Johannes Kepler didn't discover that the planets' orbits are elliptical all at once. It was a process of observation, analysis, and refinement. Here's a breakdown:

* 1600: Kepler began working with Tycho Brahe, who had amassed a wealth of precise astronomical observations.

* 1609: Kepler published his first two laws of planetary motion, which described the elliptical orbits of planets around the Sun. He derived these laws by analyzing Brahe's observations of Mars.

* 1619: Kepler published his third law of planetary motion, which related the orbital period of a planet to its distance from the Sun.

So, while Kepler published his laws in 1609 and 1619, his discovery of elliptical orbits was the result of years of dedicated work analyzing Brahe's observations.