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SCALE · Learning guide · 2026-09-22

From the universe to the atom,
a world connected by size

We keep zooming into the same space and compare how the cosmos, Earth, the human body, cells and atoms relate. The explanations below use the same material as the explorer’s learning panel.

Three things to know before you start

1. Same input, same zoom. If W is the screen width in meters, the internal scale is s = log₁₀(W). When s drops by 1, the width shrinks to a tenth and objects on the focal plane look 10 times larger. 1,000 km → 100 km and 100 km → 10 km are the same logarithmic step.

2. Object size and screen width are different. The number next to the description is the object’s representative size; the number at the bottom is the screen width. The diameter of markers and the glow of starlight is not the real size of the object. Objects at different depths are subject to perspective.

3. Tell zooming apart from cutaways. Inside the skin and inside cells, the front part is cut away or made transparent. Colors and layout are models to aid understanding, not footage. Below the quark scale, we compare exploration scales rather than zooming into confirmed objects.

10³ m

Class activities

ActivityWhat to record
Cosmic web → Milky WayHow filaments, voids and the galactic disk differ
Earth → Seoul → GwanghwamunThe screen width at each step and the new structures that appear
Human → hand → cellWhere zooming switches to cutaway views
Cell → DNA → atomRatios of representative sizes and the limits of the models

Try the math

① If the screen width goes from 100 km to 1 km, how many times have you zoomed in?
② How many times larger is a height of 1.7 m than a diameter of 20 μm?
③ How many times smaller is DNA, 2 nm wide, than a 20 μm cell?

Answers for teachers

① 100 times, a log step of 2. ② About 85,000 times, about 4.93 orders of magnitude. ③ 10,000 times. These compare lengths only, not area, volume or mass.

Jump to

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Observable universe

The observable universe is the region from which light and signals can reach us. It does not mean the size of the whole universe is known. Galaxies are not scattered evenly; they form a web-like pattern.

Comparing sizes
Representative size: 91,960,000,000 light-years. The screen width and the size of the object itself are different values.
Link to the next world
Don’t mistake a bright dot at this scale for a single star. At this size, the dots help you find where galaxies and groups of galaxies are.
Observation vs. model
Observed scale · galaxy layout is a statistical model · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · Why isn’t the radius of the observable universe simply the age of the universe multiplied by the speed of light?

NASA · The cosmic web

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Cosmic web

Between the filaments where galaxies gather lie voids, where matter is thin. A void is not a hole with no matter at all. The large-scale structure is a pattern formed as gravity pulled matter together.

Comparing sizes
Representative size: 1,057,000,000 light-years. One level up, “Observable universe” is about 87× as large. The screen width and the size of the object itself are different values.
Link to the next world
The glowing lines are not photographs of dark matter. Within this big pattern, we move into a smaller region around our galaxy.
Observation vs. model
Observed scale · galaxy layout is a statistical model · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · How do filaments and voids differ in the density of matter?

NASA · The cosmic web

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Laniakea region

Laniakea is a region of large-scale flow, defined using the motions of galaxies. It does not mean the whole thing is bound by gravity like a single stable object.

Comparing sizes
Representative size: 517,900,000 light-years. One level up, “Cosmic web” is about 2.04× as large. The screen width and the size of the object itself are different values.
Link to the next world
It has no hard edge like the surface of an object. This scene is a representative picture of the surrounding galaxies, not a reconstruction of measured flows.
Observation vs. model
Observed scale · galaxy layout is a statistical model · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · Why do we need to know how galaxies move, not just where they are?

Tully et al. · original Laniakea paper

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Local Sheet

The Local Sheet is the region where galaxies around the Milky Way are spread out in a fairly flat layer. Rotate the view to compare its thickness and width.

Comparing sizes
Representative size: 52,850,000 light-years. One level up, “Laniakea region” is about 9.8× as large. The screen width and the size of the object itself are different values.
Link to the next world
It is not a continuous surface like a sheet of paper. We narrow down from the wider surroundings to our nearest neighbor galaxies.
Observation vs. model
Observed scale · galaxy layout is a statistical model · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · How does the same distribution look different from the front and from the side?

