What Is Astronomy?

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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, derived from the Greek words for "star law", is the scientific study of all objects beyond our world. It is also the process by which we seek to understand the physical laws and origins of our universe. Both professional and amateur astronomers have interests in understanding the objects in the universe, although at different levels. This article focuses on the work of professionals. 

Pioneers of Astronomy

Over the centuries there have been countless innovators in astronomy, people who contributed to the development and advancement of the science.

Here are some key individuals. Today there are more than 11,000 trained astronomers in the world, men and women who are dedicated to the study of the stars.

Nicolaus Copernicus (1473 - 1543): He was a Polish physician and lawyer by trade, but is now regarded as the father of the current heliocentric model of the solar system.

Tycho Brahe (1546 - 1601): A Danish nobleman, Tycho designed and built instruments of greater power and resolution than anything that had been developed previously. He used these instruments to chart the positions of planets and other celestial objects with such great precision, that it debunked many of the commonly held notions of planetary and stellar motion.

Johannes Kepler (1571 - 1630): A student of Tycho’s, Kepler continued his work, and from that discovered three laws of planetary motion.

Galileo Galilei (1564 - 1642): While Galileo is sometimes credited (incorrectly) with being the creator of the telescope, he was the first to use the telescope to make detailed studies of heavenly bodies.

He was the first to conclude that the Moon was likely similar in composition to the 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): Considered one of the greatest scientific minds of all time, Newton 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): Einstein is 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 for energy.

Edwin Hubble (1889 - 1953): During his career, 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.

Stephen Hawking (1942 - ): Very few scientists alive today have contributed more to the advancement of their fields than Stephen Hawking.

His work has significantly increased our knowledge of black holes and other exotic celestial objects. Also, and perhaps more importantly, Hawking has made significant strides in advancing our understanding of the Universe and its creation.

Branches of Astronomy

There are really 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). You can break down "non-optical" into the wavelength ranges, such as infrared astronomy, gamma-ray astronomy, radio astronomy, and so on. 

Optical Astronomy: Today, when we think about optical astronomy, we most instantly visualize the amazing images from the Hubble Space Telescope (HST), or close up images of the planets taken by various space probes.

What most people don’t realize though, is that these images also yield volumes of information about the structure, nature and evolution of objects in our Universe.

Non-optical Astronomy: There are other types of observatories that function beyond the visible to make significant contributions to our understanding of the universe. These instruments allow astronomers to create a picture of our universe that spans the entire electromagnetic spectrum, from low-energy radio signals, to ultra high-energy gamma rays. They give us 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 us 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.

Planetary Astronomy: 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: while the Sun has been studied for centuries, scientists are interested in learning how it changes, and to understand how these changes affect the Earth.

Stellar Astronomy: simply, stellar astronomy is the study of stars, including their creation, evolution and death. Astronomers use instruments to study different objects across all wavelengths, and use the information to create physical models of the stars.

Galactic Astronomy: the Milky Way Galaxy is 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.

Extragalactic Astronomy: astronomers study other galaxies in the Universe to learn how galaxies are grouped and interact on a large scale.

Cosmology: cosmologists study the structure of the Universe in order to understand its creation.

They typically focus on the big picture, and attempt to model what the Universe would have looked like only moments after the Big Bang.

Updated and edited by Carolyn Collins Petersen.