The Moon doesn’t make its own light—it reflects sunlight! As the Moon orbits Earth, we see different amounts of its sunlit side, creating the phases we observe.

The Moon takes about 29.5 days to go through all its phases. This is called the lunar cycle. During this time, the Moon travels in an elliptical (oval-shaped) orbit around our planet.

Moon phases result from the changing geometric relationship between the Sun, Earth, and Moon. As the Moon orbits Earth in approximately 29.53 days (a synodic month), different portions of its illuminated hemisphere become visible from Earth.

The Moon’s orbit is elliptical rather than circular, with an eccentricity of about 0.0549. This elliptical path causes the Moon’s distance from Earth to vary by approximately 50,000 kilometers (31,000 miles) between perigee and apogee.

The Moon’s orbit around Earth is elliptical (oval-shaped), not circular. This means the Moon’s distance from Earth changes as it travels along its path.

The closest point is called perigee, and the farthest point is called apogee. The difference between these two points is about 30,000 miles (50,000 kilometers)!

When a Full Moon happens at or near perigee, we get a Supermoon – the Moon appears about 14% bigger and 30% brighter than when it’s at apogee.

The Moon’s orbit has an eccentricity of approximately 0.0549, making it an ellipse rather than a perfect circle. At perigee (closest approach), the Moon is about 356,500 km from Earth, while at apogee (farthest point), it’s approximately 406,700 km away—a difference of roughly 50,000 km.

A supermoon occurs when the Moon reaches perigee during its full phase. This astronomical alignment, called perigee-syzygy, results in the Moon appearing approximately 14% larger in diameter and 30% brighter than an apogee full moon (sometimes called a micromoon).

The term “supermoon” was coined by astrologer Richard Nolle in 1979, though astronomers prefer “perigee full moon.” These enhanced full moons can also create slightly higher tides due to increased gravitational pull.

Even though a supermoon is 14% bigger, it’s hard to notice the size difference when the Moon is high in the sky. The best time to observe is during moonrise or moonset, when the Moon is near the horizon.

When the Moon appears near trees, buildings, or mountains, an optical illusion called the Moon illusion makes it seem even larger! Scientists aren’t completely sure why this happens, but it’s probably related to how our brains compare the Moon to objects on the ground.

Observation tip: Check a moon phase calendar to find the next Full Moon, then look for it just after sunset on the eastern horizon. That’s when it will appear largest and most impressive!

Although a supermoon is approximately 14% larger in angular diameter and 30% brighter in luminosity than a micromoon, the human eye struggles to detect this difference when viewing the Moon in isolation against the vast night sky.

The optimal viewing occurs during moonrise or moonset when the Moon is positioned near the horizon. At these times, the Moon illusion—a cognitive phenomenon rather than an atmospheric effect—makes the Moon appear dramatically larger. This perceptual effect occurs because our brains interpret the Moon’s size relative to foreground objects like buildings and trees.

Scientific observation: You can measure the Moon illusion effect by holding your thumb at arm’s length. The Moon’s angular diameter remains constant at about 0.5 degrees whether it’s on the horizon or overhead, despite appearing larger at the horizon. Photographers can capture this effect using telephoto lenses with foreground subjects in silhouette.

Tidal effects: Supermoons can produce perigean spring tides—higher than normal tides that occur when the Moon’s gravitational pull is strongest due to its proximity to Earth.

Like the Sun, the Moon rises in the east and sets in the west. This happens because Earth rotates from west to east. However, unlike the Sun, the Moon’s rise and set times change every day!

The Moon moves about 12.5 degrees eastward in its orbit each day. This means Earth has to rotate a little longer each day to bring the Moon back into view. That’s why moonrise happens about 50 minutes later each night.

Different phases, different times:

• Full Moon: Rises around sunset, sets around sunrise
• First Quarter: Rises around noon, sets around midnight
• New Moon: Rises and sets with the Sun (we can’t see it!)
• Last Quarter: Rises around midnight, sets around noon

Both the Sun and Moon rise in the east and set in the west due to Earth’s west-to-east rotation. However, the Moon’s position in the sky is not fixed because it orbits Earth, completing one orbit approximately every 27.3 days (sidereal month).

The Moon advances approximately 12.5 degrees eastward in its orbit each day. Consequently, Earth must rotate an additional 50 minutes (on average) to bring the Moon back to the same position in the sky, causing moonrise to occur later each successive night.

Phase-dependent visibility:

• New Moon: Conjunction with Sun—rises/sets with Sun, invisible due to solar glare
• First Quarter: 90° east of Sun—rises ~noon, transits ~6pm, sets ~midnight
• Full Moon: Opposition to Sun—rises ~sunset, transits ~midnight, sets ~sunrise
• Last Quarter: 90° west of Sun—rises ~midnight, transits ~6am, sets ~noon

The Moon’s orbital plane is inclined about 5° to the ecliptic (Earth’s orbital plane), causing slight deviations from these idealized times. This inclination also explains why we don’t have lunar eclipses every month—the Moon must be near a node (intersection point) for its shadow to align with Earth.