An AFSIG article by Paul Trittenbach

In the classical Niels Bohr model of the atom, the one that we were taught in first-year chemistry, electrons whorl around the nucleus in what appears to be an analog of a miniature model of our solar system. In the four dimensional atom (I have included the time dimension) electrons occupy a fuzzy area— the electron cloud— of a specific orbital. These orbitals are not arranged in a “plane of the ecliptic” flat fashion like the planets in our solar system (please note that many minor planets of the Kuiper Belt do not occupy the plane of the ecliptic) but within clouds that appear balloon-like and spreading in all directions from the nucleus. To make it clear, the electron cloud is not a physical bellowing, misty mass of suspended particles or smoke but the area of uncertainty occupied by the electron. The true whereabouts of the electron is unknown; defined by the Heisenberg uncertainty principle which states that we can measure one of a subatomic particle’s properties — location, speed or direction — but not all three. Measuring one will change the others.

Each orbital of the atom has a specific maximum number of electrons that can occupy it. Within the atom electrons jump from one orbital level up to another and then return back again, analogous to children bobbing around on a trampoline. As electrons return to their original ground state (the children descending to the head of the trampoline) they release a packet of energy known as a photon—light. The activities and numbers of electrons of each chemical element or compounds release a specific light signature that helps us to identify that chemical or compound and the nature of its behavior. These light signatures encompass a broad gamut of energies known collectively as the electromagnetic spectrum.

Over millions of years, humans and other animals have evolved to develop specialized photon receptors: eyes. Although they are an ingenious invention, eyes are limited to a very narrow range of the electromagnetic spectrum that we call the visible spectrum. This is the bright, white light that is emitted by our sun and glows in the 5000°K temperature region. It is needless to say how invaluable this adaptation has been for us. Moving about on the surface of the Earth, this visible light range has helped us to perceive and adapt to our world, and manipulate our surroundings to our desires. For the majority of human existence, our eyesight provided us with evidence of reality and “proof” of matters that required validation.

Light has been so essential to our reality that over the millennia humans have coined a number of phrases to express just how important it is. Everyone knows “seeing is believing” and that light is truth. “I am the light…” Christ is quoted as saying in the Bible. “Children go into the light” is expressed by the psychic in the in Steven Spielberg’s Poltergeist.  Light is both truth and good. When we want to be deceptive or keep something from someone else we keep them in the dark. Monsters lurk in the dark and hide under our beds when we are children. Scary movies play upon this to take advantage of our strongest primal fears. But we live in an age where we know “seeing” is not always believing and sometimes when we see something it is merely a ruse to keep us in the dark.

The curiosity and ingenuity of humans has led us to the discovery of the electromagnetic spectrum and the pursuit to identify exactly what light is and to understanding its behavior. But more importantly it has also led us to the awareness that seeing something with our eyes alone is not always the whole story. Nature does, in fact, keep most of her secrets hidden in a realm way beyond the limitations of our eyesight.

Located 1500 light years away in the constellation Orion is IC 434 and the associated Horsehead Nebula.  The Horsehead Nebula itself is a dark absorption nebula that is very difficult to spot. Large aperture, an H-beta filter and careful hunting will help you to find it nested inside of its companion emission nebula, IC 434. IC 434 is believed to be excited by the star Sigma Orionis, the star at the eastern end of Orion’s belt. IC 434 appears as a cloud with streamers, of gas rising from it. In images the cloud glows pink because of ionized hydrogen gas. The streamers are believed to be the result of magnetic fields produced within the nebula. The Horsehead itself is a projection of the cloud and is a protostellar factory similar to the Pillars of Creation in the Eagle nebula.

In my research I have discovered that the expression “a horse of a different color” has been attributed to at least three different sources: Shakespeare and medieval knights. One source claims that Shakespeare was the first to use the reference of  “a horse of that colour” to refer to the same matter, in his play Twelfh Night.

MARIA 

My purpose is, indeed, a horse of that colour.

SIR ANDREW 

And your horse now would make him an ass.

MARIA 

Ass, I doubt not.

SIR ANDREW

O, ’twill be admirable!

Twelfh Night, Act2, Scene 3

According to that source, Shakespeare used this phrase several times in his writing, which the source believes indicates that the phrase “A horse of a different color” originated before Shakespeare’s time.

In today’s parlance the phrase refers to something of a different matter altogether. Since it’s unlikely that the true historical origins of the phrase will ever be known, I will lay claim to it in this article. I am employing the expression “a horse of a different color” to briefly describe the electromagnetic spectrum and its relationship to astronomical objects. In this example I employ the great stallion in IC 434.

