The visible part of the universe. Dimensions of the Universe: from the Milky Way to the Metagalaxy
The portal site is an information resource where you can get a lot of useful and interesting knowledge related to Space. First of all, we will talk about our and other Universes, about celestial bodies, black holes and phenomena in the depths of outer space.
The totality of everything that exists, matter, individual particles and the space between these particles is called the Universe. According to scientists and astrologers, the age of the Universe is approximately 14 billion years. The size of the visible part of the Universe occupies about 14 billion light years. And some claim that the Universe extends over 90 billion light years. For greater convenience, it is customary to use the parsec value in calculating such distances. One parsec is equal to 3.2616 light years, that is, a parsec is the distance over which the average radius of the Earth's orbit is viewed at an angle of one arcsecond.
Armed with these indicators, you can calculate the cosmic distance from one object to another. For example, the distance from our planet to the Moon is 300,000 km, or 1 light second. Consequently, this distance to the Sun increases to 8.31 light minutes.
Throughout history, people have tried to solve mysteries related to Space and the Universe. In the articles on the portal site you can learn not only about the Universe, but also about modern scientific approaches to its study. All material is based on the most advanced theories and facts.
It should be noted that the Universe includes a large number of different objects known to people. The most widely known among them are planets, stars, satellites, black holes, asteroids and comets. At the moment, most of all is understood about the planets, since we live on one of them. Some planets have their own satellites. So, the Earth has its own satellite - the Moon. Besides our planet, there are 8 more that revolve around the Sun.
There are many stars in Space, but each of them is different from each other. They have different temperatures, sizes and brightness. Since all stars are different, they are classified as follows:
White dwarfs;
Giants;
Supergiants;
Neutron stars;
Quasars;
Pulsars.
The densest substance we know is lead. In some planets, the density of their substance can be thousands of times higher than the density of lead, which raises many questions for scientists.
All planets revolve around the Sun, but it also does not stand still. Stars can gather into clusters, which, in turn, also revolve around a center still unknown to us. These clusters are called galaxies. Our galaxy is called the Milky Way. All studies conducted so far indicate that most of the matter that galaxies create is so far invisible to humans. Because of this, it was called dark matter.
The centers of galaxies are considered the most interesting. Some astronomers believe that the possible center of the galaxy is a black hole. This is a unique phenomenon formed as a result of the evolution of a star. But for now, these are all just theories. Conducting experiments or studying such phenomena is not yet possible.
In addition to galaxies, the Universe contains nebulae (interstellar clouds consisting of gas, dust and plasma), cosmic microwave background radiation that permeates the entire space of the Universe, and many other little-known and even completely unknown objects.
Circulation of the ether of the Universe
Symmetry and balance of material phenomena is the main principle of structural organization and interaction in nature. Moreover, in all forms: stellar plasma and matter, world and released ethers. The whole essence of such phenomena lies in their interactions and transformations, most of which are represented by the invisible ether. It is also called relict radiation. This is microwave cosmic background radiation with a temperature of 2.7 K. There is an opinion that it is this vibrating ether that is the fundamental basis for everything filling the Universe. The anisotropy of the distribution of ether is associated with the directions and intensity of its movement in different areas of invisible and visible space. The whole difficulty of studying and research is quite comparable with the difficulties of studying turbulent processes in gases, plasmas and liquids of matter.
Why do many scientists believe that the Universe is multidimensional?
After conducting experiments in laboratories and in Space itself, data was obtained from which it can be assumed that we live in a Universe in which the location of any object can be characterized by time and three spatial coordinates. Because of this, the assumption arises that the Universe is four-dimensional. However, some scientists, developing theories of elementary particles and quantum gravity, may come to the conclusion that the existence of a large number of dimensions is simply necessary. Some models of the Universe do not exclude as many as 11 dimensions.
It should be taken into account that the existence of a multidimensional Universe is possible with high-energy phenomena - black holes, the big bang, bursters. At least, this is one of the ideas of leading cosmologists.
The expanding Universe model is based on the general theory of relativity. It was proposed to adequately explain the redshift structure. The expansion began at the same time as the Big Bang. Its condition is illustrated by the surface of an inflated rubber ball, on which dots - extragalactic objects - were applied. When such a ball is inflated, all its points move away from each other, regardless of position. According to the theory, the Universe can either expand indefinitely or contract.
