Artificial selection is one example, eyes another, of the well-documented and inescapable process of evolution--change in a population of species over time--by natural selection. These are some of the things that molecules do.
How does light escape from the sun? We take a journey from the centre of the sun, following the path of light. We witness its fiery birth from in the core, its 430,000 mile battle against gravity and magnetism, and its escape from the solar surface.
Today on Crash Course Astronomy, Phil explains comets. Comets are chunks of ice and rock that orbit the Sun. When they get near the Sun the ice turns into gas, forming the long tail, and also releases dust that forms a different tail. We’ve visited comets up close and found them to be lumpy, with vents in the surface that release the gas as ice sublimates. Eons ago, comets (and asteroids) may have brought a lot of water to Earth -- as well as the ingredients for life.
This year we said goodbye to one of our most intrepid planetary explorers, the Opportunity rover. Take a look back at its storied 15-year mission on Mars, and how it revolutionized our understanding of not just the red planet, but our solar system at large.
Today Phil’s explaining the stars and how they can be categorized using their spectra. Together with their distance, this provides a wealth of information about them including their luminosity, size, and temperature. The HR diagram plots stars’ luminosity versus temperature, and most stars fall along the main sequence, where they live most of their lives.