Radio waves reside at the low-end of the electromagnetic spectrum and range in size from one millimeter to over 96 kilometers in length. They are the longest wavelengths of the electromagnetic spectrum and the lowest detectable energy. Because of their size, radio waves are unaltered by other types of light. They are also able to pass through most materials uninhibited and unaffected by the molecules of the substances through which they pass.

We are familiar with radio waves and their applications to communications, which       includes radio, television and cellular telephones. Radio sources are naturally occurring too. On earth, lightning produces radio waves and in space all celestial objects emit them as products of atomic interactions. Nebulas, such as the Horsehead Nebula,     appear as clouds of  gas and dust in optical instruments. These clouds visually occlude stars and protostellar matter and prevent observations of objects within them.

Because of their long wavelengths, radio waves require large metal receiving dishes to focus them and achieve resolution. Today’s radio telescopes are combined into arrays of multiple large dishes — such as the Very Large Array (VLA) in New Mexico and the Atacama Large Millimeter \ Submillimeter Array (ALMA) in Chile. Radio telescopes can push back the veil of secrecy in celestial objects and reveal information about the location, density and motion of the gases — including hydrogen, which constitutes three quarters of all matter in the universe — in addition to studying Astrochemistry, the chemistry of astronomical objects. It reveals nascent stars forming within the hydrogen columns of gas and dust that create the fingerlike extensions seen in close-ups of nebulae.

Of course, radio astronomy is applicable to all celestial objects and in my example I use IC 434 to demonstrate how these invisible wavelengths of light can help us to examine the structures of the universe. IC 434 is an emission nebula over which a dark absorption nebulosity is laid. The structures of celestial objects beyond the visible spectrum of light are color-coded in Representative Colors (sometimes referred to as false color) by scientists to help them understand the processes and composition of them.

Using the 30m radio telescope near the Pico del Veleta in the Spanish Sierra Nevada, astronomers have discovered hydrocarbon molecules within the Horsehead Nebula. Here on earth, these molecules provide humans with their primary source of energy (in addition to their primary problems of global climate change). Examinations have revealed 30 different hydrocarbon molecules — more than 200 times the total hydrocarbons available on earth! These molecules, like much of the nebula itself are eroded away by the ultraviolet light from the star that powers of nebula.

Microwaves are wavelengths of electromagnetic radiation that range from 1 millimeter to 1 meter in length. Some sources include them within the radio wavelengths of the spectrum, however their name indicates that they are smaller, more compact waves than those of typical radio broadcasts. While microwaves do have applications in communications, such as cellular and satellite, in addition to microwave cooking and radar, microwaves are also emitted by cosmological sources. Radio telescopes, such as the Atacama Large Millimeter \ Submillimeter Array in Chile are able to tune to the smaller wavelengths and study everything from the cosmic microwave background, to galaxy formation, stellar and planetary formation and the composition of planetary atmospheres within solar systems.

In nebulae, such as IC 434, microwave analysis can be used to study protoplanetary systems and their formation and to discover and analyze organic compounds. Combining the light of x-ray and visual astronomy to microwave imaging provides a more complete picture of how galaxies, nebulae, supermassive black holes and all other cosmological objects work. Microwaves can reveal invisible extensions in cosmological objects, such as the outpouring gases from supermassive black holes, in greater detail than other wavelengths of light.

Just below the visible red portion of the spectrum, between wavelenghts of 30 centimeters and 740 nanometers (a nanometer is 1 billionth of a meter),  resides infrared light.  This bandwidth covers more than 1000 times the range of the visible spectrum of light!  We are familiar with infrared light as heat that warms our skin on a sunny day or rises up from our cooking devices. Some sources divide the infrared  portion of the spectrum into several divisions but astronomers generally speak of infrared as near and far.

At the near end of the infrared spectrum lies light of low intensity. We generally use this light for broadcasting through fiber optics and controlling channels from a remote, such as your TV remote. Everything operating at a temperature of about  268°C (514°F) and above emits infrared radiation. More than half of the energy coming from our sun is in the infrared wavelengths. Even the light bulbs in your home emit most of their energy as infrared light.

Infrared light is easily absorbed by water vapor, therefore astronomers have to place telescopes in very high and dry locations in order to be able to detect and analyze the near infrared portion of the spectrum. The far infrared portion of the spectrum never passes through our atmosphere.  Therefore, the best location for analyzing the infrared spectrum is from space-based telescopes. Over the past few decades advances in CCD  imaging has allowed for detailed observations of celestial infrared sources.

