Thousands of years ago people looked into the sky and, frankly, didn’t understand anything. Maybe he saw God. Perhaps the comet. Let understand the historians. Thousands of years passed, and the man looked again at the sky — with the help of, for example, the Hubble space telescope. He saw a myriad of stars, zillions of planets, huge distances and… nothing (dark matter). We learn quickly. Space telescope the James Webb will be 100 times more powerful than Hubble and will show more. But what we discovered without it.
The sky change as the planets move
Our ancient ancestors tracked the changing seasons across the sky. It told them when to hunt certain types of animals, for example. When they developed agriculture, civilization like Ancient Egypt used the stars to determine when to sow crops and when to harvest. We used the sky as a giant clock to count the time during the year. When there was Eclipse or comets, they were considered unexpected events, a sign of the gods. Today we know that they occur because of gravitational interactions and orbital position in space.
Over time, some smart people noticed that stars move across the sky in a predictable manner. They walked the same path that the Sun and moving in the background of other stars. We now know that this planet (from the Greek word meaning “Wanderers”). In many cultures these planets were named after gods. Mercury, Venus, Mars, Saturn and Jupiter, Neptune, Uranus are named after Supreme beings revered in ancient times.
The earth and the Sun are not the center of the Universe
Early beliefs (depending on religions) often indicated the Earth the center of the Universe. But when the first astronomers observed the sky, they did not understand many things. Why Mars, for example, sometimes changes its course in the sky, and then again starts marching in the same direction as other planets? Some astronomers came up with a complex geometric construction — the epicycles — which were supposed to predict chaotic at first glance, the movement of the planets.
A simple solution was the suggestion by Nicolaus Copernicus in the 1500’s, when he put the Sun in the center of the Universe, and the Earth started to rotate around him like planets. (In the third century it was also proposed by Aristarchus of Samos from Greece, but his works were not well known in the Western world at the time). This arrangement solved the problem of the epicycle and corroborated by other evidence. For example, the discovery by Galileo of Jupiter’s moons in 1610 showed that not everything orbits the Earth. Religious authorities were unhappy, but eventually everything fell into place.
With the development of telescopic technology, we also learned that the Sun is not the center of the Universe. In 1750-ies it was thought that the milky Way is a large collection of stars with their own center. By the early 1900s, observation of new stars in other galaxies showed that they were farther away than the milky Way. Finally, the astronomer Edwin Hubble uncovered evidence that the universe is expanding uniformly in all directions, without a true center.
It all depends on the gravity
Although we see the motion of the planets, why they move, it was unclear for thousands of years. In the 1600’s, that all changed when sir Isaac Newton began to apply mathematical theory to observations of the Universe. He determined three basic laws of motion and law of universal gravitation, whereby any two things in the Universe are mutually attracted. Planets have greater force of attraction, pebbles in the rings of Saturn — less.
In the early 1900s, our understanding of gravity has changed together with the observations of physicists like albert Einstein who discovered that time can vary depending on the coordinate system. If you are traveling at speeds close to that of light, your sense of time slows down compared to the feeling of living on Earth. Time began to consider the fourth dimension (after the width, height and length), and this has led to a better understanding of the incredible gravitational conditions around black holes and other massive gravitational objects. The gravity of the object was a consequence of the “curvature” of space-time.
In early 2016 the gravitational waves were detected by the LIGO Observatory. The ripples in space-time, due to the mutual rotation of massive objects like black holes. Einstein predicted their existence, and astronomers were looking for them for over 50 years.
Beyond Saturn is the planet
The telescope showed many small objects that are unattainable to the naked eye. William Herschel discovered Uranus in 1781 by accident when catalogued all the stars that I could find, eighth magnitude or brighter. When he found Uranus moving against the background of stars. He planned to name it in honor of king George III, but other astronomers decided to name the planet in honor of the God, like the rest.
For this discovery was rapidly followed by others: Ceres (then it was called an asteroid, not a dwarf planet) was discovered in 1801. Neptune in 1846, and Pluto (first became a planet) in 1930. The solar system was much larger than previously thought. Over time, models suggest that comets remain outside the orbit of Neptune, among other icy objects in the Kuiper belt. In the early 2000s, several new objects the size of Pluto were discovered in the Kuiper belt, which allowed the International astronomical Union to create a new category of “dwarf planet” and placed Pluto and Ceres in this category.
Not less striking has been the discovery of planets outside our Solar system. First, astronomers have found three planets near the pulsar PSR B1257+12 in 1992, then a large exoplanet near the main sequence star 51 Pegasi in 1995. Today we know of the existence of more than 1,000 planets outside the Solar system, and thousands more waiting in the wings. Most of them discovered by NASA space telescope Kepler, launched in 2009.
There is a cosmic speed limit
We use the speed of light as a way of measuring the Universe. For centuries we have specified its rate, and today she is about 300,000 kilometers per second in vacuum. The sun is eight light minutes from Earth. The nearest star system (alpha Centauri) is four light years from us, and the nearest major galaxy (Andromeda) is 2.5 million light years.
