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History Vault. Recommended for you. Rather, it was an illusion caused by the time it takes for light to span the extra distance when Earth and Jupiter are on opposite sides of the sun. His calculations showed that light travels , miles a second — a remarkably good estimate, considering that he was doing this work just 60 years after the invention of the telescope. At first, these ideas were necessarily vague because scientists had only a rough idea of how far away the stars are.
The breakthrough moment came in , when German astronomer Friedrich Bessel measured the exact distance to the star 61 Cygni. Within a couple of decades, the light-year was commonplace in popular science writing. But Arenou says professional astronomers long resisted using the term — and for a surprising reason.
They considered the light-year insufficiently scientific, since it cannot be measured directly. Beyond the Milky Way, where parallaxes are too small even for Gaia to detect, astronomers calculate distances by observing certain types of variable stars or brilliant supernova explosions. Those approaches still rely on parallax measurements as their point of reference, however. One parsec equals 3. Sometimes the parsec is more scientifically relevant, but researchers often switch between the two terms for no obvious reason except style.
Better to stick with the light-year. IE 11 is not supported. For an optimal experience visit our site on another browser. Share this —. By Corey S. Science Space junk is a huge problem, but this high-tech satellite net just might help.
Where to begin? An important stage of the evolution of the Universe occurred around , years after the Big Bang, when the temperature was cool enough around degrees for neutral atoms to form. Before that time, there were too many charged particles to allow light to travel more than a very short distance. After atoms were formed, light could travel immense distances.
Perhaps of more importance to us was the formation of the Sun and the solar system - including our planet - about 4. Earth has been bathed with light from the Sun ever since; it is our most important source of energy. Sunlight warms us, causes weather patterns, allows plants to manufacture oxygen and our food from carbon dioxide and water, and it allows us to find our way around in the daytime!
The use of sunlight in photosynthesis, to make oxygen and carbohydrates from carbon dioxide and water, is a process first established over two billion years ago by cyanobacteria. They made the large quantities of oxygen in the atmosphere which allowed oxygen-breathing life to evolve.
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