NASA · The cosmic web

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Local Group

The Local Group includes the Milky Way, Andromeda and many small galaxies. The distances between galaxies are much larger than the diameters of their disks.

Comparing sizes
Representative size: 10,040,000 light-years. One level up, “Local Sheet” is about 5.26× as large. The screen width and the size of the object itself are different values.
Link to the next world
The Milky Way and Andromeda are separate galaxies. Select the Andromeda marker to take a side trip and compare their real sizes.
Observation vs. model
Representative range · Andromeda is about 2.5 million light-years away · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · Which is larger: the diameter of the Milky Way, or the distance to Andromeda?

NASA · The cosmic web

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Milky Way halo

Sparse stars and star clusters also lie outside the bright disk of the galaxy. Where the halo ends can be defined differently depending on what you measure.

Comparing sizes
Representative size: 211,400 light-years. One level up, “Local Group” is about 47.5× as large. The screen width and the size of the object itself are different values.
Link to the next world
Tell the stellar halo apart from the dark matter halo. Dark matter does not glow like the dots on the screen.
Observation vs. model
Estimated range · the boundary depends on the definition · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · Is the visible edge of the disk where all of the galaxy’s matter ends?

NASA · The solar system and the galaxy

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Milky Way

The Milky Way is a galaxy with a central bar and spiral arms. The Sun sits near the Orion Arm, about 26,000 light-years from the center.

Comparing sizes
Representative size: 100,000 light-years. One level up, “Milky Way halo” is about 2.11× as large. The screen width and the size of the object itself are different values.
Link to the next world
Try to tell apart the core, the spiral arms and the dark dust lanes. As you approach the Sun’s position, the view shifts from the whole galaxy to interstellar space.
Observation vs. model
Disk about 100,000 light-years · Sun about 26,000 light-years from the center · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · How is the Milky Way you see in the night sky different, in viewpoint, from the whole galaxy on screen?

NASA · The solar system and the galaxy

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Around the Orion Arm

The bright pattern of a spiral arm is a distribution of stars and gas. It is not a solid, connected object like an arm. The neighborhood of the Sun is a tiny part of the galaxy.

Comparing sizes
Representative size: 10,570 light-years. One level up, “Milky Way” is about 9.46× as large. The screen width and the size of the object itself are different values.
Link to the next world
We approach the same position inside the galactic disk. The galactic center has gone off screen, but it has not physically disappeared.
Observation vs. model
Sun’s distance from the galactic center: approximate · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · Why does the empty space between stars look larger the more you zoom in?

NASA · The solar system and the galaxy

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Local Bubble

A scale for comparing the interstellar environment around the Sun. The Local Bubble is a region where the density and state of interstellar matter differ. It is not a solid spherical shell.

Comparing sizes
Representative size: 1,057 light-years. One level up, “Around the Orion Arm” is about 10× as large. The screen width and the size of the object itself are different values.
Link to the next world
How big starlight looks on screen is different from a star’s real diameter. The star layout is illustrative and does not reproduce a measured catalog.
Observation vs. model
Representative range · nearby star layout is illustrative · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · What kind of matter might be in space that looks like it has no stars?

NASA · The solar system and the galaxy

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Stars near the Sun

The real distances between stars are vastly larger than the stars’ diameters.

Comparing sizes
Representative size: 42.28 light-years. One level up, “Local Bubble” is about 25× as large. The screen width and the size of the object itself are different values.
Link to the next world
A light-year is a unit of distance, not time. How big starlight and markers look on screen is different from the real diameter of an object.
Observation vs. model
Exploration range · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · Roughly how many times bigger is the current object than the next one? Check it with the scale.

NASA · The solar system and the galaxy

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Between nearby stars

We cross empty space that light takes years to travel and approach the solar system.

Comparing sizes
Representative size: 4.228 light-years. One level up, “Stars near the Sun” is about 10× as large. The screen width and the size of the object itself are different values.
Link to the next world
A light-year is a unit of distance, not time. How big starlight and markers look on screen is different from the real diameter of an object.
Observation vs. model
Exploration range · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · Roughly how many times bigger is the current object than the next one? Check it with the scale.

