Geology: The Universe and the Solar System

Comprehensive vocabulary flashcards covering the core concepts of the Universe, stellar properties, and the Solar System from the B1103 Geology course.

Astronomical Unit (AU)

A unit used to measure distances in the solar system, defined as the Earth-Sun distance, approximately equal to $150 \times 10^{6}\,km$.

Light-year (LY)

The distance traveled by light in a vacuum during one year, calculated as $9.47 \times 10^{12}\,km$.

Big Bang

The event that occurred $13.7$ billion years ago in which space, time, matter, and energy were created.

Galaxy

Regions of the Universe where billions of celestial bodies (planets, asteroids, comets), gases, interstellar dust, and stars are grouped together.

Local Group

The galactic cluster containing around $30$ galaxies, including our Milky Way.

Elliptical galaxies

A class of galaxies (making up $2/3$ of all galaxies) that contain few young stars, little gas and dust, many old red stars, and show little rotation.

Spiral galaxies

Huge rotating, flattened systems of stars, gas, and dust (making up $1/4$ of all galaxies) that are rich in bright young stars.

Irregular galaxies

Galaxies (less than $1/10$ of all galaxies) located near large galaxies which disturb them and change their appearance.

Stars

Giant balls of gas that represent the building blocks of galaxies and are responsible for producing elements such as carbon, nitrogen, and oxygen.

Luminosity

The total amount of energy that a star radiates into space per unit of time (power).

Absolute magnitude

How bright a star would appear if it were placed at a standard distance of $32.6\,LY$ from Earth.

Apparent magnitude

The brightness of a star as seen from Earth, which depends on both its absolute magnitude and its distance.

Hertzsprung-Russell (H-R) diagram

A diagram showing the relationship between the surface temperature and absolute magnitude of stars.

Main sequence

The region of the H-R diagram where $90\%$ of stars belong and spend most of their lifetime getting energy from hydrogen fusion into helium.

Population I stars

Stars located in the central disk of the galaxy that are of all ages (including many young stars) and are richer in heavy elements.

Population II stars

Mainly old stars located in the halo of the central zone of the galaxy that are poorer in heavy elements.

Protostar

The stage of star formation where a central nucleus and a disk of matter are formed from a collapsing nebula before nuclear fusion begins.

Hydrostatic equilibrium

The state in which a star's internal nuclear pressure resists the gravitational pressure of the upper layers, resulting in a stable star size.

Red giant

A late-stage star that has depleted its hydrogen reserves, causing it to contract, heat up, and then expand to $100$ times its original size.

White dwarf

The end-state of a Sun-like star that has shrunk and will eventually stop shining to become a black dwarf.

Supernova

A violent explosion of a massive star that causes the formation of heavy elements and sends them into space.

Neutron star

A very dense body that remains after the supernova explosion of a massive star.

Black hole

The remain of an extremely massive star after its death, or a massive object thought to exist at the center of the Milky Way with a mass approximately $3.7$ million times that of the Sun.

Telluric planets

Inner planets (Mercury, Venus, Earth, Mars) characterized by being small, rocky, and metallic with high density and slow rotation.

Jovian planets

Outer planets (Jupiter, Saturn, Uranus, Neptune) characterized by being large, gaseous, and icy with low density and fast rotation.

Planetesimals

Grains of matter that aggregate within the accretion disk of the solar nebula to eventually form planets.

Frostline

A temperature limit of $175\,K$ in the solar nebula beyond which water vapor, methane, and ammonia condense into ice.

Photosphere

The surface of the Sun, which has a temperature of approximately $5800\,K$.

Asteroid Belt

A ring of thousands of rocky and metallic bodies located beyond the orbit of Mars.

Meteorites

Meteoroids that reach the ground after burning through the Earth's atmosphere.

Kuiper Belt

A donut-shaped reservoir of short-lived comets (less than $200$ years old) located between $30$ and $50\,AU$ from the Sun.

Oort Cloud

A thick bubble of icy debris surrounding the solar system between $5000$ and $100000\,AU$ that acts as a reservoir for long-period comets.

Sublimation

The process by which volatile materials in a comet turn into gas as they approach the Sun, creating a tail.