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We report the results of the stellar occultation by (UII) Umbriel onSeptember 21st, 2020. The shadow crossed the USA and Canada, and 19 positivechords were obtained. A limb parameter accounted for putative topographicfeatures in the limb fittings. Ellipse fittings were not robust - only upperlimits were derived for the true size/shape of a putative Umbriel ellipsoid.The adopted spherical solution gives radius = 582.4 +/- 0.8 km, smaller/closeto 584.7 +/- 2.8 km from Voyager II. The apparent ellipse fit results in a truesemi-major axis of 584.9 +/- 3.8 km, semi-minor axes of 582.3 +/- 0.6 km andtrue oblateness of 0.004 +/- 0.008 for a putative ellipsoid. The geometricalbedo was pV = 0.26 +/- 0.01. The density was rho = 1.54 +/- 0.04 g cm-3. Thesurface gravity was 0.251 +/- 0.006 m s-2 and the escape velocity 0.541 +/-0.006 km s-1 . Upper limits of 13 and 72 nbar (at 1 sigma and 3 sigma levels,respectively) were obtained for the surface pressure of a putative isothermalCO2 atmosphere at T = 70 K. A milliarcsecond precision position was derived: RA= 02h 30m 28.84556s +/- 0.1 mas, DE = 14o 19' 36.5836" +/- 0.2 mas. A largelimb parameter of 4.2 km was obtained, in striking agreement with oppositesouthern hemisphere measurements by Voyager II in 1986. Occultation and Voyagerresults indicate that the same strong topography variation in the surface ofUmbriel is present on both hemispheres.

Kilometer-precise (UII) Umbriel physical properties from the multichord stellar occultation on 2020 September 21