Unit 1: Earth's Place in the Universe

Vocabulary flashcards covering key terms from Unit 1 notes.

Nebula

A cloud of gas and dust in space from which stars and planets form.

Solar Nebular Theory

A model explaining solar system formation from a collapsing, rotating cloud (nebula) of gas and dust.

Orbit

The gravitational path of a body as it moves around another body.

Orbital period

The time required for a body to complete one orbit.

Meteoroid

A small rocky or metallic object traveling in space.

Meteor

A meteoroid that burns up as it enters Earth's atmosphere.

Comet

An icy body with a glowing coma and tail when near the Sun.

Asteroid belt

A region between Mars and Jupiter where many asteroids orbit the Sun.

Gravity

The force of attraction between masses; depends on mass and distance.

Terrestrial planets

Rocky inner planets: Mercury, Venus, Earth, Mars.

Gas giants (Jovian planets)

Large outer planets made mostly of hydrogen and helium: Jupiter, Saturn, Uranus, Neptune.

Solar system

The Sun and all objects that orbit it.

Star

A massive, luminous sphere of hot plasma fusing hydrogen into helium.

Geocentric model

Earth-centered view of the universe.

Heliocentric model

Sun-centered view of the solar system.

Ptolemy

Ancient astronomer who refined the geocentric model with epicycles.

Copernicus

Astronomer who proposed the heliocentric model.

Epicycle

A small circular motion used in the geocentric model to explain retrograde motion.

Elliptical orbit

An orbit that is oval-shaped rather than perfectly circular.

Kepler's First Law

Planets orbit the Sun in ellipses with the Sun at one focus.

Kepler's Second Law

A line from the Sun to a planet sweeps out equal areas in equal times.

Kepler's Third Law

P^2 ∝ a^3; the square of a planet's period is proportional to the cube of its average distance from the Sun.

Angular momentum

Quantity of rotation that helps determine the motion of bodies in orbit and disk formation.

Planetesimals

Small building blocks that collide and merge to form planets.

Nuclear fusion

Process powering stars where small nuclei fuse to form heavier nuclei, releasing energy.

Inner planets

Terrestrial planets close to the Sun (Mercury, Venus, Earth, Mars).

Outer planets

Gas/ice giants farther from the Sun (Jupiter, Saturn, Uranus, Neptune).

Moon

Earth's natural satellite that orbits due to gravity.

Tides

Daily rise and fall of oceans caused by the Moon's gravity.

Eclipse

Alignment of Sun, Moon, and Earth; solar eclipse blocks the Sun, lunar eclipse occurs when Earth blocks sunlight from reaching the Moon.

Barycenter

Center of mass of a system; causes a wobble in the Sun due to planetary pull.

Solar wind

Stream of charged particles emitted by the Sun.

Solar flare

Sudden eruption of energy on the Sun's surface that releases particles into space.

Photosphere

Visible surface of the Sun that emits most of the Sun's light.

Chromosphere

Thin solar layer above the photosphere that glows red.

Corona

Outer atmosphere of the Sun, visible during eclipses.

Sunspots

Cooler, darker regions on the Sun linked to magnetic activity.

Radiative zone

Solar layer where energy moves outward mainly by photon diffusion.

Convection zone

Layer where hot plasma rises and cools, aiding energy transport and activity.

Core

The Sun's center where nuclear fusion occurs at extremely high temperature.

Kuiper Belt

Region beyond Neptune containing comets, asteroids, and dwarf planets.

Dwarf planet

A roundish body that orbits a star but has not cleared its orbit of other debris.

Pluto

Example of a dwarf planet in the Kuiper Belt.

Milky Way

Our galaxy; a disk-shaped collection of stars, including the Sun.

Galaxy

A large system of stars, gas, and dark matter bound by gravity.

Big Bang

The theory that the universe began ~13.7 billion years ago from a hot, dense state.

Solar radiation

Energy emitted by the Sun that travels through space and Earth's atmosphere.

Visible light

Wavelengths of light that humans can see; part of the electromagnetic spectrum.

Infrared

Longer-wavelength radiation felt as heat; not visible to the human eye.

Ultraviolet

Short-wavelength light that can be harmful in high doses.

Gamma rays

High-energy radiation; mostly blocked by Earth's atmosphere.

Atmosphere

Layered gaseous envelope surrounding Earth.

Troposphere

Lowest atmospheric layer where weather occurs.

Stratosphere

Atmospheric layer containing the ozone layer.

Mesosphere

Layer where meteors burn up.

Thermosphere

High layer containing the ionosphere and auroras.

Exosphere

Outermost atmospheric layer blending into space.

Ozone Layer

Stratosphere layer that absorbs most harmful UV radiation.

Albedo

Measure of how much light a surface reflects.

Heat budget

Balance of incoming and outgoing energy keeping Earth's climate in balance.

Photosynthesis

Process by which organisms convert light energy to chemical energy, producing oxygen.

Water cycle

Cycle of evaporation, condensation, and precipitation driving weather and life.