M. Vázquez - Böcker

The Sun is nowadays observed using di?erent techniques that provide an almost instantaneous 3-D map of its structure. Of particular interest is the studyofthevariabilityinthesolaroutputproducedbythedissipationofm- netic energy on di?erent spatial and temporal scales – the so-called magnetic activity. The 11-year cycle is the main feature describing this phenomenon. Apart from its intrinsic scienti?c interest, this topic is worth studying because of the interaction of such processes with the terrestrial environment. A ?eet of space and ground-based observatories are currently monitoring the behaviour of our star on a daily basis. However, solar activity varies not only on this decadal time-scale, as has been attested mainly through two methods: (a) records of the number of sunspots observed on the solar surface from 1610, and (b) the records of 14 10 cosmogenic isotopes, such as Cand Be, measured in tree-rings and i- cores, respectively. The study of the long-term behaviour of solar activity may be comp- mented by the study of historical accounts describing phenomena directly or indirectly related to solar activity. Numerous scienti?c and non-scienti?c d- uments have reported these events and we can make use of them as a proxy of solar activity in past times.

In the history of science the opening up of a new observational or experimental window is always followed by an increase in knowledge of the subject concerned. This is also the case with the subject of this book, ultraviolet radiation (hereafter UV). In principle, the ultraviolet range might be just one more of these windows, of no particular importance. However, the energy per UV photon provides the main peculiarity, its magnitude being great enough to produce important ch- ical reactions in the atmospheres of planets and satellites, thereby a?ecting the transmission of this radiation to the ground. The Sun is the main natural source of UV radiation in the Solar System and our planet is the body where its in?uences can be best tested and the only one where its relation with life can be studied. However, the terrestrial atmosphere blocksmostofthephotonsinthiselectromagneticrangeandastronomershavehad to develop various techniques (balloons, planes and rockets) to cross this barrier and access the information. These tools have been used in parallel to investigate the physical properties of the terrestrial atmosphere and the interaction of its constituents with light. This book will addresses most of these topics.

In The Earth as a Distant Planet, the authors become external observers of our solar system from a distance and try to determine how one can understand how Earth, the third in distance to the central star, is essentially unique and capable of sustaining life. The knowledge gained from this original perspective is then applied to the search for other planets outside the solar system, or exoplanets.Since the discovery in 1992 of the first exoplanet, the number of planet detections has increased exponentially and ambitious missions are already being planned for the future. The exploration of Earth and the rest of the rocky planets are Rosetta stones in classifying and understanding the multiplicity of planetary systems that exist in our galaxy. In time, statistics on the formation and evolution of exoplanets will be available and will provide vital information for solving some of the unanswered questions about the formation, as well as evolution of our own world and solar system.  Special attention is paid to the biosignatures (signs of life) detectable in the Earth's reflected spectra and the search for life in the universe.The authors are experts on the subject of extrasolar planets.  They provide an introductory but also very much up-to-date text, making this book suitable for researchers and for advanced students in astronomy and astrophysics.

The Sun is nowadays observed using di?erent techniques that provide an almost instantaneous 3-D map of its structure. Of particular interest is the studyofthevariabilityinthesolaroutputproducedbythedissipationofm- netic energy on di?erent spatial and temporal scales – the so-called magnetic activity. The 11-year cycle is the main feature describing this phenomenon. Apart from its intrinsic scienti?c interest, this topic is worth studying because of the interaction of such processes with the terrestrial environment. A ?eet of space and ground-based observatories are currently monitoring the behaviour of our star on a daily basis. However, solar activity varies not only on this decadal time-scale, as has been attested mainly through two methods: (a) records of the number of sunspots observed on the solar surface from 1610, and (b) the records of 14 10 cosmogenic isotopes, such as Cand Be, measured in tree-rings and i- cores, respectively. The study of the long-term behaviour of solar activity may be comp- mented by the study of historical accounts describing phenomena directly or indirectly related to solar activity. Numerous scienti?c and non-scienti?c d- uments have reported these events and we can make use of them as a proxy of solar activity in past times.

In The Earth as a Distant Planet, the authors become external observers of our solar system from a distance and try to determine how one can understand how Earth, the third in distance to the central star, is essentially unique and capable of sustaining life.

The Sun is our main source of UV radiation and its description occupies the first two chapters of the book. The Earth is the only known location where life exists in a planetary system and therefore where the interaction of living organism with UV radiation can be tested through different epochs and on distinct species. The development of the human technology has affected the natural shield of ozone that protects complex lifeforms against damaging UV irradiation. The formation of the ozone hole and its consequences are described, together with the possible contribution of UV radiation to recent climate changes. Finally, we will discuss the the potential role of ultraviolet light in the development of life on bodies such as Mars, Europa and Titan. The Solar System is not isolated; other external sources can contribute to the enhancement of the UV radiation in our environment. The influence of such events as nearby supernovae and gamma-ray bursts are described, together with the consequences to terrestrial life from such events.