Massive stars explode as supernovae of Type II or Ib/c and eject with a velocity of about 15,000 km/s most of its mass into the circumstellar material left over from the dying star. There charged particles are accelerated and give rise to radio emission, The ejected amterial expands further eventually interacting with the interstellar material, forming a supernova remnant and enriching the space between the starswith most of thye eementsthat are building blocks for planets, molecules and life as we see it on Earth. At the center of the explosion, a neutron star or a black hole is left behind. With the technique of very-long-baseline interferometry (VLBI) and a network of several large radio telescopes girdling the globe, we are able to image the supernovae and measure the expansion of the ejected gas in detail. Our angular resolution is 1000 times better than that of any optical telescope. A wide range of astrophysical questions can be answered. We make movies of the exploding supernovae that show how the blast wave overruns the circumstellar material and expands into space. We have developed a technique to measure the distance to a supernova and its host galaxy directly.  Combining the transverse expansion of the supernova measured with VLBI with the radial expansion measured through optical spectroscopy allows us to obtain a geometric distance determination. This is the Expanding Shock front method (ESM).

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Movie of SN 1993J
Movie of SN 1986J