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Astrophysics is a fascinating field of science that studies objects and events in the universe. This area of physics is based on observations and experiments since it's challenging to gather and interpret information about celestial bodies. A related field, called cosmology, focuses on developing mathematical models to explain the history of the universe.

What is astrophysics?

To get a better understanding of what astrophysics is, we are going to explore the difference between astrophysics and astronomy.

Astrophysics compared to historical astronomy

The study of celestial bodies has a long and rich history, dating back to ancient times. While some of the approaches to studying the universe were not scientific or physics-based, many significant breakthroughs were made through rigorous scientific investigation. Some historical disciplines in astronomy, like astrology and astronomical theology, focused on human behaviour and the search for divine evidence in the universe. Others, like astronomical musicology, searched for musical structures in outer space.

On the other hand, astrophysics has led to groundbreaking discoveries that have transformed our understanding of the universe. These include understanding the structure of the solar system, creating catalogues of positions and predicted distances of stars and galaxies, and discovering that the light coming from stars is not infinite. These breakthroughs were achieved through scientific observation and experimentation, and they continue to shape our understanding of the cosmos today.

Astrophysics compared to contemporary astronomy

As scientific rigour became more important, the historical disciplines in astronomy lost their significance. Today, astronomers use radiation measurements to study celestial objects, and new paths have opened up to study phenomena beyond physics. These include astronomical biology, geology, and chemistry, which are not fully independent from astrophysics, but broaden our understanding of the universe.

Telescopes are crucial tools in astrophysics for observing celestial objects. Traditional telescopes have limitations as they rely on human measurements and the visible spectrum of light. The Hubble telescope, named after Edwin Hubble, takes measurements in the ultraviolet, visible, and near-infrared regions from orbit around the Earth.

To gather more information about the universe, telescopes that measure other frequencies of light have been developed. These telescopes serve different purposes and vary in characteristics such as size, orientation system, and placement on Earth or in outer space. Observation from outer space is generally more accurate as the Earth's atmosphere interferes with signals. However, some telescopes detecting long wavelengths are too large and expensive to fly into space.

Tianma 65-metre radio telescope at Shanghai Astronomical Observatory
Tianma 65-metre radio telescope at Shanghai Astronomical Observatory

Why are stars relevant in astrophysics? In the early universe, clouds of gas made of hydrogen (the most abundant element in the universe) and some other elements were its primary components. However, gravity, the only relevant force acting on an interplanetary scale, started to pull everything together. When enough mass is pulled together, a fusion process starts, and stars begin to form. Stars are the most common astrophysical objects and, through their fusion processes, act as industries creating the rest of the elements found in the universe, apart from hydrogen and helium. It should be mentioned that the clouds of gas and other elements commonly named ‘space dust’ still fill most of the universe and keep getting attracted to form new stars. Stars are, essentially, the result of a clash between the gravitational force pulling everything inwards and the nuclear fusion reactions happening inside, pushing outwards. When the nuclear fuel runs out, they can turn into supernovas, black holes, white dwarves, etc. However, stars have a very long life, and their study provides a lot of information about the composition of galaxies and larger structures in the universe. Many complex classifications of stars have been developed in order to have a better understanding of the basic constituents of our universe at big scales.

Schema of the layers of a star after a long life of nuclear reactions
Schema of the layers of a star after a long life of nuclear reactions


Summarising what we have reviewed so far, astrophysics is a highly experimental branch of physics that proceeds by means of the observation of data. The gathering of data to construct better models of the universe and its components is an ongoing process that is constantly generating progress in technical aspects, such as telescopes (optics) and signal processing.

Cosmology is the study of the history of the universe, beginning with the very first seconds, but cosmology also attempts to predict its future. Of course, it is fed by evidence gathered by astrophysicists, but it involves many theoretical models, such as general relativity (regarding the expansion of the universe or black holes) or quantum physics (regarding the first seconds of the universe or, again, black holes).

With experimental input from other disciplines, such as chemistry, physics, and mathematics, cosmology’s main goal is to fit the current picture given by astrophysics as an observational description inside the bigger picture of how everything was, is, and will be.


Astrophysics - Key takeaways Astrophysics is the branch of physics that studies processes and structures in the universe, such as stars, galaxies, etc. The universe is studied by many disciplines, not just physics. All these taken together, including physics, constitute astronomy. Telescopes are the basic observational tools in astrophysics. Their most important or relevant characteristic for astrophysics concerns the range of frequencies in which they take measurements. Stars are the most common celestial body in the universe. A lot can be known of galaxies, stellar systems, etc., by studying them. Cosmology is a theoretical branch of astrophysics whose goal is to study and predict the history of our universe.



Frequently Asked Questions about Astrophysics

What is cosmology?

Cosmology is the branch of astronomy and, more precisely, of astrophysics that studies the evolution of the universe, both past and future.

What is quantum cosmology?

Quantum cosmology is the description of cosmology in extreme situations where a quantum treatment is needed, such as the very early stages of the universe.

What is the cosmological principle?

The cosmological principle is a postulate stating that, at sufficiently large scales, the universe looks the same in every direction. The earth, therefore, is not in a privileged place.

What is the difference between astronomy and cosmology?

Astronomy is the study of different phenomena and entities in outer space. It may do so from different perspectives, such as those of chemistry, biology, etc. The branch of astronomy that has to do with physics is called astrophysics, which, in turn, has another subdiscipline called cosmology.

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