🪐Intro to Astronomy Unit 1 – Science and the Universe – A Brief Tour

Key Concepts and Terminology

• Astronomy studies celestial objects, phenomena, and the universe as a whole
• Astrophysics applies physics principles to understand astronomical objects and events
• Cosmology examines the origins, evolution, and ultimate fate of the universe
• Light-year measures distance light travels in one year (9.46 trillion km or 5.88 trillion miles)
• Astronomical unit (AU) equals the average Earth-Sun distance (149.6 million km or 92.96 million miles)
• Parsec approximately 3.26 light-years, used for measuring cosmic distances
• Electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays
  • Different wavelengths provide unique information about celestial objects

The Scientific Method in Astronomy

• Observation gathers data through senses or instruments
• Hypothesis proposes a testable explanation for observations
• Experiment tests the hypothesis under controlled conditions
• Analysis interprets data to support or refute the hypothesis
• Theory provides a well-substantiated explanation of a natural phenomenon
  • Supported by a large body of evidence from repeated observations and experiments
• Scientific laws describe a natural phenomenon that always occurs under the same conditions (law of gravity)
• Peer review process validates research through expert scrutiny before publication

Our Place in the Universe

• Earth is the third planet from the Sun in the Solar System
• Solar System consists of the Sun, eight planets, dwarf planets, moons, asteroids, comets, and other small bodies
• Milky Way galaxy contains the Solar System, a barred spiral galaxy with an estimated 100-400 billion stars
• Local Group includes the Milky Way, Andromeda, and dozens of smaller galaxies
• Virgo Supercluster contains the Local Group and thousands of other galaxies
• Observable universe extends as far as light has traveled since the Big Bang (approximately 93 billion light-years in diameter)
  • Actual size of the universe may be much larger or even infinite

The Scale of the Cosmos

• Astronomical scales range from subatomic particles to the entire observable universe
• Earth's diameter is 12,742 km (7,917.5 miles)
• Sun's diameter is 109 times that of Earth (1.39 million km or 864,000 miles)
• Solar System extends beyond Neptune, including the Kuiper Belt and Oort Cloud
  • Kuiper Belt contains dwarf planets like Pluto and Eris
  • Oort Cloud is a hypothesized sphere of icy bodies up to a light-year from the Sun
• Proxima Centauri, the nearest star to the Sun, is 4.24 light-years away
• Milky Way spans approximately 100,000 light-years
• Andromeda galaxy, the nearest major galaxy to the Milky Way, is 2.5 million light-years away

Stars, Galaxies, and Beyond

• Stars form from collapsing clouds of gas and dust called nebulae
• Main sequence stars fuse hydrogen into helium in their cores (Sun)
• Red giants are cool, expanded stars nearing the end of their lives (Betelgeuse)
• White dwarfs are hot, dense remnants of low to medium-mass stars (Sirius B)
• Supernovae are explosive deaths of massive stars, leaving behind neutron stars or black holes
• Galaxies come in three main types: spiral (Milky Way), elliptical (M87), and irregular (Large Magellanic Cloud)
• Dark matter is invisible matter detected through its gravitational effects on visible matter
• Dark energy is a mysterious force causing the accelerating expansion of the universe

Tools and Techniques in Modern Astronomy

• Optical telescopes gather and focus visible light (Hubble Space Telescope)
  • Refracting telescopes use lenses to focus light
  • Reflecting telescopes use mirrors to focus light
• Radio telescopes detect radio waves from celestial objects (Arecibo Observatory)
• Infrared telescopes observe heat radiation from cool objects (Spitzer Space Telescope)
• X-ray telescopes detect high-energy radiation from hot, energetic sources (Chandra X-ray Observatory)
• Gamma-ray telescopes observe the most energetic photons in the universe (Fermi Gamma-ray Space Telescope)
• Spectroscopy analyzes the composition and properties of celestial objects by studying their spectra
• Adaptive optics corrects for atmospheric distortion in ground-based telescopes

Big Questions and Current Research

• Search for exoplanets and potentially habitable worlds (Kepler mission, TESS)
• Study of dark matter and dark energy to understand the universe's composition and evolution
• Investigation of the early universe and cosmic microwave background (CMB) radiation (WMAP, Planck)
• Exploration of the possibility of extraterrestrial life and intelligence (SETI)
• Research into the nature of black holes and their role in galaxy evolution (Event Horizon Telescope)
• Development of theories to unify quantum mechanics and general relativity (string theory, loop quantum gravity)
• Examination of the universe's ultimate fate (Big Freeze, Big Rip, or Big Crunch)

Real-World Applications and Cool Facts

• GPS satellites rely on general relativity to accurately determine positions on Earth
• Astronomical research has led to advancements in medical imaging, computer processing, and wireless communication
• The Sun loses about 4 million tons of mass per second through nuclear fusion
• The Great Wall of China is not visible from space, but many human-made structures are (Great Pyramids, highways, cities at night)
• If a star passes too close to a supermassive black hole, it can be torn apart in a "spaghettification" process
• The universe is estimated to be 13.8 billion years old based on observations of the cosmic microwave background
• The most distant known galaxy, GN-z11, is 32 billion light-years away due to the expansion of the universe
• Astronomers have discovered a planet-sized diamond orbiting a pulsar (PSR J1719-1438)