An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Capable of being or liable to be observed.
2) A quantity that can be measured.
3) Quantum mechanics: A → real dynamical variable whose → eigenstates form a → complete set.

From → observe + → -able.

The extent of the Universe that we can see with the aid of the largest telescopes. Its ultimate boundary is determined by the → cosmic horizon size.

→ observable; → universe.