Telescopes in orbit avoid the blurring caused by Earth's atmosphere when observing galaxies.

The longer version

Atmospheric turbulence blurs incoming light and absorbs much of the infrared and ultraviolet spectrum, so ground based instruments cannot see certain wavelengths at all. Above the air, a telescope reaches the diffraction limit set by its own mirror size. The same advantage helps measurements of distant stars.

Orbiting observatories also escape the glow of city lights and airglow, giving a much darker background for faint galaxies. They are harder to service and repair, and their instruments must survive radiation and temperature extremes. Many are placed far from Earth to reduce stray heat and reflected light. Long exposures then reveal objects far fainter than any ground view.

Where this entry sits

The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.