From the Invisible to the Visible – Milestones in the History of Telescopes

 

Note:  A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory [Photo]. Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Galileo_telescope_replica.jpg). CC BY-SA 3.0.

 

From the Invisible to the Visible – Milestones in the History of Telescopes

 by Vicky L. Oldham, March 7, 2022

We live in a time of breakthrough advances in telescopes, their progress featured in headline news almost daily.  On Christmas Day 2021, the James Webb Space Telescope began its journey to the LaGrange 2 (L2) point in space, a gravitationally stable location orbiting the Sun, approximately a million miles from Earth (NASA, 2022).  Now in the process of aligning its eighteen beryllium gold-coated mirrors, the newly deployed telescope is about to make history as it focuses on its first targets. 

Conceived as the next-generation space telescope, the James Webb Space Telescope continues the mission of the Hubble Space Telescope and others like the infrared-detecting Spitzer Space Telescope.  However, Webb's leading-edge design, location outside Earth's orbit, and advanced infrared-detecting capabilities are predicted to revolutionize our understanding of the universe (Royal Museums Greenwich, 2022).  A book on the history of the recently decommissioned Spitzer Space Telescope, aptly titled Making the Invisible Visible, referred to its ability to observe infrared radiation, a wavelength of light that our eyes cannot see (Rottner, 2017).  However, the phrase "making the invisible visible" really describes the purpose of all telescopes—devices designed to reveal the otherwise hidden wonders of the cosmos.  With expectations high for the world's most powerful telescope to date, the James Webb Space Telescope promises to make the invisible visible in a way unimagined before, to lift the veil of mystery shrouding the farthest depths of space 100 times more powerfully than Hubble could.

When we consider the history of telescopes, it's not just the mundane story of a device that somehow grew larger over time.  Instead, telescopes have played a unique role in the forces propelling civilization, a metaphor symbolizing the progress of human evolution.  Besides initiating new chapters in our scientific understanding of space, telescopes have pointed the way to the future, leading humankind to explore new worlds with the potential to one day discover life beyond Earth.

Seriously—What is a Telescope?

What exactly is a telescope, particularly in the context of today's advanced technology?  Our perceptions and expectations have transformed with the new-fangled telescope designs and their accompanying complexities.  Merriam-Webster (n.d.) defines a telescope as "a usually tubular optical instrument for viewing distant objects by means of the refraction of light rays through a lens or the reflection of light rays by a concave mirror" (para. 1).  Although true throughout most of its history, now this description begs for an update.  Surprisingly, the seventeenth-century definition is more in step with our current understanding as it simply means far-seeing: "telescopos" in Greek and "telescopium" in Latin.  No matter how obsolete or advanced a telescope is, essentially, it is "a 'bucket' for collecting radiation" (Fraknoi et al., 2016a, para. 1).  Its ability to resolve, sort, and record the radiation it collects distinguishes it from earlier incarnations.  A consistent definition for a telescope is ultimately challenging because the technology and methodology to perform specific tasks may vary greatly, depending on whether it is ground-based or space-based and incorporated into a satellite, probe, or spacecraft.

The First Telescopes

The best way to describe a telescope may ultimately lie in what it does—making the invisible visible.  Once Galileo turned his three-powered, hand-crafted refracting telescope to the sky, he was able to see what could never be seen before.  Instead of viewing Venus as a bright star-like object, the telescope enabled Galileo to see a partially shadowed planet, like the phases of the Moon.  Our place in the universe shifted almost overnight from the millennia-old Earth-centered view to the Copernican, Sun-centered view.  Galileo's public promotion of the telescope as a method for observing the sky provided evidence that could be confirmed by many of his contemporaries: astronomers and star-watching enthusiasts using personal telescopes.  Soon, telescope makers, craving greater magnification, began extending the tubes of refracting telescopes, sometimes to absurd lengths.  However, chromatic aberrations caused by light bending through thick lenses caused image blurring that was difficult to solve (BBC Earth Lab, 2017, 00:03:08).  Then, just sixty years after Galileo, Isaac Newton introduced his "reflecting" telescope, a significant design improvement using curved concave mirrors instead of convex optical lenses.  Newton's first model enabled thirty times magnification with only a six-inch tube.

Going Into the Light

Continuing the mission to make the invisible visible, the development of time-lapse photography represented another significant advance in the history of telescopes.  In the late 1800s, the first time-lapse photos of the night sky recorded an astounding number of stars that could not be seen with the naked eye.  By the mid-20th-century, discoveries about the nature of light meant turning to unprecedented new ways to collect and record radiation in other wavelengths besides visible light.  Decades later, the development and deployment of a dizzying variety of telescopes and space probes covering all parts of the electromagnetic spectrum would forever change our knowledge of space.

