Omri Solan, speaking in the joint IAS/Princeton Groups and Dynamics Seminar, presents a proof of equidistribution for expanding horospherical measures on the moduli space of translation surfaces. He starts from the construction: a translation surface comes from gluing the edges of a polygon in parallel, and the group GL_2(R) acts on the space of such surfaces of fixed genus. Fixing a surface S, rotating it by a uniform angle, then applying diag(e^t, e^-t) produces a probability measure, and Solan shows this sequence equidistributes as t goes to infinity. The result settles a conjecture of Giovanni Forni and strengthens an earlier theorem of Eskin and Mirzakhani, which established the same conclusion only as a Cesaro average. Solan closes with an application to billiard dynamics in polygons with rational angles. The talk assumes graduate-level familiarity with dynamics on moduli spaces and homogeneous dynamics, and moves through the argument at a research-seminar pace with no concessions to a general audience.