Week 1: The Sky Above - - Our senses indicate a geocentric model of the universe o Geocentric: Earth is the center of the universe o Obviously not true Geocentric view reinforced religious/philosophical beliefs of the past The Celestial Sphere - - - Zenith: Top of the dome in your field of view Horizon: Where the dome meets the Earth Celestial sphere: Term used to describe star movements like jewels on a sphere Celestial sphere turns because the Earth spins on its axis Celestial Pole: Earth’s north and south poles extended into the celestial sphere Celestial Equator: Same thing, but with the Earth’s equator Motion of celestial sphere depends on your latitude o North pole observers would see stars rotate around the celestial north pole o Equator observers see the stars move from north to south in a straight line) o In between those, stars appear at an angular height Circumpolar zone: Area in which stars do not set below the horizon o Dependent on the viewer’s latitude. Ex. Latitude of 38* places their circumpolar zone at 38* of the north pole Polaris: Most northern star to Earth right now. Barely rotates. Rising and Setting of the Sun - Stars are there during the day, just hidden by the Sun’s brightness Year: Time it takes for the Earth to revolve around the sun once Ecliptic: Sun’s path around the celestial sphere o Sun travels on its ecliptic once a year o Lies at an angle of 23.5, not on the celestial equator Fixed and Wandering Stars - Moon and planets also change positions from day to day “Planet” means “wanderer” in ancient Greek o Sun and moon counted as planets in the past Individual paths of planets and moon lie close to ecliptic o Path of sun, moon, and Earth all nearly in the same plane Zodiac: an 18* wide belt centered on the ecliptic that contains the planets, sun, and moon Constellations - Used in ancient times to navigate o Big dipper, Orion Today we use constellations to divide up the sky into 88 sectors Imaginary line between constellations run north/south, east/west to divide up the sky Asterism: Easily noticeable star pattern within a constellation o Ex. Big dipper inside Ursa Major Week 2: Earth and Sky Locating Places on Earth - - Directions north, south, east, and west are clearly defined on Earth except at the poles. Coordinates on spheres more complicated that on flat surface Great circle: A circle on the surface of a sphere that shares its center with the center of the sphere o Ex: Equator on earth Each of these are called a meridian, longitude o Meridians are perpendicular to the equator o Specify east-west direction based on degree of arc between itself and the prime meridian (0*) o Greenwich chosen as prime meridian because it’s between Europe and USA Latitude: North south location o Degree of arc you are away from the equator along your meridian o Measured from 0 to 90, where 0 is Equator and 90 are the poles Locating Places in the sky - Convenient to make a fake celestial sphere o Celestial equator: Great circle in the celestial sphere that’s lined up with our equator Declination: Measured like latitude Right ascension: Measured like longitude, but with vernal equinox as 0 instead of Greenwich o Vernal equinox: Point in sky where sun’s path (ecliptic) crosses celestial equator o Can be expressed in degrees or time The Turning Earth - Generally accepted that Earth turned, but only proved in 1851 by Jean Foucault o Swung a big ass pendulum from Paris, and the swing shifted not because the pendulum moved by itself, but because the Earth rotated The Seasons - People thought seasons were the result of Earth’s distance from the sun changing o Only deviates about 3% Seasons are caused by Earth’s 23.5* tilt on its axis Seasons and Sunshine - - Axis always points in the same direction no matter what Northern Hemisphere leans into sun in June, and leans away in December o Sun hits us at a more direct angle, heats Earth more effectively o Days also get longer in winter because Sun is higher up than the celestial equator in the summer Summer solstice: Longest day of the year o Sunlight hits the surface in a really straight line Ancient people celebrated summer solstice to thank the gods for warmth o Stonehenge may have been built for this purpose. Poles have 6 months of light followed by 6 months of darkness Clarifications - Although Earth’s horizon blocks our view, atmosphere allows us to see beyond it o Refraction: Bending of light passing through air or water Longest day doesn’t mean hottest day; Earth needs time to heat up Keeping Time The Length of the Day - Day: Amount of time it takes for Earth to spin on its axis once o Also called solar day Sidereal day: Rotation of Earth with respect to the stars o Shorter than a solar day by 4 minutes Apparent Solar Time - Time determined by