Astronomy is the scientific study of stars, planets, comets, galaxies, and other phenomena that occur outside Earth’s atmosphere (e.g. cosmic radiation). Astronomy deals with the evolution, physics, chemical makeup, meteorology, and motion of celestial objects, and also the formation of the universe. The word Astronomy comes from the Greek words astron (meaning “star”) and nomos (meaning “law”).
Astronomy is one of the oldest sciences. Since the dawn of man, people always looked to the night sky and wondered about the cosmos. Ancient astronomical artifacts have been found from early periods of civilization. However, modern astronomy never would have become what it is without the invention of the telescope. Historically, astronomy has included several subfields and sub-disciplines including observational astronomy, celestial navigation, astrology, and the making of calendars. In more recent times, astronomy has been considered synonymous with astrophysics. The field has also split into two branches (observational astronomy and theoretical astronomy).
Observational astronomy deals with the acquisition and analysis of data, mainly through the basic principles of physics. Theoretical astronomy relies on computer and analytical models to describe celestial objects and phenomena. Both fields compliment each other, with theoretical astronomy explaining observational results, and observational astronomy being implemented to confirm theoretical results.
Astronomy is one science that is not limited to professional scientists. Many amateur astronomers have made important astronomical discoveries. Amateur astronomers still play an active role, especially in the discovery and observation of transient phenomena. Astronomy should not be confused with astrology. Astrology is the belief system that human affairs are linked to certain positions of celestial objects. Although the two sciences share common origins, they are distinct from one another.
Astrophysics is an important part of astronomy that deals with the behavior, physical properties, and dynamic process of celestial objects and phenomena. However, astronomy can actually be called astrophysics as it deals with subjects related to physics. The usual acceptance of this is regarding on if a particular subject is affiliated with a physics department, and if the astronomer has a physics degree or not. By rule, all astrophysicists are astronomers, but not all astronomers are astrophysicists.
In ancient cultures, astronomy was only comprised of observations and predictions of the motions of objects that were visible to the naked eye. Early civilizations assembled massive artifacts (e.g. Stonehenge, the Nazca lines) that most likely served some astronomical purpose. In some cases, these objects were possibly used to determine seasons, length of the year, and when to plant crops. The earliest known tool dealing with astronomy was a device called the Antikythera mechanism (c. 150-80 BC). It was an ancient Greek device used for calculating movements of planets. It was the first ancestor of the astronomical computer and was discovered in an ancient shipwreck near the Greek island Antikythera, in the Aegean Sea. It became famous for its use of a differential gear and its complex parts and mechanisms, both of which weren’t thought to be invented until the 16th to 18th centuries. The original mechanism is displayed at the National Archaeological Museum in Athens.
As cultures developed (e.g. Mesopotamia, Greece, Egypt, Maya, China, etc) astronomical observatories were built and the nature of the universe began to be explored. Most astronomy of early civilizations consisted of mapping the stars and planets. This science is now referred to as astrometry. These early observations led to ideas of how the motions of celestial objects were formed and how the Sun, Moon and Earth reacted to one another. The Earth was believed to be the center of the universe, with all other objects revolving around it. This was known as the geocentric model of the universe.
Astronomy was mostly non-existent in Europe during the Middle Ages until around the 13th century. Observational astronomy was widespread in the Islamic world during these times however, and many contributions to the science were made from prominent Arab astronomers, of which many Arabic names that are now used for individual stars today. Europeans had previously believed that there were no astronomical observations during the pre-colonial Middle Ages sub-Saharan Africa, but modern discoveries have shown otherwise.
A heliocentric model of the solar system was proposed by Nicolaus Copernicus during the Renaissance. His work was expanded upon and corrected by Galileo and Johannes Kepler. Galileo used telescopes to enhance his observations. Kepler was the first to create a system that correctly described the motion of planets with the Sun at the center. Kepler, did not however, succeed in creating a theoretical formula to back his work. Sir Isaac Newton’s invention of celestial dynamics and the law of gravitation finally explained the motions of the planets. Newton is also credited with the development of the reflecting telescope.
With the improvements of the telescope came more and more discoveries by prominent scientists. William Herschel discovered the first new planet (Uranus) in 1781. The distances to stars was first calculated in 1838 by Friedrich Bessel. With the introduction of new technologies (e.g. the spectroscope and photography) in astronomy, considerable advances came into being. Stars were proven to be very similar to our own Sun, but with a wide array of temperatures, sizes and mass. In the 20th century came the discovery of the Milky Way and other unique galaxies. Modern astronomy has also discovered quasars, pulsars, blazars, radio galaxies, and other exotic celestial beings. Cosmology provided evidence of the Big Bang through the advances made by astronomy and physics.
Observational astronomy today is divided according to whatever electromagnetic spectrums of space are being explored. Some of these fields can be studied from the Earth’s surface, while others can only be studied from higher altitudes or even from space. These sub-disciplines are radio astronomy, infrared astronomy, optical astronomy, x-ray astronomy, and gamma-ray astronomy. Other than electromagnetic radiation, few things can be observed from the Earth that originate from deep space. Neutrino astronomy, is a field of astronomy that is studied underground in special facilities that detect neutrinos. These neutrinos are originated from the Sun and other supernovae. Planetary astronomy has benefited greatly from observations of spacecraft and satellites that return from missions in space.
Theoretical astronomy deals with a wide range of tools (e.g. analytical models and numerical models). Each has some advantages. Analytical models are better for giving insight into the heart of what is happening within objects and phenomena. Numerical models reveal the existence of phenomena and other effects that are otherwise not detected. There are several topics studied by theorists. These include: stellar dynamics and evolution, galaxy formation, large-scale structure of matter in the Universe, origin of cosmic rays, general relativity and physical cosmology, including string cosmology and astroparticle physics. Some widely studied theories and models in astronomy, include Big Bang, Cosmic inflation, dark matter, and fundamental physics.
There are a number of subfields of astronomy. These include solar astronomy, planetary astronomy, stellar astronomy, galactic astronomy, extragalactic astronomy, and cosmology. Along with these subfields, arise interdisciplinary fields.Archaeoastronomy is an interdisciplinary field which is the study of ancient or traditional astronomies utilizing archaeological and anthropological evidence. Astrobiology is the study of the evolution of biological systems in the universe and also the possibility of non-terrestrial life. Astrochemistry is the study of chemicals found in space. Cosmochemistry is the study of chemicals found within our Solar System, including the origins of the elements.
There are many questions that arise in the field of astronomy which astronomers seek to find the answers to. Some important questions have remained unanswered, and to answer them correctly new developments in technology may be provide future solutions. Some of these questions are: What is the origin of the stellar mass spectrum? Is there other intelligent life in the universe? What is the nature of dark matter and dark energy? What caused the cosmic inflation that produced our homogeneous universe? What will be the ultimate fate of the universe? It may be decades before any or all of these questions have answers. Some may never be answered.