AST01: Major Historical Events in Astronomy

Major Historical Events in Astronomy

• 1054: Chinese astronomers observed the supernova that formed into Crab Nebula
• 1570: Tycho Brahe conducted a detailed survey of the night sky
• 1609: Johannes Kepler developed the Laws of Planetary Motion
• 1687: Isaac Newton developed the Universal Law of Gravitation
• 1781: Discovery of Uranus by William Herschel
• 1801: Discovery of Ceres by Giuseppe Piazzi
• 1846: Discovery of Neptune by Urbein Le Verrier
• 1930: Discovery of Pluto by Clyde Tombaugh
• 1957: Launch of Sputnik 1
• 1961: Yuri Gagarin becomes the first man in space
• 1965: Discovery of Cosmic Microwave Background
• 1975: Venera 9 becomes the first probe to land on Venus
• 1976: Viking 1 becomes the first probe to land on Mars
• 1977: Voyager 1 and 2 launch
• 2015: New Horizons Pluto Flyby

Astronomy in the Philippines

• 1865: Astronomy in the Philippines started with the establishment of the Manila Observatory (Meteorologica De Manila) in Intramuros by Jesuit Scientists, founded by Fr. Federico Faura
• 1993: Former President Fidel V. Ramos signed Proclamation Decree No. 130, declaring the celebration of National Astronomy Week every third week of February
• 2000: Philippines registered as an Associate Member of the International Astronomical Union (IAU)
• 2019: Philippine Space Agency was established through R.A. 11363

Branches of Astronomy

• Cosmology: focused on the largest structure of the universe, studying its origin and evolution since the Big Bang
• Astrochemistry: focuses on the chemical abundance, reactions, and interactions inside stars, interstellar medium, solar system, galaxies, and the Universe
• Astrobiology: covers the origin, evolution, and future of life in the universe, investigating the possible migration of the human race to other worlds
• Ethnoastronomy/Archaeoastronomy/Historical Astronomy: describes unique practices, beliefs, and traditions of a certain group of people in relation to astronomy
• Astronomy Education: deals with the transmission of astronomical learning, concepts, and knowledge for formal education or community outreach
• Planetology: studies the comparative analysis of the chemical, physical, environmental, astrophysical, biological, and atmospheric inquiry of different planets in the solar system and exoplanets

Conversions in Astronomy

• Light Year: distance traveled by light in one year
• Astronomical Unit (AU): average distance between the Earth and the Sun (149 million kilometers or 93 million miles)
• Parsec: 3.26 light years

Models and Theories of the Solar System

• Laplace's Nebula Theory (1796): the theory states that the solar system began from a huge cloud of gas that collapsed under gravity, flattening to conserve angular momentum, and formed planets by condensation of annular rings around the Sun
• Schmidt-Lyttleton Accretion Theory (1944): the Sun passed through a huge cloud of gas, acquiring matter to form planets, with the material getting focused gravitationally
• Proto-planet Theory (1960): the solar system started with a cloud of dust and gas in a state of hypersonic turbulence, resulting in aggregation of masses at various places
• Capture Theory (1964): the theory considers an interaction between a condensed solar mass star and a protostar of lesser mass, resulting in the formation of planets with planar structure and highly elliptical orbits
• The Solar Nebula Theory (1973): the theory begins with a slowly rotating nebula, with planet formation starting with a disc of 0.01 to 0.1 solar masses
• The Modern Laplacian Theory (1974): the theory starts with a cool gas cloud that condensed, with the angular momentum of the central body being only 1% of the system

