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Thousands of galaxies and bright foreground stars in Webb's first deep field

A VISUAL JOURNEY / 01

How we learned
to see the universe.

Four images that changed the size of our world.

Begin with the evidence
FOUR OBSERVATIONS · FOUR CENTURIESIMAGE: NASA, ESA, CSA, STScI
THE FIELD GUIDEFOR THE CLASSROOM ↓

THE QUESTION

How did the visible universe grow?

The universe did not change when we built a better telescope. What we could know about it did. At each stop, study the image before opening the explanation. Ask what the image shows and what it cannot show on its own.

BY THE END, YOU CAN

Trace how better observations and ways to measure distance changed what people could know about the universe. Explain what each image shows and how it was made.

OBSERVATION 01 / 04

1610

The Moon has a landscape

A familiar light in the sky became a place with mountains and hollows.

Two of Galileo's black-and-white drawings of the partly lit Moon, with dark shading and an uneven edge between light and shadow.Historical drawing
A digital reproduction of drawings published in 1610. Galileo drew the Moon from observation; this is not a photograph.IMAGE: World Digital Library
01 / LOOK FIRST

Follow the uneven boundary between the bright and dark parts of Galileo's Moon.

Take a moment with the image before reading on.

Reveal the interpretation

Galileo aimed a telescope at the Moon and drew what he saw. Shadows and bright peaks showed that its surface was rough, not a perfectly smooth sphere.

WHAT CHANGEDTelescope evidence challenged an old picture of the heavens as flawless and unchanging.
PEOPLE BEHIND THE EVIDENCE

Galileo Galilei

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OBSERVATION 02 / 04

1923

A galaxy beyond our own

One changing star helped measure a distance that seemed impossible.

An illustrated montage of the Andromeda galaxy, a modern star-field inset, and a copy of Hubble's 1923 glass plate marked VAR!Historical and modern image composite
This explanatory montage was released in 2011. It combines a photograph by R. Gendler, a modern Hubble image, and a copy of Hubble's October 6, 1923 glass plate; the whole image is not a 1923 photograph.IMAGE: Illustration Credit: NASA, ESA and Z. Levay (STScI). Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)
01 / LOOK FIRST

Find Hubble's handwritten "VAR!" beside a star on the 1923 plate at lower right.

Take a moment with the image before reading on.

Reveal the interpretation

Henrietta Swan Leavitt found a link between a Cepheid star's pulse and its true brightness. Edwin Hubble identified such a star in Andromeda; that method placed Andromeda far beyond the Milky Way.

WHAT CHANGEDThe Milky Way became one galaxy among many, rather than the whole universe.
PEOPLE BEHIND THE EVIDENCE

Henrietta Swan Leavitt · Edwin Hubble

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OBSERVATION 03 / 04

1995

An empty patch fills with galaxies

Hubble stared at a tiny, seemingly dark part of the sky for ten days.

A dark field crowded with tiny galaxies of different shapes and colors, with a few brighter foreground stars.Processed telescope image
A color image assembled from 342 exposures taken through different filters over ten days. These faint galaxies are not visible to the unaided eye.IMAGE: R. Williams (STScI), Hubble Deep Field Team, NASA/ESA
01 / LOOK FIRST

Pick out several shapes and colors. Most of these small smudges are entire galaxies, not individual stars.

Take a moment with the image before reading on.

Reveal the interpretation

The Hubble team combined 342 exposures from December 1995. The long observation revealed thousands of galaxies in a patch of sky that had looked nearly empty.

WHAT CHANGEDA small view became evidence that galaxies fill the universe across vast distances and ages.
PEOPLE BEHIND THE EVIDENCE

Robert Williams · Hubble Deep Field Team

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OBSERVATION 04 / 04

2022

Gravity makes a cosmic lens

Webb saw distant galaxies through a foreground cluster's bending light.

Webb's deep field filled with distant galaxies, bright foreground stars, and curved arcs of gravitationally lensed galaxies.Processed near-infrared image
Webb recorded near-infrared light in several filters. Colors were assigned to the filtered exposures and combined; they are not the colors an unaided human eye would see.IMAGE: NASA, ESA, CSA, STScI
01 / LOOK FIRST

Find the stretched arcs around the bright galaxies near the center. They are distorted views of galaxies farther away.

Take a moment with the image before reading on.

Reveal the interpretation

Webb recorded near-infrared light from galaxy cluster SMACS 0723. The cluster's gravity bent and magnified light from galaxies behind it, revealing details that would otherwise be harder to see.

WHAT CHANGEDInfrared instruments and gravitational lensing gave astronomers a sharper view of very distant galaxies.
PEOPLE BEHIND THE EVIDENCE

James Webb Space Telescope science and engineering teams

CHECK THE RECORD

TAKE IT INTO THE CLASSROOM

Look. Infer. Question.

Pause at each image before opening its interpretation. Ask students to separate what they can observe from what they infer. Then follow the linked sources to test their ideas.

  1. What detail do you notice first? What might you be missing?
  2. What did the instrument reveal that unaided eyes could not?
  3. What can this image support, and what needs other evidence?

Adapted from the Library of Congress approach to primary source analysis. See its teacher guides