the actual position of the Sun in the sky o Measured with sundials First half of day where sun has not reached meridian labelled ante meridiem hours (a.m.) Second half where Sun is past meridian labelled post meridiem (p.m.) Simple, but not convenient to use o Solar time does not move at a constant rate because of Earth’s revolution Mean Solar Time and Standard Time - - - Mean solar time: Exactly 24 hours long o Progresses in a uniform rate but inconvenient because it’s determined by the sun’s position o If we followed mean solar time, we would have to adjust our watches every minute when we travelled This is to match to local mean time Larger time zones introduced in 1883 o Standard time followed in each of zones o Local mean time is moved to just the center of those zones o Only need to change times when we move an hour Daylight savings time: Local time +1 hour o “Saves” daylight by making days an hour longer o Actually doesn’t do anything International Date Line - If you go around the world, you’ll eventually be 24 hours ahead of everyone International Date Line solves this problem o Runs down Pacific Ocean, next to Alaska and some islands The Calendar Challenges of the Calendar - - Keep track of time over long periods of time Needs to run on natural time intervals that everyone agrees on o Defined by the motions of Earth, moon, maybe other planets Rotation of Earth: 1 day Length of one month: 29.5306 days Length of one tropical year: 365.24 days Inconvenient rations for calculations Ancient civilizations all used different types of calendars o Stonehenge used to precisely determine solstices o Mayans predicted movements of Venus and stuff o Chinese used the 12 year cycle of Jupiter to come up with their zodiacs Western civilization used Julian calendars, which wrote years to be 365.25 days long The Gregorian Calendar - Julian calendar was only off by 11 minutes, which stacked up after centuries Pope Gregory reformed the calendar to catch up on those missing days Adopted immediately by the Catholic church, but not other branches Week 3: Phases and Motions of the Moon - Moon does not shine on its own, but reflects sunlight Follow the moon and you will see a cycle of phases Lunar Phases - - The Moon rotates around the earth once every four weeks Phases o New: Moon is in same direction as sun, appears invisible to us o Waxing crescent: Moon moves 12* and small crescent shows o First quarter: Moon travelled for a week, covered a quarter of its path, half moon o Waxing gibbous: Moon travels more, illuminates more of its surface o Full: Side of moon that faces sun also faces us Folklore says full moon influences bad behaviour o Waning gibbous: Moon starts to disappear 2 weeks after full phase o Waning crescent: Moon is about to disappear again Seems like eclipses should happen during every full and new moon, but don’t o Moon is 30 Earths away from us, and the moon’s orbit and path of the sun almost never line up. o Eclipses happen when they do Moon’s Revolution and Rotation - Sidereal Month: Length of moon’s rotation around Earth o 27.3217 days Solar month: Time it takes for Moon to go through all phases o 29.5306 days Difference is due to Earth’s revolution around the sun Synchronous rotation: Moon rotates on its axis in the exact same time it takes to revolve around the sun o This means same side of the moon faces us all the time o No such thing as ‘true dark side of the moon’ Ocean Tides and the Moon - Early historians thought tides were caused by the moon Moon’s Pull on Earth - Moon’s gravity pulls on different parts of the earth at the same time Not all parts are equidistant Earth isn’t completely rigid, so differential force makes Earth distort a little o Differential forces stretch earth into a prolate spheroid (football shape) If Earth was 100% water, there would be distortion of 1m o Only 20cm in reality o Force only affects water The Formation of Tides - Tides occur over hours Side of Earth facing moon gets biggest bulge, along with opposite side earth - Moon doesn’t compress, expand, or “lift water” o Water just piles up more where Moon’s pull is stronger When water is deep, tide comes in o When water is shallow, tide goes out Sun also creates tides, but only half as strong o Happens when sun and moon line up (new or full moon) and created tides stack Eclipses of the Sun and Moon - - - Sun is 400 times further away than moon, but also 400 times bigger This makes eclipses possible Eclipse: When either Earth or Moon enters the other’s shadow o Solar eclipse: Earth enters Moon’s shadow o Lunar eclipse: Moon enters Earth’s shadow Shadows made of two parts o Umbra: Darkest cone o Penumbra: More diffused area of shadow o Most spectacular eclipses when object enters umbra If Moon’s path was identical