“The sky, our common and universal heritage, is an integral part of the environment perceived by humanity. Humankind has always observed the sky either to interpret it or to understand the physical laws that govern the universe”
Explanatory Note concerning the Proclamation of 2009 as International Year of Astronomy
(33rd session of the UNESCO General Conference).

The scientific and technological dimension of a starry night is an essential part of the legacy of the sky. The ability of the planet’s astronomical sites and observatories to detect and interpret data from outside the world we live in should be considered sacrosanct. Dark skies are the windows to knowledge of the universe. However, unlike ancient monuments and technological tools related to astronomy, current areas devoted to astronomical observation do not enjoy appropriate recognition.

Ground-based observatories have historically provided the vast majority of our knowledge of outer space. However, present technical requirements restrict suitable areas to very specific and limited locations offering good conditions for the development of advanced astronomy, of optical and infrared astronomy in particular.

Ground-based observatories are exceptional windows for the observation of the universe, and they have provided the vast majority of our knowledge of astronomy. However, present technical requirements restrict suitable areas to very specific and limited locations offering good conditions for the development of advanced astronomy, and of optical and infrared astronomy in particular. The Earth’s atmosphere is a major limiting factor for astronomy at optical wavelengths. Although astronomy from space does not suffer from this blurring, space astronomy is extremely expensive.

The best astronomical sites must be places located at high altitudes, with little turbulence, such as on the west coasts of continents or on oceanic islands. They must also be located at sites with less air pollution and low aerosol content. With the exception of a few exceptional cases, high mountain areas isolated from the temperature of the ocean and coastal mountains near to cold oceans with stable, subtropical anticyclone conditions are the best possibilities. We are talking about a few places on the planet where we find a unique combination of environmental and natural circumstances, well conserved spaces with very little alteration to natural starlight. These are a limited resource that needs to be recognised and protected.

Having reached this point, it is essential to remember that the World Heritage Convention refers to science in Articles 1 and 2. More specifically, in Article 2 it establishes that the following shall be considered as natural heritage: “natural sites or precisely delineated natural areas of outstanding universal value from the point of view of science, conservation or natural beauty”. For this reason, in the process of developing the Thematic Study “Starlight Reserves and World Heritage” the few places that can offer these properties as relevant case studies have been identified, and the future possibility of analysing a serial nomination for these very special spaces in places like Hawaii, Canaries and Northern Chile, has been suggested.

Having reached this point, it is essential to remember that the World Heritage Convention refers to science in Articles 1 and 2. More specifically, in Article 2 it establishes that the following shall be considered as natural heritage: “natural sites or precisely delineated natural areas of outstanding universal value from the point of view of science, conservation or natural beauty”. For this reason, it is hardly surprising that in the process of developing the Thematic Study “Starlight Reserves and World Heritage” the few places that can offer these properties as relevant case studies have been identified, and the future possibility of analysing a serial nomination for these very special spaces in places like Hawaii, Canaries and Northern Chile, has been suggested.

The sky quality in many of these privileged zones can be perturbed by external factors of different kinds. Optical astronomy needs dark skies. Therefore light pollution is one of the main threats because it increases the natural sky brightness. Atmospheric pollution is a further impact to the astronomical quality of the sky.

Radio astronomy made decisive contributions to several fundamental discoveries in the last century. Nowadays this branch of astronomy is also threatened due to radio interference, generated by several causes such as mobile phones or radio/TV frequency signals, which invade the radioelectric spectrum in which astrophysical observations are made. In addition to the very best astronomical sites, there are many other valuable locations that must also be identified and preserved. These other sites are excellent for many aspects of astronomical research, and are also valuable for educational and outreach activities.

Astronomy has had an undeniable influence within science development and has contributed to many technological advances that defined human progress throughout the history. Nevertheless, the continual stream of benefits brought by this branch of science is often not known by most people.