# How Big Is the Universe? From Earth to the Edge of Everything > Earth is only the beginning. Beyond our planet lie billions of stars, distant galaxies, enormous cosmic structures, and an observable universe roughly 93 billion light-years across. But how big is the entire universe, what lies beyond what we can see, and will humanity ever reach another star? - Published: 2026-10-13 - Updated: 2026-10-13 - Author: Keval - Section: Science Explained - Canonical: https://www.wonderunfold.com/blog/how-big-is-the-universe-from-earth-to-the-edge-of-everything - Markdown: https://www.wonderunfold.com/blog/how-big-is-the-universe-from-earth-to-the-edge-of-everything.md - Tags: How Big Is the Universe, Size of the Universe, Observable Universe, Universe Explained, Space Exploration, Milky Way Galaxy, Light Years, Cosmic Expansion, Big Bang, Voyager 1, Oort Cloud, Laniakea Supercluster, James Webb Space Telescope, Astronomy Facts, Mysteries of Space Travel from Earth through the solar system, Milky Way, and cosmic web to the ~93-billion-light-year observable universe—and why the full size may remain unknown. ## Key takeaways - The universe is approximately 13.8 billion years old, but the observable universe is about 92–93 billion light-years in diameter because space has expanded while light travelled toward us. - A light-year measures distance, not time. It is approximately 9.46 trillion kilometres—the distance light travels in one year. - The Milky Way is roughly 100,000 light-years across and contains hundreds of billions of stars. Our solar system occupies only a tiny region within it. - Voyager 1 and Voyager 2 have crossed the heliopause into interstellar space, but they remain within the Sun's much larger gravitational domain as defined by the distant Oort Cloud. - The observable universe has a limit determined by the age of the universe, cosmic expansion, and the distance light has been able to travel to us. It is not a physical wall at the edge of space. - Scientists do not know the full size of the entire universe. It could extend far beyond the observable region; whether it is finite or infinite remains unknown. Imagine stepping into a spacecraft and travelling away from Earth. At first, your home planet fills the window. Then it shrinks into a blue marble. The Moon disappears behind you, the Sun becomes one bright point among countless stars, and eventually even the entire Milky Way becomes a tiny island of light in a darkness filled with galaxies. How far could you keep travelling before reaching the edge of the universe? Would you eventually arrive at a wall, a boundary, or a place where space simply ends? And if the universe is about 13.8 billion years old, how can the observable universe be roughly 93 billion light-years across? These questions sound like science fiction, but they lead directly into modern cosmology. Astronomers can measure the distances to nearby planets, map our galaxy, detect galaxies whose light has travelled for billions of years, and estimate the size of the observable universe. Yet the farther we look, the stranger the picture becomes. The solar system is enormous by human standards but tiny compared with the Milky Way. Our galaxy is one of many in a universe whose full extent we cannot currently measure. So let's begin where every cosmic journey begins: on Earth. From there, we will travel outward, one scale at a time, until we reach the limits of what humanity can observe—and confront the possibility that the universe extends far beyond our cosmic horizon. ## 1. Earth: The Tiny World Where Our Cosmic Journey Begins Everything humanity has ever built, discovered, loved, feared, and imagined has happened on one small planet orbiting an ordinary star. Earth is about 12,742 kilometres in diameter, and its surface is home to billions of people and an extraordinary variety of life. From the ground, the universe can feel close. The Moon hangs in the night sky, the Sun rises each morning, and stars appear like tiny lights scattered above us. But those familiar views conceal extraordinary distances. Imagine shrinking Earth until it is the size of a small marble. The Moon would still be several metres away in a model built to that scale. The Sun would be much farther away, and the nearest stars would be separated by distances that are difficult to represent in an ordinary room. The first lesson of astronomy is that our eyes make the cosmos look more compact than it really is. Objects that appear beside one another in the sky can be separated by enormous distances, and the space between stars is far more vast than the stars themselves. ![Earth as a small blue sphere suspended in the darkness of space](https://www.wonderunfold.com/images/blog/earth-pale-blue-dot.jpg) *Earth feels enormous to us because it is our entire world. From space, it becomes one small planet among countless celestial objects.