Baryonic asymmetry of the Universe
The significant increase in the number of elementary particles over the entire number of antiparticles observed in the Universe is called baryon asymmetry. Baryons include neutrons, protons and some other short-lived elementary particles. This disproportion occurred during the era of annihilation, namely three seconds after the Big Bang. Up to this point, the number of baryons and antibaryons corresponded to each other. During the mass annihilation of elementary antiparticles and particles, most of them combined into pairs and disappeared, thereby generating electromagnetic radiation.
Age of the Universe on the portal website
Modern scientists believe that our Universe is approximately 16 billion years old. According to estimates, the minimum age may be 12-15 billion years. The minimum is repelled by the oldest stars in our Galaxy. Its real age can only be determined using Hubble's law, but real does not mean accurate.
Visibility horizon
A sphere with a radius equal to the distance that light travels during the entire existence of the Universe is called its visibility horizon. The existence of a horizon is directly proportional to the expansion and contraction of the Universe. According to Friedman's cosmological model, the Universe began to expand from a singular distance approximately 15-20 billion years ago. During all the time, light travels a residual distance in the expanding Universe, namely 109 light years. Because of this, each observer at moment t0 after the start of the expansion process can observe only a small part, limited by a sphere, which at that moment has radius I. Those bodies and objects that are at this moment beyond this boundary are, in principle, not observable. The light reflected from them simply does not have time to reach the observer. This is not possible even if the light came out when the expansion process began.
Due to absorption and scattering in the early Universe, given the high density, photons could not propagate in a free direction. Therefore, an observer is able to detect only that radiation that appeared in the era of the Universe transparent to radiation. This epoch is determined by the time t»300,000 years, the density of the substance r»10-20 g/cm3 and the moment of hydrogen recombination. From all of the above it follows that the closer the source is in the galaxy, the greater the redshift value for it will be.
Big Bang
The moment the Universe began is called the Big Bang. This concept is based on the fact that initially there was a point (singularity point) in which all energy and all matter were present. The basis of the characteristic is considered to be the high density of matter. What happened before this singularity is unknown.
There is no exact information regarding the events and conditions that occurred at the time of 5*10-44 seconds (the moment of the end of the 1st time quantum). In physical terms of that era, one can only assume that then the temperature was approximately 1.3 * 1032 degrees with a matter density of approximately 1096 kg/m 3. These values are the limits for the application of existing ideas. They appear due to the relationship between the gravitational constant, the speed of light, the Boltzmann and Planck constants and are called “Planck constants”.
Those events that are associated with 5*10-44 to 10-36 seconds reflect the model of the “inflationary Universe”. The moment of 10-36 seconds is referred to as the “hot Universe” model.
In the period from 1-3 to 100-120 seconds, helium nuclei and a small number of nuclei of other light chemical elements were formed. From this moment on, a ratio began to be established in the gas: hydrogen 78%, helium 22%. Before one million years, the temperature in the Universe began to drop to 3000-45000 K, and the era of recombination began. Previously free electrons began to combine with light protons and atomic nuclei. Atoms of helium, hydrogen and a small number of lithium atoms began to appear. The substance became transparent, and the radiation, which is still observed today, was disconnected from it.
The next billion years of the existence of the Universe was marked by a decrease in temperature from 3000-45000 K to 300 K. Scientists called this period for the Universe the “Dark Age” due to the fact that no sources of electromagnetic radiation had yet appeared. During the same period, the heterogeneity of the mixture of initial gases became denser due to the influence of gravitational forces. Having simulated these processes on a computer, astronomers saw that this irreversibly led to the appearance of giant stars that exceeded the mass of the Sun by millions of times. Because they were so massive, these stars heated to incredibly high temperatures and evolved over a period of tens of millions of years, after which they exploded as supernovae. Heating to high temperatures, the surfaces of such stars created strong streams of ultraviolet radiation. Thus, a period of reionization began. The plasma that was formed as a result of such phenomena began to strongly scatter electromagnetic radiation in its spectral short-wave ranges. In a sense, the Universe began to plunge into a thick fog.
These huge stars became the first sources in the Universe of chemical elements that are much heavier than lithium. Space objects of the 2nd generation began to form, which contained the nuclei of these atoms. These stars began to be created from mixtures of heavy atoms. A repeated type of recombination of most of the atoms of the intergalactic and interstellar gases occurred, which, in turn, led to a new transparency of space for electromagnetic radiation. The Universe has become exactly what we can observe now.
