Radio-astronomy

Radio astronomy used the new technology developed for radar and opened a new window for astronomers to gaze through. Roto-vibrational^3.1 transitions in molecules have low excitation levels, which are ideally suited to probe the low temperatures in interstellar clouds. Because the wavelengths of these transitions are long, one can build very large dishes to observe them, and also it is more straightforward to build interferometers.^3.2

An electron moving in a magnetic field will feel an acceleration, causing it to circle around the field lines. Such synchrotron radiation can also be observed in the radio.

Today, one regularly combines data from radio-observatories across the earth to get Very Long Baseline Interferometry, which gives superb angular resolution ( $10^{-6}{\hbox{\rm arcsec}}$!). Another great advantage of radio over optical observations, is that radio waves are not absorbed by dust. (By now you know why: it's because the wavelengths are much larger than the size of the dust grains.) And so, yo can use radio-waves to probe into very dense regions, for example where star formation occurs. One of the bigger problems facing radio-astronomy today, is mobile phones ...