Due to its longer wavelengths, infrared light is subject to less scattering through the gases and dust of interstellar space.  This allows astronomers to make discoveries inside of structures such as galaxies and nebulae which would otherwise be obscured by the clouds.  Infrared light can also be emitted by objects that are otherwise too cool to radiate in visible light.  Because of this property astronomers have discovered objects such as the streamers of dust in IC 434 and other nebulae, in addition to asteroids, comets and other objects too cool to be picked up by visible light astronomy.  Infrared detection has allowed astronomers to cut through the dust lanes of the Milky Way and reveal structures on the opposite side of our galaxy. Infrared astronomy is also applicable to the study of planets and Astrochemistry.

In the visible light spectrum, our eyes see IC 434 as a grayscale image. Our eyelids are designed to flicker several times per minute, like the shutter on a video camera, to help us see moving objects;  to avoid becoming prey or to capture prey. This adaptation to survival on planet Earth has rendered us virtually colorblind to deep space objects. Unlike the shutters on our cameras, our eyelids do not remain open long enough to saturate our retinas with the light coming from nebulae such as IC 434.

Our cameras, however, are capable of leaving their shutters open for lengthy periods of time, in addition to being sensitive to fainter emissions, and saturating the photoreceptors of our digital chips with the low intensity light of deep space objects until we can render an image of intense color. This compensation for nature’s adaptation to survive on our planet has allowed us to study and appreciate these cosmological horses of a different color. Where a nebula such as IC 434 is spread out over such a broad swath of space, reducing our eye’s perception of it, our time exposures compensate and gift us with an awesome image that we only wish we were capable of seeing in the full colors of the cosmological palette. Moreover, these colors reveal a great deal about the mechanisms of nebulae and the stars that created them.

Undoubtedly, the discovery of the spectrum and the invention of photography which followed (the discovery of the Camera Obscura not withstanding) led to a craving among scientists to find out whether more secrets of the cosmos lay hidden deep within the invisible parts of the spectrum. Even the early black and white plate photographs revealed previously hidden characteristics of cosmological objects. In addition, the beginning amateur astronomer must realize, at least to some degree, the impact that photography has had upon astronomy. One can only imagine the amazement that astronomers themselves felt when they looked upon those early photographic plates.

But this does not devalue visual observation! In the centuries preceding photography — including the centuries preceding the development of the telescope — careful observation honed the analytical skills of astronomers and opened up a whole new universe to humankind. There is a special visceral experience that only visual observation can offer a type of “seeing is believing”. If you are a casual observer — that is if you are not an astroimager — then you have to tease out details in celestial objects with patience and persistence. IC 434 and the Horsehead Nebula will challenge your patience and persistence.

Another source says that the phrase “A horse of a different color” originated from jousting medieval knights who rode horses of different colors to identify themselves to their supporters — much in same way as modern sports teams wear different uniforms to identify themselves to their fans. The third reference says that the phrase derives from the gambling habits of medieval knights. “A horse of a different color” implied that the opposite gambler or team had won a bet.

Spanning a range of 380 nanometers to 10 nanometers is the ultraviolet portion of the spectrum.  Ultraviolet light falls into a frequency range between visible and x-rays.  We  are familiar with some of this spectrum because of the warnings issued about damage to our skin and cancer.  However, the majority of ultraviolet light does not reach Earth’s surface. Ultraviolet light is divided into three sub-bands: UVA, UVB and UVC (far ultraviolet). The wavelengths from 10-180nm range propagate only in a vacuum and are referred to as extreme wavelengths. UV radiation possesses enough energy to cause atoms and molecules to ionize by stripping off electrons that would otherwise keep them bound to each other. It results in the breakdown of chemicals that would otherwise remain stable.   This makes UV light harmful to life but renders the colorful gases we see in images of nebulas, such as IC 434.

Since most of the UV frequencies are absorbed by the upper atmosphere, ultraviolet astronomy is performed by satellites, either in Earth orbit or in space.  In addition to the sun, numerous celestial objects emit ultraviolet light. Large young stars are a significant source of these wavelengths. Ultraviolet light helps to reveal details in planetary atmospheres and highlight filaments of gas that can be found in nebulas.  Ultraviolet measurements of inter-stellar gas clouds is used to understand densities, temperatures and chemical compositions of stars and galaxies. If the Milky Way galaxy was viewed in ultraviolet light most of the stars would disappear.

My first recollection of the expression “A horse of a different color” is from the 1939 movie the Wizard of Oz, starring Judy Garland as Dorothy. When Dorothy and her dog Toto, along with the Straw Man, the Cowardly Lion and the Tin Man arrive at the gates of the Emerald City they have trouble convincing the guardian of the gates to let them in. They finally convince him that they just have to see the wizard, to which he replies:

“Well, bust my buttons! Why didn’t you say that in the first place? That’s a horse of a different color! Come on in!”