Observable structure of the Universe on the website portal
The observed part is spatially inhomogeneous. Most galaxy clusters and individual galaxies form its cellular or honeycomb structure. They construct cell walls that are a couple of megaparsecs thick. These cells are called "voids". They are characterized by a large size, tens of megaparsecs, and at the same time they do not contain substances with electromagnetic radiation. The void accounts for about 50% of the total volume of the Universe.
The universe is everything that exists. The universe is limitless. Therefore, when discussing the size of the Universe, we can only talk about the size of its observable part - the observable Universe.
The observable Universe is a ball with a center on Earth (the observer’s place), has two sizes: 1. apparent size - Hubble radius - 13.75 billion light years, 2. real size - particle horizon radius - 45.7 billion light years .
The modern model of the Universe is also called the ΛCDM model. The letter "Λ" means the presence of a cosmological constant, which explains the accelerated expansion of the Universe. "CDM" means that the Universe is filled with cold dark matter. Recent studies indicate that the Hubble constant is about 71 (km/s)/Mpc, which corresponds to the age of the Universe 13.75 billion years. Knowing the age of the Universe, we can estimate the size of its observable region.
According to the theory of relativity, information about any object cannot reach an observer at a speed greater than the speed of light (299,792,458 km/s). It turns out, the observer sees not just an object, but its past. The farther an object is from him, the more distant the past he looks. For example, looking at the Moon, we see as it was a little more than a second ago, the Sun - more than eight minutes ago, the nearest stars - years, galaxies - millions of years ago, etc. In Einstein's stationary model, the Universe has no age limit, which means its observable region is also not limited by anything. The observer, armed with increasingly sophisticated astronomical instruments, will observe increasingly distant and ancient objects.
Dimensions of the observable Universe
We have a different picture with the modern model of the Universe. According to it, the Universe has an age, and therefore a limit of observation. That is, since the birth of the Universe, no photon could have traveled a distance greater than 13.75 billion light years. It turns out that we can say that the observable Universe is limited from the observer to a spherical region with a radius of 13.75 billion light years. However, this is not quite true. We should not forget about the expansion of the space of the Universe. By the time the photon reaches the observer, the object that emitted it will be already 45.7 billion light years away from us. This size is the horizon of particles, it is the boundary of the observable Universe.
So, the size of the observable Universe is divided into two types. Apparent size, also called the Hubble radius (13.75 billion light years). And the real size, called the particle horizon (45.7 billion light years).
The important thing is that both of these horizons do not at all characterize the real size of the Universe. Firstly, they depend on the position of the observer in space. Secondly, they change over time. In the case of the ΛCDM model, the particle horizon expands at a speed greater than the Hubble horizon. Modern science does not answer the question of whether this trend will change in the future. But if we assume that the Universe continues to expand with acceleration, then all those objects that we see now will sooner or later disappear from our “field of vision”.
Currently, the most distant light observed by astronomers is . Peering into it, scientists see the Universe as it was 380 thousand years after the Big Bang. At this moment, the Universe cooled down enough that it was able to emit free photons, which are detected today with the help of radio telescopes. At that time, there were no stars or galaxies in the Universe, but only a continuous cloud of hydrogen, helium and an insignificant amount of other elements. From the inhomogeneities observed in this cloud, galaxy clusters will subsequently form. It turns out that precisely those objects that will be formed from inhomogeneities in the cosmic microwave background radiation are located closest to the particle horizon.
Real size of the Universe
So, we have decided on the size of the observable Universe. But what about the real size of the entire Universe? modern science does not have information about the real size of the Universe and whether it has boundaries. But most scientists agree that the Universe is limitless.
Conclusion
The observable Universe has an apparent and true boundary, called respectively the Hubble radius (13.75 billion light years) and the particle radius (45.7 billion light years). These boundaries depend entirely on the observer's position in space and expand over time. If the Hubble radius expands strictly at the speed of light, then the expansion of the particle horizon is accelerated. The question of whether its acceleration of the particle horizon will continue and whether it will be replaced by compression remains open.
Each of us has thought at least once about what a huge world we live in. Our planet is an insane number of cities, villages, roads, forests, rivers. Most people don’t even get to see half of it in their lifetime. It is difficult to imagine the enormous scale of the planet, but there is an even harder task. The size of the Universe is something that, perhaps, even the most developed mind cannot imagine. Let's try to figure out what modern science thinks about this.
