Understanding the science behind lunar phases, orbital mechanics, and the Moon's influence on Earth
The Moon is our closest celestial neighbor and has fascinated humans for millennia. Understanding lunar astronomy helps us appreciate the complex dance of celestial bodies and the forces that shape our world.
From ancient civilizations using lunar calendars to modern space exploration, the Moon continues to play a crucial role in human culture and scientific advancement.
The Moon orbits Earth approximately every 29.5 days, which we call a lunar month. This orbit is slightly elliptical, meaning the Moon's distance from Earth varies between about 356,500 km (perigee) and 406,700 km (apogee).
Moon phases are caused by the changing angles of the Sun, Earth, and Moon. As the Moon orbits Earth, we see different portions of its sunlit surface, creating the familiar cycle from new moon to full moon and back.
The Moon's gravitational pull creates tides on Earth. The side of Earth facing the Moon experiences a stronger pull, creating high tide, while the opposite side also has high tide due to centrifugal force.
The Moon is tidally locked to Earth, meaning it rotates once on its axis in the same time it takes to orbit Earth. This is why we always see the same side of the Moon from Earth.
Moon phases are not caused by Earth's shadow (that's a lunar eclipse). Instead, they result from the changing angles between the Sun, Earth, and Moon as the Moon orbits our planet.
The Moon doesn't produce its own light - it reflects sunlight. As the Moon moves in its orbit, we see different portions of its sunlit surface, creating the familiar cycle of phases.
New Moon
Moon between Earth and Sun
First Quarter
Moon at 90° angle from Sun
Full Moon
Earth between Moon and Sun
Last Quarter
Moon at 270° angle from Sun
Dark, flat areas formed by ancient volcanic activity
Circular depressions formed by meteorite impacts
Bright, mountainous regions of ancient crust
Bright streaks extending from young craters
The Moon's gravity pulls on Earth's oceans, creating a bulge of water on the side facing the Moon. Surprisingly, there's also a bulge on the opposite side due to centrifugal force as the Earth-Moon system rotates around their common center of mass.
As Earth rotates, different parts of the planet pass through these bulges, creating the twice-daily cycle of high and low tides.
The Moon is about 1/4 the size of Earth
It takes 27.3 days for the Moon to orbit Earth
The Moon is moving away from Earth at 3.8 cm per year
The same side of the Moon always faces Earth
The Moon has no atmosphere or weather
Temperatures range from -173°C to 127°C
The Moon's gravity is about 1/6 of Earth's
The Moon was likely formed from a giant impact
The most widely accepted theory suggests that the Moon formed about 4.5 billion years ago when a Mars-sized object called "Theia" collided with the early Earth. This catastrophic impact ejected material into orbit around Earth, which eventually coalesced to form the Moon.
Theia collides with early Earth
Material ejected into Earth orbit
Debris coalesces to form Moon
Now that you understand the basics, explore our calendar to track lunar phases and plan your own observations.