* ## 2. The Moon and Sun: Our First Steps Into Space The Moon is about 384,400 kilometres from Earth on average. That sounds manageable compared with the distances we will encounter later, but it is still a journey of hundreds of thousands of kilometres. If you could drive continuously at 100 kilometres per hour without stopping, reaching the Moon would take around 160 days. In reality, a road trip is impossible, and spacecraft must account for orbital mechanics, propulsion, navigation, and the need to arrive at a moving target. Next comes the Sun, approximately 150 million kilometres away. Astronomers use this average Earth–Sun distance as one astronomical unit, or AU, a convenient yardstick for distances inside the solar system. Sunlight travels at about 300,000 kilometres per second. Even at that extraordinary speed, light takes roughly eight minutes and twenty seconds to reach Earth. When you look at the Sun, you are seeing it as it was several minutes ago. That delay is a small example of a profound fact: astronomy is a way of looking into the past. The farther away an object is, the longer its light takes to reach us. Later, this simple idea will help explain why observing the distant universe is also observing its history. ## 3. How Big Is Our Solar System? The solar system is much more than the eight planets orbiting the Sun. It includes moons, asteroids, comets, dwarf planets, icy bodies, and immense regions where the Sun's gravity or magnetic influence still matters. Neptune, the most distant planet from the Sun, orbits at an average distance of about 30 astronomical units. Sunlight takes roughly four hours to reach Neptune. Beyond it lie the Kuiper Belt and other distant populations of small icy objects. But where does the solar system end? The answer depends on what we mean by 'end.' If we count the major planets, Neptune provides a convenient marker. If we follow the Sun's outward-flowing solar wind, the heliopause marks the boundary where that wind meets the surrounding interstellar environment. If we instead consider the distant icy objects gravitationally associated with the Sun, the solar system extends much farther. The hypothesized Oort Cloud may reach tens of thousands of astronomical units from the Sun, potentially approaching 100,000 AU. Its exact structure and extent remain uncertain because it has not been directly imaged as a cloud. This distinction matters because crossing into interstellar space does not necessarily mean leaving every part of the solar system behind. The Sun's magnetic influence and its gravitational reach have different boundaries. ![Scale illustration of the Sun, planets, Kuiper Belt, heliosphere, and distant Oort Cloud](https://www.wonderunfold.com/images/blog/solar-system-scale.jpg) *The planetary region is only the inner portion of a solar system whose gravitational reach extends much farther.* ## 4. Voyager: Humanity's Farthest Journey In 1977, NASA launched Voyager 1 and Voyager 2 to explore the outer planets. Their journeys transformed our understanding of Jupiter, Saturn, Uranus, Neptune, and the distant environment surrounding the Sun. Voyager 1 later became the most distant human-made object from Earth. In 2012, it crossed the heliopause and entered interstellar space. Voyager 2 followed in 2018. Both spacecraft have provided direct measurements from beyond the heliosphere, giving scientists a rare opportunity to study the region between the Sun's environment and the wider galaxy. Yet these spacecraft have not travelled to another star. They are moving incredibly fast by human engineering standards, but the distances between stars are so enormous that even a spacecraft travelling tens of thousands of kilometres per hour needs thousands of years to cover a few light-years. The Oort Cloud adds another perspective. NASA estimates that Voyager 2 could take roughly 300 years to reach the cloud's inner edge and perhaps 30,000 years to pass beyond its outer edge. These are estimates, not precise appointments, because the cloud's structure is uncertain and its boundary is not a solid shell. Voyager's achievement is therefore both extraordinary and humbling. We have sent machines beyond the Sun's magnetic bubble, but we have barely begun to cross the enormous distances separating one star system from another. > info: **Interstellar space is not the same as interstellar travel.** Voyager 1 and Voyager 2 entered interstellar space by crossing the heliopause. Neither has reached another star, and both remain gravitationally associated with the Sun in the broad sense that the Oort Cloud is part of our solar system. ## 5. Alpha Centauri: The Next Star Is Still Incredibly Far Away After leaving the Sun's neighbourhood, our next destination is the Alpha Centauri system, which includes the stars Alpha Centauri A and B and the red dwarf Proxima Centauri. Proxima Centauri is the nearest known star to the Sun, at about 4.24 light-years away. One light-year is the distance light travels in a year—about 9.46 trillion kilometres. It is a unit of distance, not a measure of how old something is or how long a journey must take. At the speed of light, a signal from Proxima Centauri takes a little