AS101: Our Place in the Cosmos - Chapter 1 Vocabulary

Vocabulary practice flashcards covering fundamental physical units, measurement conventions, astronomical terms, the scientific method, and cosmic scales based on Chapter 1 lecture notes.

Système International (SI)

An international system of standardized units agreed upon in $1960$ by an international committee to describe physical quantities.

Meter

The SI unit of length, defined as the distance traveled by light in a vacuum during a given time interval.

Kilogram

The SI unit of mass, defined based on a specific cylinder kept at the International Bureau of Standards.

Second

The SI unit of time, defined in terms of the oscillation of radiation from a cesium atom.

Scientific Notation

The system of recording very large or very small numbers by using powers of $10$.

Light-Year (ly)

A unit of distance equal to the distance traveled by light in one year, which equals $9.46053 \times 10^{12}\text{ km}$ or $9.46 \times 10^{15}\text{ m}$.

Astronomical Unit (AU)

A unit of distance equal to the average distance from the Earth to the Sun, which is $1.5 \times 10^{11}\text{ m}$.

Planet

A non-luminous body in orbit around a star that is large enough to be spherical and to have cleared its orbital zone of other objects.

Star

A globe of gas held together by its own gravity and supported by the internal pressure of its hot gases, which generate energy by nuclear fusion.

Proton-Proton Chain Reaction

A nuclear fusion reaction that converts four hydrogen nuclei into a helium nucleus, releasing energy from mass according to $E=mc^2$.

Solar System

The Sun and its surrounding celestial objects, including planets, asteroids, and comets.

Galaxy

A large system of stars, planets, star clusters, gas, dust, and nebulae orbiting a common centre of mass.

Spiral Arms

Long spiral patterns of bright stars, star clusters, gas, and dust that extend from the centre to the edge of the disk in spiral galaxies.

Supercluster

A large group of smaller galaxy clusters or galaxy groups, representing some of the largest known structures in the universe.

Alpha Centauri

A star system comprising three stars located $4.2$ to $4.4$ light-years from Earth, making it the closest star system to Earth.

Scientific Method

The process by which scientists form hypotheses and test them against evidence gathered by experiment and observation.

Hypothesis

A working explanation or trial answer to a problem that can be tested against observational or experimental evidence.

Scientific Theory

An explanation that connects and explains evidence and observations, which has been repeatedly confirmed through testing and leads to testable predictions.

Scientific Law

A statement or equation that predicts what will happen in a specific situation.

Objective Observation

An observation based on fact, which is a piece of information that can be strictly defined and proven true.

Subjective Observation

An observation based on opinion, expressing a belief, value, or feeling.

Quantitative Data

Data consisting of numerical measurements or values.

Qualitative Data

Data consisting of verbal descriptions or information gathered using scales without numbers.

Observable Universe

The portion of the universe visible from Earth, limited by the light travel time of $13.8$ billion years since the Big Bang.

Cosmic Calendar

A conceptual model created by Dr. Carl Sagan that compresses the $13.8$ billion year history of the universe into a single calendar year.