Astro 10-Lecture 1: Introductions

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Astro 10-Lecture 1Introductions

• Who am I?
• Dr. Eric Korpela
• korpela_at_ssl.berkeley.edu
• http//setiathome.ssl.berkeley.edu/korpela/
• [phone]

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Course Goals

• To give you an understanding of what science is,
  how it works, and what it can and cant tell us.
• To give you an appreciation of the night sky
• To make you excited about and interested in
  astronomy
• To allow you to critically assess popular
  portrayals of astronomy

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A promise and a warning

• The promise
• You will learn a lot.
• The warning
• Each lecture builds on material from earlier
  lectures, so its easy to fall behind and hard to
  catch up again.

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Expected Work-load

• Expect to put in 2-3 hours outside class for each
  hour of lecture. (6-9 hours per week)
• Read the assigned material before coming to
  class.
• Homework will be assigned every 2-3 weeks.
• Homework is accepted up to 1 week late for half
  credit
• Homework will not be accepted after solutions are
  available.
• There will be 2-3 projects assigned during the
  semester
• The will be handed out a long time before they
  are due.
• DONT WAIT UNTIL THE LAST MINUTE TO DO THEM!

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Exercises, Quizzes and Exams

• There will be an in class exercise or a quiz each
  week as a means of taking attendance.
• If you arrive late and miss a quiz, be sure to
  let me know you attended class.
• There will be 3 exams.
• In class, one hour followed by a guest lecture.
• Final is non-cumulative.
• Let me know at least 2 weeks in advance if you
  have a conflict.

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Grading

• Grading is on a curve.
• Breakdown
• Homework 20
• Exercises and Quizzes 15
• Projects 20
• Exams 45

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What is Astronomy?

• Literally
• aster star
• nomienaming
• (Astrology was already taken)
• Astronomy, in modern terms, is observational
  scientific study of the universe and its
  contents.
• Astrophysics is the combination of astronomy with
  theoretical understanding of the processes taking
  place in astronomical objects.

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A more basic question What is science?

• Is science a collection of facts?
• No!
• Science is a process. Its a means by which we
  try to understand how the world works.
• Example
• Watch a football game. Try to figure out the
  rules without knowing them or having a rule book.
• Science is the process of trying to create a
  universal rule book.

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A gallery of the skies
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A gallery of the skies
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A gallery of the skies
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A gallery of the skies
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A gallery of the skies
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A gallery of the skies
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A review of scientific notation.

• Astronomy deals with very large and very small
  numbers
• Distance from Earth to Sun
• 150 000 000 000 meters
• Mass of hydrogen atom
• 0.000 000 000 000 000 000 000 000 001 67 kg

1.5x1011 meters
1.67x10-27 kg
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A review of scientific notation.

• Significant figures (Number of digits before the
  x)
• 2 significant figures
• 3 significant figures

1.5x1011 meters
1.67x10-27 kg
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How far does light travel in 65.1 millionths of a
second?

• dv x t 3.0x108 m/s x 6.51x10-5 s
• Multiply the mantissas (the numbers before the
  x)
• 19.53 x 108 x 10-5 m/s s
• Add the exponents (the numbers above the 10)
• 19.53 x 103 m/s s
• Shift the decimal to the first place by adding or
  subtracting from the exponent.
• 1.953 x 104 m/s s
• Round to the minimum number of significant digits
  in the original numbers.
• 2.0 x 104 m/s s
• Cancel units to get the correct units
• 2.0 x 104 m 20,000 meters 12 miles

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How long does it take light to get from the Sun
to the Earth?

• t d/v 1.5x1011 m / 3.0x108 m/s
• Divide the mantissas (the numbers before the x)
• 0.5 x 1011 / 108 m / (m/s)
• Subtract the exponents (the numbers above the 10)
  
• 0.5 x 103 m/(m/s)
• Shift the decimal to the first place by adding or
  subtracting from the exponent.
• 5 x 102 m/(m/s)
• Round to the minimum number of significant digits
  in the original numbers.
• 5.0 x 102 m/(m/s)
• Cancel units to get the correct units
• 5.0 x 102 s 500 s 8.3 minutes

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How fast are you moving right now?

• Rotation of the Earth
• radius of the earth Re 6400 km 6.4x103 km
• 1 day 86400 seconds 8.64x104 sec
• v d/t 2?Re/1 day
• 4.0x104 km/day / 8.64x104 s/day
• 4.6x10-1 km/s 1000 mph

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How fast are you moving right now?

