Frontiers in Astronomy- Week 1
Frontiers in Astronomy- Week 1 PHY 21430
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This 8 page Class Notes was uploaded by Kathryn Notetaker on Friday September 2, 2016. The Class Notes belongs to PHY 21430 at Kent State University taught by Spyridon Margetis (P) in Fall 2016. Since its upload, it has received 53 views. For similar materials see FRONTIERS IN ASTRONOMY in Physics at Kent State University.
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Date Created: 09/02/16
Frontiers in Astronomy Week 1 Intro Astronomy is a natural science greek words ‘astro’ + ‘Nomos’ (the law of stars) initially was the science of heavens but in a narrower sense mapping the night sky recording the position of the stars and planets unusual events : eclipses, supernova explosions, etc today vastly expanded that initial scope today it deals with the study of the UNIVERSE the collection of all that exists a collection of celestial objects (stars, planets, comets, nebulae, galaxies, etc) universe is everything almost 99% of all brightness in the sky are stars the sun is a star too, but it’s so close that its brightness dominates during the day, obscures any object in the sky the stars seem to be fixed on the background sky but the planets seem to have more relative to fixed stars after a week or so comets are much smaller than stars, have a tail The universe is also called cosmos by the ancient greek philosopher Pythagoras the word cosmos means order but also ornament to denote the order and beauty one finds in the universe an orderly and harmonious system as opposed to a disorderly one or chaos appears static to us but it is an extremely active entity in reality today is primarily concerned with: evolution physics laws chemistry composition meteorology motion of celestial objects formation and development of the universe Astronomy is a branch of physics and mathematics but a lot of other fields contribute, like chemistry, geology, biology, etc represents a synthesis of our state of the art knowledge of nature in general the most ancient of natural sciences the night sky was always there for humans to see humans started wondering about their place in the universe early on why and how celestial objects moved? by observing the sky our ancestors were able to make calendars uses mathematics as its language to describe the laws of the world science of rules or logic the physical world interacts with the world of logic very closely when it comes to its laws and their deeper understanding There is still a philosophical debate on what comes first, what generates what, something that shows their intimate relationship “the world is the totality of facts, not of things”- tractatus logicophilosophicus Ancient times plato/Aristotle debate what comes first? the physical or mathematics? school of Athens painting Aristotle paradigm points downward, towards physical world saying physical reality is fundamental platonic argument points up, multiverse mathematical structure is the true reality http://universe-review.ca/F02-cosmicbg.html More on astronomy astrophysics and cosmology questions related what is the cosmos made of? how it all begun and evolved to this point? what is our fate and the fate of our universe how stars are born and die how things work in the cosmos what are the physical laws governing celestial motion and phenomena can we interfere? ex. avoiding a cosmic collision with an asteroid? are there other worlds with intelligent life like ours? Why bother with questions? understanding- quenching the intrinsic thrist for knowledge, the need to know, the need to comprehend to find meaning in life use the power of knowledge to better our lives energy resources, hydrogen fusion (stars) on earth ability to inhabit other planets ability to find and communicate with other life forms safe space travel etc Scientific Method Science of measurement backbone of all sciences 3 components facts, measurements (data) collected via observation of nature or lab experiments leads to theory explaining it hypotheses and theory development laws of physics are extracted leads to predictions consistent with previous observations verification repeatability, predictability and testing testing is VERY IMPORTANT and a key element of the method predictions of new phenomena are observed Scientific theories must be testable must be continually tested should be as simple as possible should be elegant… we believe that truth should be beautiful can be proven wrong, but they can never be proven right with 100 percent certainty The scientific method and the fundamental ideas in physics Key Modern Ideas of physics used in astronomy Laws of physics are universal the same everywhere in the universe and at any scale, human or cosmic the way nature is every onbject in the universe is made up of same elements life development might be similar in other places and the search for ET is based on this why we look for exo-planets that are similar to earth gravitation and celestial mechanics the force that makes an apple fall, is the same force that keeps earth revolving around the sun, stars move around the center of galaxy symmetries and conservation laws nature has symmetrical behavior-leads to effects in the laws of physics this indifference of nature leads to many conservation laws (something stays the same over time) ex. the energy of an object, the way it moves for every symmetrical behavior, there must be some physical quantity that is conserved Quantum mechanics and particle duality (particle-wave) in microcosm particles behaving like waves and vice versa the death of determinism and birth of probable nothing is certain in most cases several possibilities for outcome of identical experiments most of our modern-life tech is based on it theory of relativity things like space and time are relative they depend on the point of view their flow can be modified the tyranny of speed of light light speed is constant for everyone light speed is the speed limit in the universe for any object with mass we believe nothing moves faster than the speed of light big bang cosmology the theory about origin