One of nature’s best clocks is a millisecond pulsar. These exotic stellar corpses are neutron stars: incredibly dense, rotating hundreds of times per second, and emitting powerful jets or beams of light. This creates a “pulsing” effect, much like a lighthouse.
The link between a pile of data and a physical explanation is the fun part. Astronomers spend countless hours gathering data, and countless more thinking up physical models for different pieces of the Universe. But reconciling these two things—finding a model that not only agrees with observations, but is the sole likely explanation—isn’t easy.
Our Solar System is pretty straightforward. Roughly speaking, all the planets orbit in the same plane, most spin on their axes in the same direction in that plane, and even the Sun rotates in a manner consistent with all this. The small, rocky planets are closer to the Sun, and the big, gaseous planets are farther from the Sun. Simple. Now that we are finding planets orbiting other stars, many are turning out to be multiplanet systems like our own Solar System.