Our Place in the Universe

Vocabulary flashcards reviewing cosmic structures, astronomical distance scales, density estimates, and Earth's location hierarchy based on the lecture notes.

Proxima Centauri

The nearest star to Earth beyond the Solar System, located $4\text{ light years}$ away and orbiting a binary pair of Sun-like stars.

Stellar Density within 12 Light Years

The region of space surrounding our Sun that contains about $20$ stars.

Stellar Density within 250 Light Years

The region of space surrounding our Sun that contains approximately $1500$ stars.

Stellar Density within 5000 Light Years

The volume of space surrounding our Sun containing about $600\text{ million}$ stars.

Milky Way Galaxy

Our home galaxy containing approximately $200\text{ billion}$ stars and spanning a diameter of $100{,}000\text{ light years}$.

Band of Light (Milky Way)

The luminous band seen in the night sky formed by the combined light of billions of unresolvable stars located within the flattened disk of our galaxy.

Dark Nebulae

Clouds of cosmic dust that obstruct and block light from stars and objects behind them.

Bright Nebulae

Clouds of cosmic dust illuminated and lit up by nearby stars.

Galactic Plane Visibility

The observational contrast where looking out of the galactic disk allows viewing up to $400{,}000{,}000\text{ light years}$, whereas looking into the disk blocks line-of-sight view.

Andromeda Galaxy

A large neighboring galaxy near the Milky Way.

Local Group

The group of galaxies within $5\text{ million light years}$, which includes the Milky Way, Andromeda Galaxy, Triangulum Galaxy, and surrounding dwarf galaxies.

Virgo Cluster

A cluster of galaxies within $200\text{ million light years}$ of Earth, with our Local Group situated on its edge.

Laniakea Supercluster

The supercluster of galaxies within $1\text{ billion light years}$ that encompasses the Virgo Cluster, Local Group, and Milky Way Galaxy.

Hercules Supercluster

A supercluster where every individual dot in astronomical images represents an entire galaxy of billions of stars.

Observable Universe Distance Limit

The maximum distance humans can observe in the universe, extending to $14\text{ billion light years}$ and containing about $100\text{ billion}$ galaxies in total.

Cosmic Address

The full hierarchical position of Earth in space: Earth, Solar System, Milky Way Galaxy, Local Group, Virgo Cluster, Laniakea Supercluster, Universe.

Earth Scale

The physical diameter of planet Earth, which measures $12{,}000\,\text{km}$ across.

Solar System Scale

The spatial scale of our planetary system, measuring roughly $100\,\text{AU}$ or $15\text{ billion}\,\text{km}$.

Galaxy Scale

The spatial dimension of the Milky Way Galaxy, measuring $100{,}000\text{ light years}$ or $10^{18}\,\text{km}$.

Local Group Scale

The spatial scale of our local galactic group, measuring $5\text{ million light years}$ or $5 \times 10^{19}\,\text{km}$.

Universe Scale

The scale of the observable universe, measuring $14\text{ billion light years}$ or $1.4 \times 10^{23}\,\text{km}$.