By Christian Mullen – Updated Mar 24, 2022
When viewed from orbit, Earth is commonly called the “Blue Planet.” The color results from a combination of atmospheric scattering, vast ocean coverage, and the way water absorbs light.
The atmosphere is mostly nitrogen and oxygen, which scatter short‑wavelength light more efficiently than long‑wavelength light—a phenomenon known as Rayleigh scattering. Blue photons are redirected in many directions, giving the sky its familiar hue and contributing to the overall blue appearance of the globe when illuminated by the Sun.
Water covers roughly 71 % of Earth’s surface. The deep, clear ocean reflects and absorbs sunlight; it preferentially absorbs reds, oranges, and greens while transmitting blue wavelengths. This selective absorption gives the oceans—and thus Earth—its characteristic blue tone.
Even a pure body of water filters light. Short‑wavelength blue light travels far, whereas longer wavelengths are absorbed. The scattered blue light we see in lakes, seas, and oceans is the same process that makes the sky appear blue.
When the Sun is not illuminating a region, the atmosphere no longer scatters light, and the surface becomes dark. Satellites orbiting the planet see a black sphere at night, punctuated by faint city lights. During daylight, the sun’s rays provide the light needed for scattering, and the planet glows blue.
Had Earth consisted mainly of land, its visual appearance would differ dramatically. Land reflects a broader spectrum of light, giving a muted, grayish tone rather than the vibrant blue that dominates our view from space.
For more details, see the NASA Blue Planet page.
