Presentation on theme: "One purpose of a liberal arts education is to make your head a more interesting place to live inside of for the rest of your life. President McPherson,"— Presentation transcript:
1 One purpose of a liberal arts education is to make your head a more interesting place to live inside of for the rest of your life.President McPherson, Bryn Mawr College
2 PhilosophyKnowledge, and understanding, are wild things, to be hunted down and subdued.Ignorance, stupidity and superstition are infectious, treatable conditions;but their successful treatment requires the cooperation of the patient.
3 IntroductionBooksSyllabusOther stuff you’ll need
4 What is Astronomy? Oldest “science” dating back to ~4000 B.C. First of sciences to be quantitativeUnusually appealing since it’s often observational and outsideModern astronomy is primarily astrophysicsStudy of laws guiding celestial phenomenaStudy of theories which explain celestial phenomena
5 What Astronomy Isn’t Astronomy is not, repeat… not ASTROLOGY Astrology is an ancient religionResults of many studies:No evidence exists that astrology has any predictive power at any statistical level of confidence. Period.But… the records of ancient astrologers have been useful for studying paleoastronomy
6 Some Basic Observations from a Geocentric (Homocentric) P.O.V. Every daySun moves from east to westEvery nightStars move from east to westWhen it can be seen,Moon moves east to west…Slightly slower than the stars
7 Some Basic Observations from a Geocentric (Homocentric) P.O.V. About every month (~28 days)Moon cycles from new to full to newMoon moves ~1 h (15°) east every 24 hWhich means it rises ~1 h earlier every dayEvery nightA constellation sets ~4 min earlierTherefore the sun appears to move from one zodiacal constellation to anotherEvery 12 monthsThe same constellation will be in the south
8 Some Basic Observations from a Geocentric (Homocentric) P.O.V. The ZodiacSun moves along a path through a specific group of constellationsPath = eclipticAries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, PiscesEvery now and then a bright “star” wanders along the ecliptic, gradually moving east, but generally following the stars’ nightly motion.
10 As we proceed through the course, we will jump back and forth through time. We will start with modern thought then take a historical view and work our way back to the 20th century (and beyond).But first….The Persistence of Memory, S. Dali
11 Some Important Definitions Astronomical Unit, AUDistance of 1.5 x 108 km (93 million miles)c = s.o.l.Cosmic speed limit:3.00 x 108 m/s, 186,000 mi/sDistance can be measured by the amount of time the light traveled from an object.Recall d = r x t
12 Some More Important Definitions Light year, lyDistance light travels in 1 yr9.461 x 1012 km (that’s 9.5 trillion km to you and me)That’s… 9,461,000,000,000 km5.879 x 1012 mi (5.9 trillion miles!)Parsec, pcParallax-second (but that’s not important now)3.26 ly
25 Gravitational Collapse Regions with more particles (higher density) become gas cloudsGas clouds become stars and galaxiesGalaxies congregate together in filaments, groups and clusters
26 But we are inside one of these galaxies, so all we see are the nearby stars. We can see other galaxies if we use a telescope
27 The Cosmic Microwave Background Still, limited evidence for a Big Bang. Gamow and Peebles predicted that there should be a “glow” left over from this huge, hot expansion in the microwave region of EM radiation.Objects and even “empty” space give off a characteristic spectrum of electromagnetic radiation depending on their temperature: called “blackbody” radiation. You glow in the infrared.Gamow calculated that if the temperature then was 20,000 degrees; today it would be about 6 degrees.
28 In 1964, the radiation predicted by Gamow was finally detected, with this antenna …antennaPenziasWilson… by Penzias and Wilson, two physicists from the Bell labs, who got the Nobel prize in 1978
29 In fact, the snow that one can see on an untuned TV is also due in part to that radiation emitted by the Universe as it was just 380,000 years old !
30 COBE FluctuationsWilson Microwave Anisotropy ProbeGamow was wrong. It’s not 6 K, but ~2.7 K. This means the universe is older than he predicted.
31 In 1992, the COBE satelite (Cosmic Background explorer) gave the first image of the radiation Before correction of the Earth movement around the Sun Before correction of the microwave radiation emitted by our own galaxy The final image of the microwave Radiation
32 The CMBR and the Copernican Principle The Copernican Principle: The universe should appear the same regardless of the location of the observerJust how homogeneous and isotropic is the universe? Reasonably so for galaxies on scales of 100’s of millions of light years.What about the CMBR?-- the temperature is the same to a part in 10,000 in every direction in the sky!Small variations only observed in Now studied with great precision.
33 Results of detailed nucleosynthesis calculations: More support for BB CosmologyResults of detailed nucleosynthesis calculations:The fraction of the universe made ofBaryons = protons + neutrons
34 Helium Abundance in the Universe More support for BB Cosmology:Helium Abundance in the UniverseAt the late time (as we shall see) of 3 minutes in the history of the universe, atomic nuclei were created.Big Bang theory predicts that the relative abundances of hydrogen and helium were:Hydrogen 76%Helium %Lithium part per 1010Due to nuclear fusion in stars since the Big Bang, current abundances:Hydrogen %Helium %Everything else 1%
35 COMPOSITION OF THE UNIVERSE If 5% of the universe is baryons, what is the rest?From studies of CMBR, of distant supernova explosions, and from Hubble and ground-based observations we know:5% baryons (protons, neutrons)35% dark matter (zero pressure)65% dark energy (negative pressure)
36 A Confusing Picture: Where Do We Stand? We have a good understanding of the history of the universe, both from observations and well understood theory, from t = 180 seconds.BUT:We don’t know why there are baryons at all!We don’t know what constitutes 95% of the energy/matter of the universe.We know that the universe underwent a period of inflation. But we have little idea what inflation is.
37 A Confusing Picture: Where Do We Stand? To answer these questions, we need to know how the universe behaved when the temperature was extremely high. Temperature equates to energy. So we need to know about high energies.Experiments at higher energy accelerators at CERN (Geneva) and Fermilab (Chicago) are testing our understanding at extremely high energy.
38 What do we know?Particle physicists know the laws of nature on scales down to one-thousandth the size of an atomic nucleus. The ``Standard Model”. This corresponds to temperatures about 1,000,000 times those of nucleosynthesis.BUT THIS IS NOT ENOUGH TO ANSWER OUR QUESTIONSExperiments at higher energy accelerators at CERN (Geneva) and Fermilab (Chicago) are testing our understanding at even shorter distances. Expect to discover new phenomena.
41 Summary of Cosmologic Measurements The Big Bang theory is consistent with observations. SpecificallyHubble Telescope can view the universe ~1,000,000,000 years after the Big BangThe COBE satellite can view the universe ~300,000 years after the Big BangThe Hydrogen/Helium ratio can view the universe ~3 minutes after the Big Bang