NASA · The solar system and the galaxy

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Oort Cloud

The Oort Cloud is a region thought to be a reservoir of distant comets. It is studied through indirect evidence such as comet orbits; no one has photographed the whole cloud.

Comparing sizes
Representative size: 3.171 light-years. One level up, “Between nearby stars” is about 1.33× as large. The screen width and the size of the object itself are different values.
Link to the next world
Even if icy bodies are there, they are extremely far apart. The shell of dots is there to show the range.
Observation vs. model
Estimated range · distribution is illustrative · Layout and brightness are illustrative, not a reconstruction of an observed catalog.

Think about it · How can comet orbits help us infer a reservoir we cannot see?

NASA · The solar system and the galaxy

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Heliosphere

The region where the solar wind interacts with the surrounding interstellar matter. Its boundary changes with direction and with solar activity.

Comparing sizes
Representative size: 240.6 AU. One level up, “Oort Cloud” is about 833× as large. The screen width and the size of the object itself are different values.
Link to the next world
The reach of gravity, the range of planetary orbits and the reach of the solar wind are three different measures.
Observation vs. model
Representative range, varies with direction · Colors, shapes and internal layout are a teaching model.

Think about it · Why is it hard to give the edge of the solar system as a single number?

NASA · The solar system and the galaxy

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Kuiper Belt region

The region of small bodies beyond Neptune.

Comparing sizes
Representative size: 100.3 AU. One level up, “Heliosphere” is about 2.4× as large. The screen width and the size of the object itself are different values.
Link to the next world
This object is a sample of representative size. Colors and internal layout are for learning and should be told apart from real observed images.
Observation vs. model
Field of view · Sun-centered · Colors, shapes and internal layout are a teaching model.

Think about it · Roughly how many times bigger is the current object than the next one? Check it with the scale.

NASA · The solar system and the galaxy

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Solar system

The planets orbit the Sun, and the Sun holds most of the solar system’s mass. This scene fixes positions on a reference date to compare distances and diameters.

Comparing sizes
Representative size: 60.16 AU. One level up, “Kuiper Belt region” is about 1.67× as large. The screen width and the size of the object itself are different values.
Link to the next world
The orbit lines are ellipses calculated from JPL osculating orbital elements for the reference date. The Sun sits at one focus of each ellipse, and the real eccentricities and inclinations are included. Pluto’s pink orbit is tilted about 17.27° from the reference ecliptic. Each orbit is nearly flat, but the planes point in different directions. They do not show long-term perturbed paths or live positions.
Observation vs. model
JPL Horizons · 2026-09-21 00:00 TDB · Colors, shapes and internal layout are a teaching model.

Think about it · Why is Earth almost invisible on a screen that shows the whole solar system?

NASA · The solar system and the galaxy

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Giant planet orbits

We pass the scale of Jupiter’s and Saturn’s orbits and move inward.

Comparing sizes
Representative size: 20.05 AU. One level up, “Solar system” is about 3× as large. The screen width and the size of the object itself are different values.
Link to the next world
This object is a sample of representative size. Colors and internal layout are for learning and should be told apart from real observed images.
Observation vs. model
Sun-centered field of view · Colors, shapes and internal layout are a teaching model.

Think about it · Roughly how many times bigger is the current object than the next one? Check it with the scale.

NASA · The solar system and the galaxy

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Asteroid belt region

The asteroid belt lies between Mars and Jupiter. It is not a tunnel packed with rocks as in the movies; it is mostly empty space.

Comparing sizes
Representative size: 6.016 AU. One level up, “Giant planet orbits” is about 3.33× as large. The screen width and the size of the object itself are different values.
Link to the next world
This scene shows the distance scale and does not reproduce the position of every asteroid.
Observation vs. model
Sun-centered field of view · Colors, shapes and internal layout are a teaching model.

Think about it · Would a probe passing through the asteroid belt have to keep dodging rocks?

NASA · The solar system and the galaxy

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Inner solar system

The Sun, Mercury, Venus, Earth and Mars, at true size and in their real positions.

