Astronomy 2141 - Life in the Universe, Autumn 2024

SYLLABUS: MWF 3:00-3:55 PM, Smith Lab 1009

The exam questions will be from the material covered in class. The daily topics listed below cover only the main points. Make sure to attend lectures and study powerpoint lecture files below. Exam questions are composed of multiple choice questions to test basic concepts. You are expected to know important facts, figures and the meaning of equations.

DAILY TOPICS

• Jan 8, Monday: Overview of syllabus - Extraterrestrial Life; Basic Astronomy - no proven connection between astrology and astronomy; since stars also move, the position of the Sun relative to the 12 Constellations of the Zodiac changes over centuries and is different from the dates given in the 'horoscope' section of newspapers; science and religion: faith vs. inquiry; ancient astronomy; use of Geometry by the Greeks, belief in the Geocentric system (Aristotle,Ptolemy), Geocentric model (Ptolemy) vs. the Heliocentric model (Copernicus); the Metric system - used in science and in all countries except the U.S.; powers of ten in exponents; Universal spatial and temporal history; observational astronomy.
• Jan 10, Wednesday: Ground and space astronomy - need space observations to cover all kinds of radiation, such as X-ray, UV, etc. that are absorbed by the atmosphere of the Earth. The distance scale; angular size; the Earth moves about 1 degree in its orbit around the Sun each day; basic fundamental constants such as speed of light, 1 AU = (E-S) distance, etc. distance measures in astronomy are the AU and the Light year (LY); parsec - another distance unit is based on the method of parallax.
• Jan 12, Friday: Angular distances; the Earth moves about 1 degree in its orbit around the Sun each day. PARALLAX: apparent change in angular position due to motion; define 1parsec (pc) = 1/alpha(arcseconds), where alpha is the angle usually mesured relative to the orbit of the E-S orbit. The Celestial Sphere - stars 'fixed' in the Sky as a globe; Ecliptic - path of the Sun in the Sky; Celestial Equator - extension of Earth's equator to the celestial sphere; Vernal (Spring) and Autumn Equinoxes and Summer and Winter Solstices, related to seasons. Celestial 'longitude' - Right Ascension, Celestial 'latitude' - Declination, enable the location of an object in the Sky.
• Jan 17, Wednesday: Life: Life in the universe; Definition: DNA - made of common light CHON elements; search for extraterrestrial life - SETI; criteria for existence; organic molecules; Miller-Urey experiment; probability of finding life: Drake equation; physical requirements: solar type stars, number of stars, "intelligence", etc., candidates for life within solar system.
• Jan 19, Friday: Extra-solar planets, recent discoveries; "Hot Jupiters"; techniques for discovering exoplanets; Kepler spacecraft; Habitable "Goldilocks" zone with liquid water. Age, time: astronomical, geological and climate timescales, radioactive dating, half-life.
