There are 4 cursors on the screen: above each cursor the name and current value of that parameter is indicated, while the cursor can be activated by clicking with the mouse on the dot and dragging it to the right or left; the value of that parameter will change interactively, and the program will immediately adapt to the new parameter. The two cursors at the top right are linked to the parameters of the lunar orbit: 1. indicates the inclination of the lunar orbit, in degrees. Inclination =0 indicates a plane of the lunar orbit coplanar with that of the ecliptic, while inclination =90 indicates a plane of the orbit orthogonal to the ecliptic. 2. "velnodemoon" indicates the angular speed with which the line of nodes moves, in units of its true angular speed. The program starts with this value =1, but with the correct value the movement of the node line is so slow that it appears almost imperceptible, and therefore it is advisable to experiment with larger values as well. The two sliders at the bottom right are instead linked to the viewing mode: 3. "moviespeed" indicates the "speed of the movie" (even if it is not a movie, previously produced, but a real simulation, calculated every moment by the program based on the set data). Initially this is set to the maximum level. The simulation appears very fast, useful for appreciating the dynamics but not for analyzing the details of individual eclipses. For this reason this speed can be slowed down, almost to a stop, or even set to negative values, to go back in time. 4. "tilt" indicates "viewing angle", in degrees. An angle =0 represents a view from above, with the Earth's orbit appearing as a circle, while an angle =90 represents a view from above, with the Earth's orbit appearing as a segment; from here you can best appreciate the inclination of the lunar orbit. In particular, by setting "inclinmoon"=0 we will have an eclipse at every new moon. In this case the red segment indicating the line of nodes disappears, as it would no longer even make sense to talk about nodes of the orbit. It is also a good idea to set a low value for "moviespeed" (0.1 or lower) to be able to appreciate the various phases of the eclipse. Too fast? No problem: you can wait for the next step, or simply reverse the direction of time by setting "moviespeed" to a negative value, to go back to enjoying the show.
Rino Bandiera and Maria Teresa Fulco
