Stars, Galaxies & the Universe Vocabulary

Vocabulary flashcards derived from Chapter 1 notes on Stars, Galaxies & the Universe.

Cosmic Address

The hierarchy of increasingly larger astronomical neighborhoods: Earth $\rightarrow$ Solar System $\rightarrow$ Milky Way Galaxy $\rightarrow$ Local Group $\rightarrow$ Virgo Supercluster $\rightarrow$ Laniakea Supercluster $\rightarrow$ Observable Universe.

Milky Way Galaxy

A disk-shaped galaxy containing gas, dust, and several hundred billion stars, with our Sun located about halfway from its center.

Local Group

A galactic group containing a few dozen galaxies, including the Milky Way, Andromeda Galaxy, Triangulum Galaxy, and about 20 smaller galaxies.

Laniakea Supercluster

The massive supercluster of galaxies that contains the Virgo Supercluster, which encompasses the Local Group.

Observable Universe

The portion of the universe we can currently see, containing roughly 2 trillion galaxies and millions of superclusters.

Dark Matter

Matter that does not interact with light, making up part of the approximately $95\%$ of the universe associated with dark matter and dark energy.

Dark Energy

A form of energy that permeates space, making up part of the approximately $95\%$ of the universe associated with dark matter and dark energy.

Speed of Light

The constant rate at which light travels through space, equal to approximately $300,000\,\text{km/s}$.

Light-year

A unit of distance equal to the distance light travels in one year, or approximately $9.5\,\text{trillion}\,\text{km}$.

Scientific Method

A systematic process of developing and testing ideas through observation, hypothesis, prediction, experiment or testing, and revision or acceptance.

Hypothesis

A testable explanation for an observation.

Falsified

In science, the state of an idea or hypothesis being shown to be incorrect by evidence.

Reproducible

A characteristic of a scientific test meaning that someone else can perform the test and get the same result.

Repeatable

A characteristic of a scientific test meaning that a researcher can perform the test again later and get the same result.

Scientific Theory

A well-developed explanation that agrees with known evidence, explains relevant data, makes testable predictions, and has survived many attempts to disprove it.

Scientific Law

A description of a predictable pattern of what happens in nature without necessarily explaining why it occurs.

Model

A representation of a system based on known laws and theories, often implemented as computer simulations to predict complex systems.

Cosmological Principle

The assumption that the laws of physics work the same throughout space and time, implying the universe has no special location or direction.

Occam's Razor

The principle stating that when two hypotheses explain observations equally well, one should choose the explanation requiring the fewest assumptions.

Exoplanet

A planet orbiting a star other than the Sun.

Black Hole

An extremely massive object whose gravity prevents light from escaping, predicted theoretically prior to direct observational evidence.

Slope

The rate telling how quickly one quantity changes compared with another on a graph, calculated as $\text{Slope} = \frac{\Delta y}{\Delta x}$.

Linear Relationship

A relationship between variables that changes by the same amount each step, appearing as a straight line on a graph.

Exponential Relationship

A relationship between variables that changes by the same factor or multiplier each step, growing faster and faster.

Logarithmic Scale

A scale on a graph axis where each equal step represents a constant multiplier, such as $10\times$, compressing very large ranges of data.

Big Bang Theory

The cosmological theory stating that the universe began expanding from an extremely small state about $13.8\,\text{billion}$ years ago.

Astrobiology

The study of the possibility and origins of life in the universe.