Comparing sizes
Representative size: 3.209 AU. One level up, “Asteroid belt region” is about 1.88× as large. The screen width and the size of the object itself are different values.
Link to the next world
This object is a sample of representative size. Colors and internal layout are for learning and should be told apart from real observed images.
Observation vs. model
JPL Horizons · fixed reference date · Colors, shapes and internal layout are a teaching model.

Think about it · Roughly how many times bigger is the current object than the next one? Check it with the scale.

NASA · The solar system and the galaxy

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Around Earth’s orbit

The view moves from the center of the Sun to Earth’s real position.

Comparing sizes
Representative size: 0.4011 AU. One level up, “Inner solar system” is about 8× as large. The screen width and the size of the object itself are different values.
Link to the next world
This object is a sample of representative size. Colors and internal layout are for learning and should be told apart from real observed images.
Observation vs. model
JPL · Earth–Sun distance 1.00414 AU · Colors, shapes and internal layout are a teaching model.

Think about it · Roughly how many times bigger is the current object than the next one? Check it with the scale.

NASA · The solar system and the galaxy

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Earth and Moon

The Moon is a separate body, on average about 380,000 km from Earth. Compared with their diameters, there is a lot of space between them.

Comparing sizes
Representative size: 770,000 km. One level up, “Around Earth’s orbit” is about 77.9× as large. The screen width and the size of the object itself are different values.
Link to the next world
You can select the Moon to take a side trip. Its position uses JPL data for a fixed reference date.
Observation vs. model
JPL Horizons · geocentric lunar orbit · real relative position · Colors, shapes and internal layout are a teaching model.

Think about it · How does the true scale differ from the Earth–Moon drawings in textbooks?

NASA · The solar system and the galaxy

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Earth

Earth is a planet with a mean diameter of about 12,742 km. Beneath the air and clouds are continents and oceans, and Seoul is on the Korean Peninsula in East Asia.

Comparing sizes
Representative size: 12,740 km. One level up, “Earth and Moon” is about 60.4× as large. The screen width and the size of the object itself are different values.
Link to the next world
As we descend toward Seoul, the same surface coordinates are kept. The brightness of the clouds and atmosphere is there to make the structure easier to see.
Observation vs. model
Mean diameter 12,742 km · spherical Earth approximation · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · How does the size of the whole Earth compare with the thickness of its atmosphere?

NASA · Blue Marble · OpenStreetMap · map data

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East Asia

In East Asia you can see how the Korean Peninsula, eastern China, Japan and the seas around them sit relative to one another. Map borders are not lines actually drawn on the ground.

Comparing sizes
Representative size: 5,000 km. One level up, “Earth” is about 2.55× as large. The screen width and the size of the object itself are different values.
Link to the next world
The curve of the surface seems to shrink, and the view turns into regional terrain.
Observation vs. model
Tangent plane at Gwanghwamun · north is up · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · Why can a small part of a spherical Earth be approximated by a flat map?

NASA · Blue Marble · OpenStreetMap · map data

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Korean Peninsula

Look at the coastline and mountains of the Korean Peninsula. Height is shown by combining NASA regional imagery with public elevation data.

Comparing sizes
Representative size: 1,000 km. One level up, “East Asia” is about 5× as large. The screen width and the size of the object itself are different values.
Link to the next world
The data sets differ in resolution and date, and they do not show current weather or the live surface.
Observation vs. model
NASA regional imagery · USGS elevation data · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · Apart from color, what clues help you tell mountains from plains?

NASA · Blue Marble · OpenStreetMap · map data

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South Korea

We narrow from the whole country to the Seoul Capital Area. A country and a city inside it are on different length scales.

Comparing sizes
Representative size: 500 km. One level up, “Korean Peninsula” is about 2× as large. The screen width and the size of the object itself are different values.
Link to the next world
Check whether the positions of the coast and the cities stay the same as you zoom in.
Observation vs. model
Earth surface field of view · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · If the screen width goes from 500 km to 50 km, how many times have you zoomed in?

NASA · Blue Marble · OpenStreetMap · map data

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Seoul Capital Area

The Seoul Capital Area is a continuous spread of cities, mountains and rivers. Seoul’s administrative boundary is not the same as its built-up area.