to ecliptic, we would see an eclipse every month o Moon’s tilted orbit of 5* forbids this Solar Eclipses - Most of the time, Moon appears smaller than the sun and makes a ring of light around it (annular eclipse) When Sun and Moon align perfectly, total eclipse occurs on eclipse path, covering a small area o Observers in the penumbra will see partial eclipse o Eclipses don’t last more than 7 minutes Appearances of a Total Eclipse - Solar eclipses start when moon starts silhouetting on the edge of the Sun Moon slowly covers more of sun in partial phase Sun is completely hidden an hour later o Sun’s corona (outer atmosphere) flashes during this phase Total phase ends as moon starts moving out Lunar Eclipses - When the moon enters Earth’s shadow o Visible to anyone that can see the moon, unlike solar eclipse Total lunar eclipse happens when moon enters Earth’s umbra o Lasts longer than solar eclipse because Earth’s umbra is massive compared to the moon Moon starts as full moon before entering umbra, which makes the darkening more dramatic o Moon appears reddish in the umbra because sunlight bends through earth’s atmosphere Week 4: 2.2 Ancient Astronomers - Ancient astronomers in Middle East figured out the 365 day calendar Chinese astronomers kept track of comets, meteors, sunspots, and guest stars Britain astronomers built Stonehenge to keep track of sun, moon, and stars Early Greek and Roman Cosmology - Cosmology: Concept of cosmos Ancient Greeks knew Earth was round - - o Sphere believed to be a perfect sphere, and gods love spheres, so Earth and moon are spheres Aristotle used eclipses to figure out that moon is closer than the sun o Since moon covers the sun it must be closer to the Earth than the sun Figured out Earth is round with lunar eclipses o Edges of the moon’s shadows are round, which means Earth is round too o Can’t be a disc because that means there should be a line shadow on the Moon sometimes Travelling to the south revealed stars that were not visible from the northern hemisphere o If earth was a disc, all stars would be visible everywhere to everyone Aristarchus proposed that the Earth moved around the sun, but this was rejected o Rejected because the stars didn’t move as much Parallax: The apparent shift in an object’s motion as a result of observer’s motion. o Stellar parallax: Apparent shift in star due to Earth’s orbital motion o Was impossible to observe o Either Earth wasn’t moving or stars were ridiculously far away, which philosophers rejected o Earth centered view became dominant philosophy of Western world Measurement of Earth - Eratosthenes measured Earth’s size with observations of the sun Sun is so far away its rays hit us at a parallel line o If sun was closer, it would hit at an angle between the poles Sun isn’t infinitely far away, but 150 million km is pretty damn far On the first day of summer, the sun hit the bottom of the well in Syene. o Sun is directly overhead At the same time, the sun was at a slight angle in Alexandria, 7* (1/50 of a circle) o If sun’s rays are parallel, then this deviation is caused by the curvature of the Earth Alexandria is 1/50 of Earth’s circumference north from Syene, 5000 stadia o Stadium: Unit of measurement based on length of stadium track Earth’s circumference is about 250,00 stadia o If stadium is 1/6 km long, he is off by 1% Precession - - Hipparchus built an observatory on Rhodes to measure position of celestial objects Designated celestial coordinates Also divided stars into apparent magnitudes o Ordered according to brightness (1st is brightest) o Still used, but not as much Discovered that the position of the sky changed over a century and half Also deduced that this change was happening all the time Precession: The motion in which Earth’s axis points change in o Sun and Moon’s pull on Earth make it wobble o Takes 26000 years to make one rotation o Also changes where our axis points over time Ptolemy’s Model - Wrote the Almagest, a compilation of astronomical knowledge Also predicted the positions of planets in any given time Planets’ independent motion made tracking difficult Only using sphere also made this difficult Ptolemy resolved this by using an epicycle o o A small orbit for each planet Also celestial bodies usually move in ellipticals 2.4 The Birth of Modern Astronomy - Astronomy was further enhanced by Muslim and Arab scholars Trades between Europe and Middle East brought these new ideas into Europe, opening a renaissance Copernicus - Famous for introducing the heliocentric model of the solar system o All the planets orbit the sun while the moon orbits the Earth He still assumed that celestial bodies had an elliptical orbit Had convincing arguments for the heliocentric model, but didn’t catch on for a long time o If the