The moon's apparent height in the sky is a complex phenomenon determined by several factors, including seasons, lunar orbits, and an interesting psychological effect called the "moon illusion."
Seasons and Earth's Tilt
Earth's rotational axis is tilted relative to its orbital plane around the sun. This tilt causes the seasons and also affects the path we see the moon take across the sky.
- Winter: During winter, the sun follows a lower path across the sky. Since the full moon is roughly opposite to the sun, the full moon follows a higher path across the sky.
- Summer: Conversely, during summer, the sun follows a higher path across the sky, causing the full moon to follow a lower path across the sky. This is why you might notice the moon closer to the horizon on summer nights.
The Moon Illusion
This is a powerful optical illusion where the moon appears much larger when it's near the horizon compared to when it's high in the sky. Your brain compares the moon near the horizon to trees, buildings, and other objects, making it seem unusually large and closer (and thus "lower").
When the moon is high overhead, there are no reference objects, so it appears smaller and feels more distant. Despite this perception, the moon's actual size doesn't change throughout the night.
Lunar Orbit
The moon's orbit around Earth is not a perfect circle but an ellipse. This means the moon's distance from Earth varies throughout its orbital cycle. When the moon is at its perigee (closest to Earth), it may appear slightly larger, which can contribute to the moon illusion.