What Are the Main Branches of Astronomy?

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Humankind has always been intrigued by what lies beyond the Earth’s atmosphere. A desire to understand the secret workings of the universe has influenced many branches of religion, mathematics, and philosophy. The observation and study of space have come a long way, though. Today, it’s encompassed by the science of astronomy.

What Is Astronomy?

Astronomy is the scientific study of the universe beyond Earth, including all celestial objects and related phenomena. Planets, stars, galaxies, their formation, development, motion, physics, chemistry, meteorology, etc., are all part of this science. Astronomy even intersects with other sciences, resulting in interdisciplinary fields like astrobiology.

The term “astronomy” is derived from the ancient Greek word “astronomía,” in which “astron” means star and “nomos” means law. The “law of stars,” or as it’s sometimes translated, “star-arranging,” should not be confused with the similar-sounding term “astrology.” While the former is established science, the latter aims to interpret the influence of celestial bodies on human affairs and bears little scientific significance.

The Branches of Astronomy

Astronomy is considered the oldest natural science. Historically, it was used for various purposes, from navigation through time-keeping to architecture and agriculture. It’s no wonder, therefore, that today this vast science has many branches and even more sub-branches.

We can divide astronomy in various ways. For instance, professional astronomy is often separated into observational and theoretical astronomy. When we look at the specific subfields, however, we’ll find a colorful array of disciplines, ranging from astrochemistry through physical cosmology to stellar, solar, and galactic astronomy. In addition, some academics divide astronomy into four main branches: astrophysics, astrobiology, astrogeology, and astrometry.

Read on to learn more about the main branches of astronomy and some of the most popular subfields.


Astrophysics is not only one of the most significant areas of the scientific study of the universe. It’s also one of the most popular points of interest for those curious about all things celestial.

As the name suggests, this branch studies the physics of the universe. It mainly focuses on the physical properties of celestial objects, alongside their interactions and behaviors. But instead of determining their positions and movement, astrophysics is more interested in uncovering what these objects really are. Essentially, this branch aims to answer how the universe and all these fantastic celestial bodies work. It examines their properties, including their chemical composition, luminosity, temperature, density, etc.

Unsurprisingly, the laws of physics play an essential role in this process. In astrophysics, scientists take the principles of physics (and sometimes chemistry) and apply them in the context of astronomy. As a result, you’ll come across numerous disciplines of physics within astrophysics, from classical mechanics, thermodynamics, and quantum mechanics to relativity and particle physics, among others.

Astrophysics has an enormous scope. Besides having several sub-branches, it can also be separated into observational and theoretical astrophysics. Theoretical astrophysics includes fields such as solar physics, stellar, galactic, extragalactic astronomy, physical and quantum cosmology, etc., some of which will be mentioned in more detail below.


The second major branch of astronomy intersects with another natural science: biology. Astrobiology (exobiology) is an interdisciplinary science that borrows elements from more fields than biology. Chemistry, biochemistry, geology, paleontology, physical cosmology, and exoplanetology play an essential role in the goal of astrobiology—to examine the possibility of life outside our own planet.

Astrobiology is coined from the words “astron,” meaning star, “bios,” meaning life, and “logia,” referring to study. So, essentially, it’s the study of life in the universe. However, astrobiology is concerned with more than just “searching for signs of life” in the vast vacuum of space.

Astrobiology tackles the questions that intrigue us most: Where did we come from? Are we alone in the universe? Is there a chance of life on other planets? In search of answers, astrobiology studies the origin and evolution of life forms on our planet and outside it.

A significant focus of astrobiology is determining the conditions necessary for life to appear on a planet, in addition to the events that kick-start the entire process. Astrobiologists investigate whether other planets can support life. They may also look for environments where water and primitive unicellular organisms could be present.


The next major branch of astronomy takes a more grounded approach to investigate foreign celestial bodies. Astrogeology (planetary geology, surface geology, or exogeology) is a discipline that studies the geology of extraterrestrial objects.

Our geography classes taught us that the “geo-” prefix from the Greek “gē” refers to the Earth. So, while astrogeology doesn’t directly deal with our planet, the Earth’s geology still serves as an important foundation for investigating other planets in the universe.