• Jan 22, 24, 26 MWF: Big Bang, Hubble's law, expansion and age of the Universe, matter, atoms, Periodic Table. GEOCENTRIC MODEL: Ptolemy, Aristotle - All heavenly objects revolve around the Earth, with planets also describing Epicycles that account for the observed Retrograde Motion of outer (Superior) planets; HELIOCENTRIC MODEL (COPERNICUS) - The Sun is at the Center with all planets revolving around it in circular orbits (not quite correct, but basically right); Inferior Planets (Mercury, Venus) - orbits inside the Earth's orbit (inferior and superior conjuction), Superior Planets (Mars,Jupiter,etc.) with orbits outside (opposition and superior conjunction). Eight solar planets: Terrestrial planets (Mercury,Venus,Earth,Mars) with solid surfaces and thin atmospherers compared to Jovian planets (Jupiter,Saturn,Uranus,Neptune) with massive extended atmospheres. Synodic (apparent) and Sidereal (w.r.t. stars) periods of revolution of planets around the Sun; e.g. Synodic period of Jupiter is 399 days, but its sidereal period is 11.9 years. The Copernican System - determination of relative distances of planets from the Sun from the angle of greatest eastern and western elongation (the maximum angular separation of the planet from the Sun as seen from the Earth). TYCHO - the most famous pre-telescopic astronomer; made careful observations of the orbit of Mars. KEPLER's LAWS: First Law - planetary orbits are elliptical with the Sun at one focus; `eccentricity' (ellipticity) e = distance from center to a focus/ semi-major axis. Kepler's Laws (Contd.): Second law - planets trace out equal area triangles in equal time ('equal triangles law'); Third law - P-squared = a-cubed, or P*P = a*a*a, where P is the period in years, and a is the semi-major axis of the orbit in AU. The Earth and the Moon (or any two objects orbiting under gravity) revolve around a common center of mass called the Barycenter that lies 1700 kms inside the Earth. GALILEO: defended the Copernican Heliocentric system; first one to use the telescope; made many discoveries to support the Heliocentric model - phases of Venus, moons of Jupiter, Sunspots; also discovered mountains on the Moon, found that the Milky way is made of stars, etc; Galileo did pioneering experiments on gravity - "all things fall at the same rate regardless of weight or mass".
• Jan 29, 31, Wednesday, Friday: Newton's Law of GRAVITATION - F (grav) = G * (m1*m2)/(r*r), i.e. the force of gravity between two masses is directly proportional to their product, and inversely proportional to the square of the distance between them; your weight is the force of gravity between you and the Earth, i.e. F = G * m(you) * M(Earth) / R(Earth)-squared; the constant G is known as the Universal gravitation constant and is the same for all masses in the Universe. Escape velocity, kinetic and potential energy, orbits, angular momemtum.
• Jan 31, Wednesday: In-class pop-quiz
• Feb 2, Friday: First mid-term exam Quiz 1 (35 min) The Partial Study guide has been posted together with the lecture files on Carmen. It is a summary of the main topics, not a substitute for all the material covered in the lectures and does not correspond directly or entirely to detailed questions on the mid-term exam. Please study both, as well as supplementary reading material.
• Feb 5, Monday - LIGHT and MATTER: spectroscopy, color (wavelength), electromagnetic spectrum - Gamma-Rays to Radio waves in increasing wavelength; Visible spectrum: 4000 - 7000 Angstroms; continuous, emission, and absorption spectra; LIGHT - electromagnetic energy. Spectrum of visible light, blue to red; waves and wavelength. Light does not require a medium to propagate (unlike water or sound waves); particle of energy or quanta are called photons; c = wavelength x frequency; color depends on wavelength. Blue light has higher frequency, hence shorter wavelength, than red light; the e.m. spectrum extends from gamma rays (highest frequency) to radio waves (longest wavelengths); visible light is a small part of the spectrum, from blue (4000 A) to red (7000 A), where A is the Angstrom unit = 100 millionth of a cm. The hotter an object the more energetic ("bluer") its light, and vice versa. Atoms and Light -- photons have energy E = h * nu, where nu is the frequency = c/wavelength (h is called the Planck's Constant); each photon has a definite wavelength and hence 'color'.
• Feb 7, Wedenesday - ATOMS and SPECTRA - Quantum Theory: The positively charged nucleus is surrounded by negatively charged electrons arranged in definite and discrete energy orbits. Electrons can absorb or emit photons at definite energies (wavelengths) equal to the energy difference between orbits e.g. H-atom has one electron and one proton. An electron in H-atom emits a photon at wavelength 6562 Angstroms (red color!) when jumping from the third to the second orbit. SPECTRUM of a source (e.g. the Sun) is its light resolved according to lines at characterstic wavelengths. Emission spectrum is bright `color' lines, i.e. light emitted by atoms at certain wavelengths; and absorption spectrum is dark lines i.e. energy removed by atoms at corresponding wavelengths.
