We present a statistical analysis of a complete sample (255) of northern planetary nebulae (PNe). Our analysis is based on morphology as a main parameter. The major morphological classes are: round (26&#37 of the sample), elliptical (61&#37), and bipolar (13&#37) PNe. About a half of the round and 30 &#37 of the elliptical PNe present multiple

Multiple shell planetary nebulae (MSPNe) are most likely a consequence of the modulation of the mass-loss rate during the thermal pulses on the AGB. By using numerical simulations of their formation, the models' predictions and the history of the winds can be investigated. As their halos have low densities and expansion velocities, MSPNe are

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A radio interferometer array in space providing high dynamic range images with unprecedented angular resolution over the broad frequency range from 0.03 - 30 MHz will open new vistas in solar, terrestrial, galactic, and extragalactic astrophysics. The ALFA interferometer will image and track transient disturbances in the solar corona and

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