AST101 Sun and its Neighbors Lecture 1-5 Practice Flashcards

This set of vocabulary flashcards covers key concepts from the first five lectures of AST101, including solar system objects, celestial mechanics, Kepler's and Newton's laws, and the properties of the Sun and light.

Star

A ball of high energy plasma driven by nuclear fusion that produces its own energy.

Sunspots

Magnetically active, cooler areas on the photosphere (~3500 $^{\circ}C$) that appear dark because magnetic activity prevents energy from reaching the surface.

Astronomical Unit ($1\,AU$)

The average distance between the Earth and the Sun, approximately used to measure distances within the solar system.

Terrestrial Planets

Small, rocky planets of the inner solar system, including Mercury, Venus, Earth, and Mars, which have thin or no atmospheres and few or no moons.

Maria

The large, dark, rocky, and heavily cratered plains on the Moon that are not geologically active.

Dwarf Planet

Objects massive enough to be approximately spherical but not massive enough to have cleared their orbit of other massive objects; examples include Ceres, Pluto, and Eris.

Ceres

The only dwarf planet inside the orbit of Jupiter and the largest object in the asteroid belt, composed of ice and rock.

Jovian Planets

The large, 'Jupiter-like' gas and ice giants of the outer solar system, including Jupiter, Saturn, Uranus, and Neptune.

Titan

A moon of Saturn with a thicker atmosphere than Earth, methane lakes and rivers, dune fields, and cryovolcanoes.

Eris

The most massive dwarf planet, similar in size to Pluto, which prompted astronomers to reconsider the definition of a planet.

Celestial Sphere

A model of the sky as a dome above Earth where the North and South Earth poles point to the North and South celestial poles.

sky looks different depending on your latitude and the time of year, affecting star visibility and constellation appearances.

Ecliptic

The plane of the solar system along which the Sun and planets move, inclined at $23.5^{\circ}$ from the celestial equator.

Right Ascension

Angles used to measure positions on the celestial sphere that are analogous to longitude lines on Earth.

Declination

Angles used to measure positions on the celestial sphere that are analogous to latitude lines on Earth.

Circumpolar

Stars or objects close enough to the celestial pole that they never set below the horizon from a given latitude.

Zodiac

The group of constellations that the ecliptic passes through, including a 13th constellation named Ophiuchus.

Axial Precession

The slow gravity-induced 'wobble' of Earth's rotational axis that changes the pole star over long periods (e.g., from Polaris to Vega in $12,000$ years).

Tidal Locking

A state where an object's rotation period matches its orbital period, resulting in the same face always pointing toward the body it orbits.

Annular Solar Eclipse

Often called a 'ring of fire' eclipse, it occurs when the Moon is farther away in its elliptical orbit and cannot completely cover the Sun.

Retrograde Motion

The apparent motion of a planet moving in the opposite direction (East to West) relative to the stars, which occurs as Earth overtakes outer planets.

Epicycles

Secondary circular motions within the Ptolemaic geocentric model used to explain the retrograde motion of planets.

Kepler's First Law

The law stating that all planets move in ellipses, with the Sun at one focus.

Kepler's Third Law

The orbital period squared is proportional to the semi-major axis cubed, expressed as $P^2 = a^3$ when $P$ is in years and $a$ is in AU.

Mass

A measurement of how much matter is in an object, which remains constant regardless of the local force of gravity.

Universal Law of Gravitation

The force of gravity between two objects is defined by $F = \frac{Gm_1m_2}{r^2}$, where $m_1$ and $m_2$ are masses and $r$ is the distance between them.

Hydrostatic Equilibrium

The stable balance in a star where the internal pressure produced by nuclear fusion matches the inward force of gravity.

Photosphere

The visible surface of the Sun ($5500^{\circ}C$) where visible light can freely escape into space.

Chromosphere

A layer of the Sun extending $2000\,km$ above the photosphere, characterized by features like prominences and filaments.

Corona

The outermost layer of the Sun's atmosphere consisting of ultra-hot gas (~$1\,million^{\circ}C$) with very low density.

Blackbody Radiation

Idealized thermal radiation emitted by an object in equilibrium that reflects its temperature, where hotter objects peak at shorter wavelengths.

Redshift

The shift of spectral lines toward longer wavelengths that occurs when an object is moving away from the observer.

Blueshift

The shift of spectral lines toward shorter wavelengths that occurs when an object is moving toward the observer.