How Big Is Space? Planets, Stars and Galaxies Compared

The Size Of Space As Depicted Here Is Truly Mind-Blowing

How big is space? Bigger than our brains are built to picture. We can understand a mountain or an ocean, but the jump from Earth to the Sun, from the Sun to a supergiant star, and from one galaxy to thousands of them is so large that numbers alone stop meaning much. That is why size-comparison images became so popular online: they let your eyes do the work.

The series below starts with Earth and its nearest neighbours, scales up through the giant planets and the Sun, then moves to some of the best-known stars in the night sky. It finishes with one of the most important photographs in astronomy, the Hubble Ultra Deep Field, which revealed thousands of galaxies in a patch of sky that looks empty to the naked eye.

Each image comes with a short explanation and real figures. Where the original slides made claims that are out of date or could not be confirmed, the captions say so. Distances are given in light-years, the distance light travels in a year, about 9.46 trillion kilometres.

Earth and its rocky neighbours

The earth is bigger than the Moon, Mercury and Mars.

Earth, at about 12,742 km across, is the largest of the rocky worlds in this picture. Mars is roughly half Earth's width, Mercury a little over a third, and our Moon, at about 3,475 km, just over a quarter. Mercury is barely larger than the Moon, even though one is a planet and the other a satellite.

Earth is just about the same size as Venus.

Venus is Earth's near twin in size, about 12,104 km across, which is why it is often called our sister planet. The resemblance ends there: its thick carbon dioxide atmosphere traps so much heat that its surface is hot enough to melt lead.

The giant planets

Neptune and Uranus are much bigger (insert “your anus” jokes here).

Uranus and Neptune, the ice giants, are each about four times wider than Earth. Uranus measures roughly 50,700 km and Neptune about 49,200 km. Both are made largely of water, methane and ammonia ices around a rocky core, and methane in their atmospheres gives them their blue-green colour.

Jupiter, about 139,800 km across, could line up 11 Earths along its equator, and Saturn is not far behind at about 116,500 km. In this frame all the rocky planets shrink to specks along the bottom. Saturn's rings, though spectacular, are mostly made of ice and are only tens of metres thick in many places.

The Sun and nearby stars

No wonder this keeps us warm. The Sun is giant. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields.

The Sun is about 1.4 million km wide, and NASA estimates that around 1.3 million Earths could fit inside it. It holds 99.8% of all the mass in the solar system. Rather than a solid surface, it is a ball of hydrogen and helium in the form of plasma, an electrically charged gas, threaded by powerful magnetic fields.

Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star.

Sirius is the brightest star in our night sky, with an apparent magnitude of −1.46, almost twice as bright as Canopus in second place. Its brilliance is partly about distance: at about 8.6 light-years it is one of our closest stellar neighbours. Sirius A is only about 1.7 times wider than the Sun and has a tiny white dwarf companion, Sirius B.

Pollux is a star in the northern constellation of Gemini, the Twins. Pollux is the brightest star in the constellation. The distance away from Earth is measured at a distance of about 33.78 light-year

Pollux, the brightest star in Gemini, is an orange giant about nine times wider than the Sun, roughly 34 light-years away. At this scale the Earth is reduced to about a single pixel. Astronomers have proposed a giant planet orbiting Pollux, although some think the signal may come from the star's own magnetic activity.

Arcturus of the constellation Boötes is the brightest star in the northern celestial hemisphere. It is the fourth brightest star in the night sky

Arcturus, in the constellation Boötes, is the brightest star in the northern half of the sky and the fourth brightest overall. It is a red giant roughly 25 times the Sun's width, about 37 light-years away. Next to it the Sun becomes a small dot, and Jupiter would be barely visible.

Giants and supergiants

Rigel is the brightest star in the constellation Orion and the seventh brightest star in the night sky. Aldebaran is an orange giant star located about 65 light years away in the zodiac constellation

Rigel, the bright blue-white star in Orion's foot, is a supergiant around 74 times wider than the Sun and roughly 850 light-years away; it is usually the seventh brightest star in the sky. Aldebaran, the orange eye of Taurus, is a red giant about 45 times wider than the Sun and roughly 65 to 67 light-years away. Next to them the Sun shrinks to a tiny dot.

This frame adds Betelgeuse, Orion's red shoulder star, estimated at roughly 640 to 760 times the Sun's radius. Placed in the Sun's position, its surface would swallow the orbits of Mercury, Venus, Earth and Mars. Its sudden "Great Dimming" in 2019–2020 turned out to be caused mainly by a cloud of dust, not an approaching supernova. The glowing cloud at upper right is Eta Carinae, a massive double-star system about 7,500 light-years away surrounded by the Homunculus Nebula, material blasted out during an eruption in the 1840s.