Earth is moving how come nothing is moving? The Heliocentric Model - Earth is one of the six known planets in the solar system Copernicus ordered the six planets correctly He couldn’t prove that the Earth revolved around the sun, but said the Ptolemaic view was clumsy and inelegant Heliocentric model was debated for 50 years without having means to test it Galileo - - Galileo studied forces o If it wasn’t for friction, everything would be sliding around o You need force to move around an object, and to stop it o Also studied acceleration Adopted the heliocentric theory Church did not like this theory Galileo’s resistance led to this theory becoming banned by the church Galileo’s Astronomic Observations - - Used telescopes (called spyglasses back them) to look at far away things o Don’t know who came up with this idea Created the 9x magnification telescope, which got him a lot of money and tenured position Originally planned to look at earthly stuff, but turned to the skies o Created a stable mount and increased magnification to 30x o Did experiments to determine what he saw was what was truly there Found stars that he couldn’t see with his eyes, and discovered that Milky way held many stars Tested the Copernican model by observing Venus o Noticed that it had phases like the moon, which meant it revolved around the sun Also observed craters, mountains, and “seas” on moon Put under house arrest by Catholic Church for these findings 3.1 The Laws of Planetary Motion Tycho Brahe’s Observatory - Born into Dutch nobility Made observations of the Sun, moon, and planets for 20 years o Used this data to note the positions of the planets o Couldn’t publish his work because he lacked the connections - Later met Johannes Kepler Johannes Kepler - Born into a poor family, studied at Tubingen and became an assistant to Brahe Had to find a satisfactory theory for planetary movement o Brahe didn’t give him everything he needed because he didn’t want Kepler to take all the glory o Kepler got full access after Brahe died, and worked on this for 20 years First 2 Laws of Planetary Motion - - Orbit: Path of an object through space o Initially thought orbits were circles, but this didn’t work with Brahe’s observations o Conic sections: Curves formed by the intersection of a plane with a cone Focus: Two points inside the ellipses where the sum of the distance from them to the edges are the same Major axis: Widest diameter of ellipse Semimajor axis: Center of ellipse to one end Eccentricity: Ratio between foci and length of major axis Rule 1 : All orbits are ellipses Rule 2: Planets move faster if nearer the sun than further away Kepler’s Third Law Week 8: 3.2 Newton’s Great Synthesis Newton’s Laws of Motion - - Worked on his ideas during the plague years, where he stayed home Published his findings in 1687 as an encyclopedia, Principia Listed three laws that governed the laws of all objects o First law: Objects at rest will stay at rest unless acted on by an external force o Second law: Change in motion is proportionate to and in the direction of the force o Third law: For every action there is an equal and opposite reaction These laws set the stage for modern science Interpretation of Newton’s Laws - - First law: A rewording of Galileo’s conservation of momentum o Momentum: Measure of body’s motion o Also called the law of inertia o Velocity: Speed and direction of motion o Friction slows things down, but with no frictions things will move forever Second law: Force is expressed in terms of ability to change momentum with time o Force has size and direction Third law: Momentum of items must stay constant o Any change in momentum must be balanced by another change to maintain current momentum o Shooting a gun has recoil, because the force of the bullet propelling forward also pushes back at you o This is how rockets work Mass, Volume, and Density - Mass: How much of an object there is Volume: How much physical space an object takes up - Density: How tightly packed an object is Angular Momentum - Measure of rotation of a body as it revolves around a fixed point o Planet orbiting the sun A product of its mass, velocity, and distance from the fixed point o If these quantities are constant then so is the angular momentum Kepler’s second law is about the conservation of angular momentum 3.3 Newton’s Universal Law of Gravitation - - A straight line is the most natural state of motion o But planets move in ellipses Gravity bends their paths o Gravity was associate with just Earth at the time Earth exerts gravitational force upon objects on its surface Newton hypothesized a universal attraction among all bodies in space o Had to figure out this nature of attraction o Limited by the technology of his time, but didn’t give up o This tool