Without telescopes and related technologies, we could not conceive of exploring outer space.  Our short lifespans and fragile biology ensure our dependence on advanced technologies to "go where no man has gone before" (Peeples, 1978).  Telescopes have lifted us out of astronomy's "dark ages" when studying the heavens was more concerned with astrology and divination.

Interestingly, the development of telescopes grew from the crafting of spectacle lenses and spyglasses, offering better ways to read or view distant objects at sea, especially in military applications.  Who would have guessed the effort to improve sight or wage war would spark the transition from meeting personal or tribal needs to humankind's desire to understand the universe from a scientific perspective?

Losing Weight

As with other technologies, the story of telescopes is the story of radical developments that often occur when limitation ignites innovation and leads to invention.  For part of the 20th century, insurmountable problems plagued telescope manufacturers as their building specs demanded larger and substantially heavier mirrors.  Mirrors eventually grew so large they deformed under their weight, rendering them useless.  As a result, ingenious ways to make mirrors finally resulted in significantly larger, precision-built reflecting surfaces—minus the tonnage.  Notwithstanding substantial progress in telescopes over several centuries, the most remarkable strides in their history belong to "The Space Age."

From More Powerful Telescopes to More Telescopes with Powers

One misconception about telescopes is that greater magnification leads to more detailed images; instead, increased light-gathering and higher resolution (discerning greater image detail) make telescopes better.  Besides building ever-larger telescopes, several revolutionary technologies have significantly raised the bar for telescopes.  First, they have transitioned from observing visible light to all wavelengths of light, from gamma rays to radio waves, revealing the universe in multifaceted ways impossible through the visible spectrum alone.  Second, observatories, primarily radio telescope arrays, have exponentially increased their power using a synchronized detection strategy known as interferometry.  Third, ground-based telescopes have begun to use adaptive optics to correct image blurring due to atmospheric turbulence.  Thanks to adaptive optics, the next generation of Earthbound observatories may rival what was once only possible in space.

Exponential Power through All Wavelengths

Exploring light in all wavelengths of the electromagnetic spectrum (EM), from radio waves to gamma rays, has uncovered surprising information about space objects that would otherwise be invisible.  Analysis of the full range of emitted light allows astronomers to determine characteristics of stars, planets, and other bodies, including their mass, composition, and atmosphere, regardless of their almost inconceivable lightyears' distance (CrashCourse, 2015, 00:07:48).  Depending on target wavelengths, telescopes may be limited to operating outside Earth's atmosphere.  The space-based Hubble telescope has already revealed subtle detail about our Milky Way as well as other distant stars and galaxies, observing in both visible and ultraviolet wavelengths.  The James Webb Space Telescope will "see" in both the visible spectrum and infrared to the edge of the universe and the moment of its creation approximately 13.5 billion years ago.  Other space telescopes designed to detect X-rays, microwaves, and gamma rays have made extraordinary contributions to astronomy only possible through their ability to collect light in specific wavelengths. 

Exponential Power through Interferometry

Interferometry is particularly important to radio astronomy to increase the angular resolution or the telescope's "ability to distinguish fine detail" (Kellermann, 2021).  Since radio waves are extremely long, making the largest collecting area possible is essential.  The Very Large Array (VLA) in New Mexico "is an interferometer array using the combined views of its 27 antennas to mimic the view of a telescope as big across as the farthest distance between its antennas.  For the VLA, this can range from less than a mile to over 22 miles across!" (National Radio Astronomy Observatory, The Array, para. 1, n.d.).  As the antennae move apart on tracks, an atomic clock records the exact time differential between each dish to accurately combine signals.  Among the world's most powerful radio telescopes, the Very Large Array and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile's Atacama Desert attain extremely high resolutions using interferometry to combine signals from multiple receivers.

Exponential Power through Adaptive Optics

Adaptive optics represents another quantum leap in the history of telescopes, making it possible for the latest ground telescopes with massive light-collecting capabilities to precisely compensate for the ever-present distortion in Earth's atmosphere, resulting in unencumbered focusing capabilities.  The Keck Observatory, located atop the 13,796-foot summit of Maunakea, Hawaii, a location with relatively stable atmospheric conditions and operational since 1993, is considered a pioneer in adaptive optics technology (W.M. Keck Observatory, 2018).  Following two decades of development and use, a substantial revamping of its adaptive optics is planned for completion in 2023.  The upgrade will use laser tomography to correct atmospheric blurring 1000 times per second.  While the Keck Observatory is updating its adaptive optics, other ground-based telescopes like the Giant Magellan Telescope currently under construction will be similarly equipped (The Center for Astrophysics | Harvard & Smithsonian, n.d.).  The latest adaptive optics systems calibrate using artificial "guide stars" created by lasers that focus on sodium atoms high in Earth's atmosphere.  Guide stars allow the system to compensate for the slightest perturbations in the air as collected light descends to the telescope, resulting in a sharply focused view.

