When we look at the sky with the unaided eye its angular resolving power of about one arcminute allows us to see many hundreds of separate stars. We can also see structure in the brightness distribution of the full Moon. A telescope of only 10 cm diameter already provides us with a resolution of about one arcsecond at optical wavelengths. In the early 1940s Grote Reber made the first systematic radio observations of the sky with a parabolic dish of 10 m diameter at a wavelength of about 1.9 m. It resulted in an intensity map of the "radio sky" with an angular resolution of about 12 degrees! Although some regions of higher intensity protruded from the smooth radiation from the Galactic Plane, it was out of the question to learn about their character such as determining the celestial position and angular size. Any comparison with an optical companion was impossible.In this frustrating situation the early radio astronomers, many of whom came from wartime radar laboratories, notably in Australia and England, quickly turned to the use of interferometers in order to improve the angular resolution that would be proportional to the distance between the two elements of the interferometer rather than their individual size. In early experiments in Australia a "sea-cliff" interferometer was realised with a single antenna located about 100 m above sea level using the direct and reflected path from the ocean surface to create interference fringes. The improved resolution led to the optical identification of the powerful radio sources Cygnus A and Taurus A with a distant galaxy and a supernova in our Galaxy, respectively. In the early 1950s several large interferometric radio telescopes were built that operated at relatively long wavelengths of the order of one meter. Both in Australia and in England the method of aperture synthesis was developed in which data from a number of interferometers with different spacing were combined to synthesise a two-dimensional telescope. With the advent of fully steerable parabolic reflectors operating at shorter cm-wavelengths the method of earth rotation synthesis was introduced. The object under observation was now tracked for up to 12 hours along its daily path. This causes the projection of the EW-interferometer baseline to rotate with respect to the source, thus providing baselines in all orientations. From these observations a two-dimensional picture of the brightness distribution of the source can be derived.

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Applications of a global small animal tracking systemSongbird movements as an example Imagine tracking the individual movements of red-billed queleas (Quelea quelea) across the African continent (Ward, 1971;Dallimer and Jones, 2002). Queleas are the world's most abundant birds and have a breeding population in excess of 1.5·billion. Single colonies can contain up to 30·million birds and these large individual colonies can destroy up to 5% of grain crops in the Sahel zone of Africa (Bruggers and Elliott, 1989). Queleas can migrate long distances, sometimes more Tracking animals over large temporal and spatial scales has revealed invaluable and spectacular biological information, particularly when the paths and fates of individuals can be monitored on a global scale. However, only large animals (greater than ~300·g) currently can be followed globally because of power and size constraints on the tracking devices. And yet the vast majority of animals is small. Tracking small animals is important because they are often part of evolutionary and ecological experiments, they provide important ecosystem services and they are of conservation concern or pose harm to human health. Here, we propose a small-animal satellite tracking system that would enable the global monitoring of animals down to the size of the smallest birds, mammals (bats), marine life and eventually large insects. To create the scientific framework necessary for such a global project, we formed the ICARUS initiative (www.IcarusInitiative.org), the International Cooperation for Animal Research Using Space. ICARUS also highlights how small-animal tracking could address some of the 'Grand Challenges in Environmental Sciences' identified by the US National Academy of Sciences, such as the spread of infectious diseases or the relationship between biological diversity and ecosystem functioning. Smallanimal tracking would allow the quantitative assessment of dispersal and migration in natural populations and thus help solve enigmas regarding population dynamics, extinctions and invasions. Experimental biologists may find a global small-animal tracking system helpful in testing, validating and expanding laboratory-derived discoveries in wild, natural populations. We suggest that the relatively modest investment into a global small-animal tracking system will pay off by providing unprecedented insights into both basic and applied nature.Tracking small animals over large spatial and temporal scales could prove to be one of the most powerful techniques of the early 21st century, offering potential solutions to a wide range of biological and societal questions that date back two millennia to the Greek philosopher Aristotle's enigma about songbird migration. Several of the more recent Grand Challenges in Environmental Sciences, such as the regulation and functional consequences of biological diversity or the surveillance of the population ecology of zoonotic hosts, pathogens or vectors, could also be addressed by a global small-animal tracking system. Our discussion ...

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A transient species with properties similar to the hydrated electron produced previously by electron irradiation has been observed by flash photolysis of aqueous solutions of inorganic salts and aromatic compounds including amino acids.

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