Popular observatories (PO) are an important link between astronomers and the public. Fig.1 represents the flow of information about the Cosmos and the role of POs.

The flow of information about celestial bodies starts with photon emission. The emitted photons carry the information about the moment when they are born. They transfer the encoded information through cosmic space in all directions, among others towards our planet. By ground-based or space-based instruments astronomers decode the information in the photons. The size and shape of celestial bodies are determined with great precision (by photography and interferometry). Direction from which the photons arrive determines the position of their source (astrometry). The amount of photons (photometry), their frequency (spectrophotometry) and the direction of their oscillation (polarimetry) are other information decoded from the incident photons. The observational instruments are the interface between the Cosmos and astronomers’ minds.