• Feb 9, Friday: Continuous, absorption, and emission spectra from astronomical objects; spectra outside the visible range (say X-ray) is not seen by human eye, but but may be present nonetheless. Hydrogen - Lyman (UV), Balmer (visible), Paschen (IR) series of lines; Red line of H - 6562 Angstroms. Demostration: Emission spectra from fluorescent Tubes with H, He, Ne, Hg, H2O, CO2, Ar. The Sun has a surface temperature of 5600 K and emits its peak light at yellow color. Brightness (luminosity) increases as temperature to the fourth power; brigtness of a source decreases as the inverse of the distance; Inverse Square Law due to geometry -- the area of a sphere increases as 4*pi*radius-squared. DOPPLER Effect, and Red- and Blue-shift. TEMPERATURE: Kelvin and Celsius temperature scales; room temperature is about 300 K. Temperature T of `blackbodies' - perfect radiators and absorbers at one T, with peak radiation at one wavelength.
• Feb 12, Monday: Hubble's Law: v = H_o d --> velocity increases with distance of galaxies; implies expansion of the Universe; H_o is Hubble's constant; 1/H_o is the age of Universe (uncertainty due to measurement of vast distances); Cosmic Microwave Background (CMB); indicates uniform and isotropic expansion; however, recent results show accelerating expansion --> Dark Energy ? Rotation curves of galaxies are flat, rather than decreasing with radius --> Dark Matter?
• Feb 14, Wednesday: Observatories and telescopes; reflecting mirrors and refracting lenses; telescope power = pi*r*r; ground based telescopes such as Large Binocular Telescope (LBT) and space based telescopes such as the Hubble Space Telescope (HST); two main components of a telescope: objective and eyepiece; former is the most important since the main function of a telescope is to collect and focus light through the objective; refracting vs. reflecting telescopes; chromatic aberration of lenses; large telescopes use reflecting mirrors; wavelength ranges of ground and space observatories; ground based radio telescopes at the long wavelength end and gamma-ray space-based observatories at the short wavelength end; spectrographs and spectra.
• Feb 16, Friday: Overview of PLANETS: Terrestrial and Jovian planets; comparison and contrast; unique features of each of the eight planets, and Pluto. EARTH: Atmospheric layers - Troposphere: clouds, planes, weather; Stratosphere: embedded, thin Ozone layer absorbs harmful UV radiation from the Sun; CFC's destroy O_3; Mesosphere: molecules break up into atoms; Ionosphere: atoms break up into charged ions and electrons from the solar UV, reflects radio waves making radio transmission possible; and the Magnetosphere: The magnetic field of the Earth traps highly energetic charged particles, streaming from the Sun in the form of the Solar wind, into huge radiation belts (named Van Allen Radiation Belts) surrounding the Earth, thus protecting the Earth.
• Feb 19, Monday: Greenhouse Effect - visible radiation gets through re-radiated by the surface as heat in the IR, which is then absorbed and by heavy molecules in the atomosphere, mainly H_2O and other compounds such as CO_2, SO_2, i.e. energy from sunlight is retained; delicate balance; increase in pollutants such as CO_2,SO_2 may lead to `global warming'; the 'runaway' Greenhouse effect can lead to extremely hot temperatures, such as on Venus. Earth's geology - primordial icy matter from solar nebula and comets are most likely source of water. Structure of the Earth - crust, mantle, core; crust+upper mantle (lithosphere) "float" on the partially molten mantle; continents and oceans lie on the lithosphere, which is broken into 16 pieces called "plates". Movement of plates - Plate Tectonics - resoponsible for much geological activity such as volcanoes, formation of mountain ranges; plate boundaries - rift zones (e.g. mid-atlantic ridge), subduction zones (e.g. Japan oceanic trench), fault zones (e.g. San Andreas fault); "hot-spot" volcanoes (e.g. Hawaiin islands); magnetic field is due to convective motions of the molten iron core - electromagnet, the dynamo effect.