over four years to reach Earth. But a spacecraft cannot simply travel at light speed under known physics. At speeds comparable to Voyager 1, the journey would take tens of thousands of years. Even our nearest stellar neighbour is separated from us by a vast ocean of space. The Milky Way contains hundreds of billions of stars, yet the space between them makes interstellar travel a much greater challenge than reaching any planet in our solar system. ### A Simple Way to Understand a Light-Year Imagine that a beam of light could circle Earth roughly seven and a half times in a single second. Now imagine that it continues travelling for an entire year without stopping. The distance it covers is one light-year. Because light is so fast, light-years are useful for describing distances that would be awkward to express in kilometres. They also reveal the delay built into astronomical observations: when we see a star 100 light-years away, we see light that began its journey about 100 years ago. ## 6. The Milky Way: Our Galactic Home The Sun is not at the centre of the universe, or even at the centre of our galaxy. It is one star in the Milky Way, a barred spiral galaxy roughly 100,000 light-years across, containing hundreds of billions of stars along with gas, dust, planets, and other objects. Our solar system lies about 26,000 light-years from the galactic centre, within one of the galaxy's spiral-arm regions. The Sun and its planets orbit that centre, taking roughly 225–250 million years to complete one galactic orbit. This means that dinosaurs lived on Earth during a very different part of the Sun's journey around the Milky Way. Since our solar system formed, the Sun has completed only a small number of galactic orbits. The Milky Way is so large that even light needs about 100,000 years to cross its disk from one side to the other. Human civilization, by comparison, has existed for only a tiny fraction of that time. And the Milky Way is not the universe. It is one galaxy among an enormous population of galaxies in the observable cosmos. Once we look beyond our galactic home, the scale of the universe grows beyond anything our everyday experience can easily represent. ![A luminous spiral galaxy resembling the Milky Way, filled with stars, dust lanes, and glowing nebulae](https://www.wonderunfold.com/images/blog/milky-way-galaxy.jpg) *Our galaxy is about 100,000 light-years across. Every star visible in a dark night sky belongs to the Milky Way, except a small number of nearby galaxies visible to the naked eye.* ## 7. How Far Have Humanity's Signals Travelled Into Space? Since the early twentieth century, humanity has transmitted radio and television signals, radar pulses, and other forms of electromagnetic radiation. Radio waves travel at the speed of light, so some of our oldest signals have had nearly a century to move outward from Earth. It is tempting to imagine a neat sphere around Earth marking the exact distance at which every alien civilization could detect us. In reality, there is no single, clearly defined human radio bubble. Signals differ enormously in power, direction, frequency, duration, and how easily they could be distinguished from natural cosmic noise. Some powerful radar transmissions can be detectable in principle at much greater distances than ordinary broadcast signals, while many everyday transmissions would become extremely faint and difficult to identify even relatively nearby. Detecting a signal is not simply a matter of being inside a sphere; the receiver needs suitable instruments, the right timing, and enough sensitivity. Still, the idea offers a striking perspective. Our technological presence has expanded outward for only a tiny period of cosmic history. A civilization thousands of light-years away would not have received our earliest radio transmissions yet, even if it possessed the technology to detect them. The universe is not only vast in space. It is vast in time. Two civilizations could exist in the same galaxy and never detect one another because their technological eras did not overlap or their signals never reached the other. ## 8. The Local Group: A Neighbourhood of Galaxies The Milky Way belongs to a collection of galaxies called the Local Group. It includes Andromeda, the Triangulum Galaxy, and many smaller dwarf galaxies bound together by gravity. The Local Group stretches across several million light-years. Andromeda, our largest nearby galactic neighbour, is roughly 2.5 million light-years away. Its light began travelling toward Earth long before humans appeared. The Local Group makes the Milky Way look less like a cosmic continent and more like a city within a much larger landscape. Our galaxy is enormous, but it is just one member of a gravitationally connected collection of galaxies. As we move outward, galaxy groups and clusters become part of larger patterns. Gravity gathers matter into structures, while vast regions between them contain far fewer galaxies. The universe is not distributed like a uniform sprinkling of lights; on