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Astronomy is the scientific study of celestial objects-such as planets, stars, galaxies, and black holes-as well as the phenomena that occur within the observable universe. This field encompasses both observational astronomy, which relies on telescopes like the Hubble Space Telescope to gather data on cosmic bodies, and theoretical astronomy, which uses mathematical models such as Einstein's general relativity to explain their behavior. Key subjects of study include terrestrial planets (e.g., Mars), gas giants (e.g., Jupiter), nearby stars (e.g., Proxima Centauri), massive galaxies (e.g., Andromeda), and supermassive black holes (e.g., Sagittarius A*). Astronomy integrates physics, chemistry, and mathematics to unravel the mysteries of the cosmos, from the formation of celestial bodies to the expansion of the universe.

Modern astronomy is defined by its interdisciplinary approach and advanced observational technologies. NASA leads major initiatives such as the Artemis program, which aims to return humans to the Moon, and ongoing Mars exploration with missions like the Perseverance rover. The European Space Agency (ESA) operates the Gaia mission, mapping over a billion stars in unprecedented detail. Canada's contribution through the Canadian Space Agency (CSA), including its role in the James Webb Space Telescope (JWST), highlights international collaboration.

The JWST, launched in 2021 as Hubble's successor, has revolutionized infrared astronomy by capturing high-resolution images of distant galaxies and exoplanet atmospheres. Meanwhile, groundbreaking detections like GW150914 by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2016 marked the first direct observation of gravitational waves.

The transit method, pioneered by missions like NASA's Kepler Space Telescope, has identified thousands of exoplanets by measuring dips in starlight as planets pass in front of their stars. Research into dark matter and dark energy relies on data from satellites like WMAP and Planck, which map the cosmic microwave background radiation to refine models of the universe's composition.

The heliocentric model, formalized during the Copernican Revolution (16th century), remains foundational. The Big Bang theory is supported by evidence such as Hubble's law and the cosmic microwave background radiation, while stellar evolution is charted using tools like the Hertzsprung-Russell diagram.

Advanced telescopes, space probes, and theoretical frameworks continue to expand humanity's understanding of celestial phenomena, from planetary formation to the fate of the cosmos.

Astronomy has been interpreted through various theoretical frameworks over time, reflecting evolving scientific understanding.

In ancient and medieval astronomy, astronomy-geocentrism-viewpoint dominated, with Ptolemy's *Almagest* (2nd century CE) formalizing a model where Earth was the center of the universe. This viewpoint persisted until the 17th century, when observations by Galileo and mathematical models by Kepler undermined its plausibility.

The astronomy-heliocentrism-viewpoint emerged as an alternative, championed by Nicolaus Copernicus in *De revolutionibus orbium coelestium* (1543), which placed the Sun at the center of the solar system. This paradigm shift was later reinforced by Kepler's laws of planetary motion and Newtonian physics.

The astronomy-steady-state-theory-viewpoint, proposed by Fred Hoyle, Thomas Gold, and Hermann Bondi in the mid-20th century, posited a static, ever-expanding universe without a singular Big Bang origin. It fell out of favor following the discovery of the cosmic microwave background radiation.

- Greek Astronomy - History - geocentrism-vs-heliocentrism-consensus - james-webb-space-telescope-missions - dark-matter-research-debates

1. Nicolaus Copernicus, *De revolutionibus orbium coelestium* (Nuremberg: Johannes Petreius, 1543), https://doi.org/10.5281/zenodo.16405. 2. Edwin Hubble, *The Observational Approach to Cosmology*, The Observatory 59, no. 721 (1937): 1-9. 3. National Aeronautics and Space Administration, “James Webb Space Telescope Overview,” NASA, April 14, 2021, https://www.nasa.gov/mission_pages/webb/overview/index.html.