Once inside the Emerald City, they find themselves riding on a horse drawn carriage. The horse changes colors as it pulls them around the city. Dorothy remarks that she has never seen such a horse before and asks the driver what kind of horse it is, to which the driver responds:

“No, and never will again, I fancy. There’s only one of him, and he’s it. He’s the Horse of a Different Color you’ve heard tell about.”

Ranging above the ultraviolet spectrum between wavelengths of 10 nm and one pico meter (a pico meter is one-trillionth of a meter)  are the x-ray bands of the spectrum. X-rays are divided into two categories: soft and hard x-rays. Soft x-rays range in wavelengths of 10 nm to 100 pm and hard x-rays range in wavelengths of 100pm to  1 pm. Hard x-rays reside in the same wavelength of the spectrum as gamma rays. Gamma rays, however, are produced by atomic nuclei while x-rays are produced by the acceleration of electrons.

We are familiar with x-rays in their applications to medical diagnostics. X-rays are also used in the industry. As an astronomical tool, x-rays are used to examine neutron stars, pulsars, black holes or galaxy clusters. Massive, compact stellar remnants such as these strip material from companion stars and create discs of extremely hot gases emitting x-rays, as the gases spiral inward toward the cannibalizing star.

Our sun also produces x-rays within the chromosphere but it is not as strong as source as these other stellar objects. O and Wolf-Rayet type stars create strong solar winds, much stronger than those of the sun. These winds create shockwaves that heat their plasmas, which in turn emits x-rays. Long-term observations of these stars have revealed that the solar winds are confined by magnetic fields.

X-rays are damaging to living tissue. So while they are used in medical diagnostics and applications to the treatment and cure of cancer, they also pose a harmful threat and must be used judiciously. Fortunately for us, our atmosphere absorbs the x-rays from the sun and other celestial sources. The water vapor within our atmosphere is opaque to x-ray photons. As a result, it is necessary for us to build satellites and detect x-rays from orbit or deep space.

Occupying a frequency of less than 100 pico meters, in the hard x-ray range of the spectrum, are the gamma rays. Gamma rays are usually produced through the nuclear reactions of fusion, fission, alpha decay or gamma decay. Astronomers generally define gamma rays by their energies without specifying the processes that created them. Extremely powerful outbursts of gamma rays, known as Gamma Ray Bursts (GRBs) are  energies exceeding those of radioactive decay. Astronomers believe that these GRBs are produced by the collapse of stars into explosions known as hyper-novas.

Because gamma rays are unable to penetrate Earth’s atmosphere — an advantage to life on our planet — it wasn’t until 60 years after their discovery that theory of gamma ray production by cosmological objects was confirmed. In 1963 the United States Air Force launched the Vela satellites with the mission of monitoring nuclear tests by the Soviet Union during the height of the Cold War. The satellites flew at altitudes of up to 65,000 miles above the earth. The Vela satellites carried detectors not only capable of finding gamma rays but determining the direction they were coming from. Much to the scientists’ surprise, they were finding gamma rays from outside of our solar system. They had discovered the first Gamma Ray Bursts (GRBs).

In addition to space-based probes, gamma rays are detected by measuring the interactions of cascades of particles as they pass through the upper atmosphere. Through this analysis, astronomers are able to trace the  gamma rays back to their source of origin.  Astronomers also use gamma ray detection for determining elements on other planets in our solar system. Gamma rays are also produced within the sun when high-energy particles collide with material in the sun’s atmosphere. When cosmic rays strike the surface of the moon they blast apart atoms and molecules within the lunar surface. This also produces gamma rays.

Highly magnetized, spinning neutron stars —  pulsars — produce powerful electrical fields, millions of times more powerful than lightning on earth. These fields create showers of high-energy particles that result in beams of radiation of wavelengths from radio waves through gamma rays. Some of these pulsars are found powering nebulas. M1, the Crab nebula, is powered by a fast rotating pulsar that sends out beacons of  electromagnetic energy.

As amateur astronomers, we have few means at our disposal for examining the entire  electromagnetic spectrum. We do, however, have at our disposal numerous references for studying the universe that is invisible to us. It is our curiosity and passion for astronomy that drives us toward a deeper understanding and appreciation of the celestial objects we view through our telescopes. By combining what we learn about the cosmos with what we see through our telescopes we can employ both our eyesight and  the minds’ eye to really see the vast and incredible universe that unfolds before us  every awakening day.

It is my hope that I have instilled in you a desire to eagerly venture into the cosmos with an insight that will permit you, from this day forward, to see the unseen, to see, as it were, the light.  I am willing to wager that during your next stargazing session your combination of passion, curiosity and love for astronomy will have you seeing all of your subjects as you have never seen them before. That’s a horse I’m willing to bet on.