• Feb 21, Wednesday: The MOON - density 3.34 g/cc, therefore mostly rocky with little metallic iron core; surface has mainly two features: (i) Highlands - old (over 4 billion years), heavily cratered regions formed during early, heavy meteor bombardment, and (ii) Marias - younger regions (up to 3 billiion years); Marias - "lunar seas" - formed with crater impact basins filling up with lava; meteoroid impact on earth; number of craters indicates age: highly cratered regions are older, and lightly cratered regions are younger; lack of atmosphere leads to extreme temperatures, exposure to external material flying in, lack of surface evolution.
• Feb 23, Friday: MERCURY - surface features like the Moon, but high density, about 5.5 gm/cc, more metallic than the Earth with huge solid iron core (but little magnetic field, why?); no atmosphere, hence largest variation in day and night temperatures of any planet (though still less hot than Venus); owing to its high eccentricity (0.26), its perihelion is 1.5 times closer to the Sun than aphelion, therefore receives 1.5 x 1.5 = 2.25 times more solar energy at perihelon (recall the inverse-square law of `brightness').
• Feb 26, Monday: VENUS - hottest planet overall due to "runaway" greenhouse effect; rotates very slowly and backwards; 90 times denser atmosphere than the Earth. The Vanera landers landed on the surface without a parachute!); atmosphere is 96% CO_2 (Mars' atmosphere is also 95% CO_2, but is 90 times lighter than Earth's); little free O_2; sulfuric acid clouds, absorb sunlight that causes fast "jet stream" winds up to 300-400 Kms/hr; little magnetic field due to slow rotation; although has molten iron core like the Earth. Large volcanic planes with "shield" volcanoes associated with hot spots; no plate tectonics; contrast and compare the greenhouse effect on the Earth and Venus.
• Feb 28, Wednesday: 5-question pop quiz#2
• Mar 1, Friday: 35-question mid-term exam#2
• Mar 4, Monday: MARS - Eccentric orbit with e = 0.09; basic statistics: unlike Earth in mass and size, but with significant similarities (day, seasons, temperature); thin atmosphere due to low gravity and mostly CO_2 (95%) like Venus; robotic missions looked for 'life' but no sign (yet?). Polar caps of dry ice (frozen CO_2) and water ice underneath. Perihelion occurs during southern summers, which are hot but short; however, northern hemisphere is warmer with volcanic plains and huge shield volcanoes; southern hemisphere has a geology like the Moon with craters and marias; long ridges and canyons (e.g. Valles Marineris - 5000 Kms long!) are evidence of water flows billions of years ago; Martian dust storms are example of "anti-greenhouse" effect -- warm dusty layer absorbs sunlight and prevents it from reaching the colder surface, causing increased convection feeding the cycle; lessons for "nuclear winter" and extinction of dinosaurs; no sign of life at present (Viking lander experiments); terraforming may be possible; two small moons - Phobos and Deimos (about the size of the Columbus I-270 beltway).
• Mar 6, Wednesday: JUPITER -- largest planet; behaves like a "failed star" - insufficient mass to initiate nuclear fusion, but gravitationally producing energy by compression and expansion. Interior contains mainly H,He, like the Sun and all other Jovian planets; H_2 atmosphere and interior; H_2 in liquid and metallic form; intercomparison of Jovian planets; 2 subgroups: Jupiter and Saturn with metallic H2 interior, Uranus and Neptune much less massive and without metallic H2; temperature and pressure increase much more rapidly in Jupiter with depth than in Saturn; H_2 oceans about 40000-50000 Kms deep; due to high pressures H_2 molecules are tightly packed and electrons can move around like in metals; internal energy source due to self-gravity gives rise to vertical convection resulting in rising or falling material, or alternative bright or dark stripes, called "belts" or "zones". Convection due to fast rotation causes electric currents and a huge magnetic field, about 20000 times stronger than Earth's; rotation period about 10 hrs. Four Gallilean satellites: Io, Europa, Ganymede, and Callisto; Io and Europa are more rocky, rather than icy, in comparison with Ganymede and Callisto; Io has volcanic activity due to tides of Europa and other galilean moon have icy crust and mantle, increasing with distance from Jupier; Europa has some Oxygen in a very thin atmosphere.
