ASTR 124: Introduction to Stars and Galaxies

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ASTR 124 Introduction to Stars and Galaxies

• Instructor Ryan Lynch

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Contact Information

• Office 304 Stone Hall (National Radio Astronomy
  Observatory)
• Office Hours 200-300 pm, Mon. through Fri.
• Email rsl4v_at_virginia.edu
• Phone [phone]

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Important Information

• No required textbook
• Optional textbook is Foundations of Astronomy,
  9th ed. by Michael Seeds
• If you have not already done so you MUST buy the
  student response system clickers
• Attendance is required on all exam days
• If you know you will miss an exam you must make
  prior arrangements

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List of Exam Days
Quiz 1 Tuesday, July 17 In Class
Quiz 2 Tuesday, July 24 In Class
Quiz 3 Tuesday, July 31 In Class
Quiz 4 Monday, August 6 In Class
Final Exam Thursday, August 9 800-1030
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Grading Scheme
Quizzes Final Exam In-class Questions Extra-Credit
50 (12.5 Each) 30 20 2
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What building and room are you in?

1. Chemistry Auditorium
2. 107 Clark Hall
3. McCormick Observatory
4. 265 Astronomy Building

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Concept Review

• Some basic algebra may be needed
• This includes solving an equation with one
  unknown or using logarithms
• Metric System
• Distance, mass, temperature
• I will assume that you are already familiar with
  these
• I will review logarithms in class

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Scientific Notation

• We will use a good bit of scientific notation
• Represents big and small numbers through powers
  of ten
• 5 billion 5,000,000,000
• This has 9 places after the 5
• In scientific notation, this is
• 5 x 109

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Scientific Notation (cont.)

• Also use it for small numbers
• 0.000634 has 4 places before the 6
• Includes the zero before the decimal place
• 0.000634 6.34 x 10-4
• Note negative sign in exponent

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More Examples

• What is 654,200,000,000 in scientific notation?
• What is 0.05703 in scientific notation?

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What is 4.56 x 107 in normal notation?

1. 4,560,000,000
2. 45,600,000
3. 0.000000456
4. None of the above

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Concept Review (cont.)

• Mass vs. Weight
• Mass is a measure of how much matter
• Weight is a measure of the force on an object
• Mass cannot change unless matter is added or
  removed
• Weight can change if gravity is stronger or weaker

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Concept Review (cont.)

• Vectors consist of both a number and direction
• 30 miles a way is just a number
• 30 miles West is a vector
• Plain numbers are called scalars

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Concept Review (cont.)

• Velocity change in position over some time
• Velocity is a vector!!
• Speed scalar form of velocityno direction!
• Acceleration change in velocity over time
• Acceleration is a vector, too!!

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Concept Review (cont.)

• Forces
• Forces are vectors
• Can add and subtract
• The sum of all forces on some body is called the
  Net Force

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Forces (cont.)

• Net forces cause acceleration
• force equals mass times
  acceleration
• Measured in Newtons (metric) or pounds (imperial)

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Concept Review (cont.)

• Gravity
• Very important force
• Newtons law of gravity
• Negative because it is always attractive
• Decreases as the square of the distance

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Gravity (cont.)

• Everything feels gravity
• Self-gravity is the gravitational force an object
  exerts on itself

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Concept Review (cont.)

• Energy
• Non-directional (scalar)
• Comes in different forms
• The sum of all mass and energy in a system cannot
  change

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Concept Review (cont.)

• Atoms
• Made up of a nucleus (protons and neutrons)
  surrounded by electrons
• Protons have positive charge
• Electrons have negative charge
• Neutrons have no charge

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Concept Review (cont.)

• Atoms of different elements have different
  numbers of protons
• Ions have too many or too few electrons
• Have a charge can be positive or negative
• Ionized means to be an ion
• Usually refers to having too few electrons, or
  positive charge

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Recognizing and Correcting Misconceptions

• The Flat Earth Society

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Misconceptions

• One obstacle to learning is our own
  misconceptions
• Sometimes we dont even know we have them
• Must learn to recognize them and why they are
  mistaken

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The Flat Earth Society

• The Flat Earth Society Home Page
• This all seems rather silly to us, but it makes
  sense to some people
• Lets look at the evidence

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The Flat Earth Society (cont.)

