What Is Astronomy?

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.

Pioneers of Astronomy

Over the centuries there have been countless innovators that have contributed to the development and advancement of astronomy. Some of these key individuals include:

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:

1. Planets move in elliptical orbits with the Sun at one focus of the ellipse.
2. The orbital speed of a planet varies so that a line joining the Sun and the planet will sweep over equal areas in equal time intervals.
3. The amount of time a planet takes to orbit the Sun is related to its orbit’s size, such that he period, P, squared is proportional to the semi-major axis, a, cubed.

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 form 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).

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: While optical telescopes are sometimes considered the only pure instruments for doing astronomy research, there are other types of observatories that make significant contributions to our understanding of the Universe. These instruments have allowed us 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 Universe’s most dynamic treasures, such as neutron stars and black holes. And it is because of these endeavors that we have learned about the structure of galaxies including our Milky Way.

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, there is still a significant amount of active research conducted. Particularly, scientists are interested in learning how the Sun changes, and trying 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.