Earth's moon is the brightest object in our night sky and the closest celestial body. Its presence and proximity play a huge role in making life possible here on Earth. The moon's gravitational pull stabilizes Earth's wobble on its axis, leading to a stable climate.
The moon's orbit around Earth is elliptical. At perigee — its closest approach — the moon comes as close as 225,623 miles (363,104 kilometers). At apogee — the farthest away it gets — the moon is 252,088 miles (405,696 km) from Earth. On average, the distance from Earth to the moon is about 238,855 miles (384,400 km). However, the moon is moving away from Earth at a rate of about 1.5 inches (4 cm) per year.
The moon is in synchronous rotation with Earth. In other words, the moon rotates on its axis in about the same amount of time it takes to revolve around Earth — 27 days 8 hours, which is called sidereal month. So we always see the same side of the moon; there is no "dark side of the moon." A lunar month, also called a synodic month, is the time it takes for the moon to complete a lunar cycle — full moon to full moon. A lunar month is about 29 days 13 hours.
How long does it take to get to the moon?
Apollo missions took about three days to reach the moon. But the quickest trip to the moon was the New Horizons probe, which zipped past the moon in just 8 hours 35 minutes on its way to Pluto. However, the spacecraft didn't even slow down or approach lunar orbit.
Tides occur because of the gravitational pull of the moon. The oceans bulge in the direction of the moon. High tide happens when the moon is overhead, but it also happens on the opposite side of the planet because the moon is tugging on Earth as well.
Spring tides — so called because the water "springs up," not because of the season — occur when the moon, the sun and Earth are aligned, during a full moon or new moon. The gravitational forces of the moon and the sun both contribute to these especially strong tides. Neap tides are weak and occur during quarter moons when the forces of the sun and the moon are perpendicular to each other.
— Tim Sharp, SPACE.com Reference Editor
- How Big is the Moon?
- Atmosphere of the Moon
- What is a Blue Moon?
- How Moon Phases Work
- Lunar Eclipses: What is a Total Lunar Eclipse & When is the Next One?