Lunar Phases, Eclipses, and Celestial Phenomena

Moon Phases and the Lunar Cycle

New Moon: The Moon's unilluminated side is facing the Earth. The Moon is not visible, except during a solar eclipse.

First Quarter: One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.

Full Moon: The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.

Last Quarter: One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.

The Lunar Month

A complete cycle (one lunar month) lasts approximately 28 days.

Solar and Lunar Eclipses

The Solar Eclipse

A solar eclipse occurs when the Moon passes between the Sun and Earth, and the Moon blocks (or "occults") the Sun. This can happen only at a New Moon. In a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses, only part of the Sun is obscured.

The Lunar Eclipse

A lunar eclipse occurs when the Moon passes directly behind the Earth into its shadow. A lunar eclipse can occur only on the night of a Full Moon. A total lunar eclipse has the direct sunlight completely blocked by the Earth's shadow.

Synchronous Rotation

Synchronous Rotation: The Moon rotates at the same rate as it orbits the Earth.

Comets, Asteroids, and Meteors

Comets

A comet is an astronomical object made mainly of frozen gases and dust (small rocky particles). It is irregularly shaped and orbits the Sun.

Asteroids

Asteroids are minor rocky bodies orbiting the Sun, distributed mainly in a disk located roughly between the orbits of the planets Mars and Jupiter. They are considered the debris of a planet that never formed.

Meteoroids, Meteors, and Meteorites

• Meteoroid: A small rocky or metallic body traveling through space. Meteoroids are significantly smaller than asteroids and range in size from small grains to one-meter-wide objects.
• Meteor: Often called a "shooting star" or "falling star," this is the passage of a meteoroid into the Earth's atmosphere, heated from collisions with air particles in the upper atmosphere. It is visible as a streak of light. Meteors typically occur in the mesosphere at altitudes from 76 to 100 km (47 to 62 mi).
• Meteorite: A portion of a meteoroid or asteroid that survives its passage through the atmosphere and hits the ground without being destroyed.

Fundamental Space Movements of Earth

• Revolution: Movement around the Sun.
• Rotation: Spinning on its axis.
• Precession: A change in the orientation of the rotational axis of a rotating body.
• Oscillation: The oscillation of axial tilt.

Twilight and Meteor Showers

Twilight

Twilight is the illumination of the Earth when the Sun itself is not directly visible because it is below the horizon. The categories include: Day, Civil, Nautical, Astronomical, and Night.

Meteor Shower

A meteor shower is an astronomical event in which a number of meteors are observed to radiate, or originate, from one point in the night sky.