of our universe how it all started what is the fate of our universe? are there other or parallel universes out there? what is dark energy and dark matter? Unification of particles, forces and space-time strong evidence that all different forces are nothing but facets of the same fundamental force what is the nature of the fundamental entity ? TOE (theories of everything) is it a string likt he string theory suggests? is it just an abstract number ? something else? what are the fundamental particles of force? are there more than we know now? super particles, higgs particle, tachyons, mini-black holes, etc The philosophical idea of things being ultimately unites is in the core of these theories Entropy and the arrow of time some processes are irreversible aging the breaking of a piece of glass what is the nature of time flow as we live it and why the arrow fo time points only to future? this idea has to do with order and disorder in the cosmos it relates to the ultimate thermal death of the universe and the struggle of life to create order and diversity A short tour of the universe The night sky at first sight, appears as a sphere patterns of fixed stars appear stable in time Celestial sphere and the stars on it are fixed stars Orion- only visible in the summer Sun- star closest to us creates its own energy and light Moon- satellite that rotates around earth Planets- move slowly in the sky Stars and galaxies milky way Clusters and super clusters of galaxies berenices coma galaxy cluster Universe possibility of existence of parallel universes Charting the heavens our place in space earth is average-we don’t occupy any special place in the universe earth is just 1 of many planets that exist The sun is about 100 times larger in diameter than earth in astronomy miles are too small a unit to measure distances light year and the AU (astronomical unit) Light year-the distance a beam of light travels in a calendar year a light year is equal to 10 trillion kilometers or about 6 trillion miles light travels 300,000 km or 186 miles a second the distance between earth and sun is about 93 million miles (1 AU) 1 AU is travelled by light in 8.3 minutes there are 100-500 billion galaxies in the universe scales are unfathomable The universe has 2 parts from our point of view visible(what we can see) and invisible (resides beyond the limit we can see) The obvious view from earth simplest observation: looking at the night sky about 3000 stars are visible at any 1 time; distributed randomly but human brain tends to find patters the 3 stars in a line is orion’s belt and the bright spot is his sword the group of stars in such an image is called a constellation 88 constellations in the whole sky Taurus example for a sign to be a zodiacal sign, it has to pass the sun’s path The “Real” view stars that appear close in the sky may not actually be close in space ex. orion seems to be a group of stars, just an illusion due to inability of the human eye to perceive the actual depth of each star The celestial sphere for us, stars seem to be fixed on the inner surface of a sphere surround the earth they are actually all over the space, but lack depth perception the extension of earth’s rotation axis passes today near Polaris and it defines the North celestial pole the projection of earth’s equator on the celestial sphere is called the celestial equator the actual rotation of earth is from west to east from above, which is why it looks like from earth it is east to west 3 movements of earth more than 20 movements earth’s rotation around itself revolves around an imaginary axis that goes through the south and north poles 24 hours to complete full revolution motion of earth around the sun earth moves almost in a perfect circle around the sound completes a revolution in a year earth’s rotational axis is not parallel to the earth’s rotation around the sun but have a relative inclination of 23.5 degrees-major consequences for us on earth wobbling of its axis like a spinning top’s axis is not fix the axis is slowly moving around completes a revolution every 25000 years consequences in a few thousand years, the the earth’s axis is not going to point to Polaris st thuban was the pole star in 3000 b.c. 1 movement of earth stars appear to move in circular paths the course of a night daily motion- the apparent motion from east to west true motion- the earth rotates around its axis from west to east the earth’s axis points near Polaris Daily star motion picture- discussion topic if the picture was taken for a full day and night, then the trace of each star would be a complete circle (bc earth makes a full rotation in 24 hours) but in the picture, the traces aren’t complete by looking at star traces, give an estimate on how many hours this exposure took Earth’s Days 2 kinds of days Solar day- about 24 hours noon to noon not a true day how the sun appears to be in the same place at 2 consecutive times sidereal day when the earth makes a full revolution true day shorter than the solar day- 4 mins shorter in a week, the sidereal time is about 28 mins shorter how to get the 4 min difference? every day, the earth moves about 1 degree around the sun earth has to cover this extra degree 360 degree in 24 hours 24*60 =1440 minutes to cover the extra degree it needs 1440/360=4! Angular measure full circle contains 360 degrees each degree contains 60’ arc-minutes each arc-minute contains 60” arc-seconds angles are useful when we refer to objects on a circle Earth’s orbital motion around the sun (second movement) as earth moves around the sun, the parts of the sky that are visible to us at night are also changing 6 months from now, we see different stars in the sky the apparent yearly motion of the sun is from west to east sun has 2 motions where it rises in the east and sets in the west, the yearly motion in the opposite direction seasonal changes to night sky are due to earth’s motion around the sun the Zodiac as the sun moves in the sky, goes through 12 constellations today the sun goes through 13 constellations (Ophiuchus entered before scorpio and before Sagittarius)
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