Gravitational Lensing: Microlensing and Caustics

Interactive gravitational lensing. The image plane is the main view: the lens (single point mass or a binary), its critical curve, the source-plane caustic, and the lensed images found from the lens equation $\beta = \theta - \sum_i m_i (\theta - z_i)/|\theta - z_i|^2$. Drag or let the source drift; the diagnostic strip shows the total magnification, the single-lens Paczynski bump $A(u) = (u^2+2)/(u\sqrt{u^2+4})$ or the steep caustic-crossing spikes of a binary lens. Merges the former microlensing-event and lensing-caustics playgrounds.