Title: The Radio Sky
Author(s): R. Wielebinski   Main Session Speaker

ABSTRACT
At first man observed the sky with unaided eye. The advent of the optical telescope 'zoomed' the sky into a new dimension. The sensitivity of the optical detectors increased, revealing a whole new universe. The discovery of radio waves of cosmic origin made us realize that we can 'see' the sky also in other ranges of the electromagnetic spectrum. The mapping of spectral lines followed the maps of radio continuum, allowing us to study the universe in many of its chemical constituents. The latest additions to our knowledge came from the use of space satellites that allow us to 'see' the invisible universe beyond the Earth's atmosphere. We now can study the sky in X-rays and γ-rays. In this talk the development of radio sky mapping from the first surveys to the present most sensitive maps will be described. I will describe the various single dish radio methods and the aperture synthesis procedures to map the sky. The significance of radio polarimetry in revealing cosmic magnetic fields will be discussed. Spectral line mapping especially with the on-the-fly method will also be described. Comparisons between the various spectral ranges will be shown, demonstrating the importance of a full spectral study of all the cosmic objects.