is called calculus Gravitational attraction between two bodies must be proportional to their masses Force of gravity on the surface of Earth gives us sense of weight o Weight depends on local force of gravity, unlike mass Gravity is a built in property of mass o Wherever there is mass, they will interact with gravity Gravity never becomes zero, but just gets weaker the further away items are Why to astronauts in ISS look like they’re floating then? o They’re falling o Falling: accelerating at the same rate as everything around them o Astronauts are falling around the Earth, not towards it 3.4 Orbits in the Solar System - Orbit: Path of an object in space under the influence of gravity Perihelion: Place where the planet is closest to the sun, and therefore moves the fastest Aphelion: Opposite of that o For moons: perigee and apogee are used Orbits of the Planets - Kepler’s law states that Mercury has the fastest orbit since it’s the closest while Neptune has the longest since it’s the furthest All planet orbits have low eccentricity Orbits of Asteroids and Comets - Asteroids and comets: small chunks of leftover material in the solar system Asteroids generally have smaller semimajor axes than comets o Most of them lie in the asteroid belt between Mars and Jupiter Comets generally have larger and more eccentric orbits than asteroids Week 9: 18.4 The H-R Diagram Measuring Star Characteristics - - - Surface temperature o Determine colour o Measure spectrum and get spectral type Chemical composition o What lines are present in spectrum Luminosity o Measure brightness, compensating for scale Radial velocity o Measure doppler shift in spectrum Rotation o Measure with of spectral lines Mass o Measure period and redial velocity curves Diameter o Measure how star’s light is blocked by moon o Measure light curves and doppler shifts for eclipsing binary stars Henry Russell plotted luminosity of stars based on their spectral classes o Discovered that temperature and luminosity are related Features of the H-R Diagram - - - - A scale used to chart stars based on luminosity and spectral class o Named after Hertzsprung and Russell Stars line up on ‘main sequence’ o Line of best fit that shows relationship between temperature and luminosity o More luminous stars are hottest Some stars lay beyond it o Supergiants are cool, but appear bright due to their size. o White dwarves are small and hot, but appear dim due to their size Incomplete collection of data o Many stars are too faint to be observed o Not many giants and dwarves that we can observe 90% of stars are on the main sequence o Stars spend 90% of their lives here Understanding the Main Sequence - Suns convert hydrogen into helium through nuclear fusion, creating energy If all stars are doing this then why are they distributed on a sequence of points? o Total mass and composition of star determine energy made from nuclear fusion Bigger stars are brighter because they have more mass, which means more fuel to burn and more nuclear fusion to take place 90% of stars follow this Stars of the Extreme Ends - Cool super giants are brighter and larger than the sun Cool dwarf stars are smaller than the sun, but super dense White Dwarves - First white dwarf discovered in 1862 7% of stars in our neighbourhood are white dwarves Bright for its size, which means its super dense 20.5 Cosmic Life Cycle Flows in Interstellar Gas - It’s not static o Orbits the galaxy and can change in density, temperature, and state of ionization Majority of interstellar gas in Milky Way is hydrogen Dense molecular clouds are 30% of total mass between stars Hot gas from supernovas contribute a little bit Dust falls onto milky way all the time because of gravity Giant gas clouds can collapse to form new stars o When they die they expel material outwards o This process is called the baryon cycle The Cycle of Dust and Heavy Elements - - Stars fuse heavier elements from lighter ones Lose some newly made material in the process Dust grains get bigger when they spend more time in interstellar medium, where they stick together and get bigger Eventually covered in ice, which protects molecules on the inside from breaking up due to radiation Newly formed stars melt the ice, and the grains combine to create planets and stuff o Some scientists say Earth water came from space o Or it was brought over by asteroids Interstellar grains are incorporated into new stars and destroyed, but cycle begins again when the star goes supernova 22.1 Star Evolution - - - Left side of H-R Sequence called zero age main sequence o Zero age: When a star stops contracting and starts fusing hydrogen in the core o Continuous line that shows stars of different masses Fusion doesn’t change mass of star since it only uses 0.7% of hydrogen