Cosmic Horizons

Educator Materials Case Study: Friedrich Bessel and the Companion of Sirius Bessel discovered Sirius' unseen companion star long before technology allowed us to see Sirius B and even longer before quan... Educator Materials Case Study: Gerard Kuiper and the Trans-Neptunian Comet Belt A dusty snowball orbiting the Sun, trailing gas and dust as it melts—a poetic and highly accurate way to describe a comet. Fi... Educator Materials Case Study: John Michell And Black Holes Imagine gravity so strong that even light is contained by its force. When a country parson first described black holes in 178... Educator Materials Case Study: Fossil Microbes on Mars? A meteorite that escaped from Mars 16 million years ago was found recently in Antarctica. Does it, or doesn't it, hold eviden... Educator Materials Case Study: Neutrino Observatories Update your image of astronomers. Today they spend most of their time peering into computer screens rather than through the e... Educator Materials Case Study: The Cosmic Microwave Background Radiation At this distance in time and space, can we prove that the universe was created with a single explosion? See how scientists ha... Educator Materials Profile: Ernst Chladni and Rocks from the Sky Today, we accept the notion that enormous rocks exist within our solar system and that some of them fall to Earth. A little o... Educator Materials Profile: Georges Lemaître, Father of the Big Bang When a Catholic priest—cosmologist first proposed that the universe began as a "primeval atom," it seemed preposter... Educator Materials Profile: Cecilia Payne and the Composition of the Stars What are the stars made of? At 25, Cecilia Payne answered this fundamental question in her Ph.D. thesis. Her pioneering work... Educator Materials Profile: Ole Roemer and the Speed of Light While studying one of Jupiter's moons, Ole Roemer happened upon the first good estimate of the speed of light. Before his 167... Educator Materials Profile: Vera Rubin and Dark Matter For every visible star in the observable universe, there are nine masses that are invisible and unidentified. Learn more abou... Educator Materials Profile: Carl Sagan and the Quest for Life in the Universe Cosmos, Contact, Icarus and Billions and Billions—from TV and movies to professional journals and best-selling books, Carl Sa... Educator Materials Profile: Lyman Spitzer and the Space Telescope The idea of launching a telescope into orbit was first suggested in 1923, but the idea wasn't realized until nearly 70 years... Educator Materials Profile: Fritz Zwicky's Extraordinary Vision Astronomer Fritz Zwicky was the first person to conceive of supernovas, neutron stars, dark matter, and gravitational lenses.... Educator Materials Profile: Harold C. Urey This Nobel Prize–winning chemist contributed to several scientific fields. His remarkable body of work spanned chemistry, geo...