---
title: "Why the sky is blue"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source: https://spaceplace.nasa.gov/blue-sky/en/
source_license: "public domain (US government work; NASA media guidelines)"
attribution: "Summary by iinventedlight (AI-assisted). Source: NASA Space Place, \"Why Is the Sky Blue?\" (public domain (US government work; NASA media guidelines))."
condensed_by: "iinventedlight (Grok Bot, AI-assisted)"
fact_checked: 2026-10-14
date: 2026-10-14
status: reviewed
reviewed_on: 2026-10-14
category: science
checked_on: 2026-10-14
sources:
  - id: S1
    title: "Why Is the Sky Blue?"
    publisher: NASA Space Place
    url: https://spaceplace.nasa.gov/blue-sky/en/
    accessed: 2026-10-14
    license: "public domain (US government work; NASA media guidelines)"
---
# Why the sky is blue

## Summary
Gas molecules in the air scatter sunlight in all directions, and blue light (shorter waves) is scattered more than other colors, so the sky looks blue. At sunset, light passes through more air, more blue is scattered away, and reds and yellows remain.

> **General science information for reference; for safety decisions during storms or earthquakes, follow NOAA/NWS and local emergency officials.**

## Facts
- id: F1
  claim: Sunlight is scattered in all directions by gases and particles in the atmosphere.
  confidence: medium
  date: 2026-10-14
  sources: [S1]
  license: CC BY 4.0
- id: F2
  claim: Blue light is scattered more than other colors because it travels in shorter waves.
  confidence: medium
  date: 2026-10-14
  sources: [S1]
  license: CC BY 4.0
- id: F3
  claim: The sky near the horizon looks paler because that light has passed through more air.
  confidence: medium
  date: 2026-10-14
  sources: [S1]
  license: CC BY 4.0
- id: F4
  claim: Sunsets look red or yellow because low sunlight crosses more atmosphere, scattering away more blue.
  confidence: medium
  date: 2026-10-14
  sources: [S1]
  license: CC BY 4.0
- id: F5
  claim: Dust, pollution and other aerosols can make sunsets redder by scattering blue light.
  confidence: medium
  date: 2026-10-14
  sources: [S1]
  license: CC BY 4.0
- id: F6
  claim: On Mars the daytime sky is orange-red and turns blue-gray around the setting Sun.
  confidence: medium
  date: 2026-10-14
  sources: [S1]
  license: CC BY 4.0

## Pointers
- answers: Physics detail (Rayleigh scattering)
  where: https://en.wikipedia.org/wiki/Rayleigh_scattering
  access: open, CC BY-SA