Exploring Gravitational Lensing: https://arxiv.org/abs/1905.07174
In this article, we discuss the idea of gravitational lensing, from a systematic, historical and didactic point of view. We show how the basic lensing equation together with the concepts of geometrical optics opens a space of implications that can be explored along different dimensions. We argue that Einstein explored the idea along different pathways in this space of implication, and that these explorations are documented by different calculational manuscripts. The conceptualization of the idea of gravitational lensing as a space of exploration also shows the feasibility of discussing the idea in the classroom using some of Einstein's manuscripts.
Comments: 19pp, 11 figs
Subjects: History and Philosophy of Physics (physics.hist-ph); Physics Education (physics.ed-ph)
Journal reference: Eur. J. Phys. 40 (2019) 035301
Measuring Mountains on the Moon: https://arxiv.org/abs/1905.08191
Following a technique of Galileo we compute the height on a mountain on the Moon. It is based on a simple observation that precisely on a half Moon day, the Earth, the Moon, and the Sun form the vertices of a right triangle with the Moon at the 90 degree vertex.
Comments: 2 pages, 3 figures
Subjects: Popular Physics (physics.pop-ph); History and Overview (math.HO)
Journal reference: Math Horizons 26 (2019), no. 4, 24-25