AS101: Our Place in the Cosmos - Chapter 1 Vocabulary

Vocabulary flashcards covering fundamental physical units, astronomical distances, cosmic structures, the scientific method, and time scales from AS101 Chapter 1.

SI System (Système International)

An international system of standardized measurement units agreed upon in 1960 by an international committee.

Meter

The SI base unit of length ($\text{m}$), defined as the distance traveled by light in a vacuum during a specific time interval.

Kilogram

The SI base unit of mass ($\text{kg}$), historically defined based on a standard cylinder kept at the International Bureau of Standards.

Second

The SI base unit of time ($\text{s}$), defined in terms of the frequency of radiation emitted during oscillations of a cesium atom.

Derived Quantities

Physical quantities in mechanics and physics that can be expressed as mathematical combinations of fundamental quantities, such as area, speed, and density.

Scientific Notation

A system of recording very large or very small numbers in a compact form using powers of 10.

Significant Figures

The digits in a measured quantity that are reliably known, including all certain digits plus the first estimated digit.

Light-Year

A unit of astronomical distance equal to the distance that light travels in a vacuum over one year, approximately $9.46 \times 10^{12}\,\text{km}$ or $9.46 \times 10^{15}\,\text{m}$.

Astronomical Unit

A unit of distance ($\text{AU}$) defined as the average distance from the Earth to the Sun, equal to $1.5 \times 10^{11}\,\text{m}$.

Planet

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

Star

A self-luminous globe of gas held together by its own gravity and supported by internal pressure generated by nuclear fusion in its core.

Proton-Proton Chain Reaction

The nuclear fusion reaction process in stars that converts four hydrogen nuclei into one helium nucleus, releasing energy according to $E = mc^2$.

Solar System

A gravitationally bound system consisting of a star, such as the Sun, and all the objects orbiting it, including planets, asteroids, and comets.

Galaxy

A large system of stars, planetary systems, star clusters, gas, dust, and nebulae orbiting a common center of mass.

Spiral Arms

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

Supercluster

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

Alpha Centauri

A triple-star system located between $4.2\,\text{light-years}$ and $4.4\,\text{light-years}$ from Earth, containing the closest stars to Earth outside the Solar System.

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 about how nature works, often formatted as an 'If…, then…, because…' statement.

Scientific Theory

An explanation that connects and explains evidence and observations, continually tested against evidence to make reliable predictions.

Scientific Law

A statement or equation that predicts what will happen in a certain situation under specific physical conditions.

Objective Observation

An observation based on verifiable facts that can be strictly defined and proven true.

Subjective Observation

An observation based on personal opinion, belief, value, or feeling rather than verifiable facts.

Quantitative Data

Scientific data consisting of numerical values, such as a heart rate measurement of $80\,\text{beats/minute}$.

Qualitative Data

Scientific data consisting of verbal descriptions or information gathered using non-numerical scales.

Observable Universe

The portion of the entire Universe that can be seen from Earth, limited by the light travel time of $13.8\,\text{billion years}$ since the Big Bang.

Cosmic Calendar

A conceptual timeline created by Dr. Carl Sagan that compresses the $13.8\,\text{billion-year}$ history of the universe into a single 12-month year.