Water molecule size and scale context

Water is a small bent molecule with outsized cosmic reach. Astronomers have detected its vapor or ice in star-forming regions, planet-forming disks, comets, and debris around other stars, making it part of planetary chemistry long before it reaches a world like Earth. Read its scale context, comparisons, and journey links on the canonical object page.

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Between the smallest and the largest, perspective is everything.

About

Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.

Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.

Editorial

Solar System Planets From Electron to Atoms Stars To Scale Birth And Death Of Stars Black Holes To Scale

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Planets of the Solar System Stars of the Universe Black holes Subatomic scale

Open Scale of Space

Between the smallest and the largest, perspective is everything.

About

Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.

Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.

Editorial

Solar System Planets From Electron to Atoms Stars To Scale Birth And Death Of Stars Black Holes To Scale

Views

Planets of the Solar System Stars of the Universe Black holes Subatomic scale

Open Scale of Space

Atoms

Hydrogen atom

Hydrogen is the universe’s simplest and most common atom. Most hydrogen nuclei were forged in the first minutes after the Big Bang, and neutral hydrogen atoms emerged only after the universe cooled enough for electrons and protons to combine about 380,000 years later.

Scale fact100 pmdiameter

Object class: Atom
Composition: 1 proton, 1 electron

Molecules

Water molecule

Scale fact270 pmmaximum extent

Object class: Molecule
Composition: H2O

Atoms

Cesium atom

Cesium is one of the largest neutral atoms that can exist under ordinary conditions, with a very loosely held outer electron. The hyperfine transition of cesium-133 defines the SI second, so one unusually large atom quietly sets the pace for the world’s clocks.

Scale fact520 pmdiameter

Object class: Atom
Composition: Cs-133: 55 protons, 78 neutrons, 55 electrons