Beyond Our Solar System

Our sun is one of at least 100 billion stars in the Milky Way, a spiral galaxy about 100,000 light years across. The stars are arranged in a pinwheel pattern with four major arms, and we live about two-thirds of the way up one of them. Many if not most of the stars host their own families of planets. More than a thousand of these extrasolar (or exoplanets) have been discovered and thousands more are awaiting confirmation. Continue reading

Hypothetical ‘Planet X

Caltech researchers have found evidence suggesting there may be a “Planet X” deep in the solar system. This hypothetical Neptune-sized planet orbits our sun in a highly elongated orbit far beyond Pluto. The object, which the researchers have nicknamed “Planet Nine,” could have a mass about 10 times that of Earth and orbit about 20 times farther from the sun on average than Neptune. It may take between 10,000 and 20,000 Earth years to make one full orbit around the sun.  Continue reading


In the distant past, people were both awed and alarmed by comets, perceiving them as long-haired stars that appeared in the sky unannounced and unpredictably. Chinese astronomers kept extensive records for centuries, including illustrations of characteristic types of comet tails, times of cometary appearances and disappearances, and celestial positions. These historic comet annals have proven to be a valuable resource for later astronomers. Continue reading


The ice giant Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. (Galileo had recorded it as a fixed star during observations with his small telescope in 1612 and 1613.) When Uranus didn’t travel exactly as astronomers expected it to, a French mathematician, Urbain Joseph Le Verrier, proposed the position and mass of another as yet unknown planet that could cause the observed changes to Uranus’ orbit. After being ignored by French astronomers, Le Verrier sent his predictions to Johann Gottfried Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Seventeen days later, its largest moon, Triton, was also discovered. Continue reading


The seventh planet from the sun with the third largest diameter in our solar system, Uranus is very cold and windy. The ice giant is surrounded by 13 faint rings and 27 small moons as it rotates at a nearly 90-degree angle from the plane of its orbit. This unique tilt makes Uranus appear to spin on its side, orbiting the sun like a rolling ball. Continue reading


The second largest planet in our solar system, adorned with thousands of beautiful ringlets, Saturn is unique among the planets. It is not the only planet to have rings — made of chunks of ice and rock — but none are as spectacular or as complicated as Saturn’s. Like fellow gas giant Jupiter, Saturn is a massive ball of mostly hydrogen and helium. Continue reading