Basic concept
The Universe is everything that surrounds us, what we know and guess about, what was, is and will be. If we reduce the intensity of romanticism, then this concept defines in science everything that exists physically, taking into account the time aspect and laws governing the functioning, interconnection of all elements, and so on.
Naturally, it is quite difficult to imagine the real size of the Universe. In science, this issue is widely discussed and there is no consensus yet. In their assumptions, astronomers rely on existing theories of the formation of the world as we know it, as well as on data obtained as a result of observation.
Metagalaxy
Various hypotheses define the Universe as a dimensionless or ineffably vast space, most of which we know little about. To bring clarity and enable discussion of the area available for study, the concept of Metagalaxy was introduced. This term refers to the part of the Universe accessible to observation by astronomical methods. Thanks to the improvement of technology and knowledge, it is constantly increasing. The metagalaxy is part of the so-called observable Universe - a space in which matter, during the period of its existence, managed to reach its current position. When it comes to understanding the size of the Universe, most people talk about the Metagalaxy. The current level of technological development makes it possible to observe objects located at a distance of up to 15 billion light years from Earth. Time, as can be seen, plays no less a role in determining this parameter than space.
Age and size
According to some models of the Universe, it never appeared, but exists forever. However, the Big Bang theory that dominates today gives our world a “starting point.” According to astronomers, the age of the Universe is approximately 13.7 billion years. If you go back in time, you can go back to the Big Bang. Regardless of whether the size of the Universe is infinite, the observable part of it has boundaries, since the speed of light is finite. It includes all those locations that can affect an observer on earth since the Big Bang. The size of the observable Universe is increasing due to its constant expansion. According to recent estimates, it occupies a space of 93 billion light years.
A bunch of
Let's see what the Universe is like. The dimensions of outer space, expressed in hard numbers, are, of course, amazing, but difficult to understand. For many, it will be easier to understand the scale of the world around us if they know how many systems like the Solar one fit into it.
Our star and its surrounding planets are only a tiny part of the Milky Way. According to astronomers, the Galaxy contains approximately 100 billion stars. Some of them have already discovered exoplanets. It’s not just the size of the Universe that is striking, but the space occupied by its insignificant part, the Milky Way, inspires respect. It takes light one hundred thousand years to travel through our galaxy!
Local group
Extragalactic astronomy, which began to develop after the discoveries of Edwin Hubble, describes many structures similar to the Milky Way. Its closest neighbors are the Andromeda Nebula and the Large and Small Magellanic Clouds. Together with several other “satellites” they form the local group of galaxies. It is separated from a neighboring similar formation by approximately 3 million light years. It’s even scary to imagine how much time it would take a modern aircraft to cover such a distance!
Observed
All local groups are separated by a wide area. The metagalaxy includes several billion structures similar to the Milky Way. The size of the Universe is truly amazing. It takes 2 million years for a light beam to travel the distance from the Milky Way to the Andromeda Nebula.
The further a piece of space is located from us, the less we know about its current state. Because the speed of light is finite, scientists can only obtain information about the past of such objects. For the same reasons, as already mentioned, the area of the Universe accessible to astronomical research is limited.
Other worlds
However, this is not all the amazing information that characterizes the Universe. The dimensions of outer space, apparently, significantly exceed the Metagalaxy and the observable part. The theory of inflation introduces such a concept as the Multiverse. It consists of many worlds, probably formed simultaneously, not intersecting with each other and developing independently. The current level of technological development does not give hope for knowledge of such neighboring Universes. One of the reasons is the same finiteness of the speed of light.
Rapid advances in space science are changing our understanding of how big the Universe is. The current state of astronomy, its constituent theories and the calculations of scientists are difficult for the uninitiated to understand. However, even a superficial study of the issue shows how huge the world is, of which we are a part, and how little we still know about it.
The diameter of the Moon is 3000 km, the Earth is 12800 km, the Sun is 1.4 million kilometers, while the distance from the Sun to the Earth is 150 million km. The diameter of Jupiter, the largest planet in our solar system, is 150 thousand km. It’s not for nothing that they say that Jupiter could be a star; in the video, next to Jupiter is located working star, its size () is even smaller than Jupiter. By the way, since we touched on Jupiter, you may not have heard, but Jupiter does not revolve around the Sun. The fact is that the mass of Jupiter is so large that the center of rotation of Jupiter and the Sun is located outside the Sun, thus both the Sun and Jupiter rotate together around a common center of rotation.
