Astrophysics, what does the comparison of physics and astronomy teach us?

More or less, it has happened to all of us to look at the sky above us and see bright objects such as stars or other planets. How can the condition, location and characteristics of such objects be described using science? Can physics describe a star scientifically for us? This is where we enter the field of astrophysics. In this article, we are going to get acquainted with this branch of science and examine the different fields of work of astrophysicists.

Astronomy, physics and astrophysics

Historians of science believe that astronomy and physics are among the oldest sciences in the world. However, astrophysics, which applies the laws of physics to everything we see beyond Earth, became an official science in the 20th century. Almost everything we know about the universe beyond Earth comes from astrophysics.

Whenever a person observes and records celestial objects, he has actually performed an activity in the field of astronomy. On the other hand, if he applies the laws of physics in the study of this heavenly body, he is involved in the science of physics. For a long time, these two disciplines were thought to be independent of each other with their thousands of years of history. In other words, physics was thought to be used only for terrestrial observations and experiments, and astronomy explored the realm of the heavens.

But today we know that the laws of physics are comprehensive and just as we can rely on them for observations on earth, we can also use them to describe celestial bodies. The laws of physics are the same at all times and places and do not change.

Therefore, astrophysics overlaps astronomy with physics: a field in which everything seen beyond the earth is studied by the laws of physics.

The history of the beginning of this science Johannes Kepler It will return; Because he described the movement of objects in the solar system in the most accurate way possible with his three laws. These rules are:

Planets revolve around the sun in elliptical orbits, and the sun is located in one of the foci of this ellipse. Planets orbiting the sun travel equal distances in equal time intervals. The periodic period of a planet’s orbit is related to the semi-major axis of its orbit.


Interestingly, these laws were experimentally obtained by Kepler and have now been proven to be correct.

after that Isaac Newton With the laws he presented, he caused the birth of astrophysics in a new way. He formulated the law of gravitation – which had been studied before – in a way that it was not limited to terrestrial bodies.

Thus, astrophysics is not exclusively about applying the laws of nature that we discover on Earth to the larger universe, but about using the observations available to us in Cosmos Laboratory is to teach us about the laws and properties of the universe.

Wherever we have a physical system in the universe, physical phenomena are also observed in it, in which we can see the rejection of the laws of physics. It should be said that not all physics is astrophysics, and not all astronomy can be summed up in astrophysics; Rather, astrophysics is the intersection of these two disciplines – the observational science of astronomy and the laboratory science of physics.

Today, the science of astrophysics is divided into four branches in order to understand the truths of the world more deeply. These four branches are:

Theoretical astrophysics: In this branch, the established laws of physics are considered and applied throughout the universe, enabling us to interpret what we observe.

Observational astrophysics: Today, with the advancement of technology, we are able to observe different objects in the universe at different wavelengths. We can even record gravitational waves or the existence of some cosmic particles with more advanced methods. Observational astrophysics helps us in visual knowledge of the universe as much as possible.

Instrumental astrophysics: In order to be able to observe the universe in different wavelengths of light, we need advanced instruments and telescopes. The branch of science in which engineers help scientists build telescopes, cameras, detectors, interferometers, and other observational instruments is called instrumental astrophysics.

Computational astrophysics: This branch has emerged only in the last few decades and involves astrophysical simulations as well as observational data management. Scientists in this branch help fill the gaps in theoretical and observational astrophysics and advance tools such as artificial intelligence and machine learning in the field of astrophysics.


Questions that were once thought to be beyond the realm of scientific inquiry are now in the realm of astrophysics, and in many cases, scientists have even figured out the answers. For thousands upon thousands of years, our ancestors marveled at the vastness of the universe and posed mysteries that they could not solve; But now the answers to most of these questions are available with high accuracy.

Question answering tool

Astrophysicists use various scientific tools to answer the questions raised in this field, and in this section we are going to examine two of them together.

