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April’s Night Sky Notes: Catch the Waves!

Lagoon Nebula (Visible-light View vs. Infrared View)
These NASA Hubble Space Telescope images compare two diverse views of the roiling heart of a vast stellar nursery, known as the Lagoon Nebula. The images, one taken in visible and the other in infrared light, celebrate Hubble’s 28th anniversary in space. The colorful visible-light image at left reveals a fantasy landscape of ridges, cavities, and mountains of gas and dust. This dust-and-gas landscape is being sculpted by powerful ultraviolet radiation and hurricane-like stellar winds unleashed by a monster young star. Located at the center of the photo, the star, known as Herschel 36, is about 200,000 times brighter than our Sun. This hefty star is 32 times more massive and eight times hotter than our Sun. Herschel 36 is still very active because it is young by a star’s standards, only 1 million years old.
Credits: NASA
The headshot image of Kat Troche

Kat Troche

Apr 01, 2025
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Contents

by Kat Troche of the Astronomical Society of the Pacific

The Electromagnetic Spectrum

If you’ve ever heard the term “radio waves,” used a microwave or a television remote, or had an X-ray, you have experienced a broad range of the electromagnetic spectrum! But what is the electromagnetic spectrum? According to Merriam-Webster, this spectrum is “the entire range of wavelengths or frequencies of electromagnetic radiation extending from gamma rays to the longest radio waves and including visible light.” But what does that mean? Scientists think of the entire electromagnetic spectrum as many types of light, only some that we can see with our eyes. We can detect others with our bodies, like infrared light, which we feel as heat, and ultraviolet light, which can give us sunburns. Astronomers have created many detectors that can "see" in the full spectrum of wavelengths. 

Illustration of mountains, clouds, sky, and space, with ten observatories arranged vertically by altitude and horizontally by wavelength range: Fermi: space-based, gamma. Chandra: space-based, X-ray. Hubble: space-based, visible. Rubin and E L T’s: ground-based, visible to infrared. Euclid, Roman, and Webb: space-based, infrared. Sofia: airplane, infrared. ALMA: ground-based, microwave. SKA: ground-based, radio.
Planets, stars, galaxies, and other objects in space give off a wide range of visible and invisible forms of light. Because different forms of light have different characteristics, no single observatory can detect all wavelengths. Astronomers typically rely on data from multiple ground- and space-based telescopes to fully understand the objects and phenomena they are studying. This illustration shows the wavelength sensitivity of a number of current and future space- and ground-based observatories, along with their position relative to the ground and to Earth’s atmosphere. The wavelength bands are arranged from shortest (gamma rays) to longest (radio waves). The vertical color bars show the relative penetration of each band of light through Earth’s atmosphere.
NASA, STScI

Telescope Types

While multiple types of telescopes operate across the electromagnetic spectrum, here are some of the largest, based on the wavelength they primarily work in:

  • Radio: probably the most famous radio telescope observatory would be the Very Large Array (VLA) in Socorro County, New Mexico. This set of 25-meter radio telescopes was featured in the 1997 movie Contact. Astronomers use these telescopes to observe protoplanetary disks and black holes. Another famous set of radio telescopes would be the Atacama Large Millimeter Array (ALMA) located in the Atacama Desert in Chile. ALMA was one of eight radio observatories that helped produce the first image of supermassive black holes at the center of M87 and Sagittarius A* at the center of our galaxy. Radio telescopes have also been used to study the microwave portion of the electromagnetic spectrum.
  • Infrared: The James Webb Space Telescope (JWST) operates in the infrared, allowing astronomers to see some of the earliest galaxies formed nearly 300 million years after the Big Bang. Infrared light allows astronomers to study galaxies and nebulae, which dense dust clouds would otherwise obscure. An excellent example is the Pillars of Creation located in the Eagle Nebula. With the side-by-side image comparison below, you can see the differences between what JWST and the Hubble Space Telescope (HST) were able to capture with their respective instruments.
Comparison of Pillars of Creation. Hubble’s visible-light view, left, shows darker pillars rising from the bottom to the top, ending in three points. Webb’s near-infrared image, right, shows the pillars, but they are semi-opaque and rusty red-colored.
NASA's Hubble Space Telescope made the Pillars of Creation famous with its first image in 1995, but revisited the scene in 2014 to reveal a sharper, wider view in visible light, shown above at left. A new, near-infrared-light view from NASA’s James Webb Space Telescope, at right, helps us peer through more of the dust in this star-forming region. The thick, dusty brown pillars are no longer as opaque and many more red stars that are still forming come into view.
Credits: NASA, ESA, CSA, STScI; Joseph DePasquale (STScI), Anton M. Koekemoer (STScI), Alyssa Pagan (STScI).
  • Visible: While it does have some near-infrared and ultraviolet capabilities, the Hubble Space Telescope (HST) has primarily operated in the visible light spectrum for the last 35 years. With over 1.6 million observations made, HST has played an integral role in how we view the universe. Review Hubble’s Highlights here.
Compass and Scale Image for Crab Nebula
The Crab Nebula, located in the Taurus constellation, is the result of a bright supernova explosion in the year 1054, 6,500 light-years from Earth.
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL/Caltech; Radio: NSF/NRAO/VLA; Ultraviolet: ESA/XMM-Newton
  • X-ray: Chandra X-ray Observatory was designed to detect emissions from the hottest parts of our universe, like exploding stars. X-rays help us better understand the composition of deep space objects, highlighting areas unseen by visible light and infrared telescopes. This image of the Crab Nebula combines data from five different telescopes: The VLA (radio) in red; Spitzer Space Telescope (infrared) in yellow; Hubble Space Telescope (visible) in green; XMM-Newton (ultraviolet) in blue; and Chandra X-ray Observatory (X-ray) in purple. You can view the breakdown of this multiwavelength image here.

Try This At Home

Even though we can’t see these other wavelengths with our eyes, learn how to create multiwavelength images with the Cosmic Coloring Compositor activity and explore how astronomers use representational color to show light that our eyes cannot see with our Clues to the Cosmos activity.