the largest scales, it forms an intricate cosmic web. ## 9. Laniakea and the Cosmic Web: Galaxies on a Colossal Scale Galaxies are arranged in groups, clusters, filaments, and enormous regions separated by cosmic voids. Together, these patterns form what astronomers call the cosmic web. It developed over billions of years as gravity amplified small differences in the early universe's distribution of matter. Our Local Group is part of the larger Laniakea supercluster, a region identified by mapping galaxy motions and the large-scale flow of matter. Laniakea extends roughly 500 million light-years and contains many galaxy groups and clusters, including our own neighbourhood. These structures are not solid objects with sharply defined outer walls. Their boundaries depend on how astronomers define gravitational flows and large-scale organisation. On the largest scales, cosmic expansion also means that not every structure will remain gravitationally connected forever. The Great Attractor is a region associated with the gravitational flow of galaxies in our local cosmic environment. It is not a mysterious object pulling the entire universe toward a single point. Rather, it is part of a complex distribution of mass whose gravitational effects influence the motions of galaxies. At this scale, even the Milky Way becomes a small component of a much larger structure. The universe's architecture is built from galaxies, but the distances between those galaxies are so immense that the structure can only be understood through astronomical observation and large-scale modelling. ![Scientific visualization of the cosmic web showing glowing galaxy filaments and dark voids across a vast region of space](https://www.wonderunfold.com/images/blog/cosmic-web-galaxies.jpg) *On enormous scales, galaxies form a cosmic web of filaments and clusters separated by vast, relatively empty regions.* ## 10. The Observable Universe: A Sphere About 93 Billion Light-Years Across Now we reach a number that sounds almost impossible: the observable universe is roughly 92–93 billion light-years in diameter. That means the farthest regions we can observe today are about 46 billion light-years away in terms of their current distance from us. This does not mean the universe is only 92–93 billion light-years across. It means that this is the approximate diameter of the region from which light has had time to reach us since the universe began, accounting for the expansion of space. The observable universe is defined by our position and by the history of light reaching us. An observer in a distant galaxy would have a different observable region, because light from some places visible to us might not yet have reached them, and vice versa. The observable universe is therefore not a special wall at the edge of all existence. It is our cosmic horizon: the limit of what we can observe in principle from our location, given the universe's history and expansion. - **≈ 93 billion light-years** — Estimated diameter of the observable universe (NASA Science: How Big Is Space?) ### If the Universe Is 13.8 Billion Years Old, Why Is It So Much Wider? This is one of the most common questions in cosmology. If the universe is about 13.8 billion years old, one might expect the most distant observable matter to be no more than 13.8 billion light-years away. That would be true in a simple picture where space remained static while light travelled. But the universe has not been static. Space itself has expanded throughout cosmic history. While ancient light was travelling toward us, the space between us and its source continued to stretch. As a result, the galaxies that emitted that light are now much farther away than the distance the light travelled at the speed of light multiplied by its travel time. A useful analogy is to imagine an ant walking along a stretching elastic band. The ant moves forward, but the band itself is also stretching, so the distance between the ant and its starting point can grow faster than the ant could cover on a fixed band. The analogy is not a complete model of cosmology, but it helps illustrate why expansion changes the relationship between travel time and present-day distance. Cosmic expansion does not mean that a spacecraft locally flies through space faster than light. Rather, the metric describing distances between faraway regions changes over time. In general relativity, this is compatible with the speed-of-light limit applying to local motion and to the travel of light through nearby space. > info: **The crucial difference.