Difference Between Astrophysics and Astronomy

Main Difference – Astrophysics vs. Astronomy

Astrophysics and astronomy are both fields of science concerned with studying phenomena taking place beyond the Earth’s atmosphere. There is no clear-cut boundary between the two fields, although a qualitative distinction can be made. The main difference between astrophysics and astronomy is that astronomy is mainly concerned with observing space, whereas the main concern of astrophysics is to apply principles of physics in order to interpret these results. In practice, scientists who make observations are also involved in developing theories, and vice versa.

What is Astronomy

Humans have been interested in observing and understanding the motion of celestial bodies for thousands of years. Galileo’s invention of the telescope was a major milestone. With his telescope, Galileo could observe the skies in great detail. William Herschel, in the late 1700s, started out to systematically catalogue astronomical objects. Better telescopes were continually being built, and it was becoming possible to observe the cosmos with ever-improving detail.

Difference Between Astrophysics and Astronomy - Galileo_moon_observations

Galileo’s drawings of The Moon

Today, astronomical observations are not done solely using visible light. We make observations using many other types of  electromagnetic radiation such as radio waves and x-rays as well.

Observation  is not a simple process either: in order to extract meaningful data, telescopes must be properly calibrated and must use various filters. The data that is taken during observations also need to be processed and analysed using sophisticated algorithms. And, in order to work with the huge amounts of data, astronomers may sometimes enlist the help of public volunteers.

What is Astrophysics

Where astronomy is mainly concerned with the observation, astrophysics is concerned with the explanations of these observations. Classically, the laws of motion described by Kepler and Newton’s law of motion had been remarkably successful at describing celestial objects. In order to explain seemingly small irregularities in Mercury’s motion, Einstein proposed his theory of general relativity, which revolutionized physics. By observing how the light from distance galaxies seem to change as they reach Earth, Edwin Hubble could deduce that the entire that the universe was expanding.

Later, it was confirmed that the universe was expanding at an accelerated rate. Today, astrophysicists believe that about 73% of the universe’s mass-energy content is made up of a mysterious dark energy and 23% to be made of dark matter. Only 4% of the universe seems to be made of the type of matter that we are familiar with. These claims may seem extraordinary. However, they are a direct interpretation of astronomical observations. Indeed, new discoveries that we are making also seem to support these theories.

Difference Between Astrophysics and Astronomy - Galaxy Interaction

A pair of interacting galaxies. In order to describe such complex phenomena, sophisticated mathematical models are required.

Difference Between Astrophysics and Astronomy


Astronomy describes the discipline of observing celestial objects.

Astrophysics describes the application of the laws of physics to describe astronomical observations.

Nature of Discipline

Astronomers are mainly concerned with the instrumentation, collection and subsequent analysis of astronomical data.

Astrophysicists are mainly concerned with the development of mathematical models in order to explain astronomical data.


Image Courtesy

“Galileo’s sketches of the moon from en:Sidereus Nuncius, published in March 1610.” by Galileo [Public Domain], via Wikimedia Commons

“The Advanced Camera for Surveys (ACS), the newest camera on NASA/ESA Hubble Space Telescope, has captured a spectacular pair of galaxies engaged in a celestial dance of cat and mouse or, in this case, mouse and mouse…” by NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA (APOD 2004-06-12) [Public Domain], via Wikimedia Commons

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