Comparing sizes
Representative size: 100 km. One level up, “South Korea” is about 5× as large. The screen width and the size of the object itself are different values.
Link to the next world
Seoul’s main roads and rivers come from map data. Buildings outside central Gwanghwamun are representative models placed along the roads.
Observation vs. model
Field of view based on geographic coordinates · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · What changes if you define a city by administrative boundaries rather than geography?

NASA · Blue Marble · OpenStreetMap · map data

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Seoul

In Seoul you can compare the Han River, roads, mountains and district boundaries. The shape of the city is shaped by terrain and transport networks.

Comparing sizes
Representative size: 40 km. One level up, “Seoul Capital Area” is about 2.5× as large. The screen width and the size of the object itself are different values.
Link to the next world
Gwanghwamun is in the city center, north of the Han River. Zoom in and you approach Jongno-gu and the area around Sejong-daero.
Observation vs. model
Administrative boundaries and real roads · surrounding buildings are representative models · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · How might the Han River and the mountains have influenced the direction of roads and the layout of the city?

NASA · Blue Marble · OpenStreetMap · map data

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Jongno-gu

The scale shifts from all of Seoul to one where you can pick out individual roads and buildings. Gwanghwamun is part of Jongno-gu.

Comparing sizes
Representative size: 7 km. One level up, “Seoul” is about 5.71× as large. The screen width and the size of the object itself are different values.
Link to the next world
The outlines of central buildings come from map data, but heights and facades are estimated for buildings without a height tag.
Observation vs. model
Gwanghwamun coordinates 37.57295°N, 126.97685°E · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · What can you only learn if you have building height data?

NASA · Blue Marble · OpenStreetMap · map data

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Sejong-daero

Look at where the roads and buildings around Sejong-daero sit relative to one another. The small building blocks of the city appear as separate objects.

Comparing sizes
Representative size: 1.1 km. One level up, “Jongno-gu” is about 6.36× as large. The screen width and the size of the object itself are different values.
Link to the next world
Fixtures and trees are representative models. This is not an exact reconstruction of the city at the time the imagery was taken.
Observation vs. model
© OpenStreetMap contributors · some building heights estimated · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · Compare the width of the roads and the height of the buildings using the meter scale.

NASA · Blue Marble · OpenStreetMap · map data

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Gwanghwamun Square

Gwanghwamun Square is a space hundreds of meters long. You can compare buildings, the square and people in the same real units of length.

Comparing sizes
Representative size: 550 m. One level up, “Sejong-daero” is about 2× as large. The screen width and the size of the object itself are different values.
Link to the next world
The next object is a 1.7 m human sample standing on the square. It does not represent any real citizen.
Observation vs. model
Representative square length · some fixtures modeled by hand · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · If you laid 1.7 m-tall people end to end along the square, roughly how many would it take?

NASA · Blue Marble · OpenStreetMap · map data

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Walking space

Compare the person and the square’s paving on the same scale.

Comparing sizes
Representative size: 30 m. One level up, “Gwanghwamun Square” is about 18.3× as large. The screen width and the size of the object itself are different values.
Link to the next world
As the screen width shrinks, roads and individual objects appear. The map, imagery and elevation data differ in date and resolution.
Observation vs. model
The human figure is an illustrative sample placed on the square · The data come from different dates, and some building heights, shapes and fixtures are estimated.

Think about it · Roughly how many times bigger is the current object than the next one? Check it with the scale.

NASA · Blue Marble · OpenStreetMap · map data

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Human

The human body is made of organs and tissues, and tissues are made of cells. Here we explore the hand of a representative 1.7 m person.

Comparing sizes
Representative size: 1.7 m. One level up, “Walking space” is about 17.6× as large. The screen width and the size of the object itself are different values.
Link to the next world
We move toward the wrist and hand of the same person. Body shape and skin color are one sample.
Observation vs. model
Representative human, 1.7 m tall · Colors, shapes and internal layout are a teaching model.

Think about it · Roughly how many orders of magnitude separate a person’s height from the size of one cell?

NCBI · Structure and renewal of the epidermis

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Hand

The hand is a structure in which bones, muscles, tendons, nerves, blood vessels and skin work together. On this journey we move into a small patch of skin on a finger.

