ELEMENTS OF ASTRONOMY AND COSMOLOGY OUTLINE 1. The Solar System The Four Inner Planets The Asteroid Belt The Giant Planets The Kuiper Belt 2. The Milky Way Galaxy Neighborhood of the Solar System Exoplanets Star Terminology 3. The Early Universe Twentieth Century Progress Recent Progress 4. Observation Telescopes Ground-Based Telescopes Space-Based Telescopes Exploration of Space 1 – The Solar System The Solar System - 4.6 billion years old - Planet formation lasted 100s millions years - Four rocky planets (Mercury Venus, Earth and Mars) - Four gas giants (Jupiter, Saturn, Uranus and Neptune) Figure 2-2: Schematics of the Solar System The Solar System - Asteroid belt (meteorites) - Kuiper belt (comets) Figure 2-3: Circular orbits of the planets in the solar system The Sun - Contains mostly hydrogen and helium plasma - Sustained nuclear fusion - Temperatures ~ 15 million K - Elements up to Fe form - Is some 5 billion years old - Will last another 5 billion years Figure 2-4: Photo of the sun showing highly textured plasma, dark sunspots, bright active regions, coronal mass ejections at the surface and the sun’s atmosphere. The Sun - Dynamo effect - Magnetic storms - 11-year cycle - Solar wind (energetic protons) Figure 2-5: Close up of dark spots on the sun surface Probe Sent to Observe the Sun - Distance Sun-Earth = 1 AU - 1 AU = 150 million km - Light from the Sun takes 8 minutes to reach Earth - The solar wind takes 4 days to reach Earth Figure 5-11: Space probe used to monitor the sun Venus - Brightest planet at night - 0.7 AU from the Sun - Hot at 400 oC - Remnant of atmosphere - Rotates in the opposite direction - 1 Venus year = 225 earth days - 1 Venus day= 243 earth days Figure 2-6: Flyby photo of Venus (taken by the Mariner 2 spacecraft) showing a mountainous terrain The Earth Core No Halfnium Core-mantle separation Tungsten Radioactive decay Radioactive decay complete Halfnium Tungsten Radioactive decay not complete Halfnium Tungsten Figure 2-9: The Halfnium-Tungsten decay and its implication that the core-mantle separation happened less than 45 million years after the formation of Earth The Earth Interior 35 700 crust - Mantle formed of silicates (rocks) upper mantle - Core formed of metals (iron, nickel) lower mantle 2885 - Hot temperatures in core (4-5,000 oC) outer core - Lower temps in mantle (> 600 oC) 5155 inner core 6371 - Top crust (ambient to 600 oC) Depth in km Figure 2-10: Schematics showing the Earth’s inner solid core, outer liquid core, mantle and thin curst. The Moon - As old as Earth - Apollo manned missions brought rocks back - The Grail mission Figure 2-7: Photo of the lunar surface showing many craters Mars - Viking missions (1970s) - Rover missions (10 years) - Thin atmosphere of CO2 - Presence of water ice at the poles Figure 2-11: One of the Mars rovers Mars - Lack of magnetic field - Exposed to solar wind - Some chemical analysis was performed - Methane was detected. Is it of a geological or biological origin? Figure 2-14: The Mars Curiosity Science Lab The Asteroid Belt - Spacecrafts do not travel in straight lines - They use the gravity of planets - Ceres and Vesta are large asteroids - The Dawn craft just reached Ceres Figure 2-15: The Dawn craft sent to Asteroid Ceres Jupiter - Contains hydrogen on the outside and helium on the inside - Has 318 times Earth’s mass - It’s a gravitational giant - Galileo spacecraft (1989-2003) Figure 2-16: The Galileo spacecraft that was sent to Jupiter Jupiter - Has distinctive cloud bands (ammonia) - Has 67 moons including Io, Callisto, Ganymede, Europa Figure 2-17: Photo of Planet Jupiter with its distinctive cloud bands. Jupiter - The Juno spacecraft was launched in 2011 - Arrived in 2015 for detailed studies of Jupiter and some of its moons Figure 2-24: The Juno spacecraft is on its way to Jupiter Jupiter - Cassini spacecraft mission - Moon Io contains volcanoes - Ganymede and Callisto contain cores containing rocks and metals Figure 2-19: Close up of Jupiter and its moon Io. A volcano eruption can be seen on Io Saturn - Cassini spacecraft explored Saturn (1997-2017) - Landed Huygens probe on Titan Figure 2-20: The Cassini spacecraft Saturn - Saturn has rings of rocks and ice - Saturn has 62 moons such as Enceladus and Titan - Titan has methane atmosphere and methane lakes Figure 2-21: Photo of Planet Saturn with its rings and of a few of its satellites (moons) passing in front of it (four on the left side and a larger one at the top). Voyager 1 and 2 - Were launched in 1977 - Voyager 2 reached Jupiter in 1979, Saturn in 1981, Uranus in 1986 and Neptune in 1989 - Is crossing the Kuiper Belt which extends to 150 AU - Comets come from the Kuiper Belt - Halley comet (every 75 years) - Sun’s gravity dies out at 125,000 AU = 2 light years Figure 2-25: One of the