As hydrogen depletes, helium accumulates o This changes luminosity and temperature o Moves to the right on the H-R diagram As helium accumulates, temperature and density increase in the center region of star Lifetimes on the Main Sequence - - How long a star remains on the main sequence depends on its mass Star lifetime determined by how much nuclear fuel it has and how quickly it uses it up o Rate of fusion strongly depends on star’s core temperature o Temperature of star core depends on mass o This is why massive stars don’t last as long as smaller stars We look for sun-like stars when searching for aliens, because it gives time for complex organisms to evolve From Main Sequence to Red Giant - - All the hydrogen in a core will be used up eventually Core is now only helium contaminated with heavier elements the star started with No more energy since hydrogen is gone and fusion of helium needs higher temperatures Core contracts when it cools o Energy of collapsing material creates heat o This heat flows outward, where it heats up the hydrogen layer around the core o New energy heats up outer layers, causing it to expand Star become cooler and brighter at the same time o Move to top right on H-R sequence Week 10: Stars - Collect light from each star to measure its spectrum of light o Used as a unique fingerprint for each star Every combination of atoms absorb light differently Used for DNA analysis Spectral Classes and Temperature - From hottest to coldest: OBAFTKM Our sun is G2 Week 11: 7.1 Overview of Our Planetary System - Solar system consists of the sun and many other things All these things formed 4.5 billion years ago Clumps of material that condensed from an enormous cloud of gas and dust, and center became sun We sent probes all across the solar system An Inventory - Sun is the most massive part of solar system o 99.8% of all mass in solar system Jupiter is 0.1% o More massive than all other planets combined Trans-Neptunian objects: Smaller worlds beyond Neptune o Largest ones are dwarf planets, like Pluto All planets and dwarf planets spin on an axis and rotate in the same direction around the sun o Except Venus (retrograde direction) 4 planets closest to the Sun are terrestrial planets Next 4 are giant planets Smaller Members - More than 180 known moons in solar system Gas giants also have rings around them Asteroids: Rocky bodies that orbit the sun, mostly between Mars and Jupiter 7.4 Origin of Solar System - Superearth: Large, earthlike exoplanets Looking for Patterns - - All our planets like in nearly the same plane and revolve in the same direction around the sun Sun also spins on its own axis o This is interpreted as evidence that Sun and planets formed in a spinning cloud of gas and dust called solar nebula Composition of planets is another clue o Sun, Jupiter, Saturn made up of hydrogen, which means they’re from the same reservoir o Terrestrial planets made of heavier elements o This is because it’s close to the Sun, and its heat removed gas closer to it The Evidence from Far Away - Younger solar systems resemble ours when it was younger o Circumstellar disks: Flat clouds of spinning gas that revolves a star Building Planets - Planetesimals: Small proto-planets Planet forming process was violent o All planets were heated until they were liquid and gas o This process explains many regularities but not many irregularities Week 12: 30.1 The Cosmic Context for Life What made Earth hospitable to life? - Dust and stuff combining to form Earth a long time ago eventually collected a lot of water Chemical variety and moderate conditions led to creation of molecules that could reproduce by dividing Many different species of life came and went, bringing us to the present Atoms in our body are from space o We are stardust The Copernican Principle - Earth isn’t in the middle of anything, doesn’t look that special Planets are natural formations Copernican Principle states that there is nothing special about the Earth Are we an exceedingly rare outcome of cosmic evolution or is life normal So where are they? - Fermi paradox: If life is common then how come it doesn’t look like it? o Maybe life is common, but intelligence isn’t o Maybe communication systems will form in the future o Streams of data pass by us because we can’t detect them o Sophisticated aliens don’t meddle with primitive lifeforms like us o Other civilizations reached a self-destruct point in their development 30.2 Astrobiology - Study of biology in an astronomy context The Building Blocks of Life - Have been found in extraterrestrial environments - - Amino acids: Organic compounds that are the molecular building blocks of protein o Protein: Molecules that make cells work Many organic molecules found in space by radio telescopes Miller