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Levels of understanding – what are X-rays?

Ask people on the street “What are X-rays?” and you’ll likely get a variety of replies. About medical and dental X-rays. Stories about Superman’s X-ray vision. (Why does lead block X-rays?) Invisible particles that allow us to see through stuff. Technical explanations about electromagnetic radiation.

So, street surveys typically reveal levels of understanding, which I’ll discuss later. But first, let’s ease into this topic with some examples and visualizations.

For most of us, X-rays are not part of an everyday experience. (Other than man-made sources, are there any sources of X-rays that we need to care about?) But there’s a general characteristic of X-rays that connects with our everyday world: light.

We see things when there is enough light and nothing interferes with our view. There are small things which we cannot see right in front of our eyes. They are large things that are far away which we cannot see at all. Standard microscopes and telescopes help us see more.

The light by which we see is composed of a spectrum (rainbow) of colors of light, and that visible spectrum is part of a vaster range of types of light beyond our sight. Some animals can see what we cannot, especially at night, without night-vision goggles or other imaging devices.

Light is electromagnetic radiation. Visible light is a narrow band in the electromagnetic (EM) spectrum. And there are special names for particular bands (or ranges) of that spectrum. And the properties of light vary across that spectrum. In particular, the energy of light varies.

X-rays are one of those bands outside the visible one. Radios operate in that part of the EM spectrum called radio waves. Night scopes operate in that part of the spectrum called infrared radiation. Is there a difference between wave or radiation and a ray? (Same question for gamma rays.) Well, historical artifacts. Convention.

Here’s a link (below) to a video overview of X-rays: YouTube > Clover Learning > “Understanding the X-Ray Beam and Photon Wavelengths” (Dec 27, 2019) [1] >


Once we break out of the limits of imaging only with visible light, we can learn some amazing things, refine our view of the universe. A fuller visualization, as profiled in this SciTechDaily article “Astronomers Build Incredible 3D Visualization of Exploded Star Using NASA’s Great Observatories [Video]” by Space Telescope Science Institute (January 5, 2020).

This video demonstrates the power of multiwavelength astronomy. It helps audiences understand how and why astronomers use multiple regions of the electromagnetic spectrum to explore and learn about our universe.

SciTech Daily channel (January 5, 2020) >

This new multiwavelength image of the Crab Nebula combines X-ray light from the Chandra X-ray Observatory (in blue) with visible light from the Hubble Space Telescope (in yellow) and infrared light seen by the Spitzer Space Telescope (in red). This particular combination of light from across the electromagnetic spectrum highlights the nested structure of the pulsar wind nebula.

The X-rays reveal the beating heart of the Crab, the neutron-star remnant from the supernova explosion seen almost a thousand years ago. This neutron star is the super-dense collapsed core of an exploded star and is now a pulsar that rotates at a blistering rate of 30 times per second. A disk of X-ray-emitting material, spewing jets of high-energy particles perpendicular to the disk, surrounds the pulsar. The infrared light in this image shows synchrotron radiation, formed from streams of charged particles spiraling around the pulsar’s strong magnetic fields.

The visible light is emission from oxygen that has been heated by higher-energy (ultraviolet and X-ray) synchrotron radiation. The delicate tendrils seen in visible light form what astronomers call a “cage” around the rich tapestry of synchrotron radiation, which in turn encompasses the energetic fury of the X-ray disk and jets. These multiwavelength interconnected structures illustrate that the pulsar is the main energy source for the emission seen by all three telescopes.

The Crab Nebula resides 6,500 light-years from Earth in the constellation Taurus.
Credit: NASA, ESA, J. DePasquale (STScI), and R. Hurt (Caltech/IPAC)
Levels of understanding

So, what really inspired this post was the “5 Levels” series of videos with titles like “Watch [expert scientist] explain [concept] in 5 levels of difficulty (increasing complexity).” Here’re some examples:

• Wired > “Astrophysicist Explains One Concept in 5 Levels of Difficulty” (released on 12-20-2019) [includes transcript].