A Revolution in Progress

Telescopes have revolutionized our expectations, not just for what is possible but what may be possible in the future.  The journey to the stars began by just looking up at the sky.  The view radically transformed when Galileo's earliest refracting telescope and Newton's innovative reflector focused on our Solar System's Sun, planets, and moons. 

Centuries later, George Ellery Hale pioneered the building of large telescopes such as those at Mount Wilson and Mount Palomar in California.  The 100-inch reflector at Mount Wilson in California, the largest in the world in 1918, attracted the renowned astronomer, Edwin Hubble.  Hubble and his talented assistant Milton Humason worked to solve the question of "spiral nebulae," now known as galaxies, confirming that our Milky Way Galaxy is not unique (Simmons, n.d.).  Continuing his achievements, in 1943, Hubble recorded the first observations at the Palomar Observatory's 200-inch Hale Telescope (then among the largest in the world).  There, he discovered we live in an expanding universe, where "every galaxy is moving away from every other" (Byrd, 2021).  The trailblazing importance of this discovery is impossible to underestimate as it relates to modern cosmology—another example of telescopes making the invisible visible.

Space Telescopes—The Final Frontier

In recent decades, space telescopes designed to target different electromagnetic spectrum bands have forged new frontiers in astronomy that would have been impossible by relying solely on ground-based telescopes.  NASA's fleet of "Great Observatories" and dozens of other space telescopes designed to detect radiation beyond the visible spectrum have either completed their missions, are currently deployed, or are in the planning stages (Wall, 2021).  Notables include the Hubble Space Telescope, the Fermi Gamma-ray Space Telescope, the Spitzer Space Telescope, the Kepler Telescope, the Planck telescope, and the Chandra X-ray Observatory. 

From low Earth orbit, the Fermi Gamma-ray Space Telescope recorded "light with energies thousands to hundreds of billions of times greater than what our eyes can detect" (Garner, 2022, para. 1).  It has recorded phenomena like cosmic rays, supernovae explosions, and the origins of high-energy neutrinos.  The Spitzer Space Telescope explored the infrared band of the spectrum and "allowed scientists to peer into cosmic regions that are hidden from optical telescopes," such as centers of galaxies (Jet Propulsion Laboratory, n.d.).  Together, the Hubble and the Spitzer space telescopes imaged the furthest galaxy ever found (NASA, 2020).  The Kepler space telescope, designed to find new planets, studied "one star-studded patch in the sky" using the transit method and recorded its observations using the largest digital camera ever launched into space in 2009 (NASA, 2018).  The Chandra X-ray Observatory, currently in an elliptical orbit around Earth, "allows scientists from around the world to obtain X-ray images of exotic environments to help understand the structure and evolution of the universe" (Chandra X-ray Center, 2019, para. 1).  The European Space Agency's Planck Space Telescope studied and mapped the universe in the microwave band of the spectrum (between infrared and radio waves).  It detected the "faint afterglow of the Big Bang, resulting in the most precise measurements yet of the age, geometry, and composition of the cosmos" (Castelvecchi, 2018, para. 1).  The Hubble Space Telescope achieved great success during its mission because it could detect phenomena in ultraviolet wavelengths in addition to the visible spectrum.  Soon to "open its eyes" on the universe, the James Webb Space Telescope promises to wow us with incomparable views of the cosmos, targeting visible light in addition to extremes in the infrared to explore the furthest reaches of space.

Conclusion

Despite the many exciting new telescopes currently in the planning stage or under construction, The James Webb Space Telescope now represents "…the largest, most powerful space telescope ever" (Tavernier, 2021, para. 1).  After aligning its mosaic of 18 mirrors, adjusted in increments measuring just 1/10,000 the width of a human hair, it promises to stun and enthrall us with its capabilities and discoveries, to be unequaled by previous telescopes.  Since its mission includes observing the sky in the far-infrared, the device is super-cooled to a temperature below 50 kelvins (or minus 370 degrees Fahrenheit) to prevent interference by ambient radiation. 

When mirror alignment and testing are complete, the James Webb Space Telescope intends to reveal distant worlds and galaxies, all the way back to the Big Bang (NASA Science Space Place, 2022).  Measured in both space and time, its ability to penetrate the extremes will again make the invisible visible.  Even more exciting, it will be looking for life on other planets by spectrographically analyzing their atmospheres (NASA, 2022).  One possibility is that it may find a world with air pollution, indicating a civilization like ours! (Johnston, 2022).  Whatever new mysteries unfold, telescopes like the Webb mark their place not just in the history of telescopes but also in the history of humankind, forging giant steps in our quest to understand the nature of the universe and our place within.

 

 

 

References

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