Nebulas, Star Clusters, Galaxies

• Galaxies: huge grouping of stars, planets, star clusters, nebulae, black holes, dust, dark matter, and everything else, bound together by mutual gravity
• Types of Galaxies:
  • Lenticular Galaxies (S0 class): with galactic disk, don't have spiral arms, little sign of star-forming activity in their disk, dominated by old red and yellow stars
  • Elliptical Galaxies (E0 circular - E7 elongated): simple ball shape, old stars and globular star clusters, implying that any star formation has long since ended
  • Spiral Galaxies (Sa - Sd (loose)): have vast, rotating discs of stars, dust, and gas, with a ball-shaped nucleus inside a disc with spiral arms
  • Barred-Spiral Galaxies (SBa - SBd): are spiral galaxies in which the spiral arms don't seem to emerge from the galaxy center but from the ends of a linear or football-shaped cloud of stars that straddle the center
• Types of Nebulae:
  • Planetary Nebula: the atmosphere of old stars that started out resembling the Sun but then expelled their outer atmospheric layers
  • Emission Nebula: a hot interstellar cloud, emitting visible light, resulting in a glowing cloud
  • Reflection Nebula: the cloud is not hot enough to emit visible light, dust particles reflect light from nearby stars
  • Dark Nebula: a cloud of dust and cold gas, which does not emit visible light, hiding the stars it contains

Peculiar Galaxies

• Formed due to galactic collisions, resulting in a distorted shape of both galaxies
• Smaller galaxies can collide with a larger one, going straight to its heart

Dwarf Galaxies

• Small, with diameters of only a few thousand light-years or less
• Most abundant type of galaxy in the universe
• Low luminosity and low mass

Low Surface Brightness Galaxies

• Can be as large as other galaxies, but with few stars, making them appear less bright
• Rich in gas, but lack star formation

Galaxy Clusters

• Large-scale structures in the universe, consisting of hundreds to thousands of galaxies bound together by gravity
• Can contain masses equivalent to hundreds of trillions of solar masses
• Rich clusters contain over a thousand galaxies, mostly elliptical and concentrated towards the center
• Poor clusters contain fewer than a thousand galaxies, spread over a larger region

Milky Way Galaxy

Main Parts

• Bulge: contains older, Population II stars
• Disk: contains stars, gas, and dust, with a mix of Population I and Population II stars
• Halo: contains old stars, globular clusters, and significant amounts of dark matter

Star Clusters

• Grouping of stars, bound together by gravity

Gas and Dust

• Interstellar medium (ISM) is composed of 90% hydrogen and traces of helium
• Cold clouds or molecular hydrogen
• Important for star formation and galaxy evolution

Hertzsprung-Russell Diagram

• Plots the temperature of stars against their luminosity (theoretical HR diagram) or color of stars against their absolute magnitude (observational HR diagram)
• Helps determine a star's internal structure and evolutionary stage
• Main sequence stars spend 80-90% of their lives in this stage
• Red giant and super red giant stars have high luminosities, lower surface temperature, and larger radii

Stellar Evolution

• Helium-burning stars
• White Dwarf Stars: the shed-off core of red giant stars
• Nebulas, star clusters, and galaxies are all part of the stellar life cycle

Galaxy Types

• Lenticular Galaxies (S0 class): no spiral arms, dominated by old red and yellow stars
• Elliptical Galaxies (E0 circular - E7 elongated): simple ball shape, old stars and globular star clusters
• Spiral Galaxies (Sa - Sd): vast, rotating discs of stars, dust, and gas, with a ball-shaped nucleus and spiral arms
• Barred-Spiral Galaxies (SBa - SBd): spiral galaxies with a linear or football-shaped cloud of stars straddling the center

Interplanetary Bodies of the Solar System

Asteroid Belt

• Gap between Mars and Jupiter where hundreds of thousands of asteroids orbit the Sun
• Dwarf planet Ceres is located in this region

Kuiper Belt

• Distant version of the Asteroid Belt, extending from Neptune's orbit to beyond 50 AU from the Sun
• Dwarf planets Pluto, Haumea, Makemake, and Eris are located in this region

Oort Cloud

• Surrounds the entire solar system with a shell of frozen bits of ice and rock, stretching out to about a quarter of the way to the nearest star
• Origin of most comets