• Mar 8, Friday: SATURN - second largest planet; contains smaller metallic mantle than Jupiter and consequently smaller magnetic field; density 0.69 g/cc, less than water; 18 moons; thousands of rings made up of icy-rocky particles; made up of material from moon that either did not form or broke up; "shepherded" by gravitational interaction with small moons in gaps between rings; ring particles are in Keplerian orbits within the Roche limit - tidal stability limit, about 2.5 times the planet's radius; particles in 'gravitational resonance' with the moons are ejected, those remaining in the rings are 'guided' by moons' gravity; Titan is the most interesting moon, only one with a real atmosphere, with about 1.6 times Earth's atomospheric pressure; Titan contains 80% Nitrogen, together with other gases including Oxygen (locked in ice), methane, ethane etc.; also contain organic C-H molecules; Titan is in a primordial state like Earth's in the first billion years; slow chemical evolution due to far colder temperatures; outer moons are heavily cratered, for example Mimas.
• Mar 18, Monday: URANUS and NEPTUNE - Both discovered with telescope; Uranus discovered accidentally, but Neptune's existence was predicted mathematically. Voyager 2 used "Gravity slingshot" effect to explore all outer planets; Uranus and Neptune are "twins" in size and composition; bluish-green due to methane, which is the prime constituent in the atmosphere and mantle - not Hydrogen like Jupiter and Saturn since Uranus and Neptune are not massive enough and H escapes (however Helium is retained). Latest view of Saturn from Cassini: http://www.slate.com/blogs/bad_astronomy/2013/11/12/saturn_incredible_mosaic_of_the_ringed_wonder.html Uranus is tilted at 98 degrees, i.e. rotational axis is in the oribital plane, therefore each pole is tilted towards the Sun for half the orbital period (84 yrs); faint rings of Uranus discovered by occultation of starlight; atmospheres of both Uranus and Neptune extend into the ring systems makeing them unstable; ring particles impact the moons with heavy cratering activity; Uranus's moon Miranda has a bizarre terrain and might have broken up and re-assembled; Neptune has a moon Triton in retrograde rotation, may have been captured; Neptune also has a great black spot like Jupiter's red Triton has a very thin atmosphere and is denser than expected at this distance (2 g/cc), rather than icy like the outer Gallilean satellites, again indicating that it might have been captured.
• In-class popquiz3 and mid-term exam3 will cover some material from on solar planets including Mercury and Venus from the previous period.
• Mar 18, Monday: PopQuiz3 (note this is two classes before exam3)
• Mar 20, Wednesday: Planetarium show during class time
• Mar 22, Friday: Mid-term exam 3: Study guide
• Mar 25, Monday Pluto and Kuiper Belt Objects. Ch. 11, PLUTO: Planetesimal, minor planet, the first of the Kuiper Belt Object (KBOs); discovered in 1930 after long search; WAS the smallest planet, only 0.0022 times the mass of the Earth; has the 'largest' satellite - Charon- relative to the size of the "planet"; Charon is about 8% of Pluto's mass (our Moon is about 1% of Earth's mass); Pluto-Charon form a 'double-planet' system, tidally locked by gravity - each faces the other; Surface T ~ 40 K. Debris of the solar system - Comets,Asteroids, Meteoroids,Meteors,Meteorites; the ASTEROID BELT - rocky and metallic composition; families of asteroids with stray ones that might strike the Earth. METEORITES - small stony, irons, or stony-iron type objects; stony ones have organic material; composition similar to asteroids. A description of the meteorites displayed in claass is: Meteorites Description. The stony-iron meteorite Pallasite is embedded with olivine crystals; olivine is magnesium or iron silicates and very common mineral in the earth. COMETS - dusty ice balls about 1-10 kms; short-period comets (100's years) from the Kuiper Belt beyond the orbit of Pluto, such as Halley's comet with a period of 75-76 years; long-period comets (1000's of years or much longer) from the Oort Cloud; METEORS - icy particles like cometary material; burn up in the atmosphere like "falling stars".
