🌌 Galaxies Explorer

Galaxies: Islands of Stars in the Cosmic Ocean

A galaxy is a massive collection of stars, planets, gas, dust, and dark matter held together by gravity. Our home galaxy, the Milky Way, contains an estimated 100–400 billion stars — and it is just one of at least 200 billion galaxies in the observable universe. This interactive explorer lets students discover different galaxy types, explore their structures, and begin to comprehend the staggering scale of the cosmos.

Learning about galaxies stretches students' minds in ways that few other topics can. The distances involved are so vast that light — traveling at 186,000 miles per second — takes years to cross a galaxy and billions of years to travel between distant galaxies. Understanding these scales develops the comfort with very large numbers and scientific notation that is essential for physics, astronomy, and many STEM fields.

Galaxy Types

Galaxies come in three main types: spiral galaxies (like the Milky Way, with pinwheel arms of stars and dust), elliptical galaxies (smooth, oval-shaped collections of older stars), and irregular galaxies (chaotic shapes often resulting from galaxy collisions). The Hubble and James Webb Space Telescopes have captured stunning images of each type, showing that galaxy structures range from orderly spirals to collision-driven chaos.

One of astronomy's most remarkable discoveries is that galaxies are not stationary — they are moving apart as the universe expands. The farther away a galaxy is, the faster it is receding from us. This relationship (Hubble's Law) was the first evidence that the universe began in a Big Bang and has been expanding ever since. Understanding galaxies is understanding the structure, history, and fate of the universe itself — making this topic a powerful introduction to cosmology.

Last reviewed: May 2026 · Aligned with NGSS MS-ESS1-2