The Scale of Cosmic Structure
Travel from the Earth–Moon system through stars, galaxies, superclusters, and the cosmic web.
The Scale of Cosmic Structure Knowledge file
From the Earth–Moon system to the observable universe, the cosmos forms nested structures organized by gravity.
At a glance
- Earth–Moon distance
- About 384,000 km
- Milky Way diameter
- About 100,000 light-years
- Local Group
- Millions of light-years
- Observable universe
- About 93 billion light-years
Core concepts
Structures nest inside one another
Moons orbit planets, planets orbit stars, stars form galaxies, and galaxies gather into groups, clusters, and the cosmic web.
A light-year is a unit of distance
It is the distance light travels through a vacuum in one year—about 9.46 trillion kilometres—not a unit of time.
Matter is not evenly distributed
On large scales, galaxies gather along filaments and nodes around enormous voids, forming the cosmic web.
Ways to understand
- NearbyPlanetary and stellar systems
At smaller scales, gravity organizes a limited number of bodies into stable orbital systems.
- GalaxiesThe Milky Way and Local Group
The Milky Way contains hundreds of billions of stars and forms a gravitational group with Andromeda and other galaxies.
- Cosmic webClusters and superclusters
A dark-matter framework guides ordinary matter into the largest structures we currently observe.
What to observe
- ObserveFollow the scale bar
Watch the units at every zoom step to build an intuition from kilometres to light-years.
- ObserveSeparate reality from illustration
Object sizes, brightness, and structural density are often enhanced to keep them visible.
- ConsiderObservable is not the same as entire
The observable universe is limited by light speed and cosmic age; it is not necessarily the true edge of the whole universe.