Editing Variable star (section)

====Protostars====
{{Main|Pre–main-sequence star}}

Protostars are young objects that have not yet completed the process of contraction from a gas nebula to a veritable star. Most protostars exhibit irregular brightness variations.

=====Herbig Ae/Be stars=====
[[File:V1025 Tauri Taurus Molecular Nebula from the Mount Lemmon SkyCenter Schulman Telescope courtesy Adam Block.jpg|thumb|right|[[Herbig Ae/Be star]] [[V1025 Tauri]]]]
{{Main|Herbig Ae/Be stars}}
Variability of more massive (2–8 [[Sun|solar]] mass) [[Herbig Ae/Be stars]] is thought to be due to gas-dust clumps, orbiting in the circumstellar disks.

=====Orion variables=====
{{Main|Orion variable}}

Orion variables are young, hot [[pre–main-sequence star]]s usually embedded in nebulosity. They have irregular periods with amplitudes of several magnitudes. A well-known subtype of Orion variables are the [[T Tauri star|T Tauri]] variables. Variability of [[T Tauri star]]s is due to spots on the stellar surface and gas-dust clumps, orbiting in the circumstellar disks.

=====FU Orionis variables=====
{{Main|FU Orionis star}}

These stars reside in reflection nebulae and show gradual increases in their luminosity in the order of 6 magnitudes followed by a lengthy phase of constant brightness. They then dim by 2 magnitudes (six times dimmer) or so over a period of many years. ''[[V1057 Cygni]]'' for example dimmed by 2.5 magnitude (ten times dimmer) during an eleven-year period. FU Orionis variables are of spectral type A through G and are possibly an evolutionary phase in the life of ''[[T Tauri star|T Tauri]]'' stars.