01/19/2026
Articles in the Classroom Astronomer Newsletter the past two issues were a two parter, on Observing Kepler’s Laws of Planetary Motion in Action. In January 1st’s Issue #51 the Third Law relating a planet’s distance from the Sun to its orbital period, P-squared versus D-cubed, was explored, and shown to be universal even to moons around a planet. Using real observations or online simulations we looked at Jupiter and its Galilean Moons to see it holds there, too. In Issue #52, we looked at the Second Law, that planets must move faster when closer to the Sun, than when farther. How? By counting days between the seasons and seeing all seasons are not equal. We also find that that simple normal calendar helps show the Moon is in an elliptical orbit, too, by counting days between New, Quarter and Full phases. Simple and elegant!
In #52 also we also listed more simulations of Jupiter and its Moons, and of Saturn and its moons which you can use for these exercises, and for planning observing sessions.