Christiaan Huygens (14 April 1629 – 8 July 1695) was a Dutch physicist, mathematician, astronomer and inventor, who is widely regarded as one of the greatest scientists of all time and a major figure in the scientific revolution. In physics, Huygens made groundbreaking contributions in optics and mechanics, while as an astronomer he is chiefly known for his studies of the rings of Saturn and the discovery of its moon Titan. As an inventor, he improved the design of the telescope with the invention of the Huygenian eyepiece. His most famous invention, however, was the invention of the pendulum clock in 1656, which was a breakthrough in timekeeping and became the most accurate timekeeper for almost 300 years. Because he was the first to use mathematical formulae to describe the laws of physics, Huygens has been called the first theoretical physicist and the founder of mathematical physics.
In 1659, Huygens was the first to derive the now standard formula for the centripetal force in his work De vi centrifuga. The formula played a central role in classical mechanics and became known as the second of Newton’s laws of motion. Huygens was also the first to formulate the correct laws of elastic collision in his work De motu corporum ex percussione, but his findings were not published until after his death in 1703. In the field of optics, he is best known for his wave theory of light, which he proposed in 1678 and described in 1690 in his Treatise on Light, which is regarded as the first mathematical theory of light. His theory was initially rejected in favor of Isaac Newton’s corpuscular theory of light, until Augustin-Jean Fresnel adopted Huygens’ principle in 1818 and showed that it could explain the rectilinear propagation and diffraction effects of light. Today this principle is known as the Huygens–Fresnel principle. read more
Image credit: NASA/JPL, Commons.wikimedia
Six Moons of Saturn (Titan, Mimas, Tethys, Enceladus, Dione & Rhea)
Image Credit: Rafael Defavari
Saturn: Bright Tethys and Ancient Rings
Image Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
Vertical structures, among the tallest seen in Saturn’s main rings, rise abruptly from the edge of Saturn’s B ring to cast long shadows on the ring in this image taken by NASA’s Cassini spacecraft two weeks before the planet’s August 2009 equinox.
Credit: NASA/JPL/Space Science Institute
Images of the Earth and the moon above the Rings of Saturn taken by Cassini on April 13, 2017.
NASA/JPL-Caltech/SSI/CICLOPS/Kevin M. Gill
Possible variations in chemical composition from one part of Saturn’s ring system to another are visible in this Voyager 2 picture as subtle color variations that can be recorded with special computer-processing techniques.
Image Credit: NASA/JPL
In 40 million years, Mars may have a ring (and one fewer moon)
Nothing lasts forever – especially Phobos, one of the two small moons orbiting Mars. The moonlet is spiraling closer and closer to the Red Planet on its way toward an inevitable collision with its host. But a new study suggests that pieces of Phobos will get a second life as a ring around the rocky planet.
A moon – or moonlet – in orbit around a planet has three possible destinies. If it is just the right distance from its host, it will stay in orbit indefinitely. If it’s beyond that point of equilibrium, it will slowly drift away. (This is the situation with the moon; as it gradually pulls away from Earth, its orbit is growing by about 1.5 inches per year.) And if a moon starts out on the too-close side, its orbit will keep shrinking until there is no distance left between it and its host planet.
The Martian ring will last for at least 1 million years – and perhaps for as long as 100 million years, according to the study.
The rest of Phobos will probably remain intact, until it hits the Martian surface. But it won’t be a direct impact; instead, the moonlet’s remains will strike at an oblique angle, skipping along the surface like a smooth stone on a calm lake.
This has probably happened before – scientists believe a group of elliptical craters on the Martian surface were caused by a small moon that skidded to its demise. (If this were to happen on Earth, our planet’s greater mass would produce a crash as big as the one that wiped out the dinosaurs, the researchers noted as an aside.)
Tushar Mittal using Celestia 2001-2010, Celestia Development Team.
Saturn’s rings display their subtle colors in this view captured on Aug. 22, 2009, by NASA’s Cassini spacecraft. The particles that make up the rings range in size from smaller than a grain of sand to as large as mountains, and are mostly made of water ice. The exact nature of the material responsible for bestowing color on the rings remains a matter of intense debate among scientists.
Credit: NASA/JPL-Caltech/Space Science Institute
Saturn’s moon Dione drifts before the planet’s rings, seen here almost edge on. For all their immense width, the rings are relatively paper-thin, about 30 feet (10 meters) in most places. For its part, Dione is about 698 miles (1,123 kilometers) across.
Credit: NASA/JPL-Caltech/Space Science Institute