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Edwin HubbleEquations of astronomyLarge-scale structure of the cosmosPhysical cosmology

Hubble's law

Adapted from Wikipedia · Explorer experience

The Crab Nebula: a glowing remnant of an ancient star explosion, captured by the Hubble Space Telescope.

Hubble's Law

Hubble's law is a fun idea about how space works! It tells us that galaxies, which are big groups of stars, are moving away from Earth. The farther a galaxy is, the faster it moves away.

Imagine putting raisins in rising bread. As the bread bakes and grows, the raisins move apart. The farther apart the raisins are, the faster they move from each other. This is like what galaxies do in space!

This idea was first shared by a scientist named Edwin Hubble in 1929. Other smart people, like Georges Lemaître, had noticed something similar a little earlier in 1927. They used bright stars to measure distances and saw that galaxies were moving.

Hubble's law helps us understand that the universe is growing, just like the rising bread with raisins. It fits with the Big Bang idea, which says the universe started from a tiny point and has been expanding ever since.

Scientists use a special number called the Hubble constant to talk about how fast the universe is growing. This number helps them guess how old the universe is — about 14.4 billion years old!

Isn't it amazing how stars and galaxies help us learn about the big, beautiful universe?

Images

An animated model showing how the universe expands, illustrated using the 'raisin bread' analogy.
This image shows a map of the oldest light in the universe, helping scientists understand how our cosmos began.
An illustration showing how astronomers use stars and supernovae to measure how fast the Universe is expanding.
A graph showing how distant galaxies move away from us, helping scientists understand the expansion of the universe.
A diagram showing how the speed of distant objects relates to their redshift, helping us understand the expansion of the universe.
A diagram showing how scientists measure the expansion rate of the universe using different methods and space missions.
A scientific chart showing different estimates of a key cosmic measurement from various space observations.
A diagram showing different measured values of the Hubble constant from 2001 to 2019, used to study the expansion rate of the universe.
A stunning view of Earth rising over the lunar surface, captured by astronauts during the Apollo 8 mission in 1968.
An artist's rendering of HE 1523-0901, one of the oldest known stars in our galaxy, located about 7,500 light-years from Earth.

This article is a child-friendly adaptation of the Wikipedia article on Hubble's law, available under CC BY-SA 4.0.

Images from Wikimedia Commons. Tap any image to view credits and license.