What does astrophysics mean?
Astrophysics is the branch of science that applies the laws of physics to understand celestial objects and phenomena — stars, planets, galaxies, black holes, and the universe as a whole. Rather than merely charting where objects appear in the sky, astrophysics asks why they behave as they do: what stars are made of, how they generate energy, how galaxies evolve, and what happens inside regions of extreme gravity. The word is used both for the scientific discipline itself and, more loosely, for academic study of it, as in a university department or a degree in astrophysics. Although grammatically it ends like a plural noun, it functions as a singular mass noun: one studies 'astrophysics' as a whole. Closely related to astronomy — so closely that the terms often overlap in everyday use — it carries connotations of rigour, deep theory, and large-scale scientific instruments, from radio telescopes to space observatories. Practitioners are known as astrophysicists.
nounThe branch of astronomy that uses the principles of physics to study the nature, composition, and behaviour of stars, galaxies, and other celestial objects.
- The branch of science applying the principles of physics to the study of celestial bodies and phenomena such as stars, galaxies, black holes, and cosmic radiation.
- (Used attributively or generically) The academic discipline or field of study concerned with such work, as in a degree, department, or journal of astrophysics.
"Her research in astrophysics focuses on how black holes accrete matter from nearby stars."
"Advances in astrophysics have revealed that most of the universe consists of dark matter and dark energy rather than ordinary atoms."
"She completed her doctorate in astrophysics at Cambridge before joining an observatory in Chile."
Although the word ends in -s, it has no separate plural form; it functions as a singular mass noun referring to the field of study as a whole.
"Astrophysics is among the most popular science degrees offered by the university."
Every atom of gold in your jewellery was forged in a cataclysm that astrophysicists can now detect as ripples in spacetime itself.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of astrophysics
Astrophysics combines the Greek roots 'astro-' (from 'astron', meaning star) with 'physics' (from Greek 'physis', nature), literally suggesting 'the physics of the stars'. The compound arose in the nineteenth century, when astronomers began using spectroscopy and other physical techniques to determine the composition and temperatures of stars, marking a shift from purely positional astronomy to the physical study of celestial bodies. Its components connect it to cognates such as astronomy, astrology, astronautics, and the broader family of words built on the Greek root 'astron'.
Related word forms
How astrophysics is actually used
Astrophysics is a formal, scientific term used chiefly in academic, educational, and journalistic contexts; it is treated as a singular mass noun despite its plural-form ending. It overlaps heavily with 'astronomy', and in modern usage the two are often used interchangeably, though 'astrophysics' emphasises physical explanation over observation.
Easily confused with astrophysics
Astronomy is the broader study of celestial objects generally (including their positions and motions), while astrophysics specifically applies the laws of physics to explain their nature and behaviour.