Spectroscopy in astrophysics

Spectroscopy is one of the favorite tools of astrophysicists in identifying celestial bodies and understanding them better. Planets, stars and galaxies are very far away from us and cannot be studied in terrestrial laboratories. But it is possible to obtain valuable information by using the light that reaches our telescopes.

But keep in mind that light cannot be read by itself, and in order to gather information from it, it must be broken down into its various colors – just as raindrops break down sunlight to form a rainbow.

The first astronomical application of spectroscopy in the analysis of light that reaches us from distant objects was done in the 19th century. The white light that reaches us from the sun was expected to produce a perfect rainbow when passing through a prism; But this was not the case and for the first time a pattern of dark lines was also observed in its spectrum. These unexpected lines are like fingerprints; In the sense that these lines represent certain chemical elements that exist in that object (the object whose light has reached us and we examine its spectrum). These lines are called absorption or emission lines.

Spectroscopy also provided the first evidence that stars contain material that exists on Earth. This branch of science proved that some of the gas clouds we saw in the sky are not only nebulae, but galaxies full of stars. In the early 1920s, astrophysicists discovered that stars are mostly filled with hydrogen gas.

Astrophysicists do this using a tool calledspectrometer” They do. Spectrometers are astronomical instruments that do the same job as a prism in a more sophisticated way. spectra on a piece calledCCD» recorded and finally stored in executable files in special computer programs for the purpose of processing and analysis.


The spectrum of a star or any astronomical object not only shows the presence of certain chemical elements, but also informs about physical conditions such as temperature and density. The spectrum can also provide information about the star’s speed using the Doppler effect. With the help of this effect and the displacement of the spectral lines, the speed of the galaxy (star) moving away from the earth can be measured. The spectrum also contains information about the magnetic field present in the object.

Today, most observatories and telescopes in the world are equipped with spectrometers and cover different wavelength ranges. It is interesting to know that the higher the resolution of the spectrum, the greater the dispersion of light and more information can be extracted from the spectrum.


Photometry is one of the techniques used in astronomy to measure the flux or intensity of light emitted by astronomical objects. This light is collected and measured through the “photometer” or “photometer” of the telescope. When a light meter is calibrated against stars that are standard stars of a given color and intensity, they can measure the relative brightness or apparent magnitude of other celestial objects.

The exact methods of performing photometry depend on the wavelength in which we intend to study the celestial body or region. In conventional methods, different filters designed at different wavelengths are used to record the energy and flux of light arriving from a star. in more complex ways than a tool called Spectrophotometer are used to accurately determine the amount of radiation and spectral distribution of the star.

Photometry is also used in the observation of stars whose luminosity changes over time – they are called “Variable starsWe call it – it is used.

So now, in short, we can say that astrophysics is a branch of physics in which astronomical structures and phenomena are studied using the methods and principles of physics. As mentioned, modern astronomy requires a considerable amount of theoretical and observational work. Astrophysicists are interested in determining the properties of dark matter, dark energy, black holes, and other astronomical objects. This amazing science is progressing day by day. The advancement of technology and the construction of larger and more powerful ground and space telescopes will greatly contribute to the significant progress of this science and also to the increase of our knowledge of the universe.

How to become an astrophysicist?

There are many ways to work in astronomy and astrophysics that interested people can pursue even from childhood. For example, people can learn about the sky by attending observatory programs or astronomy classes. But in order to become an astrophysicist, one needs to have a university education in this field. Astrophysics is one of the physics majors in the postgraduate course.

What is the difference between astrophysics and cosmology?

In the science of astrophysics, universal objects are studied individually or as a group – such as a galaxy or a cosmic cluster – and the laws of physics are investigated. In the science of cosmology, they mainly consider the whole universe as a system and analyze its beginning, evolution and end. In simpler terms, we can say that the difference between astrophysics and cosmology is the scale of the universe that is examined.

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