The curving red wall is VY Canis Majoris, a red hypergiant in the constellation Canis Major, roughly 3,900 light-years away. The Sun is the speck labelled on the left. Older estimates put VY Canis Majoris at over 3,000 times the Sun's radius; more recent measurements suggest about 1,420 times, still enormous but no longer a clear record holder.

Beyond our galaxy: the Hubble Ultra Deep Field

Every star shown so far, and every star you can see with your own eyes, lies inside our own galaxy, the Milky Way. The next slides step outside it entirely, using one of the deepest images of the universe ever taken by the Hubble Space Telescope.

The slide gives the start date as 3 September 2003. According to the official records summarised on Wikipedia, the main observations actually ran from 23 September 2003 to 15 January 2004, in two blocks. The date is a small detail, but it shows why viral slideshows are worth checking.

Hubble was launched in 1990 and orbits about 540 km above Earth, above the blurring effect of the atmosphere. For the Ultra Deep Field, astronomers aimed it at a tiny region in the southern constellation Fornax, chosen because it contained very few nearby stars that would get in the way.

The target patch is 2.4 arcminutes across, about one tenth of the width of the full Moon as seen from Earth. To the naked eye and to ordinary telescopes, it looks like empty black sky. That emptiness is exactly why it was chosen.

The observations were spread over about four months, but the total exposure time added up to just under a million seconds, roughly 11 days, gathered over 400 orbits. Long exposures let the camera collect faint light from objects far too dim to see in a snapshot.

This is the result: a field crowded with galaxies of every shape and colour. Spirals, ellipticals and small irregular smudges sit side by side, many of them seen as they were billions of years ago, when the universe was much younger.

Almost every point of light here is a whole galaxy, not a star. Only a handful of objects, usually those with sharp spikes of light, are stars in our own Milky Way sitting in the foreground.

Galaxies vary enormously in size. Small dwarf galaxies may hold only millions of stars, while the largest contain hundreds of billions to around a trillion. The Milky Way is thought to contain somewhere in the range of 100 to 400 billion.

Since the 1990s, astronomers have confirmed thousands of planets around other stars, and current evidence suggests that most stars host at least one. Multiply that by the number of stars in each galaxy and the number of possible worlds becomes almost impossible to imagine.

The original Ultra Deep Field contains an estimated 10,000 galaxies. A later, more refined version called the eXtreme Deep Field, combining ten years of Hubble images of the central area, counted about 5,500 in its smaller region.

The faintest galaxies in the image are seen as they were roughly 13 billion years ago, only a few hundred million years after the Big Bang. When the slideshow was made they were among the most distant objects ever photographed. The James Webb Space Telescope has since pushed further: in 2024 it confirmed a galaxy seen just 300 million years after the Big Bang, and in 2025 it found another even more distant one.

The slide claims this large spiral holds eight times as many stars as the Milky Way and should not exist under current physics. We could not find a reliable source for that statement, so treat it as unconfirmed. Large spiral galaxies are common in deep fields, and their existence is well explained by standard models of galaxy formation.

The final slide sums up the point of the whole exercise: a speck of sky smaller than a grain of sand held at arm's length, apparently empty, turns out to contain thousands of galaxies. Astronomers estimate the observable universe holds hundreds of billions of galaxies or more.

Common myths about the size of space

"Stars are all roughly the size of the Sun." The Sun is an average star. Many are smaller and dimmer, while giants like Rigel and Betelgeuse dwarf it.

"The brightest stars are the biggest." Brightness in our sky depends heavily on distance. Sirius is the brightest because it is close, not because it is huge.

"Deep space images are just empty black backgrounds." Hubble and Webb have shown that even the darkest patches are full of distant galaxies once you collect enough light.

Why this sense of scale matters

Looking at these comparisons can be oddly calming. Everyday frustrations, a bad meeting, a traffic jam, a pile of chores, feel enormous in the moment. Seeing Earth shrink to a pixel and then disappear among thousands of galaxies is a reminder that there is far more to explore and wonder about than the routine of one day.

It is also a good argument for curiosity. Every number in these slides was earned by people building better instruments and checking their work, and the estimates keep improving. The next time the sky is clear, find Orion, Sirius or Arcturus and remember what you are actually looking at.

Sources: Original slideshow shared by Jesse Herman of PowerfulPrimates via Spirit Science and Metaphysics; NASA: Sun facts; Wikipedia: Hubble Ultra-Deep Field, JADES-GS-z14-0, Sirius, Pollux, Arcturus, Rigel, Aldebaran, Betelgeuse, Eta Carinae, VY Canis Majoris.