Urey experiment: 1950s experiment where Earth’s early atmosphere was simulated to create building blocks o They got the atmosphere wrong Possible that Earth’s life was seeded from the stars o Still doesn’t explain where that came from Origin and Early Evolution of Life - Genes in the simplest organisms are made of millions of molecular units o A giant step away from regular molecules Little direct evidence of what Earth was like early on, or of where life came from After heavy bombardment, ingredients were there to make living organisms DNA: Stores genetic information about living organism RNA: Helps flow of genetic information from DNA to proteins Photosynthesis: Ability of creating energy from light o Could’ve helped create oxygen rich atmosphere in the beginning Stromatolites: Believed to be fossils of photosynthesizing bacteria from the past Increasing oxygen in atmosphere hurt some microbes that didn’t need it to develop, but allowed other ones to generate huge amounts of energy with it Habitable Environments - An environment capable of hosting life Life needs a solvent that enables construction of biomolecules and interactions between them o Water is the solvent Identifying water crucial to finding habitable worlds Our biochemistry is based on CHNOPS (Carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur) o All of these are formed inside stars Elemental raw materials and solvent set, now we need assembly Life in Extreme Conditions - - - Humans have a narrow range of operation, but life has a large range as a whole Extremophile: Organisms that live in environments that would kill other organisms Thermophile: Organisms that live in high temperature environments Heat and cold can both be detrimental to life o Cold slows down metabolism and changes molecules Acidity level also affects survivability o Acidophiles: Microorganisms that live in acid o Alkaliphiles: Microorganisms that live in bases High salt levels also a problem for life o Salt blocks cellular functions o We used this knowledge to salt meat and prevent microbe growth High pressure compresses molecules, but some animals do fine Same with radiation 30.3 Searching for Life Beyond Earth - Biomarker: Evidence of life on a planet Life on Mars - Mars thought to have water, even life in the past o We didn’t find either early on Curiosity found existence of habitable environments on Mars o Found mudstone Mars could’ve hosted life in the past, but all that disappeared after the atmosphere thinned Life in the Outer Solar System - Gas giant moons might be habitable o Europa has a big ocean under its ice o Its contact with underlying mantle creates reducing chemistry 25.1 The Architecture of the Galaxy Herschel measures the Galaxy - Using a refracting telescope, William Herschel and his sister discovered that stars seem to lay on a flat plane Stellar system was in the shape of a wheel, with the Sun at the center Discs and Haloes - Milky way is flat and thin like a CD Stars and gas are not uniformly spread out, but concentrated in arms Central bulge: Stars are not flattened out in the middle and form a bulge instead Milky way mass near the edge of the galaxy is made of dark matter o It emits no light and can’t be detected by telescopes 26.1 The Discovery of Galaxies - Early astronomers thought Milky Way was the entire universe They were asking questions in the past, but didn’t have the tools to confirm or deny anything Nebulae: Name given to all celestial objects that were not sharp lights o Latin for cloud Other Galaxies - Some nebulae corrected to galaxies by early 20th century Edwin Hubble discovered the first galaxy outside the Milky Way o Named it Andromeda, estimated it to be about 900,000 lightyears away from us His discovery started extragalactic astronomy 26.2 Types of Galaxies Spiral Galaxies - Milky way and Andromeda Central bulge, halo, disc, spiral arms Young stars present in arms New stars are forming Barred spirals: Spiral galaxies with boxy bars in the middle through the center Milky way has bar too o Commonality of bar suggests every spiral galaxy forms a bar at some point Galaxies classified as Sa, Sb, Sc o Sa appear as lenses, while Sc have clearly defined arms Elliptical Galaxies - Consist almost entirely of old stars Have oval shapes Larger than the largest spiral galaxies Dwarf elliptical galaxies are a thing, they went unnoticed because of how dim they are Irregular galaxies - Do not have regular shapes Contain both young and old stars Best known Irregular galaxies: Large and Small Magellanic Clouds Galaxy Evolution - Early astronomers thought different galaxy shapes were different evolution stages Collisions and mergers change the shape of galaxies Increased consumption of gas may slow down galaxies, changing their shapes
