What Is Cosmological Redshift?

Extended Description

Infographic titled “What is Cosmological Redshift?” explains cosmological redshift, or the stretching of light waves due to the expansion of space between galaxies, with text and diagrams. 

The infographic is divided into three parts with the following headers:

1. When Space Expands, Light Stretches
2. Redder than Red
3. Seeing the Past 

Part 1: When Space Expands, Light Stretches

Below the headline is text that reads “Since the big bang, the physical space of the universe has been expanding. Stars and galaxies maintain their size, but the space between them grows.”

Below the text is a diagram representing the expansion of the universe over time. At the top right is a white explosion symbol labeled “Big Bang.” Projecting down from the explosion symbol, diagonally toward the lower left is an arrow labeled “Expansion over Time.” Following this arrow is a set of four spheres of increasing size. On the surface of each sphere is a set of spiral, elliptical, linear, and irregular shapes representing galaxies. The same set of shapes is on each sphere, but the distance between shapes varies with the size of the sphere. 

• On the smallest sphere, closest to the big bang explosion symbol, the shapes are so close together that they are impossible to distinguish. 
• In the second sphere, the shapes are distinct, but touching. 
• In the third sphere, there is space between each shape.
• In the largest sphere, which is farthest from the explosion symbol, the shapes are very far apart.

Projecting straight down from the big bang explosion symbol is another arrow. This one is labeled “Increasing Wavelength.” To the left of this arrow is a set of three diagrams, arranged vertically. Each diagram includes a spiral shape on the left, an irregular shape on the right, and a colored sine wave pattern in between. On each diagram, the distance between two successive wave peaks is labeled “1 Wavelength.” The distance between the shapes increases from top (closest to the big bang explosion symbol) to bottom, as does the length of one wavelength. 

• In the top diagram, which is aligned with the second-smallest sphere, the sine wave is blue and the wavelength is very short.
• In the middle diagram, which is aligned with the third sphere, the sine wave is yellow and the wavelength is longer.
• In the bottom diagram, which is aligned with the fourth and largest sphere, the sine wave is red and the wavelength is longest. 

Beneath the graphic is a caption that reads “As light travels through expanding space, it is stretched to longer wavelengths.”

Part 2: Redder than Red

Below the headline is text that reads “The longest visible wavelength is red. Beyond red are longer wavelengths that we can’t see, starting with infrared. When light is stretched by the expansion of space, we say that it is redshifted — from its original wavelength to a longer, redder one.”

Below the text is a diagram showing the relationship between bands of the electromagnetic spectrum (different types of light) and wavelengths of emitted and received light.  

Spectrum Bar

The spectrum is represented as a horizontal bar with five colored segments. From left to right: a dark brown segment labeled “microwave;” a red segment labeled “infrared;” a segment labeled “visible light” with a rainbow of colors from red, to orange, yellow, green, blue, and purple; a light blue segment labeled “ultraviolet;” and a dark blue segment labeled “X-ray.” 

Light Waves

Below the spectrum bar are three colored sine waves representing light emitted by galaxies and received by telescopes. The sine waves are stacked horizontally. Each is a different color and length. All are right-aligned to a vertical dashed line extending down from near the middle of the ultraviolet segment of the spectrum bar.

The top sine wave is labeled “emitted.” It is short and blue, and the peaks of the wave are very close together. The middle and bottom sine waves are both labeled “received” and “stretched over time.” The middle wave is yellow, and extends left to a dashed line projecting down from the yellow part of the visible light portion of the spectrum. It is longer than the blue wave and the peaks are farther apart. The bottom wave is red. It is the longest sine wave, extending left to a dashed line that projects down from the middle of the infrared portion of the spectrum bar. The peaks on the wave are very far apart.

Part 3: Seeing the Past

Below the headline is text that reads “Telescopes with infrared detectors allow us to see the ancient light of the first galaxies, which has been redshifted over space and time.”

Below the text is a diagram showing the limit of the Hubble and Webb space telescopes’ views through space and time. The nearby universe and present day are at the top while the deep universe and distant past are at the bottom. Hubble and Webb are at the top, pointing downward. Both are shown in simple grayscale as viewed from the side. 

Time and space are represented as a transparent blue funnel that is wide at the top and narrow at the bottom.  Along the left side of the diagram is an arrow pointing downward, labeled “The Past,” with five time periods labeled. From top to bottom, these are “Present Day,” “Modern Galaxies Form,” First Galaxies Form,” “First Stars Form,” and “Cosmic ‘Dark Ages’.” At the very bottom of the graphic, the tip of the funnel is labeled “The Big Bang.”

In the funnel illustration, the region between Present Day and Modern Galaxies Form is represented with the same spiral, elliptical, linear, and irregular shapes used to represent galaxies in the “When Space Expands, Light Stretches” part of the infographic. The shapes are relatively bright, large, and far apart.

The Modern Galaxies Form portion of the diagram is represented with similar spiral, elliptical, and linear shapes, but they are fainter, smaller, and closer together.

The First Galaxies Form portion of the graphic is illustrated with fuzzy red elliptical shapes, small blue dots, and a tangle of faint blue lines. The shapes decrease in size, brightness, and distance apart from the top to the bottom portion of this section. 

The First Stars Form portion of the graphic is in a very narrow region of the funnel and is illustrated with faint wisps of lighter blue within darker blue.

The Cosmic “Dark Ages” portion of the graphic is indistinguishable from the dark blue background. 

A solid vertical blue line extends down from Hubble to the top of the First Galaxies Form portion of the graphic. The bottom end of this line is dashed and is labeled “Hubble’s Limit.” A similar line extends down from Webb to the bottom of the First Galaxies Form portion of the graphic, and is labeled “Webb’s Limit.”

To the right of the diagram is a vertical wavelength bar showing bands of the electromagnetic spectrum. From top to bottom they are: “Visible Light” with a rainbow of colors, from purple, to blue, green, yellow, orange, and red; a darker red segment labeled “Near Infrared;” a reddish-brown segment labeled “mid infrared;” a dark brown segment labeled “Far Infrared;” and an even darker brown segment labeled “microwave.” The end of the Far Infrared segment and the beginning of the Microwave segment are marked with jagged lines and a space in between.

Image Alt Text

Infographic titled “What Is Cosmological Redshift?” explains cosmological redshift, or the stretching of light waves due to the expansion of space between galaxies. The infographic is divided into three parts: When Space Expands, Light Stretches; Redder than Red; and Seeing the Past. Part 1 shows the universe expanding over time, while the wavelengths of light also expand as they travel through expanding space over time. Part 2 shows the difference in wavelength between emitted light (shorter wavelength) and received light (longer wavelength), using an illustration of the electromagnetic spectrum for reference. Part 3 illustrates the universe over time, showing the limit of Hubble’s and Webb’s views through space and time.