According to some calculations, there are 400 billion stars in our galaxy, which is called the Milky Way. This is far from the largest galaxy; neighboring Andromeda has more than a trillion stars.
As stated in the video at 4:35, in a few billion years our Milky Way will collide with Andromeda. According to some calculations, using any technology known to us, even improved in the future, we will not be able to reach other galaxies, since they are constantly moving away from us. Only teleportation can help us. This is bad news.
The good news is that you and I were born at a fortunate time when scientists see other galaxies and can theorize about the Big Bang and other phenomena. If we had been born much later, when all the galaxies would have scattered far from each other, then most likely we would not have been able to find out how the universe arose, whether there were other galaxies, whether there was a Big Bang, etc. We would believe that our Milky Way (united by that time with Andromeda) is the only one and unique in the entire cosmos. But we are lucky and we know something. Maybe.
Let's get back to the numbers. Our small Milky Way contains up to 400 billion stars, neighboring Andromeda has more than a trillion, and in total there are more than 100 billion such galaxies in the observable universe. And many of them contain several trillion stars. It may seem incredible that there are so many stars in space, but somehow the Americans took and pointed their mighty Hubble telescope at a completely empty space in our sky. After watching him for several days, they received this photograph:
In a completely empty area of our sky, they found 10 thousand galaxies (not stars), each of which contains billions and trillions of stars. Here is this square in our sky, for scale.
And we don’t know what’s going on outside the observable universe. The size of the universe that we see is about 91.5 billion light years. What's next is unknown. Perhaps our entire universe is just a bubble in a swirling ocean of multiverses. In which other laws of physics may even apply, for example, Archimedes’ law does not work and the sum of the angles is not equal to 360 degrees.
Enjoy. Dimensions of the universe on video:
17:45 23/06/2016👁 916
The scale of space is difficult to imagine and even more difficult to accurately determine. But thanks to the ingenious guesses of physicists, we think we have a good idea of how big the cosmos is. “Let us take a walk around,” was the invitation American astronomer Harlow Shapley made to an audience in Washington, D.C., in 1920. He took part in the so-called Great Debate on the scale of the Universe, along with his colleague Heber Curtis.
Shapley believed that our galaxy was 300,000 in diameter. This is three times more than is thought now, but for that time the measurements were quite good. In particular, he calculated the generally correct proportional distances within the Milky Way - our position relative to the center, for example.
At the beginning of the 20th century, however, 300,000 light years seemed to many of Shapley's contemporaries to be some kind of absurdly large number. And the idea that others like the Milky Way - which were visible in - were as large was not taken seriously at all.
And Shapley himself believed that the Milky Way should be special. “Even if the spirals are represented, they are not comparable in size to our star system,” he told his listeners.
Curtis disagreed. He thought, and rightly so, that there were many other galaxies in the Universe, scattered like ours. But his starting point was the assumption that the Milky Way was much smaller than Shapley had calculated. According to Curtis's calculations, the Milky Way was only 30,000 light-years in diameter - or three times smaller than modern calculations show.
Three times more, three times less - we are talking about such huge distances that it is quite understandable that astronomers who thought about this topic a hundred years ago could be so wrong.
Today we are fairly confident that the Milky Way is somewhere between 100,000 and 150,000 light years across. The observable Universe is, of course, much, much larger. It is believed to be 93 billion light years in diameter. But why such confidence? How can you even measure something like this with ?
Ever since Copernicus declared that the Earth is not the center, we have always struggled to rewrite our ideas about what the Universe is - and especially how big it can be. Even today, as we will see, we are gathering new evidence that the entire Universe may be much larger than we recently thought.
Caitlin Casey, an astronomer at the University of Texas at Austin, studies the universe. She says astronomers have developed a set of sophisticated instruments and measurement systems to calculate not only the distance from Earth to other bodies in our solar system, but also the gaps between galaxies and even to the very end of the observable universe.
The steps to measuring all of this go through the distance scale of astronomy. The first stage of this scale is quite simple and these days relies on modern technology.
“We can simply bounce radio waves off nearby ones in the solar system, like and, and measure the time it takes for those waves to return to Earth,” Casey says. “The measurements will thus be very accurate.”
Large radio telescopes like the one in Puerto Rico can do this job - but they can also do more. Arecibo, for example, can detect and even image those flying around our solar system, depending on how radio waves bounce off the asteroid's surface.
