FORMATION AND EVOLUTION...
FORMATION
STARS...
The first stars are thought to have appeared around 180 million years after the Big Bang. They would have been truly gargantuan objects- perhaps 100 to 1,000 times the size of our Sun, and made almost completely of hydrogen and helium. The stars we see today in our own galaxy and in nearby galaxies are totally different from this first generation of stars. This is because over billions of years, generations of stars created and dispersed new chemical elements as they lived and died, enriching the universe with heavier elements. Carbon, oxygen, iron, and silicon were formed from nuclear fusion in the hot cores of the stars, and the very heaviest elements were forged by supernova explosions. As each star dies, it scatters new enriched star-forming material across space. Without these successive generations of stars we simply would not be here today, as the ingredients to make us would not exist.
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GALAXIES...
​Galaxies are huge collections of stars, and it is thought that the first galaxies began to form sometime around 400 million years after The Big Bang. These early groups would have not looked anything like "modern-day" galaxies such as the Milky Way. Observations made with orbiting telescopes such as the Hubble Space Telescope show that the earliest galaxies were small ad irregularly shaped. Studies suggest that these early galaxies underweight vigorous star formation and that they were the building blocks of the galaxies we see today. Over time these smaller galaxies collided and merged together to form much larger galaxies, full of structure, like the ones near us in the universe that we are able to observe today with amateur telescopes.
PLANETS...
The planets we see today, including the Earth, formed around 4.56 billion years ago. The Sun and all the planets in the Solar System formed from a great cloud of dust and gas called the "solar nebula". As the Sun emerged from the nebula, it was encircled by a huge disc of debris known as a proto-planetary disc. Inside this disc, material began to clump together, and before long planet embryos known as "planetesimals" were formed. Some closest to the Sun combined into the terrestrial, inner planets - Mercury, Venus, Earth, and Mars - and these were made predominantly of rock and metal. Further out in the cooler regions of the infant Solar System, icy planetesimals coalesced to form planet cores. These then captured gas from the disc and, in the process, the gas giant planets were formed: Jupiter, Saturn, Uranus, and Neptune. Astronomers have seen similar processes occurring around other stars, where new planetary systems may be forming.