How Big Is the Universe? A Ladder From You to the Edge of Everything

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Tall ladder (Moon → Sun → Nearest star → Milky Way → Everything) with chibi Pawfessor Hu on a football-sized Earth at the base, looking up.

TL;DR

Your brain can’t picture it. Nobody’s can. The trick is to climb one rung at a time and only compare neighbours.
Light is the ruler. The Moon is 1.3 light-seconds away, the Sun 8 minutes, the nearest star 4 years, the far edge 46 billion years.
Ten rungs take you from your own height to the observable universe, and each is roughly a thousand to a million times bigger than the last.
The edge is further than the age. The universe is 13.8 billion years old but 93 billion light-years across. That’s not a typo; it’s expansion.

Rung	Size or distance	Light takes
You	1.7 m	6 billionths of a second
Earth (diameter)	12,742 km	0.04 seconds
Moon	384,400 km	1.3 seconds
Sun	150 million km (1 AU)	8 min 20 s
Voyager 1	~170 AU	~1 day
Nearest star	4.24 light-years	4.2 years
Milky Way (diameter)	~100,000 light-years	100,000 years
Andromeda	2.5 million light-years	2.5 million years
Laniakea (diameter)	~520 million light-years	520 million years
Observable universe (diameter)	~93 billion light-years	13.8 billion years¹

¹ The oldest light we can see left 13.8 billion years ago. Where it came from is now 46 billion light-years away. More on that at the end.

The ladder

Scroll through it first. Every frame is to scale: the thing you just left shrinks to a ring, the numbers keep counting, and the dark stretches in between are real.

**You** About 1.7 metres. Every other frame is measured against this one. Height: 1.7 m Image: NASA

**Earth** 7.5 million of you, head to toe. Light circles it in 0.13 seconds. Diameter: 12,700 km Image: NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

**The Moon** Every other planet, side by side, fits in the gap. Light takes 1.3 seconds. Distance from Earth: 384,000 km Image: NASA/Goddard/University of Arizona (OSIRIS-REx)

**The Sun** At this scale the Sun is a dot and Earth is invisible. Light takes 8 minutes 20 seconds. Earth–Sun distance (1 AU): 1 AU Image: NASA/SDO/AIA

The heliosphere Launched 1977, still going at 17 km/s: almost one light-day out. The most distant thing we have built. Voyager 1 from the Sun: 172 AU

The nearest star At Voyager speed, 75,000 years. Everything ever called space travel happened in the last frame. Distance to Proxima Centauri: 4.25 ly

**The Milky Way** A few hundred billion stars. Every star you can see with your eyes is in a small patch of one arm. Diameter: 100,000 ly Image: NASA/JPL-Caltech/R. Hurt (SSC/Caltech), artist's concept

**Andromeda** That small smudge is another galaxy of a trillion stars. Its light left before humans existed. Distance from the Milky Way: 2.5 Mly Image: NASA/JPL-Caltech (GALEX)

**Laniakea** Every dot is a real galaxy from the 2MASS Redshift Survey. We are the dot in the middle. Diameter: 520 Mly Image: 2MASS Redshift Survey (Huchra et al. 2012), NASA/IPAC/Caltech/UMass

The observable universe The sphere is the oldest light there is, seen from outside. Beyond it, the universe keeps going; we just cannot see it. Diameter: 93 Gly Image: NASA/WMAP Science Team

The same ten rungs on one axis:

each tick is ×1,000 — a straight line on this axis is an explosion on a normal one

Notice the gaps. From you to Earth is 7 zeros. From Earth to the Sun, 4 more. From the Sun to the nearest star, 5 more. Then the galaxy adds 4, and the rest of the universe adds 6. Every rung is big; the jump to the nearest star is the one that breaks people.

Rung 1–2: You, then Earth

You are 1.7 metres tall. Earth is 12,742 km across: about 7.5 million of you lying head to toe.

Fly around the equator at airliner speed and it takes two days. Light does it in 0.13 seconds. Earth already feels large, and it’s the smallest thing on this list that isn’t you.

Rung 3: The Moon

384,400 km away, on average. Every other planet in the Solar System, lined up side by side, just fits in the gap between Earth and the Moon.

Apollo took three days. Light takes 1.3 seconds: when you look at the Moon, you see it as it was a heartbeat ago.

Rung 4: The Sun

150 million km, a distance astronomers call one astronomical unit (AU) because writing the zeros gets old. Light takes 8 minutes 20 seconds. If the Sun switched off, you’d keep tanning for eight more minutes.

The Sun itself is 1.39 million km wide, 109 Earths across and a million Earths by volume. It is 99.86% of all the mass in the Solar System. Everything else, all eight planets included, is rounding error.

Rung 5: The edge of the Solar System

Neptune orbits at 30 AU (4 light-hours). Voyager 1, launched in 1977 and still moving at 17 km/s, is now about 170 AU out: almost one light-day. It’s the most distant thing humans have ever built, and light from it takes a day to reach us.

Voyager took nearly fifty years to get there. Hold that number for the next rung.