Although we all dream about the warp engine from Star trek, which would allow us in the blink of an eye to cover vast distances, we are hampered by the limitations of physics. Another discovery was Einstein’s equation E = mc2 that defines the equivalence of mass and energy. When you are flying at a speed close to the speed of light, the required energy increases your mass. At the point immediately before the violation of the light limit the mass becomes infinite. Move faster is simply impossible.
However, theoretical physics offers ingenious short moves. Perhaps, in the Universe there are wormholes through which you will be able to travel with ease, traversing vast distances in moments. There may be ways even communication at the speed of light, because the quantum-entangled particles can communicate instantaneously, regardless of distance separating them. But as far as we know now, the speed of light is equal to the maximum possible speed of travel.
We see the echo of the Big Bang
If the universe began with a singularity and then expanded outward according to the Big Bang theory, she was supposed to be surrounded by unimaginable power. At a time when the universe became larger, this energy is dissipated, cooled and condensed in the substance that filled the space.
We can observe the remains of this huge explosion due to accidental opening in 1965. While the existence of background radiation was first suggested Ralph Alfer in 1948, two scientists from Bell Telephone Laboratories discovered him only decades later, when faced with interference in the new radio. Arno Penzias and Robert Wilson found the radiation together with the other team, which resulted in two works (one from each group) published in Astrophysical Journal in 1965.
Astronomers now know about the existence of tiny temperature fluctuations (anisotropy) in the cosmic microwave background (CMB), which reveal minor density fluctuations in the early Universe. These minor fluctuations can be detected by very sensitive instruments like WMAP, and the European Planck space telescope. It is believed that these variations can reveal much about the formation of the early Universe, the large-scale structure of the Universe and the nature of the earliest galaxies.
The universe is expanding (and faster)
In 1929 astronomer Edwin Hubble discovered that the universe is expanding. He was diligent and studious observer with his 100-inch telescope on mount Wilson in California and made many discoveries like these distances to galaxies. He peered into new stars in these galaxies, measure their brightness and then counting how much was to dim this brightness with distance. Then, based on the work of astronomer Vesto of Slipher, Hubble measured the motion of galaxies and published a paper which definitively showed the expansion of the Universe.
The opening was very loud, but even more surprised astronomers in the late 90-ies of the last century, when they discovered that the expansion is accelerating. Astronomers measure a supernova in distant galaxies, discovered that these supernovae were less bright than predicted by their redshift (which indicates that they are removed from us). This discovery eventually brought a Nobel prize scientist.
We will not be able to see most of the matter in the Universe
The accelerated expansion of the Universe has been a mystery to astronomers, but they suggested that there should be some force that “pushes” the Universe. The leading theory today is dark energy, which cannot be detected directly with the help of modern astronomical methods.
There are also several theories as to what may be this dark energy. It can be a property of space-time. With the expansion of space is born more dark energy, which pushes even further expansion. Another possible explanation is connected with the quantum theory of matter, which allowed the emergence and disappearance of particles bearing energy.
Dark energy is thought to be 68% of the mass of the known Universe, and dark matter is 27%. Scientists are not sure about the nature of dark matter, but know of its existence through gravitational effects. We see how it bends light through gravitational lensing. The rest of the Universe, less than 5%, consists of the usual energy and matter that we can see with telescopes.
In other worlds there is water and ice
Water was considered to be one of the key elements for life, and eventually we came to the conclusion that it is a universal element in the Solar system and the Universe in General. The first observations of spacecraft in the 1970-ies and 80-ies have shown the existence of icy worlds beyond Earth. The opening of the ice moons near Jupiter, Saturn and beyond was a surprise because we are accustomed to observe the near airless moon of Earth. Over time, these worlds showed a complex chemical composition.
Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, are considered the most promising for life outside of Earth, at least in the Solar system. Furthermore, water can exist in liquid form inside these moons. On Titan, the moon of Saturn, a lot of hydrocarbons, and under the surface may be hiding a liquid ocean.
More advanced observations in the 90-ies and then found water ice in the most unexpected places. Was that water ice may be on an airless moon, and even mercury — the nearest planet to the Sun — if in is permanently closed to the Sun craters or under a protective layer of dust. Polar cap, consisting partly of ice exist on Mars. There is ice on comets and small worlds like the dwarf planet Ceres.
Ahead of us a lot of interesting
Astronomy is just beginning to be interesting, because the telescopes are getting better and better, new ways to explore our Universe. One is planned for launch in 2018 telescopes, James Webb, should be 100 times more powerful than its predecessor, the Hubble space telescope.
The European Extremely Large Telescope, which will be completed in 2024, if all goes according to plan, will study the secrets of the Universe from Earth. According to plan, he will look for exoplanets, to peer into the early days of the Universe, supermassive black holes and mysterious dark matter. The new-generation telescopes will also look for planets similar to Earth in other solar systems, study their atmospheres, and orbits of the origin.
The recent discovery of gravitational waves, a key component of the General theory of relativity, opened the way for a new type of astronomy — gravitational wave astronomy. Independent of the electromagnetic spectrum, gravitational wave astronomy will measure the ripples of space-time and show massive objects that would be invisible to optical telescopes.