Comparing sizes
Representative size: 18 cm. One level up, “Human” is about 9.44× as large. The screen width and the size of the object itself are different values.
Link to the next world
Going from centimeters to millimeters, the creases and ridges of the surface appear.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · How is zooming in on the hand different from seeing through the skin?

NCBI · Structure and renewal of the epidermis

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Finger

The skin of the finger has fine ridges. The fingernail is a structure that contains hard keratin.

Comparing sizes
Representative size: 1.8 cm. One level up, “Hand” is about 10× as large. The screen width and the size of the object itself are different values.
Link to the next world
The surface texture is a representative model, not a measurement or reconstruction of anyone’s fingerprint.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · Will zooming in with a camera alone let you see inside the skin?

NCBI · Structure and renewal of the epidermis

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Skin surface

Skin is the barrier between the body and the outside world. The outer horny layer contains cells that have lost their nuclei, and below it lies a layer of living cells.

Comparing sizes
Representative size: 2 mm. One level up, “Finger” is about 9× as large. The screen width and the size of the object itself are different values.
Link to the next world
We open a cross-section to see inside. Zooming and cutting are different operations; this scene links the two for teaching purposes.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · What is the difference between the horny layer and the living cell layer?

NCBI · Structure and renewal of the epidermis

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Epidermis cross-section

The epidermis is made of several layers of cells. Its thickness varies with the body part and its condition, so no single number describes all skin.

Comparing sizes
Representative size: 120 μm. One level up, “Skin surface” is about 16.7× as large. The screen width and the size of the object itself are different values.
Link to the next world
The cross-section emphasizes how the layers and cells sit relative to one another. Colors, shapes and thicknesses are representative.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · If skin keeps flaking off but still has to stay a barrier, where must the new cells come from?

NCBI · Structure and renewal of the epidermis

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Living cell layer

A region where epidermal cells with nuclei sit next to one another. A cell is not floating alone in the air; it is part of a tissue.

Comparing sizes
Representative size: 50 μm. One level up, “Epidermis cross-section” is about 2.4× as large. The screen width and the size of the object itself are different values.
Link to the next world
We leave the neighboring cells behind and enter the target cell. Cell size varies with type and condition.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · How are cells and tissues related?

NCBI · Structure and renewal of the epidermis

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Epidermal cell

The cell membrane separates inside from outside and controls what goes in and out. The nucleus and organelles inside each do different jobs.

Comparing sizes
Representative size: 20 μm. One level up, “Living cell layer” is about 2.5× as large. The screen width and the size of the object itself are different values.
Link to the next world
The membrane is drawn as translucent so you can see inside. Real cells don’t look these colors to the naked eye.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · If a cell were a factory, what roles would the nucleus and mitochondria play?

NCBI · Structure and renewal of the epidermis

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Cell nucleus

In the nucleus, DNA is organized together with proteins. The nucleus is not the whole cell; it is one structure inside it.

Comparing sizes
Representative size: 6 μm. One level up, “Epidermal cell” is about 3.33× as large. The screen width and the size of the object itself are different values.
Link to the next world
We follow a section of folded chromatin into the way DNA is packaged.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · How do a cell nucleus and an atomic nucleus differ in size and makeup?

NCBI · Structure and renewal of the epidermis

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Chromatin

Chromatin is a structure formed by DNA together with proteins and other molecules. Long DNA is folded and organized at several levels inside the nucleus.

Comparing sizes
Representative size: 200 nm. One level up, “Cell nucleus” is about 30× as large. The screen width and the size of the object itself are different values.
Link to the next world
This shows the idea of packaging; it is not a measured layout of chromatin in a particular cell.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · How is packing DNA like fitting a long thread into a small box?

RCSB PDB · DNA and the nucleosome

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Nucleosome

The nucleosome is the basic packaging unit, in which DNA wraps around histone proteins. DNA is not always stretched out straight.

Comparing sizes
Representative size: 11 nm. One level up, “Chromatin” is about 18.2× as large. The screen width and the size of the object itself are different values.
Link to the next world
We follow the DNA wrapped around the protein core toward the double helix.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · What are the benefits of having proteins that organize DNA?

