An historical, logarithmic scale devised to represent the observed brightness of astronomical objects such as stars.
The portion of the lifetime of a star during which it produces energy via the fusion of hydrogen to helium in its core. A star will remain on the Main Seqeunce for the majority of its total lifetime.
Extra-terrestrial object that is observed by the electromagnetic radiation it emits as it enters the Earth's atmosphere. 'Shooting stars' are visible meteors.
An extra-terrestrial rock (generally a fragment of an asteroid) that has fallen to the Earth’s surface.