What is astronomy?

Astronomy is the study of the universe with particular reference to celestial bodies. The planets, the moons, the sun and other stars, galaxies, etc. all fall under astronomy.

However, astrophysics should not be confused with astronomy, vice versa. Astrophysics is the study of the physics or composition of celestial bodies. Basically, it covers gas, matter, energy, light, etc. that comprises of planets, stars, galaxies, etc. etc.


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 starsand 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.

Branches of  Astronomy:

  • Astrobiology – studies the advent and evolution of biological systems in the universe.
  • Astrophysics – branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior. Among the objects studied are galaxies, stars, planets, exoplanets, the interstellar medium and the cosmic microwave background; and the properties examined include luminosity, density, temperature, and chemical composition.
  • Planetary Science – study of the planets of the Solar System.
    • Atmospheric science – study of atmospheres and weather.
    • Exoplanetology – various planets outside of the Solar System
    • Planetary formation – formation of planets and moons in the context of the formation and evolution of the Solar System.
    • Planetary rings – dynamics, stability, and composition of planetary rings
    • Magnetospheres – magnetic fields of planets and moons
    • Planetary surfaces – surface geology of planets and moons
    • Planetary interiors – interior composition of planets and moons
    • Small Solar System bodies – smallest gravitationally bound bodies, including asteroids, comets, and Kuiper belt objects.

The subdisciplines of observational astronomy are generally made by the specifications of the detectors:

  • Radio astronomy – Above 300 µm
  • Submillimetre astronomy – 200 µm to 1 mm
  • Infrared astronomy – 0.7–350 µm
  • Optical astronomy – 380–750 nm
  • Ultraviolet astronomy – 10–320 nm
  • X-ray astronomy – 0.01–10 nm
  • Gamma-ray astronomy – Below 0.01 nm
  • Cosmic ray astronomy – Cosmic rays, including plasma
  • Neutrino astronomy – Neutrinos
  • Gravitational wave astronomy – Gravitons

General techniques for astronomical research are also convenient ways of dividing the field:

  • Photometry – study of how bright celestial objects are when passed through different filters
  • Spectroscopy – study of the spectra of astronomical objects
  • Astrometry – study of the position of objects in the sky and their changes of position. Defines the system of coordinates used and the kinematics of objects in our galaxy.

Other disciplines that may be considered part of astronomy:

  • Archaeoastronomy
  • Astrochemistry
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