RCSB PDB · DNA and the nucleosome

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DNA

DNA is a molecule in which two strands form a double helix. The roughly 2 nm is the width of the double helix, not its total length.

Comparing sizes
Representative size: 2 nm. One level up, “Nucleosome” is about 5.5× as large. The screen width and the size of the object itself are different values.
Link to the next world
Following the base pairs between the strands, we move down to the scale of the atoms that make up the molecule. The colors are there to tell the parts apart.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · What misunderstandings could arise if you don’t separate the width of DNA from its length?

RCSB PDB · DNA and the nucleosome

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Base pair

Between the two strands of DNA, complementary bases pair up. A base is part of a molecule made of bonded atoms.

Comparing sizes
Representative size: 1.1 nm. One level up, “DNA” is about 1.82× as large. The screen width and the size of the object itself are different values.
Link to the next world
Balls and sticks are a conventional model for telling atoms and bonds apart. There are no real rigid sticks.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · What do the colors and sticks in a molecular model each represent?

RCSB PDB · DNA and the nucleosome

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Nucleotide

A nucleotide is made of a base, a sugar and a phosphate, and is the unit that makes up a DNA strand. Each of these is in turn made of atoms.

Comparing sizes
Representative size: 700 pm. One level up, “Base pair” is about 1.57× as large. The screen width and the size of the object itself are different values.
Link to the next world
As we approach a single carbon atom, the frame of reference shifts from molecules to atoms.
Observation vs. model
Representative size · internal layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · Put these in order from largest to smallest: cell, DNA, nucleotide, atom.

RCSB PDB · DNA and the nucleosome

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Carbon atom

An atom is described in terms of a nucleus and electrons. Electrons are not little beads circling on fixed lines like planets.

Comparing sizes
Representative size: 152 pm. One level up, “Nucleotide” is about 4.61× as large. The screen width and the size of the object itself are different values.
Link to the next world
The electron cloud is a conceptual picture of a probability distribution of position. The diameter shown is a characteristic size based on the covalent radius.
Observation vs. model
Characteristic diameter · electron distribution is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · Why is it hard to call the edge of the electron cloud a solid surface?

RCSB PDB · DNA and the nucleosome

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Inside the atom

The nucleus is a very small region compared with the whole atom. Electrons are not distributed along fixed lines like planetary orbits.

Comparing sizes
Representative size: 10 pm. One level up, “Carbon atom” is about 15.2× as large. The screen width and the size of the object itself are different values.
Link to the next world
As we approach the nucleus, the stretch that looks empty is an important part of understanding the true scale.
Observation vs. model
Exploration scale · not a fixed particle surface · Colors, shapes and internal layout are a teaching model.

Think about it · If the inside of an atom looks empty, can objects pass through each other with no resistance?

CERN · The Standard Model

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Carbon nucleus

A carbon nucleus is made of protons and neutrons. It is much smaller than the whole atom, yet holds most of its mass.

Comparing sizes
Representative size: 5 fm. One level up, “Inside the atom” is about 2,000× as large. The screen width and the size of the object itself are different values.
Link to the next world
The colored beads are a model for telling nucleons apart, not a photograph of the inside of a nucleus.
Observation vs. model
Representative nuclear size · nucleon layout is illustrative · Colors, shapes and internal layout are a teaching model.

Think about it · Is the region that sets an atom’s size the same as the region where its mass is concentrated?

CERN · The Standard Model

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Proton

A proton is one of the parts of an atomic nucleus. Its structure is described by interactions of quarks and gluons; it is not simply a set of three little balls.

Comparing sizes
Representative size: 1.7 fm. One level up, “Carbon nucleus” is about 2.94× as large. The screen width and the size of the object itself are different values.
Link to the next world
The quark markers are a conceptual way of showing its makeup. The edge of a proton is not like the surface of an everyday object.
Observation vs. model
Characteristic size based on charge radius · Colors, shapes and internal layout are a teaching model.

Think about it · Why do we need to tell a model of the parts apart from the signals we actually observe?

