Today at the Astronomical Observatory of Kościan I gave a popular talk: How can we measure the size of a coin located on the Moon from the Earth?.
Observations in astronomy are the basic source of information. Over the centuries, the methods of conducting such observations, as well as their reduction and analysis, have undergone tremendous evolution, and in recent years even a revolution. Currently, the latest technical developments combined with the basic laws of physics allow us to perceive the unprecedented details of celestial bodies. For example, even those with the size of a coin seen from Earth on the Moon. I introduced these methods of observations and presented their applications in modern astronomy.
The direct answer to the question in the title is of course: with the use of optical interferometry. And that was the main topic of my talk.
Fig. The Astronomical Observatory of Kościan