Astronomy Glossary

Cosmology Universe

Dark energy is a mysterious component causing the Universe's expansion to accelerate, comprising ~68% of the Universe's energy density.

Cosmology Universe

Dark matter is non-luminous matter detectable only through gravitational effects, comprising ~85% of matter in the Universe.

Astronomy Concepts

Declination (Dec, δ) is celestial latitude—angular distance north (+) or south (-) of the celestial equator, analogous to latitude on Earth.

Telescopes Equipment

A Dobsonian mount is a simple altitude-azimuth mount using Teflon bearings on a rotating base, revolutionizing amateur astronomy by making large apert...

Galaxies

Dwarf galaxies are small galaxies with 10^7 to few billion stars, the most common galaxy type in the Universe.

Solar System

Dwarf planets meet criteria 1 and 2 of planethood but have NOT cleared their orbital neighborhoods—they share orbital space with similar-sized objects...