon and sets near midnight local time.
Earth is between Sun and Moon. Sunlight passes around Earth and fully illuminates the near side. The Moon rises near sunset and sets near sunrise, visible all night.
Now 270° around, the opposite half-disk is lit. It rises near midnight and sets near noon, completing its return toward the next New Moon.
During new moon and full moon, the Sun and Moon align gravitationally, producing spring tides — the largest tidal range of the cycle. Higher high tides and lower low tides, with stronger currents.
Learn about spring & neap tides →At first quarter and third quarter, the Sun and Moon pull at right angles. Their forces partially cancel, producing neap tides — the smallest tidal range, with gentler currents.
Solunar fishing guide →Moon phases are caused by the changing viewing angle of the Moon's sunlit half as it orbits Earth over 29.5 days. The Sun always illuminates exactly half the Moon — phases are NOT caused by Earth's shadow. Earth's shadow only falls on the Moon during a lunar eclipse, which is a separate and much rarer event.
During new moon and full moon (spring tides), the Sun and Moon align, producing the largest tidal range. During first and third quarter moons (neap tides), their gravitational forces partially cancel, producing the smallest tidal range. This fortnightly cycle is one of the most important factors in coastal planning. Read our full guide on spring and neap tides.
A synodic month (new moon to new moon) takes approximately 29.5 days. The Moon's sidereal orbit takes 27.3 days, but it needs an extra ~2.2 days to realign with the Sun because Earth has also moved along its own orbit.
The Moon is above the horizon for about 12 hours each day, but those hours shift. Around first quarter, it rises near noon and sets near midnight. Around full moon, it rises at sunset and sets at sunrise. Only around new moon is it up exclusively during daylight — but then it's invisible because its lit side faces away from us.
No. A blue moon is simply the second full moon within a calendar month, or the third full moon in an astronomical season that has four. It looks the same as any other full moon. The phrase “once in a blue moon” means something rare — blue moons occur roughly every 2.5 years.