Essentially, this branch of astronomy examines the physical features of celestial objects in the context of geology. It mainly focuses on terrestrial planets and moons (with a solid surface as opposed to liquid), but these bodies are not its only focus areas. Astrogeology is particularly interested in the composition of asteroids, meteorites, and comets.

This branch studies the internal structure of planets as much as their surface area, including volcanisms, craters, and other similar formations. Planetary geologists use recordings, images, and actual samples to draw conclusions about the geology of celestial bodies.

But why is all this important? Astrogeology is a valuable field of discipline in understanding what makes our planet different from others. How does the composition of other planets compare to the Earth? Does the difference relate to the fact that they can’t support life? Astrogeology can provide real insight into the evolution of our planet and is often a complementary discipline to astrobiology.

Since astrogeology is a similarly wide field of study as the previously mentioned branches, it has many related fields that focus on more specific areas. Some interesting sub-disciplines of astrogeology include the following:


Have you ever wondered why our moon looks the way it does? Selenography (or the topography of the moon) is concerned with the origin of the moon’s physical features.

Details such as the location of its craters and mountain ranges have largely been mapped already, but certain areas still require research. For example, why are the elevations higher on one side of this celestial object than on the other? Selenography has the answers to questions like these.


The branch of astrogeology that studies the Red Planet is called the geology of Mars. It’s also referred to as areology, from the Greek word for this planet, “Arēs.” Although this fierce-looking celestial body has often been the subject of fantasy, it’s pretty well-mapped today. You can explore high-quality interactive maps of Mars thanks to the efforts of areology.

Astronomy Branches

Observational Astronomy

Observational astronomy is another important branch when we look at astronomy based on the technique used for research. As the name suggests, it deals with the observation of celestial bodies and the collection of data. This is in contrast to theoretical astronomy, which uses this data to make calculations regarding physical models.

Observational astronomy uses a variety of tools to record the observable universe. Optical telescopes are one of the key instruments in this discipline. These telescopes are designed to gather enough light to make the subject of the observation visible and magnify the image to overcome the enormous distance between the observer and the subject.

Telescopes are delicate instruments, so large models are placed on unique mounts in purpose-built domes. Stable temperatures and protection from environmental conditions are crucial to the proper functioning of these instruments. While an observatory’s dome shape is efficient at dealing with the wind, the white-painted surface reflects light, so the interior doesn’t get too hot, influencing the telescope image.

Besides optical telescopes, observational astronomy also uses radio telescopes, spectrographs, micrometers, and photography to record the great expanse of space above us. So, naturally, observational astronomy also has many sub-disciplines based on the specifications of the detectors used in them.

  • Radio astronomy
  • Infrared astronomy
  • Optical astronomy
  • High-energy astronomy, such as X-ray astronomy and gamma-ray astronomy
  • Occultation astronomy


The position and movement of the planets have always been of great interest to cultures worldwide. In fact, this is what astronomy mostly comprised of until the 19th century. While we no longer build our cities according to their alignment or believe we are about to experience bad luck in love, these issues remain relevant in astronomy. Astrometry is the branch of astronomy that deals with the position and movement of stars and planets today.

Astrometry is a sub-field of observational astronomy. It investigates the complicated choreography celestial bodies have been executing for billions of years. It provides the kinematics of our Solar System, which can help us understand its origin and evolution and, beyond that, those of the Milky Way.

Astrometry has its roots in the ancient star catalogs astronomers used to keep track of celestial objects. However, astrometry has since become much more advanced. Today, it proves useful in multiple fields. It can give scientists clues in identifying stellar objects, as each has a unique movement pattern. It also plays a role in time-keeping. Astrometry can help extrasolar planet detection and tracking as well.

Planetary Astronomy

Planetary astronomy is a subfield of astronomy, or more precisely, planetary science, that focuses on the celestial bodies inside and outside our Solar System. Despite its name, planetary astronomy doesn’t study only planets. Moons, dwarf planets, and other floating objects like comets and asteroids are also prime subjects of planetary astronomers.

Planetary astronomy studies the surfaces, atmospheres, other exterior features, and the distribution of planets around stars. It also studies planetary systems as a whole. All of this can answer questions like how our Solar System and planets were formed.

But planetary astronomy is not only interested in looking at what’s already there. With careful observations, it also investigates the prerequisites of new planet formation. Planetary astronomy consists of observational and theoretical branches that work together in this process.

