Astronomy: Moon Phases, Eclipses, Orbits, and Gravity

Vocabulary flashcards covering Moon phases, eclipses, orbital mechanics, tides, and planetary motion concepts from the lecture notes.

Waxing

Moon's illuminated portion is increasing; follows the new Moon and is typically visible in the evening sky.

Waning

Moon's illuminated portion is decreasing; follows the full Moon and is typically visible in the morning sky.

Gibbous Moon

Phase when more than half of the Moon's near side is illuminated but it is not yet full.

Ellipse

A closed, oval-shaped curve; planetary orbits are ellipses with the Sun at one focus.

Sun at a Focus

In an elliptical orbit, the Sun lies at one of the two foci.

Kepler's First Law

Planetary orbits are ellipses with the Sun at one focus.

Kepler's Second Law

Planets sweep out equal areas in equal times as they orbit.

Kepler's Third Law

The square of a planet's orbital period is proportional to the cube of its semi-major axis (P^2 ∝ a^3).

P^2 ∝ a^3

Kepler's third law: orbital period squared is proportional to semi-major axis cubed.

Conic Sections

The shapes of orbital paths: circle, ellipse, parabola, and hyperbola, arising from the inverse-square gravity.

Umbra

The darkest part of a shadow (Earth's shadow during a lunar eclipse).

Penumbra

The partial outer shadow around the umbra during an eclipse.

Lunar Eclipse

Earth blocks sunlight from reaching the Moon; the Moon passes through Earth's shadow; can be total, partial, or penumbral.

Solar Eclipse

The Moon blocks the Sun as seen from Earth; can be total, partial, or annular.

Annular Eclipse

A solar eclipse where the Moon is too far to completely cover the Sun, leaving a bright ring (annulus).

Partial Eclipse

Only part of the Sun is obscured by the Moon.

Total Solar Eclipse

The Moon completely covers the Sun, briefly darkening the sky along the path of totality.

Path of Totality

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

Moon's Orbital Tilt

The Moon's orbit around Earth is inclined relative to Earth's orbital plane, causing eclipses to occur only occasionally.

Astronomical Unit (AU)

Average distance between the Earth and the Sun, about 149.6 million kilometers.

Tides

Global ocean bulges caused by the Moon's gravity; stronger on the near side due to differential gravity.

Spring Tides

When Sun and Moon align in the same direction, producing larger tidal ranges.

Neap Tides

When Sun and Moon are at right angles, producing smaller tidal ranges.

Tycho Brahe

16th-century Danish astronomer known for precise observational data used by Kepler.

Johannes Kepler

17th-century astronomer who formulated three laws of planetary motion from Tycho Brahe's data.

Planet Nine

Hypothetical distant planet proposed to explain clustering in outer Solar System orbits; associated with various trans-Neptunian object findings.

Neptune Prediction

Predicted planet due to gravitational influence on Uranus's orbit; later discovered in 1846.

Inverse Square Law

Gravitational force between two masses decreases with the square of the distance: F ∝ 1/r^2 (F = G M1 M2 / r^2).

Newton's Law of Gravity

F = G M1 M2 / r^2; the gravitational force between two masses decreases with distance as the inverse square.