** The age of the universe tells us how long cosmic history has unfolded. The diameter of the observable universe describes the present-day size of the region we can observe. Because space expanded while light travelled, these are not the same number. ## 11. What Lies Beyond the Observable Universe? Here the evidence reaches a boundary. We can estimate the size of the observable universe, but we do not know the full size of the entire universe. It may extend vastly beyond our horizon. It may be finite but much larger than the observable region. It may even be infinite. The problem is not simply that our telescopes are too small. Light from sufficiently distant regions has not had time to reach us, and cosmic expansion affects which regions can ever send us information. Some parts of the universe may remain permanently beyond our observational reach. This is different from saying that nothing exists beyond the observable universe. There is no scientific reason to assume that the visible horizon is a physical edge where space ends. It is a limit on what we can observe, not a confirmed boundary of all existence. If the universe is infinite, there may be no final edge to reach. If it is finite, its geometry could still be more complicated than an ordinary object with a surface and a boundary. Current observations do not establish a definitive answer to the universe's total size or global shape. The most honest answer is also the most fascinating: we know a great deal about the observable universe, but we do not yet know how large the whole universe is. ## 12. Could Humanity Ever Reach the Edge of the Universe? With current technology, reaching even the nearest star would be an extraordinary challenge. Reaching the edge of the observable universe is not simply a longer version of the same journey. It raises fundamental questions about cosmic expansion, the speed of light, and whether the destination is within our future reach at all. The observable universe is defined from our current cosmic location, and the distant matter we observe today may be receding from us because of expansion. Some very distant regions are beyond the range from which a signal sent now could ever reach us, depending on the universe's expansion history. That does not mean everything outside our immediate neighbourhood is forever inaccessible. Future propulsion systems might allow humanity to travel much faster than present spacecraft, and we may one day send robotic missions toward nearby stars. But no known technology can carry people across intergalactic distances on practical timescales, and the observable universe is vastly beyond any realistic travel plan. Our most powerful tool for exploring the farthest universe is not a spaceship but a telescope. By collecting ancient light, astronomers can investigate galaxies that formed billions of years ago and reconstruct the history of cosmic evolution. ## 13. How Telescopes Let Us Look Back in Time When the James Webb Space Telescope observes a distant galaxy, it is not seeing the galaxy as it exists at this exact moment. It is collecting light that began travelling toward us billions of years ago. The more distant the source, the earlier in cosmic history we see it, subject to the effects of cosmic expansion and the wavelength of the light. Webb observes infrared light, which is especially useful for studying very distant galaxies whose light has been stretched by expansion. Its observations help scientists investigate how early galaxies formed, how stars developed, and how cosmic structure evolved. There is a limit to how far back ordinary telescopes can see using light. The early universe was once hot and dense enough that light could not travel freely over long distances. The cosmic microwave background is radiation released when the universe cooled enough for light to move through space largely unhindered, about 380,000 years after the Big Bang. That background radiation is one of cosmology's most important sources of evidence. It allows scientists to study the early universe and measure properties that help determine its age, composition, and expansion history. ![Deep field view filled with distant galaxies observed across a small patch of sky](https://www.wonderunfold.com/images/blog/james-webb-deep-field.jpg) *Deep-field observations reveal galaxies from different stages of cosmic history, showing how much of the universe can be explored by collecting faint light.* ## 14. Why Does the Size of the Universe Matter? The scale of the universe is more than a collection of impressive numbers. It changes the way we think about our place in nature. Earth is not at the centre of the Milky Way, the Milky Way is not the only galaxy, and the observable universe may be only a fraction of everything that exists. The vast number of stars and planets also gives scientists a reason to investigate whether life exists elsewhere. Yet the sheer size of the universe does not prove that alien life is common. We know that life exists on Earth; we do not yet know how often life begins on other worlds. The distances also place limits on communication. Even a signal travelling at the speed of light takes years to reach nearby stars and millions of years to cross large parts of a galaxy. The universe may contain places and events that we can never observe directly, no matter how advanced our instruments become. In that sense, cosmology is a science of both discovery and limits. Every new observation expands our understanding, but it also reveals how