Astronomy vs. Astrophysics

When I tell people that I study astrophysics, about half of them are awestruck, and the other half of them are completely clueless as to what astrophysics even is. This confusion hasn't escaped the bureaucrats who run the universities that give out degrees for these fields of study. I can't speak for all colleges, but at the University of Colorado Boulder, there is nearly no distinction between astronomy and its cousin field of astrophysics. The differences between the two are subtle, but they were enough for many of my peers to be disgruntled by the fact that the diploma awarded to students who completed an astronomy track and an astrophysics track both have the same label, "astronomy".

However, the skills required to complete both degrees, I would argue, are tantamount to the difference between a degree in psychology and a degree in neuroscience. Each track requires different skills, and while both are valuable and important for humanity's understanding of the cosmos, their rigors are far apart. So if you are a non-scientist, I hope this article will help you not only understand what astronomers and astrophysicists do for a living, but also give you insight when you run into one or the other on the street. Their areas of expertise might vary dramatically.

Astronomy

The core difference between these two branches of science ultimately comes down to one of the core divisions that dichotomizes the sciences as a whole: that of experiment and theory. In chapter 6 of my book, I outline why the practice of science is the most powerful tool humanity has yet devised for understanding how the world works, and how it depends on both experimentation and the interpretation of experiments into scientific theory.

Essentially, science works because it is based on testable, repeatable, and falsifiable observation. Those observations are then interpreted mathematically into scientific theories which can then be used to guide further experimentation. We look at what nature is doing, and try to derive laws that help us not only make predictions about the future, but also manipulate nature to our whims.

However, as we all know, the world is radically complex, and trying to understand how different aspects of nature are related is no simple task. This is where experimentation comes into play. Many of us learn in our high school science classes about dependent and independent variables, and astronomy is virtually the same. The only difference is that astronomers can't control their lab quite as easily, because their lab is the entire universe. So instead, astronomers take very meticulous images, and measure the light emitted or altered by cosmic entities.

The field of astronomy is essentially based entirely around light. But you'd be surprised how much you can learn from just photons. Merely by meticulously observing the light of celestial bodies and the objects they influence, one can deduce the movement, composition, and even the age of those objects, to name a few. Hence, an astronomer is primarily someone who spends most of their professional time at an observatory, taking data through a telescope. This can be through a traditional telescope, which can observe radio or visible bands of light, or through a space telescope, which is best for getting rid of atmospheric turbulence or for viewing high energy radiation that doesn't make it to the planet's surface.

How This Translates to Academia

A student of astronomy focusses their schoolwork on just that. They take the bulk of their classes through their astronomy department. This gives them no shortage of topics they can cover or focus on. Primarily, students will focus their studies on one of two fields; planets and moons, or galaxies.

This division is relatively easy to understand, one focuses on objects within our solar system (which we can actually travel and send probes to), and includes the study of planetary atmospheres, astrogeology, the formation of rings, and the behavior of asteroids and comets. These types of researchers can often get away with using ground based telescopes. In truth, most space telescopes are actually quite terrible at taking data within the solar system, just compare Pluto images taken by The Hubble Space Telescope with the images captured by the New Horizons Satellite.

Astronomers who study galaxies on the other hand, focus their gaze at everything else, from our own Milky Way Galaxy and beyond. They study such things as the evolution of galaxies by observing galaxies merge, to the expansion of the universe itself through observations of the cosmic microwave background. Moreover, in the spirit of observation and experimentation, astronomy majors will often get more practice using telescopes and manipulating astronomical data. They learn the logistics of telescope hardware, and this is often accompanied with a study of optics. This distinguishes them from an astrophysicist, who may never even touch a telescope outside of their backyard.

Astrophysics

If astronomers find themselves primarily on the experimental side of science, astrophysicists tend to lean towards theory. Take everything I described about astronomy, add the advanced mathematics required to be a physicist, and you essentially have an astrophysicist. This is no to say that astronomers don't need to use math, but the degree of comprehension needed by astrophysicists is in a league of its own. A person could be a perfectly accomplished astronomer having done little more than use some algebra and statistical analysis for their data. Perhaps they might need to calculate a derivative or take an integral, but more than likely they can do that with a computer program.

As the title suggests, an astrophysicist takes the observed behavior of celestial bodies, and applies the laws of physics derived on Earth to understand their fundamental nature. Since physics is the most fundamental science that all others are based on, this means applying the laws of motion and interaction to celestial bodies. The most famous example of this is Albert Einstein.

Although often claimed by physics purists, his most famous contribution to science was astronomical, one that explained the universe as a whole. His General Theory of Relativity, which describes how gravity is the result of the way matter and energy warp the fabric of space and time, describes the motion of every object in space. It is paramount for fully understanding not just why planets orbit around stars, but also for understanding the behavior of black holes, and must even be taken into account for our GPS satellites to function properly. It was even verified through an astronomical observation, that of a solar eclipse. This epitomizes the difference between astronomers and astrophysicists. An astronomer needs their telescope. An astrophysicist could potentially be perfectly satisfied with nothing more than a pen, paper, and the fundamental laws of nature.

How This Translates to Academia

As you can probably surmise, getting a degree in astrophysics is fundamentally more rigorous than getting a degree in astronomy, by virtue of the difficulty inherent in studying physics and mathematics. It's more accurate to say that an astrophysics major is really just short of getting a physics degree with some astronomy classes on the side.

While astronomy majors are encouraged to take higher levels of mathematics and physics, they can technically complete their degree without ever going beyond two semesters of calculus and three semesters of physics, which covers special relativity and introduces basic quantum mechanics. That means that most of our classes weren't even with core astronomy majors.

My astrophysics classmates took our courses in tandem with the physics students, which includes two semesters of classical mechanics, two semesters of electricity and magnetism, and one semester of quantum theory. These courses are essentially advanced versions of first year introductory physics, which means they require three semesters of calculus, differential equations, and linear algebra.

I want to emphasize that this should in no way be a put down of astronomers. It's important to note that the practice of astronomy dates long before that of physics. For as long as humans have been around, they have been taking note of the sky and have used it to try and predict events, seasons, and to derive spiritual meaning. It was only by understanding the physical laws of the universe through experiment and calculation here at home could we truly put those observations into context.

So in that sense, I can sort of sympathize with the University bureaucrats who give the same degree to astronomers and astrophysicists. Applying physical laws to the stars is a natural progression of tracking their movement through the sky. The main reason my peers and I were so disgruntled about this injustice is that physics classes are noticeably much harder that astronomy classes, and those were all we really took. But professionally, the two paths aren't so different. Science functions when experiment and theory work harmoniously with one another. Observations are useless unless they can be interpreted, and theories are baseless without peer-reviewed observation.

Honestly, the main reason I would never want to be an observational astronomer is because it requires you to be outside, in the cold, working with metal. And unless you're researching the Sun or using a space telescope, you're work requires you to be up all night. Not to mention the best observing occurs in the winter when the air turbulence is lowest. There are few careers with working conditions as frigid as astronomy. Instead, I ended up working in a planetarium, where I had the power to fly anywhere in the cosmos at my whim. It may not be the real thing, but at least it could play movies. You also don't need a heating blanket.

So the next time you meet an astrophysicist, take heed at what they say. In my experience, physics is what ties the cosmos to the everyday. I may be biased, but in my view it is only with an understanding of mathematics and physics does the majesty of the universe truly come to life, and jump through a telescope to every facet of everyday. True astrophysicists see the world far deeper than a mere astronomer ever could. The least we could get is our own degree, dagnabbit.