Telescopes

A creative nonfiction piece from the archives

A telescope makes large things small or small things large, depending on perspective; it can capture the ancient light from a far-off goliath and paste it between textbook pages, or it can find a tiny speck in the sky and blow it wide enough to count the rings. All telescopes, which are cousins to cameras, have the same basic anatomy: object, image, focal length, aperture, lens. The object is the star, tens or hundreds or millions of light-years away, and the image is the version of it suspended on the other side of the eyepiece. The open mouth of the telescope, yawning toward the sky, is the aperture. After light is collected by the aperture, it is directed down the length of the telescope to the focus, where the image becomes clear. The light-gathering power of a telescope is proportional to the aperture diameter – like “light-gathering power,” everything in astronomy is made dreamy by virtue of being named for light and stars, and the pretty vocabulary tempts many an unsuspecting student into a slog of scientific notation and mysterious units (angstroms, parsecs, and the ambiguously named astronomical unit).

There are two main types of telescopes, refracting and reflecting. Refractors use a lens as their primary light-gathering element. A concave lens converges the light to the focus, like children on the playground burning ants under magnifying lenses, or perhaps like your father glaring from behind farsighted glasses. This is similar to how the human eye works – your pupil is the aperture and a crystalline lens converges the light toward your retina. The first telescopes were refractors, invented by eyeglass makers, and they were small enough to grasp in your hand, perhaps better suited for glimpsing over the hilltop than viewing the cosmos. Galileo is credited with inventing the first telescope used for scientific experimentation (and the first to be named “telescope”), with an aperture diameter of 15 millimeters. Hundreds of years later, the largest refractor is located now at Yerkes Observatory in Wisconsin, with an aperture diameter of over a meter. It is shaped like a child’s depiction of a space rocket, and one can’t help but wonder if the steel support beams are meant to prop it up or to pin it down. If given the opportunity, would the Yerkes launch itself toward that infinity? Anyhow, it is for now earthbound, and lives in an arching Romanesque dome – it is fitting, astronomers agree, to study something as beautiful as the stars only in a place that is also beautiful. The entire floor of the dome is a wooden platform that can be raised or lowered depending on the telescope’s orientation as it cranes toward the sky.

Despite the archaic, steampunk beauty of a refractor, the astronomical community has largely relegated it to just that – archaic. The larger the lens, the thicker and heavier it becomes, which can cause warping. Refracting telescopes are also susceptible to chromatic aberration: different colors of light have different wavelengths, and the thick refracting lens can cause the wavelengths to converge at different points, creating a halo of color around images (an effect perhaps loved by indie photographers but not so much by astronomers). The first reflecting telescope was invented by Isaac Newton; the design uses a concave mirror as its primary light-gathering element instead of a lens. Light comes through the aperture, strikes the mirror, and is directed to a single point where the image crystallizes. Unlike a lens, which must be transparent, a mirror can be supported from behind or compiled from many smaller panes; therefore, reflectors are typically favored for scientific study. Depending on the location of the eyepiece, the image can be moved using a series of secondary or tertiary mirrors – a shot of light in a mirror maze.

Two of the most famous reflectors are the twins Gemini North and Gemini South, each with eight-meter apertures. Both observatories are enormous; formulas for resolving power and plate scale aside, one must observe the universe from within something large in order to prepare oneself for what they will see – something infinitely larger. We shrink ourselves bit by bit, because to leap straight into the ether is to be pulverized. Gemini North is located in Hilo, Hawaii, and its sister is located in Cerro Pachón, Chile – the Andes mountains are speckled with telescopes. The Gemini observatories are not as easily romantic as the Yerkes; instead, they are bulbous metal domes cropping up from mountain peaks like the armored heads of giants. They wear a thin windowed visor that sometimes seems narrowed with dubiety and other times seems to be raising its eyebrows in surprise. The most famous photos of the Gemini observatories are taken at dusk; a strip of washed-out gold rings the horizon and flares off the steel paneling. Others show a bright beam of light shooting from the open dome into the heavens – a laser guide star, which is an artificial star projected into the sky and used to calibrate telescope results. Looking at the photo, it’s almost difficult to discern if the laser beam is emitting from the telescope or coming down to strike it like Zeus’s misplaced lightning bolt. The interior of the Gemini Observatories looks like a combination of a hospital and a Star Trek helm, with sterile white walls capable of splitting down the middle. The telescope itself looks skeletal, just a honeycombed mirror among scaffolding. The reflecting mirror rests on a blue platform that crouches on staircases. Like the Yerkes, it looks ready to jump, power building behind its haunches. Between the two Geminis, they can nearly see the entire breadth of the sky (known in astronomy as the celestial sphere) and they have glimpsed exoplanets, quasars, and blackholes. Stars die and are born beneath their watchful eyes.