much remains beyond our reach. ## The Universe May Be Bigger Than Anything We Can Ever See Our journey began on Earth, a planet that feels enormous when we stand on its surface. We travelled past the Moon and the Sun, across the solar system, beyond the heliopause, toward the nearest stars, through the Milky Way, and into the immense web of galaxies. We reached the observable universe, a region roughly 93 billion light-years across. Yet even that astonishing number does not describe the entire universe. It describes the portion of cosmic history and space from which information has been able to reach us. The universe is about 13.8 billion years old, but its expansion has stretched the distances between faraway regions while light travelled. That is why the observable universe can be far wider than 13.8 billion light-years. Beyond our cosmic horizon, the full extent of space remains unknown. Perhaps the universe is infinite. Perhaps it is finite but unimaginably larger than what we can observe. Science has not settled the question, and it would be misleading to pretend otherwise. What we do know is already remarkable: a species that evolved on a small planet has learned to measure the age of the universe, detect galaxies from the distant past, and send spacecraft beyond the Sun's magnetic boundary. The biggest discovery may not be that the universe has an enormous size. It may be that we have only just begun to understand what 'size' means on cosmic scales—and that the edge of what we can see is not necessarily the edge of what exists. So the next time you look at the night sky, remember this: every star is a distant sun, every galaxy contains its own cosmic history, and the universe beyond our vision may be far larger than the part we have learned to measure. How much more is out there? For now, that is one of the greatest questions we can ask. Continue with why humans believe in aliens, Voyager 2 at the edge of the solar system, and the deep sea. --- ## Frequently Asked Questions About the Size of the Universe ## Universe Size FAQ ### How big is the universe? The observable universe is estimated to be about 92–93 billion light-years in diameter. The size of the entire universe is unknown. It may extend far beyond the observable region, and scientists have not established whether the whole universe is finite or infinite. ### How old is the universe? The universe is approximately 13.8 billion years old, based on cosmological measurements including the expansion rate and the cosmic microwave background. ### Why is the observable universe 93 billion light-years wide if it is only 13.8 billion years old? Space expanded while light travelled toward us. As a result, distant matter is now much farther away than the distance its light travelled multiplied by the time since emission. The observable universe's current diameter is estimated at roughly 92–93 billion light-years. ### What is the difference between the universe and the observable universe? The observable universe is the region from which light or other information has had time to reach us. The entire universe includes any regions beyond that horizon, whose full extent is unknown. ### Is the universe infinite? Scientists do not know. Current observations are consistent with a universe that is very large and may be spatially infinite, but they do not establish the total size of the entire universe. ### How large is the Milky Way? The Milky Way's main stellar disk is approximately 100,000 light-years across and contains hundreds of billions of stars. Its wider halo and surrounding environment extend beyond the bright disk. ### How far away is the nearest star? Proxima Centauri, the nearest known star to the Sun, is approximately 4.24 light-years away. Light takes a little over four years to travel between the star and Earth. ### Have Voyager 1 and Voyager 2 left the solar system? Both spacecraft crossed the heliopause and entered interstellar space. However, the Sun's gravitational influence extends much farther, potentially to the distant Oort Cloud, so they have not left the solar system under every possible definition. ### What is beyond the observable universe? The full answer is unknown. Space may continue far beyond the observable horizon, but we cannot currently observe regions from which light has not reached us. The observable horizon is not known to be a physical edge of the universe. ### Can humans reach the edge of the universe? With known physics and current technology, travelling to the edge of the observable universe is not a realistic possibility. Some distant regions may also be permanently beyond the reach of signals or travel that begins today. Telescopes, rather than spacecraft, are our primary means of studying the most distant universe. ### What is a light-year? A light-year is a unit of distance: the distance light travels in one year in a vacuum, approximately 9.46 trillion kilometres. It is not a unit of time. **What this cosmic scale tour clarifies — and what remains unknown** **What this can