Celestial Tour: The Journey of Light

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The James Webb Space Telescope, located far beyond Earth's Moon in the bitter cold of space, will search for infrared light, the radiation humans perceive as heat.

Light and Distance
Produced by the Space Telescope Science Institute’s Office of Public Outreach in collaboration with NASA’s Universe of Learning partners: Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, NASA Jet Propulsion Laboratory, and Sonoma State University
All images, illustrations, and videos courtesy of NASA except:
  • Illustration of radiation from everyday objects courtesy of STScI
  • Illustration of electromagnetic waves courtesy of STScI
  • Photo of crepuscular rays courtesy of Wikimedia user Fir0002/Flagstaffphotos
  • Photo of snake courtesy of Mark Mannetti
  • Infrared image of a mouse courtesy of Julius Lab, UCSF
  • Photo of snow geese and the Moon courtesy of Brocken Inaglory
  • James Webb Space Telescope illustrations by STScI/G. Bacon
  • Ariane 5 rocket launch image ©2008 ESA – CNES – Arianespace/Photo by Optique Video CSG
  • James Webb Space Telescope animation by STScI/G. Bacon
  • Animation of traveling light pulses courtesy of Footage Island
  • Alpha Centauri animation courtesy of ESO/L. Calçada/Nick Risinger (skysurvey.org)
  • Andromeda Galaxy image courtesy of ESA/Hubble & Digitized Sky Survey 2; acknowledgment: Davide De Martin (ESA/Hubble)
  • Illustration of galaxies at different distances by STScI/A. Field
  • Cosmic redshift animation courtesy of ESO
  • Simulated JWST galaxy field image courtesy of STScI
  • Taurus constellation drawing from Firmamentum Sobiescianum sive Uranographia by Johannes Hevelius, courtesy of the United States Naval Observatory
  • Written by Tracy Vogel
  • Designed by Marc Lussier 
  • Music courtesy of Associated Production Music


Stars glow in a dark sky. Text, Visible and infrared image of Hubble Ultra Deep Field. This is the Hubble Ultra Deep Field, a view that stretches over 13 billion light-years into the cosmos.

The Hubble Ultra Deep Field is a snapshot of what we see when we look into the sky today.

Yet at the same time, it captures the universe of the far-distant past.

Everything you see in this image is ancient history, witnessed not as it is now, but as it was long ago.


The earliest galaxies in this image appear as they were just a short time after the big bang.

The idea seems incredible, like having a time machine at your fingertips.

But the reality is much simpler.

Light moves

White lines streak left to right

Text, It travels at amazing speeds, but it still takes time to cross the immense distances of space.

The Moon is Earth's closest cosmic companion, about 239,000 miles (384,000 kilometers) away.

A wavy line moves from the Moon on the right to the Earth on the left. Text, Light takes 1.3 seconds to travel that distance.

So when the light from the Moon strikes your eyes, you're seeing it as it was 1.3 seconds earlier.

A wavy line moves from the Sun on the right to the Earth on the left. Text, the Sun is 93 million miles (150 million kilometers) away, far enough for light to take more than eight minutes to travel to Earth.

Solar prominences on the sun. Text, The sunlight reaching us right now is more than eight minutes old.

Orbital rings in different colors. Neptune, Uranus, Saturn, Jupiter, Mars, Earth. Text, The farther away objects are, the longer their light takes to reach us.

A wavy line moves from Neptune to Earth. Text, Light from Neptune takes four hours to reach the inner solar system ...

... while the light from the next-nearest star system travels for four years before it reaches Earth.

A bright orb moves among the stars

A giant light at an angle. Text, Galaxies are even farther away.

The Andromeda Galaxy is our nearest large galactic neighbor.

Light must travel 2.5 million years to reach us from Andromeda.

The distance that light travels in a year is such a useful measurement for talking about immense Cosmic distances that we have a name for it - a light-year

Galaxies inside four rectangular shapes. Distant Galaxies at far left, Nearby Galaxies far right. A telescope to the right. A wavy line moves left to right. Text, When we use our telescopes to collect light from the galaxies most distant from us, we are capturing light that left them billions of years earlier.

We see them not as they were seconds or minutes ago, but as they were billions of years ago, when they were newly formed.

18 stars and galaxies in a grid. Text, The light from the universe's first stars and galaxies is still out there, traveling the vast expanses of space.

A moving three-dimensional web strung between bright points in space, Text, If we could capture that light, we could see those objects as they appeared when they first formed.

But we haven't been able to see it, not even with Hubble's powerful vision.

On a grid, a wavy line moves from a galaxy to Earth, shifting towards red as it moves. Text, That's because, as the light travels across space, it's stretched by the expansion of the universe.

The Expanding Universe Stretches Light.

An arrow from Ultraviolet and Visible Light over a galaxy points to Infrared Light over Earth. A wavy, multi-colored line between them.

Text, This changes the light from ultraviolet and visible wavelengths into infrared light.

Hubble can see only some of those infrared wavelengths.

The James Webb Space Telescope. Text, With its huge mirror and infrared-sensitive instruments, the James Webb Space Telescope can observe this infrared light and study the universe’s earliest galaxies.

The Webb and Hubble side by side. Text, Webb’s infrared images have the same resolution and detail of the visible-light images taken by Hubble.

Webb opens a window onto regions of the universe humanity has never seen before.