• Orbit of the Earth around the Sun
• radius of the earths orbit A.U. 1.5x108 km
• 1 year 3.16x107 sec
• v d/t 2?A.U./year
• 9.4x108 km/day / 3.16x107 s/day
• 30 km/s 67 000 mph

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How fast are you moving right now?

• Orbit of the Sun around the Galaxy
• 200 km/s 450 000 mph
• Movement of Galaxy with respect to the rest of
  the universe
• 540 km/s 1.2x106 mph

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A reminder The metric system

• Basic units meter (m), gram (g), second(s)
• Prefixes
• Giga (G) 109
• Mega (M) 106
• kilo (k) 103
• hecto (h) 102
• centi (c) 10-2
• mili (m) 10-3
• micro (?) 10-6
• nano (n) 10-9

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Other units used in Astronomy

• Astronomical Unit (AU) distance from Earth to
  the Sun
• 1.5x1011 m
• Light Year (ly) distance light travels in one
  year
• d v t 3.0x108 m/s x 3.16x107 s
• 9.5x1015 m
• Parsec (pc) 206264.81 AU 3.26 ly
• 3.1x1016 m

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The scale of the universe

• How can we understand these distances on a human
  scale?
• The sun is 1.5x1011 m away.
• A passenger jet travels at 600 mph 270 m/s
• If you could fly to the sun, the trip would take
• t d/v 1.5x1011 m / 270 m/s 5.6x108 s 18
  years!
• The next nearest star is 4.3 light-years away,
  270 000 times as far.
• It would take 4.8 million years to get there by
  jet!

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The scale of the universe

• Powers of Ten video

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SCALE MODELS

• Scale of the Solar System

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Solar System
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Relative Size of Earth and Moon
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Relative Sizes of Planets
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Distances Between Planets
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SCALE MODELS

• A scale model of the history of the universe

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A scale model of history

• The universe is about 13 billion years old.
• To make it a bit more comprehensible scale it to
  1 day.

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A scale model of history

• 1200 am 0 seconds The Big Bang!
• 120003 400 ky The universe becomes
  transparent
• 1222 200 My The first stars form
• 150 1 Gy Milkyway Galaxy forms
• 341 pm 8.5 Gy Solar System forms
• 403 8.7 Gy Earliest indications of life on
  Earth
• 723 9.5 Gy Continents begin to form
• 852 2.5 Gya Earliest multicellular life
  forms
• 1046 670 Mya First land plants
• 1100 530 Mya First insects
• 1113 430 Mya First fish
• 1135 230 Mya Dinosaurs evolve
• 1153 65 Mya Dinosaurs die out

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A scale model of history

• 115926 5 Mya First apes that walk erect
  (homonoids)
• 115959.33 100 kya Modern humans
  appear
• 115959.93 10 kya Agriculture
  developed
• 115959.97 5 kya Great pyramids built
• 115959.9987 204 ya American Revolution
• 115959.99989 18 ya About when most of you
  were born.

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How does science work?

• A scientist makes an educated guess about a rule
  a hypothesis.
• A hypothesis needs to be quantitative.
• It needs to make predictions about the behavior
  of the universe.
• A hypothesis builds on existing knowledge of the
  universe
• The hypothesis is tested by experiment or
  observation.
• If the hypothesis fails a test it must be
  discarded or modified.
• Example Hypothesis All objects fall when
  dropped.
• Is this hypothesis true or false?
• A hypothesis that never fails despite repeated
  tests of its predictions is called a theory. (In
  science, a theory is something that is a near
  certainty.)

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How does science work?

• Science isnt about truth. Its about what has
  worked so far.
• No hypothesis can be proven to be true. It can
  only be shown to be false. (A hypothesis must be
  falsifiable.)
• A complete hypothesis must work at all places and
  times.
• Only one bad prediction is required to falsify a
  hypothesis.
• Example Newtons Law of Universal Gravitation
• superceded by Einsteins Theory of General
  Relativity
• still a useful approximation for most situations
  despite having been falsified.

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Things that are not science...

• Astrology - It makes predictions, but the
  theory/method isnt changed when predictions fail
• Creation Science - It makes no testable
  predictions. Not falsifiable.
• Psychic precognition - theory/method isnt
  changed when predictions fail.
• Religion - Not falsifiable.
• Not science does not mean not true any
  more than science means truth.

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How would a scientist find the answer the
following questions?

• How long does it take to cook a turkey?
• Why does it take that long to cook a turkey?
• The difference between these questions is the
  difference between observational fact and
  science.