establish** - Explains cosmic distances progressively, from Earth to the observable universe. - Clarifies the difference between the heliopause, Oort Cloud, observable universe, and the entire universe. - Uses current NASA research to explain the universe's age and observable diameter. - Combines accessible analogies with accurate explanations of cosmic expansion and light-travel time. **What this cannot establish** - The total size of the universe is unknown. - The Oort Cloud has not been directly imaged as a complete structure, so its extent is estimated. - Cosmic distances and the universe's observable diameter depend on cosmological measurements and models. - The observable horizon limits what we can see, and some regions may remain permanently inaccessible. ## FAQ ### How big is the universe? The observable universe is estimated to be about 92–93 billion light-years in diameter. The size of the entire universe is unknown. It may extend far beyond the observable region, and scientists have not established whether the whole universe is finite or infinite. ### How old is the universe? The universe is approximately 13.8 billion years old, based on cosmological measurements including the expansion rate and the cosmic microwave background. ### Why is the observable universe 93 billion light-years wide if it is only 13.8 billion years old? Space expanded while light travelled toward us. As a result, distant matter is now much farther away than the distance its light travelled multiplied by the time since emission. The observable universe's current diameter is estimated at roughly 92–93 billion light-years. ### What is the difference between the universe and the observable universe? The observable universe is the region from which light or other information has had time to reach us. The entire universe includes any regions beyond that horizon, whose full extent is unknown. ### Is the universe infinite? Scientists do not know. Current observations are consistent with a universe that is very large and may be spatially infinite, but they do not establish the total size of the entire universe. ### How large is the Milky Way? The Milky Way's main stellar disk is approximately 100,000 light-years across and contains hundreds of billions of stars. Its wider halo and surrounding environment extend beyond the bright disk. ### How far away is the nearest star? Proxima Centauri, the nearest known star to the Sun, is approximately 4.24 light-years away. Light takes a little over four years to travel between the star and Earth. ### Have Voyager 1 and Voyager 2 left the solar system? Both spacecraft crossed the heliopause and entered interstellar space. However, the Sun's gravitational influence extends much farther, potentially to the distant Oort Cloud, so they have not left the solar system under every possible definition. ### What is beyond the observable universe? The full answer is unknown. Space may continue far beyond the observable horizon, but we cannot currently observe regions from which light has not reached us. The observable horizon is not known to be a physical edge of the universe. ### Can humans reach the edge of the universe? With known physics and current technology, travelling to the edge of the observable universe is not a realistic possibility. Some distant regions may also be permanently beyond the reach of signals or travel that begins today. Telescopes, rather than spacecraft, are our primary means of studying the most distant universe. ### What is a light-year? A light-year is a unit of distance: the distance light travels in one year in a vacuum, approximately 9.46 trillion kilometres. It is not a unit of time. ## Sources 1. [How Big Is Space? We Asked a NASA Expert](https://www.nasa.gov/science-research/astrophysics/how-big-is-space-we-asked-a-nasa-expert-episode-61/) — NASA 2. [Our Milky Way Galaxy: How Big Is Space?](https://science.nasa.gov/universe/exoplanets/our-milky-way-galaxy-how-big-is-space/) — NASA Science 3. [Where Are Voyager 1 and Voyager 2 Now?](https://science.nasa.gov/mission/voyager/where-are-voyager-1-and-voyager-2-now/) — NASA Science 4. [NASA's Voyager 2 Probe Enters Interstellar Space](https://www.nasa.gov/news-release/nasas-voyager-2-probe-enters-interstellar-space/) — NASA 5. [Oort Cloud: Facts](https://science.nasa.gov/solar-system/oort-cloud/facts/) — NASA Science 6. [Where Is the Edge of the Solar System?](https://science.nasa.gov/resource/where-is-the-edge-of-the-solar-system/) — NASA Goddard Space Flight Center 7. [What Is the Universe?](https://science.nasa.gov/exoplanets/what-is-the-universe/) — NASA Science 8. [NASA's Universe Overview](https://science.nasa.gov/universe/overview/) — NASA Science 9. [The Milky Way Galaxy](https://imagine.gsfc.nasa.gov/science/objects/milkyway1.html) — NASA Goddard Space Flight Center --- Source: [How Big Is the Universe? From Earth to the Edge of Everything](https://www.wonderunfold.com/blog/how-big-is-the-universe-from-earth-to-the-edge-of-everything). Written and edited by humans for WonderUnfold.