ASTR 106 Chapter 1: Cosmic Context Vocabulary

Vocabulary flashcards defining fundamental astronomical objects, distance scale units, measurement methods, and cosmic history concepts from ASTR 106.

Star

A big ball of hot gas generating light from nuclear fusion.

Planet

A large object orbiting a star, which can be rocky or gaseous.

Moon

A small object orbiting a planet.

Asteroid

A small rocky object orbiting a star.

Comet

A small icy object orbiting a star.

Solar System

A star with orbiting planets and other bodies.

Nebula

A big interstellar cloud of gas and dust.

Galaxy

A huge collection of stars orbiting a common center.

Universe

The sum total of all galaxies and matter between them.

Eratosthenes

A 3rd century B.C. scholar who determined the size of the Earth by measuring differences in shadow lengths at noon at different latitudes.

Parallax

The angular shift in an object's position resulting from a change in observer perspective, calculated as spatial shift divided by distance.

Astronomical Unit (AU)

A unit of distance equal to the Earth-Sun distance of $93,000,000\text{ miles}$ or $150,000,000\text{ km}$, equivalent to $499\text{ light seconds}$ or $8.3\text{ light minutes}$.

Transit of Venus

A rare event used to determine solar parallax by observing the apparent position of Venus as it passes in front of the Sun from different locations on Earth.

Standard Candle

A method to measure distance by comparing the received light of an object to its known radiated brightness, which decreases as distance squared.

Light Year

A unit of distance equal to the distance light travels in 1 year, which is $5.88 \times 10^{12}\text{ miles}$ or $9.46 \times 10^{12}\text{ km}$.

Observable Universe

The portion of the Universe that can be seen because its light has had enough time to reach Earth since the Universe began.

Big Bang

The event around 14 billion years ago in which the expanding Universe began from a hot, dense state.

Cosmic Calendar

A visualization proposed by Carl Sagan that places the Big Bang on January 1st and the present on December 31st, where 1 second equals 440 of our years.