Rung 6: The nearest star

Proxima Centauri is 4.24 light-years away, or 40 trillion km. At Voyager’s speed, the trip takes about 75,000 years. Fifty years to leave the Solar System; seventy-five thousand to reach the next one.

This is the rung that matters. Everything you have ever heard called “space travel” happens inside the first five rungs. The stars are a different sport.

Rung 7: The Milky Way

Our galaxy is a disc roughly 100,000 light-years across holding somewhere between 100 and 400 billion stars. The Sun sits about 26,000 light-years from the centre and takes 230 million years to orbit it once. The last time we were on this side of the galaxy, dinosaurs were just getting started.

Every star you can see with your naked eye is inside the Milky Way, and almost all of them are within a few thousand light-years, a small patch of one arm.

Rung 8: Andromeda and the Local Group

The next big galaxy over, Andromeda, is 2.5 million light-years away and heading toward us at 110 km/s. The two will merge in about 4.5 billion years. It’s the most distant thing you can see without a telescope: a faint smudge, and the light in that smudge left before humans existed.

Andromeda, the Milky Way and about eighty smaller galaxies form the Local Group, roughly 10 million light-years across.

Rung 9: Laniakea

Zoom out and galaxies clump into filaments and walls around vast empty voids, like soap foam. Our Local Group is a speck in the Laniakea Supercluster: about 520 million light-years across, holding around 100,000 galaxies, all drifting toward a gravitational centre we can’t see.

Rung 10: The observable universe

The furthest we can see in any direction is about 46.5 billion light-years, so the observable universe is a sphere 93 billion light-years across. Estimates put the number of galaxies inside it somewhere between a couple of hundred billion and two trillion. Each one is a Milky Way.

“Observable” is doing real work in that sentence. It’s not the edge of the universe. It’s the edge of what light has had time to reach us from. Beyond it, the universe almost certainly continues; we simply can’t see it, and may never.

Shrink it: the Sun as a marble

Numbers with twelve zeros don’t land. So shrink everything until the Sun is a 1 cm marble.

Thing	On this scale
Sun	1 cm marble
Earth	A speck 0.1 mm wide, 1 m from the marble
Neptune	30 m away
Voyager 1	About 180 m away, after 49 years of flying
Nearest star	Another marble, 290 km away
Milky Way	7 million km across — 18 times the real Earth–Moon distance

A marble on a table, a dust speck a metre away, and the next marble in a city three hundred kilometres down the road. That’s a star system and its neighbour. Space is mostly named after its main ingredient.

The twist: older than 13.8 billion years? No. Bigger? Yes.

The universe is 13.8 billion years old. So how can we see 46 billion light-years in every direction?

Because space itself has been stretching the whole time. The oldest light we detect, the cosmic microwave background, left its source 13.8 billion years ago when that source was about 42 million light-years from here. While the light was in transit, the space between us and the source kept expanding. Today, that source is 46 billion light-years away.

Nothing travelled faster than light. The road got longer while the light was on it.

What to keep

Compare neighbours only. You → Earth → Moon → Sun makes sense. You → galaxy doesn’t.
Use light-time. Seconds to the Moon, minutes to the Sun, years to stars, millennia across the galaxy, aeons across everything.
The nearest star is the wall. Fifty years to leave home; seventy-five thousand to arrive anywhere.
Observable ≠ all. We see a 93-billion-light-year sphere. The rest is out there, unseen.

Image and data credits

You — Bruce McCandless II on the first untethered spacewalk, STS-41B, 7 February 1984. NASA (1984-02-11).
Earth — Blue Marble 2012 (Suomi NPP / VIIRS composite). NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring (2012-01-30).
The Moon — Earth and the Moon from OSIRIS-REx MapCam, 2 October 2017, from about 5 million km. NASA/Goddard/University of Arizona (2017-10-02).
The Sun — The Sun in extreme ultraviolet (AIA 171 Å), latest SDO image at harvest time. NASA/SDO/AIA (2026-09-21).
The Milky Way — The Milky Way, artist's concept (top-down). NASA/JPL-Caltech/R. Hurt (SSC/Caltech) (2008-06-03).
Andromeda — Andromeda (M31) in ultraviolet, GALEX. NASA/JPL-Caltech (2012-05-16).
Laniakea — 2MASS Redshift Survey, supergalactic plane, 600 Mly frame, ±60 Mly slab. 2MASS Redshift Survey, Huchra et al. 2012 (ApJS 199, 26); 2MASS is a joint project of UMass and IPAC/Caltech, funded by NASA and the NSF (2012).
The observable universe — WMAP 9-year Internal Linear Combination map, Mollweide projection, Galactic coordinates. NASA/WMAP Science Team (2012-12-20).
Distances and sizes: NASA NSSDC planetary fact sheets; Voyager 1 range from JPL Horizons on the date shown; Proxima Centauri from the NASA Exoplanet Archive; nearest-star positions from RECONS; Laniakea from Tully et al. 2014; observable-universe radius from the WMAP science team. Every number is listed with its source in the component manifest.