To read part 1 of this series, click here.
The moon does rotate, but the time it takes to rotate around its axis is exactly equal to the time it takes to orbit the Earth and as a consequence, we always see the same side of the Moon. This isn’t a coincidence but this happens due to “tidal locking”, which causes the rotation of an object to sync up with its orbit. The tidal force from the Moon isn’t just making the seas and oceans move around, it also pulls at the solid bits of the Earth, ever so slightly slowing down the rotation of the Earth. If the Sun wouldn’t gobble up the Earth when it expands in 4-5 billion years, then some 50 billion years from now the Earth would be tidally locked to the Moon at which point the same side of the Earth would always be facing the Moon and the length of a day would be much longer than the 24 hours it is now.
For more than 200 years, astronomers thought that most of the stars in our galaxy were binary stars and that our sun was a unique exception. Recent discoveries however have revealed that most stars are not binary after all, although most (80%) of sun-sized stars are in pairs. Most stars in the galaxy (85%) are red dwarfs which generally form alone. Scientists also believe a few percent of stellar systems are trinary stars. Since 3-body systems are generally unstable, they only last for significant times if two of the stars are close together, with one far away (think Earth-Moon-Sun).
Dark Energy is calculated to make up 67% of the known universe, while Dark Matter makes up a further 27%, while what we can actually see and measure, i.e., conventional matter, makes up less than 5% of our universe. Therefore our current model of physics only works for 5% of the matter/energy in the universe. Dark energy should explain the expansion of the universe which is accelerating faster and faster and doesn’t match up with the expected gravity, ergo some kind of energy must be fuelling it. If it doesn’t slow down, one-day inflation of space will be exponentially faster than the speed of light.
24The Great Nothing
The Boötes void, a.k.a the Great Nothing, is an enormous spherical region of space that has a very small number of galaxies. At nearly 330 million light-years in diameter, it is one of the largest known voids in the Universe. The scale of the void is such that if the Milky Way had been in the center of the Boötes void, we wouldn’t have known there were other galaxies until the 1960s. This void has opened space for many discussions of its origin, including the hypothesis of a Type III civilization in the Kardashev scale. It would be a galactic civilization that can control energy at the scale of its entire host galaxy.
25Life in Universe
A 2015 study concluded that the Universe will form over 10 times more planets than what currently exists. Scientists assume that there are currently 40 billion earth-like planets in the habitable zone of their stars in the Milky Way Galaxy alone and a lot more such planets will form throughout the life of our universe. This would imply that there is at least a 92 percent chance that we are not the only civilization the universe will ever have.
One strange way to reach the nearest stars was proposed by astronomer Fritz Zwicky, who was the first person to theorize dark matter, supernovas, and neutron stars. He proposed accelerating the sun via a nuclear fusion-powered stellar engine and having it drag all the planets along. He warned that if the US didn't pursue this, the Russians would. According to a recently published paper, a Caplan thruster could use the sun’s own energy to transport our solar system to any desired location.
27Preventing Earth's Destruction
Our sun will get hotter over time and in about 600 million to 700 million years the conditions on earth won’t allow for photosynthesis. All the oceans will boil away a little while later. The earth will be a dead rock by the time the sun gets within a few billion years of turning into a red giant, at which point the sun will enlarge enough to engulf our planet. Europa might be nice, sunny, and perhaps habitable by then. Given the lead time that humanity has (more than 500 million years) humanity could perhaps engineer the Earth away from the heat (if humanity even survives by that time) or maybe mine the sun to prevent it from becoming a red giant in the first place, followed by moving the sun itself to a more friendly long-term location.
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16 Psyche is a large asteroid that is supposed to be worth $10,000 quadrillion. Orbiting between Mars and Jupiter, it is over 200 km (120 mi) in diameter. It could contain enough iron and nickel to sustain the world’s metal needs for millions of years. 16 Psyche is scheduled for space exploration, with a spacecraft launch planned in 2022, arrival in 2026, and orbital exploration in 2026–2027
The first known interstellar object detected passing through our Solar System is an asteroid called ʻOumuamua’, which was observed in 2017. It was a rocky, cigar-shaped object tumbling through space. Another interstellar object our solar system may have had a close encounter with happened around 70,000 years ago. A Red Dwarf star named Scholz's Star passed through the Solar System’s Oort cloud (~52,000 AU). It was so close in fact, that it nudged some Comets out of their orbits. It may have been visible to early Humans and Neanderthals.
Olbers’ Paradox disproves the old-world notion that the universe has always existed and is static in nature. Olbers’ Paradox states that since there are an infinite number of stars in the universe (i.e. any viewing angle from Earth into the night sky will eventually hit a star), the night sky should be uniformly bright. The resolution to this paradox is that the universe is not infinitely old. Additionally, it is also expanding. Both of these resolve the paradox.