CERN · The Standard Model

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Quark exploration scale

Quarks are currently treated as elementary particles. The length shown does not mean a diameter has been measured; it is a scale for probing smaller structure.

Comparing sizes
Representative size: 1.000 × 10^-19 m. One level up, “Proton” is about 17,000× as large. The screen width and the size of the object itself are different values.
Link to the next world
We need to distinguish zooming in on a confirmed object from comparing theoretical lengths.
Observation vs. model
Intrinsic size not measured · exploration scale · Colors, shapes and internal layout are a teaching model.

Think about it · Does the length we can probe mean the same thing as the size of a particle?

CERN · The Standard Model

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The unknown · 10⁻²¹ m

Current observations have not confirmed any concrete structure of space at this size. We compare a length scale, not an object.

Comparing sizes
Representative size: 1.000 × 10^-21 m. One level up, “Quark exploration scale” is about 100× as large. The screen width and the size of the object itself are different values.
Link to the next world
The grid and glow are abstract guides. Don’t read them as meaning the shape of something smaller has been discovered.
Observation vs. model
Abstract length comparison · Colors, shapes and internal layout are a teaching model.

Think about it · Try to tell observed facts apart from devices used for explanation.

NIST · Planck length

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The unknown · 10⁻²⁵ m

Current observations have not confirmed any concrete structure of space at this size. We compare a length scale, not an object.

Comparing sizes
Representative size: 1.000 × 10^-25 m. One level up, “The unknown · 10⁻²¹ m” is about 10,000× as large. The screen width and the size of the object itself are different values.
Link to the next world
The grid and glow are abstract guides. Don’t read them as meaning the shape of something smaller has been discovered.
Observation vs. model
Abstract length comparison · Colors, shapes and internal layout are a teaching model.

Think about it · Try to tell observed facts apart from devices used for explanation.

NIST · Planck length

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Toward quantum gravity

Current observations have not confirmed any concrete structure of space at this size. We compare a length scale, not an object.

Comparing sizes
Representative size: 1.000 × 10^-29 m. One level up, “The unknown · 10⁻²⁵ m” is about 10,000× as large. The screen width and the size of the object itself are different values.
Link to the next world
The grid and glow are abstract guides. Don’t read them as meaning the shape of something smaller has been discovered.
Observation vs. model
Theoretical exploration · not an observation of the structure of space · Colors, shapes and internal layout are a teaching model.

Think about it · Try to tell observed facts apart from devices used for explanation.

NIST · Planck length

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Near the Planck scale

Current observations have not confirmed any concrete structure of space at this size. We compare a length scale, not an object.

Comparing sizes
Representative size: 1.000 × 10^-33 m. One level up, “Toward quantum gravity” is about 10,000× as large. The screen width and the size of the object itself are different values.
Link to the next world
The grid and glow are abstract guides. Don’t read them as meaning the shape of something smaller has been discovered.
Observation vs. model
Theoretical scale · Colors, shapes and internal layout are a teaching model.

Think about it · Try to tell observed facts apart from devices used for explanation.

NIST · Planck length

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Planck length

The Planck length is a theoretical length defined by the gravitational constant, the speed of light and the reduced Planck constant. It comes up when thinking about how gravity relates to quantum theory.

Comparing sizes
Representative size: 1.616 × 10^-35 m. One level up, “Near the Planck scale” is about 61.9× as large. The screen width and the size of the object itself are different values.
Link to the next world
This scene does not show evidence that space is a grid or that this length is a confirmed smallest pixel.
Observation vs. model
NIST · theoretical length · Colors, shapes and internal layout are a teaching model.

Think about it · How is defining something mathematically different from observing it in an experiment?

NIST · Planck length

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Terrain sources: NASA GIBS Blue Marble (2004), Mapzen Terrain Tiles / USGS SRTM·GMTED2010 / NOAA ETOPO1. © OpenStreetMap contributors. Sentinel-2 cloudless by EOX IT Services GmbH (Contains modified Copernicus Sentinel data 2016 & 2017), CC BY 4.0. Paving and stone: Poly Haven CC0. Full terrain data credits. The ground around Gwanghwamun was flattened so the models fit, and outlying buildings are representative models.