How to “enroll” in this courseThe CourseInfo website by BlackboardThe Website Discussion ForumThe Course Syllabus and PlanGrading and ExamsFurther CommentsScience vs Non-science (nonsense?)The Solar SystemOur place in the UniversePowers of TenExponentialsThe Universe in a DayTimeline graphicSlide 14A Scale Model of the Solar System (1)A Scale Model of the Solar System (2)How to “enroll” in this course•Go to “bb” if from the campus network berkeley.edu, otherwise “blackboard.berkeley.edu”•Click “Create Account”. You will have to choose a username.•Fill out all red-starred information slots, then “create account” at the bottom•Click “Course Catalog”; “Letters & Science”; “Astronomy”•Click “Astro 10 (astron10-spr02)”•You will have to use the username & password you chose above to log in; this will be your username for the course•Choose “Enroll in this Course” and follow directions•You should end up in the Astro 10 Announcement screenThe CourseInfo website by BlackboardThe Website Discussion ForumThe Course Syllabusand PlanGrading and ExamsFurther Comments•There will be NO sections this week•You are not in the course unless a GSI has enrolled you on the course website into a section (Telebears aside)•For that to happen, you MUST get an account in Blackboard•Sections next week are all in the basement of Campbell Hall•This is not a mathematical course, but there is simple algebra in it (like L=R2 T4 ) a bit. Critical thinking IS required.•The main source of material is the book, but lectures tell you what is important (and fill out detail – the book is brief)•Falling behind in reading or homework is fatal – this material CANNOT be crammed at the end•If you aren’t used to critical thinking, or don’t need the grade, we strongly encourage you to take the course P/NPScience vs Non-science (nonsense?)•What is “science”?–Empirical : must always be based on observations–Predictive : should be able to predict new obs.–Reductionist(?) : tries to discover underlying “laws”•Why don’t astronomers believe in astrology?–Precession has moved the “Sun signs”–The constellations are not real entities–Local forces are much greater than forces due to stars or planets–Astrology is not really predictive (rigorous statistical analyses shows this)[of course, just because it is not science doesn’t mean it should be banned, just that it shouldn’t pretend to be science]The Solar SystemOur place in the UniversePowers of TenWe jump by a factor of 100in each frame. This also shows the context of the Earth in the Universe.ExponentialsWe will use scientific notation extensively - namely exponentials. The exponent indicates the number of places to the left (positive exponent) or right (negative exponent), of the units place the decimal point occurs. Another way to look at it is that the exponent for a power of ten indicates how many zeros would come before a 1 if you wrote the number out. Thus 10^6 (one million) is written as 1,000,000 (or 6 zeros). A negative power of ten means you divide by that number, eg. 10^(-6) is one millionth. I f you multiply two powers of ten together, you add the exponents. I f you divide them, you subtract the exponents, eg. 10^6/ 10^2=10^(6-2)=10^4.Another concept that is useful is the precision of a calculation. I f you multiply several numbers together, the answer shouldn't have more than one more decimal place than the number being used that had the LEAST number of places (or precision). For example, 1.2x10^4 times 3.563x10^2 is 4.3x10^6, not (as my calculator says) 4.2756x10^6. I n any case, in this class we are almost never interested in numbers to better than 2 decimal places (astronomy is a rather approximate science, for the most part).The Universe in a The Universe in a DayDay Let’s look at the entire history of the Universe as though it took place in a single day. The present is at the stroke of midnight at the end of that day. Since it is about 12 billion years old, each hour will be worth 0.5 billion years. A million years takes only a little over 7 seconds. The Big Bang (as an opaque fireball) and the formation of H and He all take place in the first nanosecond. The Universe becomes transparent in about 2 seconds. The first stars and galaxies appear after about 2am, and our Galaxy forms at perhaps 4am. Generations of stars are born and die.Timeline graphicThe Universe in a The Universe in a DayDay The Solar System does not form until 3pm. The first life (bacterial) appears on the Earth by 4pm. Our atmosphere begins to have free oxygen at 7 or 8 pm, and this promotes the development of creatures which can move more aggressively and eat each other. Life does not begin to take on complex forms (multicellular) until 10:45pm. It moves onto land at 11:10. The dinosaurs appear at about 11:40, and become extinct at 11:52. Pre-human primates appear at around 14 seconds before midnight, and all of recorded history occurs in the last 70 milliseconds. Looking to the future, we can expect the Universe of stars to go on for another at least a millennium (using the same time compression factor). After that, there are other ages of the Universe (not dominated by stars), which grow colder and more bizarre, and take place on astronomical timescales (even after this compression of timescale).A Scale Model of the Solar System (1)•Let’s make everything one-billionth (10-9) as big as it really is (9 orders of magnitude smaller)•The Earth: Diameter = 13000 km = 1.3x107 m1.3x107x10-9 ~ 10-2 = 1.3 cm (a marble)•The Sun: Diameter = 1,400,000 km = 1.4x109 m(about 100 times the Earth’s) so it must be 1.4 m (about a foot less than my height)•Earth-Sun Distance = 1.5x1011 m (1 Astronomical Unit) 1.5x1011x10-9 = 1.5x102 m = 150 mor about one-and-a-half football fieldsA Scale Model of the Solar System (2)•Jupiter Distance = 5 AU, •Saturn Distance = 10 AU (downtown Berkeley)•Pluto Distance = 35 AU (6 km: Oakland)•1 Light Year: 3x108 m/s x 3x107 s/yr ~ 1016 m or 1013 kmscaled down, that would be 1013-9 km or 10,000 km(about the distance to Europe)•The nearest star is 4 light years away....•The center of our Galaxy is 25000 ly away!! (scaled down, back out beyond the
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