Charting the Heavens II — Moon Phases, Eclipses, and Distance

Vocabulary flashcards covering key terms from the notes on Moon phases, eclipses (lunar and solar), distances, and methods for measuring cosmic distances.

Astronomy

The science that studies celestial objects, space, and the universe beyond Earth's atmosphere.

Solar system

The Sun and all objects that orbit it, including planets, moons, asteroids, and comets.

Milky Way

The barred spiral galaxy that contains our Solar System.

Universe

All of space, time, matter, and energy—the cosmos.

Constellations

Patterns of stars named for mythological figures or objects, used to identify regions of the sky.

Celestial sphere

An imaginary sphere surrounding the Earth onto which celestial objects are projected for mapping.

Seasons

Periodic changes in weather and daylight caused by Earth's tilt and orbit around the Sun.

Precession

The gradual wobble of Earth's axis that slowly shifts the orientation of the axis over time.

Moon

Earth's natural satellite that orbits Earth and reflects sunlight.

Reflect sunlight

The process by which the Moon shines by reflecting the Sun's light rather than producing light itself.

Moon’s orbit tilt

The Moon's orbital plane is tilted relative to Earth's orbit around the Sun.

Average Earth–Moon distance

About 384,400 kilometers (238,555 miles) on average.

Phase

The appearance of the Moon’s illuminated portion as seen from Earth during its orbit.

New Moon

The Moon is between Earth and Sun; the Sun-lit side faces away from Earth and is not visible.

Waxing Crescent

A Moon phase where a small crescent becomes more illuminated as it moves toward the First Quarter.

First Quarter

Half of the Moon’s near side is lit; the terminator runs down the middle.

Waxing Gibbous

More than half lit and increasing toward Full Moon.

Full Moon

The entire face of the Moon visible from Earth is illuminated.

Waning Gibbous

After Full Moon, the illuminated portion decreases.

Third Quarter

The opposite half of the Moon is lit; the other side's half is illuminated.

Waning Crescent

A small crescent shrinking toward New Moon.

Lunar phases

The sequence of Moon appearances caused by its orbit and sunlight.

Eclipse

An event when Sun, Moon, and Earth align, causing shadowing or blocking of sunlight.

Lunar Eclipse

Earth blocks sunlight from reaching the Moon when Earth is between Sun and Moon.

Solar Eclipse

Moon blocks sunlight from reaching Earth when Moon is between Earth and Sun.

Penumbral lunar eclipse

Moon passes through Earth’s penumbra, causing a subtle shading.

Partial lunar eclipse

Only part of the Moon passes through Earth’s umbra.

Total lunar eclipse

The entire Moon passes through Earth’s umbra.

Umbra

The central, darkest part of a shadow created by an opaque object.

Penumbra

The outer, partially shaded region of a shadow during an eclipse.

Total Solar Eclipse

Sun is completely obscured by the Moon along the path of totality.

Partial Solar Eclipse

Only part of the Sun is obscured by the Moon.

Annular Solar Eclipse

Moon is too far to completely cover the Sun, leaving a ring (donut) of Sun visible.

Hybrid Eclipse

An eclipse that appears total in some regions and annular in others along its path.

Corona

The Sun’s outer atmosphere visible during a total solar eclipse.

Path of totality

The narrow track on Earth’s surface where a total solar eclipse is visible.

Ecliptic plane

The plane of Earth’s orbit around the Sun; the Moon’s orbit is inclined to it by about 5 degrees.

Triangulation

A distance-measurement method using a baseline and angles to determine distance.

Parallax

Apparent motion of an object against distant backgrounds when viewed from different locations, used to measure distance.

Angular diameter

The apparent size of an object in the sky, measured as an angle.

EPIC (Earth Polychromatic Imaging Camera)

NASA instrument on the DSCOVR spacecraft that captures images of Earth.

SDO (Solar Dynamics Observatory)

NASA mission that observes the Sun to study solar activity.

LRO (Lunar Reconnaissance Orbiter)

NASA mission orbiting the Moon to map its surface.

Lunar cycle

Approximately a 29.5-day cycle of Moon phases from New Moon back to New Moon.

Corona

Sun’s outer atmosphere visible during a total solar eclipse.