Maria Elidaiana da Silva Pereira will give a "live" lecture with a "live" Q&A after the talk. (Link will be active at 10:30 am on 02/20/21.)

Galaxy Clusters are the largest astronomical objects in the Universe. These cosmic giants are bound together by gravity and are formed by galaxies, hot gas, and the mysterious dark matter. By counting them and measuring their masses, we can understand the content and evolution of the Universe. In this talk, I will present how we can use the light for weighing galaxy clusters. I will also show how the Dark Energy Survey uses them to measure the quantity of dark matter and properties of the even more mysterious component, the dark energy.