Summary
Highlights
The moon exhibits different phases because the amount of its illuminated surface visible from Earth changes. These phases range from a 'new moon' (invisible) to a 'full moon' (fully lit). Other phases include 'waxing crescent' (increasing light), 'first quarter,' 'waxing gibbous,' 'waning gibbous' (decreasing light), 'third quarter,' and 'waning crescent.'
The moon's phases are a direct result of its position relative to the Earth and the Sun. When the moon is between the Earth and the Sun, the side facing Earth is dark (new moon). As it orbits, different portions of its sunlit side become visible, leading to a full moon when the Earth is between the moon and the Sun.
The moon's rise and set times change daily, typically by about 50 minutes later each day. This phenomenon is due to the moon's orbit around the Earth and the Earth's orbit around the Sun.
The time it takes for the moon to orbit the Earth once is about 27.3 days (sidereal month). However, the time it takes for the moon to complete one full cycle of phases (from new moon to new moon) is 29.5 days (synodic month). This difference occurs because the Earth is also moving around the Sun, requiring the moon to travel slightly further to realign with the same phase relative to Earth and the Sun.
A solar eclipse happens when the moon passes directly between the Sun and Earth, casting a shadow on Earth and blocking out the Sun. These events are rare because the moon's orbit is slightly tilted relative to Earth's orbit around the Sun. The moon's shadow creates an 'umbra' (total shadow) and a 'penumbra' (partial shadow), determining whether an observer sees a total or partial eclipse. During a total solar eclipse, the Sun's corona (atmosphere) becomes visible.
A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the moon. Instead of disappearing, the moon usually turns a reddish hue, often called a 'blood moon.' This is because Earth's atmosphere scatters blue light but bends red light, directing it onto the moon's surface. This red light is essentially all the Earth's sunrises and sunsets projected onto the moon.
Eclipses happen in 'eclipse seasons' and can be predicted because the Earth's orbit around the Sun and the moon's orbit around the Earth are well understood. Future solar eclipses mentioned include those in 2024 (through Mexico, Texas, and the eastern seaboard of the US), 2020 (South America), and 2030 (South Africa).