Physical phenomenon
Physical Phenomena are observable events which are explained by physics or raise some question about matter, light, or spacetime. For example, it was observed, by Isaac Newton, that while an apple might fall from a tree, the moon, very large and massive, does not fall. See gravity
A related observation, made by Johannes Kepler after painstaking observations, was that the Planet Mars traveled in an ellipical orbit.
Another related observation, first made by James Bradley, an astronomer, is that by carefully plotting the position of a nearby star it appears to move in an elipse over the course of a year.
It is a rather commonplace obervation that some things are heavier than others.
Related Reading
- Jeremy Bernstein, A Theory for Everything, Copernicus, An imprint of Springer-Verlag, New York, 1996, hardback, ISBN: 0-387-94700-0