• Mar 27, Wednesday: Stars - Properties and structure of the Sun; State of matter: 99.9% of matter in the Universe is in plasma state (free electrons and protons); 90% of matter is H, 7.8 % is He, and the rest of the elements of the Periodic Table comprise only 2%; stellar energy from thermonuclear fusion of H --> He; stellar structure: core, radiative zone and convection zone; photosphere: visible layer of the Sun; perfect disk appearance and limb darkening - outer layers are cooler and emit less energy than central regions; H- opacity: engative hydrogen ion layer absorbs visible to infrared radiation; than chromosphere, transition region and the corona; flares and mass ejections driven by magnetic activity. elements of the Periodic Table comprise only 2%.
• Mar 29, Friday: Stellar Classification -stars are classified according to color and temperature. Hertzsprung-Russell (HR) diagram of luminosity L vs. temperature T; stellar classification scheme: O,B,F,G,K,M,L - ranging in T ~ 50,000 - 1000 K; numeral subdivision (e.g O5) according to T and strengths of characteristic atomic lines; color depends on peak emission wavelength of blackbody curve corresponding to surface T; Balmer series of H lies in the visible spectrum; stellar spectrum is classified according to strengths of atomic lines (e.g. A stars have strong H lines); stellar luminosity classes: I-V; e.g. the atomic lines (e.g. A stars have strong H lines); stellar luminosity classes: I-V.
• Apr 1, Monday: Sun is a G2V star; L depends on T as well as radius (size) of star; the Main Sequence (MS) of HR diagram reflects that stars: (i) are in H-burning (H-fusion) stage, and (ii) spend most of their lifetimes on the MS; Habitable zones of stars to search for life in exoplanets
• Apr 3, Wednesday: What is life? carbon-based compounds as organic molecules - polymers, carbohydrates, etc.; Bacteria are free-living entities, viruses require a host to live on; properties of life - reproduction and evolution according to environment; natural selection; tree of life - Bacteria, Archaea, Eukarya (which branch are humans?); Eukaryotes; common ancestor to all life on earth - 22 "left-handed" amino acids, which make up proteins that perform structural roles such as stifness in muscles; cell nuclei contain DNA which encodes herediary information; RNA carries out instructions such as making anti-viral antibodies.
• Apr 5, Friday: Planetarium show at class time + 10-point assignment
• Apr 8, Monday: No class; observe solar eclipse and write a short description as assignment.
• Apr 10, Wednesday: Pop quiz 4 Extra-solar planets (exoplanets) and interstellar travel.
• Apr 12, Friday: Mid-term exam 4 online via zoom as usual. Fourth mid-term Quiz 4 Study guide, including material covered from previous mid-term exam3 until Apr 3.
• Apr 15, Monday: Fermi paradox; revisit Drake equation.
• Apr 17, Wednesday: Special lecture on the Sun by Prof. Sultana Nahar Properties of the Sun, related to the material covered in class and stellar physics.
• Apr 19, Friday: Review and Q&A.
• Apr 22, Monday: No class; office hours by appt (please send email)
• FINAL EXAMINATION: April 26, FRIDAY, 4:00-5:45 PM, online via carmenzoom. All comprehensive final exam, 100 multiple choice questions

  Powerpoint files are accessible from the Homepage and pdf files from Carmen

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  Revised: Apr 13, 2024