Although reflectors do not suffer from chromatic aberration, all telescopes are susceptible to an array of other aberrations: spherical, coma, astigmatism, curvature of field, distortion. One might not expect a machine so large and commanding to be so tenuous. Astigmatism is an aberration commonly found in the human eye, caused when a mirror or cornea is oblongly shaped. It seems like some sort of metaphor that telescopes and people are not so different – both of us look toward something we can never touch, both of us have bad eyes. Telescope location is a delicate matter. Ideally, the site should be high elevation and have good atmospheric conditions – dry, stable, cloudless. There are many potential obstacles involved in viewing the universe from Earth’s surface, and miles of matter to cut through. Although invisible to the human eye, our sky is filled with dust motes and random molecules that push and pull. Sky background occurs when the dust scatters and emits light, causing staticky background noise. Atmospheric extinction (in astronomy, even failure is named something beautiful) occurs when the dust absorbs light from celestial objects, which makes the objects appear artificially dimmer in images. Clouds absorb and scatter light. Airglow is the natural diffusion of light through a planet’s atmosphere, caused by gases that give off light. Astronomical seeing, which describes the sharpness of a telescope image, is affected by air turbulence. This is what causes that characteristic starry twinkling, known more prosaically as scintillation – imagine standing beneath a canopy of leaves; the sunlight that filters through winks across your hands. It is an oft-recited fact that stars twinkle, and planets do not. This is because stars are much farther away, so they are reduced to concentrated drops of lights that are more easily affected by turbulence. Modern telescopes are designed to overcome some of these disturbances, using a combination of active and adaptive optics. Active optics is a preventative measure, the mirrors shaped in anticipation of interferences. They are built to withstand wind and weather conditions. Adaptive optics refers to telescopes with deformable mirrors – the mirror’s shape can be changed at will in order to compensate for disturbances as they happen.

Telescopes can also exist in outer space, a venture which is as risky as it is rewarding. The first successful space telescope was the Orbiting Astronomical Observatory 2, affectionately nicknamed “Stargazer” (OAO-1 was unfortunately lost in action). It looked like a misshapen bird with an octagonal body and blunted wings. Contact was lost several years after launch, and now OAO-2 circles the Earth darkly and quietly.

The most famous space telescope is the Hubble – it the favorite sibling of NASA’s four Great Observatory satellites. Outside the bounds of the atmosphere, the Hubble is able to capture highly detailed images both in visible light and in areas of the electromagnetic spectrum outside the realm of the human eye – ultraviolent, infrared. A telescope’s first image is called its “first light.” The Hubble’s first light image is a grainy grayscale snapshot of stars with names like computer passwords – like a baby’s first word, the first light image is rarely impressive on its own, but rather for the novelty of it. It signifies the beginning of something greater. The Hubble is also the only telescope to be continuously maintained while in space. One of its most famous images is the Pillars of Creation, which shows a blooming bruise of young stars. Theories have been built and broken over the Hubble’s observations – the age and expansion of the universe, acceleration of bodies, dark energy. To look through a telescope is to see not only space but also time. Light is the fastest thing we know, yet even it takes eons to traverse the arid voids between stars, and some of the light we see originates from the birth of the universe. It is a chilling thought, to look at the sky and know that nothing is real, that you can only observe the past, and it is impossible to know the present.

Even outside of the Earth’s atmosphere, disturbances still exist. Interstellar extinction, similar to atmospheric extinction, describes the phenomena where interstellar matter absorbs some of the light from celestial objects, making them appear dimmer. It is a misconception that space is empty – the interstellar medium is a cloud of radiation and lonely particles that exist in empty space. So much of astronomy is about trying to see things that for ages have been obscure to us; the concept of dark matter reflects this – models of the universe show that it has far more mass than can be accounted for by the things we know about, meaning that there must be something else, some invisible presence beyond detection. Go farther, go farther – your hand, a mountain outcropping, low Earth orbit. Everything dissolves under the weight of infinity. Suddenly, the beautiful names we assign these things seem silly – who are we to make poetry from something so large and uncaring, something so ancient and terrifying? Astronomy has so many misleading names: Local Interstellar Cloud, Local Interstellar Medium (not to be confused with Very Local Interstellar Medium), Local Group, solar neighborhood. On one hand, these objects are not local at all – they are so large they can rip you apart; but on the other hand, what is not close, when the universe is never-ending? Large things small or small things large, there seems like no difference. Perspective crumbles, and all of life feels like a smudge on the lens.

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Sources

Dhillon, Vik. “The Atmosphere.” Vik Dhillon: Phy217 - the Atmosphere, http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/phy217_tel_atmos.html.

Dhillon, Vik. “Basic Principles.” Vik Dhillon: Phy217 - Basic Principles, http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/telescopes/phy217_tel_principles.html.

“Legacy.” Yerkes Observatory, 20 Mar. 2023, https://yerkesobservatory.org/learn/legacy/.

Marinas, Naibi. “Detection of Light.” AST3018 - Astronomy & Astrophysics 1. Gainesville, University of Florida.

Ryden, Barbara, and Bradley M. Peterson. Foundations of Astrophysics. Pearson Education, Inc., 2010.