The moon constantly shifts its appearance. These changes are not inherent to the moon itself, but result from its dynamic relationship with the Earth and the Sun, along with other environmental factors influencing how we perceive it.
Understanding Moon Phases
The moon does not produce its own light; it shines by reflecting sunlight. As the moon orbits Earth, the amount of its sunlit surface visible from our perspective changes, creating lunar phases. This cycle repeats approximately every 29.5 days.
The cycle begins with the new moon, when the moon is positioned between the Earth and the Sun, and its sunlit side faces away from us, making it largely invisible. As it continues its orbit, a sliver of illumination becomes visible, marking the waxing crescent phase. This illuminated portion grows daily, leading to the first quarter moon, where half of the moon’s face appears lit.
The illuminated area expands into the waxing gibbous phase, where more than half of the moon is visible. The full moon occurs when the entire side facing Earth is fully illuminated, as the moon is opposite the Sun in its orbit. Following the full moon, the illuminated portion shrinks, transitioning through the waning gibbous, third quarter, and waning crescent phases before returning to a new moon.
The Spectacle of Eclipses
Beyond the regular phases, specific alignments of the Sun, Earth, and Moon create eclipses. A lunar eclipse happens when the Earth passes directly between the Sun and a full moon, casting Earth’s shadow upon the lunar surface. The moon does not disappear entirely during such an event.
Instead, it often takes on a deep reddish or coppery hue, earning it the name “blood moon.” This coloration occurs because some sunlight bends through Earth’s atmosphere, scattering shorter blue wavelengths and allowing longer red and orange wavelengths to reach and illuminate the moon. Solar eclipses also involve the moon, occurring when it passes between the Sun and Earth during a new moon phase, temporarily obscuring the Sun from our view.
How Distance and Atmosphere Alter the Moon’s Look
The moon’s appearance can also be influenced by its varying distance from Earth and the effects of our planet’s atmosphere. The moon’s orbit around Earth is elliptical, meaning its distance is not constant.
When the full moon coincides with its closest point to Earth, known as perigee, it appears slightly larger and brighter, termed a “supermoon.” Conversely, when a full moon occurs at its farthest point, or apogee, it appears smaller and dimmer, called a “micromoon.” The moon’s apparent size can vary by about 14% and its brightness by up to 30% between these extremes.
Earth’s atmosphere further alters the moon’s visual characteristics. When the moon is low on the horizon, its light travels through more of Earth’s atmosphere. This atmospheric scattering removes shorter blue wavelengths, allowing more red and orange light to pass through, causing the moon to appear with a reddish or orange tint. The “moon illusion,” where the moon seems much larger when near the horizon, is primarily a perceptual effect.