For an explanation, see the main splats page
The principles of cosmology
- All things are possible: one model of the universe we know sees it, and so us, as being contained within the event horizon of an extremely massive black hole.
- Stars are separated by large distances, and the gaps beyond and between are known as interstellar space. The stars have almost no effect on interstellar space.
- Around each star, there is a boundary where the stellar wind slows down and eventually stops as it comes in contact with material in interstellar space.
- The edge of the Sun's sphere of influence, the heliosphere, lies three times as far away as Pluto. Voyager I will take 40 years to get to the heliosphere.
- Around 150 BC, Hipparchus estimated that the Moon is 30 Earth diameters away from our planet, by taking sightings of the Moon at zenith from two places.
- Around 1450, Nicolas Cusanus asserted that the world was round, and moved, but nobody reacted to this as they would later react to Giordano Bruno and Galileo.
- In 1543, Nicolaus Copernicus suggested a heliocentric model of the solar system, but there was no great reaction, possibly because he died as the book appeared.
- Bruno of Nola, Giordano Bruno, was burned at the stake in 1600 for, among other things, saying that the Earth went around the Sun, not the Sun around the Earth.
- In 1671 Giovanni Cassini completed an accurate measurement of distance to Mars and used that, combined with a known scale of the solar system to measure it all.
- In 1796 Pierre-Simon de Laplace stated his nebular hypothesis, that the solar system was formed from a nebula of gas and dust as it became organized.
- In 1992 the Catholic Church formally acknowledged its error over Galileo Galilei, after his book was taken off the Vatican's banned list in 1835.
- Cosmology is the study of how and why the universe is as it is. These studies rely on inference based on the theories of physics, and careful observation.
- Understanding how the universe developed requires careful measurement and thought, but without the right observations and measures, can still be in error.
- The universe started with the Big Bang, a point in time when all of the material we know about was in a very small volume, after which the material spread out.
- The Big Bang happened about 15 billion years ago, and while most of the interesting changes happened fast, forming galaxies took several billion years.
- Once upon a time, there was no time. That was when the cosmic egg, the super-atom, or the Big Bang happened. Then once that had happened, there was time.
- Three minutes after the Big Bang, the temperature had dropped to 1 trillion degrees, and protons and neutrons were able to begin forming nuclei of atoms.
- Since the Big Bang, the universe has been expanding outwards. So far, there is no evidence to suggest that it will slow down and collapse in a Big Crunch.
- A few hundred thousand years after the Big Bang, the universe had cooled enough so electrons could link to nuclei and form atoms of hydrogen and helium
- Stars can change over time, and as they develop through standard sequences, types of star can be recognized, and their future development can be predicted.
- In 1910, Ejnar Hertzsprung and Henry Norris Russell studied the link between magnitudes and spectral types of stars, leading to the Hertzsprung-Russell diagram.
- Annie Jump Cannon sorted Edward Pickering's arbitrary star classes to an order that made sense: she put the spectral classes in the order O, B, A, F, G, K, M.
- Blue-white, helium-rich stars like Rigel, are known by the letter B, while G is used for the Sun and other yellow stars, and M for red stars like Betelgeuse.
- We now know that a G star like the sun is at the cool end of the range, hotter only than K and M stars, while all of the rest are bluer and hotter.
- A class A star is a white star like Sirius or Vega, in whose spectra we see a very strong series of dark lines caused by hydrogen in its atmosphere.
- Between A and G are the F stars; between G and M, the K stars. The letters B, A, F, G, K, M, stand for six divisions, including a great majority of the stars.
- Stars beyond a certain size must inevitably collapse to form black holes, dense objects which exert enough gravitational force to stop even light escaping.
- Space can be thought of as curved, the curvature being caused by the influence of gravity on space. This helps explain many otherwise puzzling observations.
- The heavier elements in the universe have been formed as the result of fusion reactions in early stars, and later stellar explosions forcing nuclei together.
- Today, the universe is thought to be made up of about 74 percent hydrogen and 25 percent helium, the other elements amounting to only about 1 percent in total.
- Edwin Hubble made his first measurement of the Hubble constant in 1929, relating redshift to distance, leading to the conclusion that the Universe is expanding.
- Stars can orbit each other in binary systems, orbiting about the joint centre of gravity, which lies between, at a place determined by their respective masses.
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