The observational aspects of planetary astronomy mainly focus on small planetary bodies in the Solar System. Astronomers use optical and radio telescopes to record the characteristics of these objects. That said, space exploration is a crucial task of observational planetary astronomy, too.

On the other hand, theoretical planetary astronomy focuses on a more dynamic aspect of these planetary bodies. Its work involves mathematical modeling and computer simulations. Each planet in the Solar System has its own branch in planetary astronomy.

Stellar Astronomy

If you’ve ever taken Latin lessons, you probably know that “stella” means star. Stellar astronomy is thus the study of stars – the spectacular luminous spheres illuminating our sky and the universe beyond.

Civilizations have taken an interest in stars since ancient times. But, while they always seemed unchanged in the night sky, scientists later found that stars aren’t as constant as they appear.

How stars are born – and how our sun, the center of the Solar System, came to be – are crucial questions in our study of the sky. Stellar astronomy investigates their constitution, evolution, and what happens when they eventually reach the end of their lifespan. They are also defining pieces of information that help us understand the universe. Stellar astronomy aims to answer these questions despite the distance that separates us from these celestial bodies.

Solar Astronomy

While stellar astronomy deals with stars in general, including the sun, there is also a sub-field explicitly dedicated to the central element of our Solar System. The word “solar” has roots in Latin, with “sol” meaning sun.

The sun is the nearest star to our planet. It’s also the most frequently studied. This 4.6-billion-year-old sphere of blazing hot plasma is one of the critical factors in life on Earth. It’s our most important energy source, so our fascination with its radiant presence is highly justified.

Solar astronomers are interested in understanding the physical processes that characterize this star. Special solar telescopes are used to do so. These were once referred to as heliographs or photoheliographs, with the “helio-” prefix from the Greek word for sun.

Obviously, solar telescopes are used during the day, which can interfere with visibility. As mentioned, temperatures can affect telescopes. In addition, the intensity of focused sunlight a solar telescope endures creates a unique problem. Besides being housed in white-painted structures, solar telescopes also have special heat stops to manage high temperatures.

Galactic and Extragalactic Astronomy

While the previously mentioned branches of astronomy focus on specific celestial bodies, galactic and extragalactic astronomy have a more holistic view of the universe. They are both sub-branches of astrophysics.

Rather than the general principles of galaxy formation, the subject of galactic astronomy is our own galaxy, the Milky Way, and everything in it. On the other hand, extragalactic astronomy focuses on objects and phenomena outside the Milky Way, like other galaxies. Those interested in the general study of galaxies should look into galaxy formation and evolution, a separate field from the two mentioned above.

Our solar system may mean the world to us, but it’s no more than a speck inside a much larger system: the Milky Way. The Milky Way is a galaxy containing countless stars and planets spinning around an ominous black hole. Galactic astronomers study the formation, evolution, and motion of this galaxy. This knowledge doesn’t only help us understand the Milky Way, but it also provides clues about how other galaxies work.

Extragalactic astronomy reaches even further and studies other galaxies in the “Local Group,” of which the Milky Way is also a part.

Physical Cosmology

Finally, while galactic and extragalactic astronomy deal with galaxies near and far, the field of astronomy that addresses the universe is physical cosmology. The name of this science comes from the Greek word “kosmos,” meaning world or universe.

Physical cosmology is concerned with the dynamics of the universe. It provides answers about its origin – with the well-known Big Bang theory – and theorizes about the ultimate fate we are heading towards. Historically, these questions were subjects of philosophy and religion. In fact, physical cosmology is a sub-branch of cosmology (a metaphysical view of the universe) and only developed into the science it is today in the 20th century.

Physical cosmology uses theoretical and applied physics to explain the universe’s various phenomena. However, it also tackles topics like dark matter and dark energy, gravitational waves, and the cosmic microwave background.

Light Years Apart

The starry night sky might be full of questions, but it’s also our gateway to understanding our universe and our place in it.

Astronomy holds the key to this gate, with thousands of years of study and research spanning many different cultures. This discipline has come an amazingly long way considering its subject is physically as far away as it’s ever been. Yet, each branch and sub-branch of astronomy uncovers minute details of the universe that fill us with awe and take us one step closer to what lies beyond the Earth’s atmosphere.

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