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We have made polarimetric observations of three Type Ia supernovae (SN Ia)and two type II supernovae (SN II). No significant polarization was detectedfor any of the SN Ia down to the level of 0.2\%, while polarization of order$1.0\%$ was detected for the two SN II 1994Y and 1995H. A catalog of all theSNe with polarization data is compiled that shows a distinct trend that all the5 SN II with sufficient polarimetric data show polarizations at about 1\%,while none of the 9 SN Ia in the sample show intrinsic polarization. Thissystematic difference in polarization of supernovae, if confirmed, raises manyinteresting questions concerning the mechanisms leading to supernovaexplosions. Our observations enhance the use of SN Ia as tools for determiningthe distance scale through various techniques, but suggest that one must bevery cautious in utilizing Type II for distance determinations. However, wecaution that the link between the asphericity of a supernova and the measured``intrinsic'' polarization is complicated by reflected light from thecircumstellar material and the intervening interstellar material, the so-calledlight echo. This effect may contribute more substantially to SN II than to SNIa. The tight limits on polarization of SN Ia may constrain progenitor modelswith extensive scattering nebulae such as symbiotic stars and other systems ofextensive mass loss.Comment: 27 pages, 3 Postscript figure

Broadband Polarimetry of Supernovae: SN 1994D, SN 1994Y, SN 1994ae, SN 1995D, and SN 1995H