What Is Astronomy and Who Does It?

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Astronomy concerns itself with stars, planets, and galaxies, and the processes by which they form, live, an ddie. Jay Ballauer/Adam Block/NOAO/AURA/NSF

Astronomy is the scientific study of all objects in space. The word comes to us from the ancient Greek term for "star law." Astrophysics, which is part of astronomy, goes a step further and applies the laws of physics to help us understand the origins of the universe and the objects in it. Both professional and amateur astronomers observe the universe and devise theories and applications to help understand the planets, stars, and galaxies. 

Branches of Astronomy

There are two main branches of astronomy: optical astronomy (the study of celestial objects in the visible band) and non-optical astronomy (the use of instruments to study objects in the radio through gamma-ray wavelengths). "Non-optical" is sorted into wavelength ranges, such as infrared astronomy, gamma-ray astronomy, radio astronomy, and so on. 

Optical observatories operate both on the ground and in space (such as the Hubble Space Telescope). Some, like HST, also have instruments sensitive to other wavelengths of light. However, there are also observatories dedicated to specific wavelength ranges, such as radio astronomy arrays. These instruments allow astronomers to create a picture of our universe that spans the entire electromagnetic spectrum, from low-energy radio signals,o ultra high-energy gamma rays. They give information about the evolution and physics of some of the most dynamic objects and processes in the universe, such as neutron starsblack holes, gamma-ray bursts, and supernova explosions. These branches of astronomy work together to teach about the structure of the stars, planets, and galaxies. 

Subfields of Astronomy

There are so many types of objects that astronomers study, that it is convenient to break astronomy up into subfields of study.

  • One area is called planetary astronomy, and researchers in this subfield focus their studies on planets, both within and outside our solar system, as well as objects like asteroids and comets.
  • Solar astronomy is the study of the Sun. The scientists who are interested in learning how it changes, and to understand how these changes affect the Earth, are called solar physicists. They use both ground-based and space-based instruments to make nonstop studies of our star. 
  • Stellar astronomy is the study of stars, including their creation, evolution, and deaths. Astronomers observe these objects across all wavelengths and apply the information to create physical models of the stars.
  • Galactic astronomy focuses on the objects and processes at work in the Milky Way Galaxy. It's a very complex system of stars, nebulae, and dust. Astronomers study the motion and evolution of the Milky Way in order to learn how galaxies are formed.
  • Beyond our galaxy lie countless others, and these are the focus of the discipline of extragalactic astronomy. Researchers study how galaxies move, form, break apart, merge, and change over time. 
  • Cosmology is the study of the origin, evolution, and structure of the universe in order to understand it. Cosmologists typically focus on the big picture and attempt to model what the universe would have looked like only moments after the Big Bang.

Meet a Few Pioneers of Astronomy

Over the centuries there have been countless innovators in astronomy, people who contributed to the development and advancement of the science. Today there are more than 11,000 trained astronomers in the world dedicated to the study of the cosmos. The most famous historical astronomers are those who made major discoveries that improved and expanded the science. 

Nicolaus Copernicus (1473 - 1543), was a Polish physician and lawyer by trade. His fascination with numbers and the study of the motions of celestial objects made him the so-called "father of the current heliocentric model" of the solar system.

Tycho Brahe (1546 - 1601) was a Danish nobleman who designed and built instruments to study the sky. These were not telescopes, but calculator-type machines that allowed him to chart the positions of planets and other celestial objects with such great precision. He hired Johannes Kepler (1571 - 1630), who started out as his student. Kepler continued Brahe's work, and also made many discoveries of his own. He is credited with developing the three laws of planetary motion.

Galileo Galilei (1564 - 1642) was the first to use a telescope to study the sky. He is sometimes credited (incorrectly) with being the creator of the telescope. That honor probably belongs to Dutch optician Hans Lippershey. Galileo made detailed studies of heavenly bodies. He was the first to conclude that the Moon was likely similar in composition to planet Earth and that the Sun’s surface changed (i.e., the motion of sunspots on the Sun’s surface). He was also the first to see four of Jupiter’s moons, and the phases of Venus. Ultimately it was his observations of the Milky Way, specifically the detection of countless stars, that shook the scientific community.

Isaac Newton (1642 - 1727) is considered one of the greatest scientific minds of all time. He not only deduced the law of gravity but realized the need for a new type of mathematics (calculus) to describe it. His discoveries and theories dictated the direction of science for more than 200 years and truly ushered in the era of modern astronomy.

Albert Einstein (1879 - 1955), famous for his development of general relativity, a correction to Newton’s law of gravity. But, his relation of energy to mass (E=MC2) is also important to astronomy, as it is the basis for which we understand how the Sun, and other stars, fuse hydrogen into helium to create energy.

Edwin Hubble (1889 - 1953) is the man who discovered the expanding universe. Hubble answered two of the biggest questions plaguing astronomers at the time. He determined that so-called spiral nebulae were, in fact, other galaxies, proving that the Universe extends well beyond our own galaxy. Hubble then followed up that discovery by showing that these other galaxies were receding at speeds proportional to their distances away from us. The

Stephen Hawking (1942 - 2018), one of the great modern scientists. Very few people have contributed more to the advancement of their fields than Stephen Hawking. His work significantly increased our knowledge of black holes and other exotic celestial objects. Also, and perhaps more importantly, Hawking made significant strides in advancing our understanding of the universe and its creation.

Updated and edited by Carolyn Collins Petersen.