Astronomy Chapter 1: Scale and Motion of the Universe

Vocabulary flashcards covering primary and secondary learning outcomes for Astronomy Chapter 1, including light-travel time, cosmic expansion, scale models, and cosmic history.

Light-Travel Time

The principle that because light takes time to travel through space, we observe distant objects as they were in the past when their light left them.

Origin of Earth's Elements

The process following the Big Bang (which formed hydrogen and helium) where gravity formed stars that created heavier elements, later becoming part of Earth to make life possible.

Earth's Motions

The combined movements of Earth rotating on its axis once a day and orbiting the Sun once a year.

Galactic Orbit of the Solar System

The movement of our solar system orbiting around the center of the Milky Way, which takes about $230\,\text{million years}$ per orbit.

Expansion of Space

The continuous stretching of space that causes distant galaxies to move farther apart, with more distant galaxies receding at faster speeds.

Age of the Universe Estimation

An estimate of about $14\,\text{billion years}$, calculated by measuring galaxies' distances and recession speeds to determine how long expansion has occurred.

Cosmic Scale Order

The structural hierarchy arranged from smallest to largest: Earth $\rightarrow$ solar system $\rightarrow$ Milky Way $\rightarrow$ galaxy cluster $\rightarrow$ observable universe.

Light-Year

A unit of measurement used for astronomical distances.

Distance to the Nearest Star

The distance to the nearest star beyond the Sun, which is about $4\,\text{light-years}$ away.

Distance to Andromeda

The distance to the Andromeda galaxy, which is about $2.5\,\text{million light-years}$ away.

Limit of the Observable Universe

The boundary beyond which we cannot see because light from those distant regions has not had enough time to reach us.

Scale Model Distance Formula

The formula where $\text{Model distance} = \text{real distance} \div \text{scale factor}$; at a $10\text{-billion-to-}1$ scale, the Sun–Earth distance becomes $15\,\text{meters}$.

Cosmic Calendar

A scale model of cosmic time where the Big Bang is on January 1, Earth forms in September, and humans appear near the end of December 31.