Voyager spacecrafts Spacecrafts – Solar System Table 2-1: Spacecrafts sent to objects of the Solar System Spacecraft Year Planet Mission Mariner 2 1962 Venus Flyby Mariner 4 and 9 1965 and 1971 Mars Flyby Mariner 10 19974 Mercury Flyby Viking 1 and 2 1976 Mars Orbit, then landing Pioneer 10 and 11 1973 and 1974 Jupiter, Saturn Flyby Apollo Missions 1969-1972 Moon Obit, man landing, returned rocks Voyager 1 and 2 1977 still going, presently Jupiter, Saturn, Uranus, Flyby located at over 100 AU Neptune, etc Galileo 1989 Jupiter and its moons Flyby, orbit, launched probes Cassini 1997-2000s Saturn and its moons Flyby, orbit, launched probes Ulysses 1990 Sun Study solar wind, etc Pathfinder, Global 1990s and 2000s Mars Oribit, landing, surveying Survey and Rover for years Missions Stardust 1999 Comet Flyby, return dust 2 – The Milky Way Galaxy The Milky-Way Galaxy Outer arm Sagittarius arm Perseus arm - Spiral galaxy Sun - Sun is at 26,000 light years from galaxy center Orion spur - Galactic revolution = 120 million years Figure 3-1: Representation of the Milky Way galaxy as viewed in its disk plane. The red dot represents the Sun’s location. The Milky-Way Galaxy Halo Sun Globular clusters - Closest star to the Sun is Alpha Centauri at 4.2 light years Disk Galaxy center - Constellation Sagittarius is Central bulge at the galaxy center - Galaxy center is site of black hole Figure 3-2: Schematics of the profile view of the Milky Way galaxy. It extends to 100,000 light years, has a thickness of some 1,000s and contains hundreds of billions of stars. Well Known Constellations The Little Dipper The North Star Polaris Ursa Minor Ursa Major The Big Bear Figure 3-3: The Ursa Major and Ursa Minor constellations in the Milky Way galaxy have the shape of a pan with handle. Polaris is also called the North Star since it indicates the north. The Kepler Space Telescope - The Kepler Space Telescope mission (2009-2013) Figure 3-4: The Kepler Space Telescope mounted on Delta rocket after launch The Kepler Space Telescope - Sent to monitor 150,000 stars in the Milky Way - From Earth’s orbit - Used ~ 1 m telescope and high-res. CCD cameras Figure 3-5: The Kepler Space Telescope after separation from its launch rocket Exoplanets - Methods for detecting exoplanets: tugging, imaging and transiting - Kepler detected hundreds of exoplanets Figure 3-6: Photo of an exoplanet transiting in front of its star Exoplanets - Hundreds of exoplanets have been identified by the transiting method - Spectroscopy used to identify water and gases essential to life - Zone where water is liquid (habitable or Goldilock zone) Figure 3-7: Data showing dimming of light from a star taken by the Kepler Space Telescope. This indicates the presence of an exoplanet Star Terminology - Stars form from giant clouds of gas and dust. - Gravitational compression raises the temperature. Starts nuclear fusion converting hydrogen into helium that sinks deep. - When hydrogen runs out, the star collapses . Fusion of helium into carbon starts, expands into a red giant. - When helium runs out, the star collapses into a white dwarf (planet size). - Very large stars finish their life cycle in supernovae explosions. - Supernova explosion leaves a neutron star. - Pulsars are small pulsating neutron stars. 3 – The Early Universe Early Telescopes - 1.5 m telescope - Reflection mirror instead of refractive lenses - 1920s - Hubble discovered galaxies - Doppler shifts allow precise measurements of speeds Figure 4-1: The telescope on Mount Wilson Space-Based Telescope - Above the atmospheric blur - Specialized over narrow window of spectrum Figure 4-2: The Wilkinson Microwave Anisotropic Probe (WMAP) Cosmic Microwave Background - In the 1960s Penzias and Wilson discovered the cosmic microwave background - Temperature of the universe around 2.72 K - Radiation left over from the Big Bang - Big Band occurred 13.7 billion years ago Figure 4-3: Infrared image showing the ever slight changes of the temperature of the universe (relative changes of 10-4). This is the black body radiation remaining from the Big Bang measured with WMAP. Anti Gravity and Dark Energy - Dark energy is a form of anti gravity - Dark energy makes the universe expand faster - Accounts for some 68 % of the universe density - Only 5 % of the universe density can be observed Universe is expanding faster – dark matter hypothesis Gravity and Dark Matter - Dark matter is an invisible form of gravity - Can be observed only through its gravitational effects - Accounts for some 27 % of the universe density - Is still not understood - Weakly Interacting Massive Particles (WIMP) - Einstein’s concept of gravity Figure 4-4: Einstein’s concept of gravity as a trough in the space/time fabric located at a heavy object. Attracted objects fall into the trough.