But using radio waves to measure distances beyond our solar system is impractical. The next step in this cosmic scale is the measurement of parallax. We do this all the time without even realizing it. Humans, like many animals, intuitively understand the distance between themselves and objects due to the fact that we have two eyes.
If you hold an object in front of you - your hand, for example - and look at it with one eye open, and then switch to the other eye, you will see your hand move slightly. This is called parallax. The difference between these two observations can be used to determine the distance to the object.
Our brains do this naturally with information from both eyes, and astronomers do the same with nearby stars, only they use a different sense: telescopes.
Imagine two eyes floating in space, on either side of our Sun. Thanks to the Earth's orbit, we have these eyes, and we can observe the displacement of stars relative to objects in the background using this method.
“We measure the positions of stars in the sky in, say, January, and then wait six months and measure the positions of the same stars in July when we are on the other side of the Sun,” Casey says.
However, there is a threshold beyond which objects are already so far away - about 100 light years - that the observed shift is too small to provide a useful calculation. At this distance we will still be far from the edge of our own galaxy.
The next step is main sequence installation. It relies on our knowledge of how stars of a certain size - known as main sequence stars - evolve over time.
First, they change color, becoming redder as they age. By accurately measuring their color and brightness, and then comparing this with what is known about the distance to main sequence stars, as measured by trigonometric parallax, we can estimate the position of these more distant stars.
The principle behind these calculations is that stars of the same mass and age would appear equally bright to us if they were at the same distance from us. But since this is often not the case, we can use the difference in measurements to figure out how far they really are.
The main sequence stars used for this analysis are considered to be one of the types of "standard candles" - bodies whose magnitude (or brightness) we can calculate mathematically. These candles are scattered throughout space and predictably illuminate the Universe. But main sequence stars are not the only examples.
This understanding of how brightness relates to distance allows us to understand distances to even more distant objects - like stars in other galaxies. The main sequence approach will no longer work because the light from these stars - which are millions of light years away, if not more - is difficult to accurately analyze.
But in 1908, a scientist named Henrietta Swan Leavitt from Harvard made a fantastic discovery that helped us measure these colossal distances. Swan Leavitt realized that there was a special class of stars - .
"She noticed that a certain type of star changes its brightness over time, and this change in brightness, in the pulsation of these stars, is directly related to how bright they are by nature," Casey says.
In other words, a brighter Cepheid star will "pulse" more slowly (over many days) than a fainter Cepheid. Because astronomers can quite easily measure the Cepheid's pulse, they can tell how bright the star is. Then, by observing how bright it appears to us, they can calculate its distance.
This principle is similar to the main sequence approach in that brightness is key. However, the important thing is that distance can be measured in different ways. And the more ways we have to measure distances, the better we can understand the true scale of our cosmic backyard.
It was the discovery of such stars in our own galaxy that convinced Harlow Shapley of its large size.
In the early 1920s, Edwin Hubble discovered a Cepheid at the nearest one and concluded that it was only a million light years away.
Today, our best estimate is that this galaxy is 2.54 million light-years away. Therefore, Hubble was wrong. But this in no way detracts from his merits. Because we're still trying to calculate the distance to Andromeda. 2.54 million years - this number is essentially the result of relatively recent calculations.
Even now, the scale of the Universe is difficult to imagine. We can estimate it, and very well, but, in truth, it is very difficult to accurately calculate the distances between galaxies. The universe is incredibly big. And it is not limited to our galaxy.
Hubble also measured the brightness of the exploding type 1A. They can be seen in fairly distant galaxies, billions of light years away. Because the brightness of these calculations can be calculated, we can determine how far away they are, just as we did with Cepheids. Type 1A supernovae and Cepheids are examples of what astronomers call standard candles.
There is another feature of the Universe that can help us measure truly large distances. This is redshift.
If you've ever heard the siren of an ambulance or police car rush past you, you're familiar with the Doppler effect. When the ambulance approaches, the siren sounds shriller, and when it moves away, the siren fades again.
The same thing happens with light waves, only on a small scale. We can detect this change by analyzing the light spectrum of distant bodies. There will be dark lines in this spectrum because individual colors are absorbed by elements in and around the light source - the surfaces of stars, for example.
The further objects are from us, the further towards the red end of the spectrum these lines will shift. And this is not only because objects are far from us, but because they are also moving away from us over time, due to the expansion of the Universe. And observing the redshift of light from distant galaxies actually provides us with evidence that the Universe is indeed expanding.