Astrophysicist Janna Levin, PhD, is asked to explain the concept of gravity to 5 different people; a child, a teen, a college student, a grad student, and an expert. Levin is the Claire Tow Professor of Physics & Astronomy at Barnard College of Columbia University and author of “Black Hole Blues and Other Songs from Outer Space.” She is also the Chair and Director of Sciences at Pioneer Works, where this video was filmed. To learn more, visit https://pioneerworks.org/

• Wired > “Physicist Explains One Concept in 5 Levels of Difficulty” (released on 10-16-2019) [includes transcript].

Theoretical physicist Sean Carroll, PhD, is challenged to explain the concept of dimensions to 5 different people; a child, a teen, a college student, a grad student, and an expert.

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Celebrating X-Ray Astronomy — Chandra


[1] Here’s an excerpt from the description of Clover Learning’s “Understanding the X-Ray Beam and Photon Wavelengths” video.

Visit www.radtechbootcamp.com today to view the entire X-Ray Beam and Photon video series and more!

Radiographic images are created by exposing the patient to an x-ray beam. The x-ray beam is composed of millions of individual x-rays.

So what is an x-ray?

• An x-ray is a tiny package of energy called a photon.
• X-ray photons have a lot of energy, but … they have no mass, no charge, and they travel at the speed of light, and in a straight line.

X-rays are actually similar to light in some ways because both visible light and x-rays are part of the electromagnetic spectrum.

The electromagnetic spectrum is the entire range of photon energies. This includes some familiar terms:

• Radio waves
• Microwaves
• Visible light
• Ultraviolet light
• X-rays
• Gamma rays

These terms simply refer to different radiation categories in the electromagnetic spectrum. They are all photons … the only difference is the energy.

The energy of a photon, including x-ray photons, is determined by the wavelength and frequency. The velocity (speed) does not change.

• Wavelength is the measurement from one peak to the next. When the peaks are closer together, the wavelength decreases and the x-ray photon has more energy.

• When wavelength decreases, something else happens … the frequency increases. This is the number of wave cycles per second, measured in Hertz (Hz).

Here’s the thing about an x-ray beam … It’s not made of up just one energy.

• The x-ray beam is polyenergetic.
• There are millions of photons in the beam and they have a wide range of energies.

Finally … When x-rays are created in the x-ray tube, they are created isotropically.

• Isotropic means the x-rays diverge equally in all directions.
• This is why the x-ray tube assembly requires a protective lead housing … to absorb all of the extra x-ray photons that we don’t need.

2 thoughts on “Levels of understanding – what are X-rays?

  1. This Hubble video is an excellent visualization of how multi-wavelength observations tell a better cosmic story.

    Hubble Space Telescope > Hubblecast 126: From Ultraviolet to Infrared: Comparing the Hubble and James Webb Space Telescopes

    This Hubblecast explores how the NASA/ESA Hubble Space Telescope’s observations differ across different wavelengths of the electromagnetic spectrum, and how these observations will be complemented by those of the upcoming NASA/ESA/CSA James Webb Space Telescope.

  2. Another take on multi-wavelength observation and visualization of the Crab Nebula.

    Space.com > “Tour the colorful Crab Nebula with this stunning new 3D visualization” by Doris Elin Urrutia (January 15, 2020) – The visualization is from a new generation of products being created by NASA’s Universe of Learning Program, an effort to connect scientific work with lay audiences. This particular video aims to highlight the reasons behind observing space through different wavelengths.

    A new 3D movie highlights the Crab Nebula, beginning with its location in the constellation Taurus and zooming in to show off its dynamic features.

    Data from the Hubble Space Telescope, Spitzer Space Telescope and the Chandra X-ray Observatory … [provide] a fuller understanding of the Crab Nebula’s world.

    The video was unveiled Jan. 5 at the 235th meeting of the American Astronomical Society in Honolulu, Hawaii.

    [Image caption] The Crab Nebula was once mistaken for a comet by French astronomer Charles Messier. …

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