• One of the favourite conversational topics among observational astronomers, seeing is the state of stillness or turbulence of the atmosphere. Good seeing – a very low level of turbulence – is one of the characteristics most sought after when telescope sites are being considered, since poor seeing increases the apparent size of images produced by a telescope, lowering its resolving power and in effect giving it the performance of a poorer instrument. Mountain sites for major observatories are selected only after exhaustive tests of their seeing quality.