• Obvious problems with evidence
• Many, many experiments confirm no ether
• Gravity keeps things on the Earth pulls towards
  center, not towards South Pole

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The Flat Earth Society (cont.)

• More problems
• No gravitational charge always attractive
• Centrifugal force from going around the Sun is
  less than 1/10th of a pound
• Grigori Eifimovich was the 19th century Russian,
  Rasputin, NOT Christopher Columbus

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Overcoming Misconceptions

• Some things we take for granted may not be
  obvious to others
• Often because some one doesnt/doesnt want to
  know

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The Method of Science

• To counter our own misconceptions it is important
  to know how science works
• Facts Something that is easily observed to be
  true

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The Method of Science (cont.)

• Speculation Ideas put forward to explain some
  phenomenon may not be fully supported or may go
  beyond current knowledge, but shouldnt violate
  things that are already known

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The Methods of Science (cont.)

• Hypothesis An idea that explains some phenomenon
  that can be tested and is based on well developed
  ideas an educated guess

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The Methods of Science (cont.)

• Theory An explanation for some phenomenon that
  has been tested and is consistent with other
  accepted theories and supporting evidence
• Only as good as the experiments that test it

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The Methods of Science (cont.)

• Law Theories that are very well tested and
  almost universally accepted
• Note that Einstein expanded Newtons Laws, but
  did not invalidate them

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The Methods of Science (cont.)

• Science is constantly changing old theories may
  be replaced with better ones as new information
  becomes available

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Correcting Misconceptions

• There are several checks you can do
• Self-consistency Are your ideas in conflict
  with one another?
• General consistency Are your ideas in conflict
  with the evidence, or with other good theories?
• Common sense Do your ideas give sensible
  results when you really think about them?

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Correcting Misconceptions (cont.)

• Of course, to recognize any problems you need
  knowledge about the subject
• What is common for one person may not be common
  for another
• Only comes with experience and study

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Correcting Misconceptions (cont.)

• One of the goals of this class is to make science
  and astronomy more common to you

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The Scale of the Universe
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What best describes the Milky Way?

1. It is our home solar system
2. It is our home galaxy
3. It is our home universe
4. None of the above

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The Universe and Everything In It

• Many people hold misconceptions about the terms
  in the last slide
• The solar system is the collection of planets,
  comets, asteroids, and other small objects
  orbiting our sun
• Astronomers have discovered dozens of other solar
  systems

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The Universe and Everything In It

• A galaxy is a collection of stars, planets, dust,
  and many other forms of matter, held together by
  gravity
• Our galaxy, the Milky Way, is one of many billions

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The Universe and Everything In It

• The Universe is the whole of everything that we,
  as scientists, can see
• The Universe may in fact be infinite in size

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How Big is the Universe?

• How far apart should we move the Earth and Sun?
• How far away is Pluto?

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How Big is the Universe?

• How far away is center of galaxy?
• How far away is nearest galaxy?
• How far to the most distant objects we can see?

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How Many Stars

• There are 6 billion people on Earth. How many
  times more stars are there in the galaxy?
• How many stars in the whole universe?

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How many universes can we see from Earth?

1. 300 billion
2. 1022
3. 1
4. Infinite
5. 5

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Extra Credit Question

• Lets say that a star has a radius of 700,000 km,
  the galaxy is a sphere with a radius of 4 x 1017
  km, and there are 300 x 109 stars in our galaxy.
  If we scaled the galaxy down to the size of the
  Earth, with a radius of 6,400 km, how big would a
  star be? What everyday objects are roughly this
  size? About how much distance separates the
  stars in this scale model, if they are
  distributed evenly? Given your answer, do you
  think it is likely that stars will every collide?
  Explain.