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Welcome to Astronomy
Notes> Please pick up a syllabus
Today> Course stuff> Astronomy and Science> Solar system and stars> Angles> Powers of ten> Length time and mass
A. Dayle Hancock
Office hours: MTWR 10-11am
Page 1http:// physics.wm.edu/~hancock/171/
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• A. Dayle Hancock> Office: Small Hall 239> Phone: 221-7844> Email: [email protected]> Web: http://physics.wm.edu/~hancock/171/
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• Office hours> MTWR 10:00 – 11:00 > Or by appointment> Or drop by …
● Let me know when you are coming (email or phone) and I will be in my office.
Instructor
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Universe by Freedman • Geller and Kaufmann
10th Edition > Publisher: W H Freeman and Co. > Available in the W&M bookstore> As an e-book with WebAssign
Text
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• Lectures (generally w/slides), some discussion questions, some examples.> Questions always taken !> A laptop, tablet or smart phone for math in lecture
will be useful many days and required for Poll EV.• I post my slides on the web site after lecture so you
can take notes based on the slide number and day> Hopefully you’ll pay more attention instead of just
madly scribbling everything down> Examples done on document camera are not posted
• Suggest to keep your reading ahead of the lecture> Check the Syllabus, which is also on the web site if
you misplace your hard copy.
Class Format
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• Additional materials including notes and links, will be posted in the web site > I will spam (email) for really important things
• Weekly homework> Mostly done online (WebAssign.net).> You will need to purchase access ( through the WebAssign
site www.webassign.net) – it is about $62.44 with e-book or $40.19 for homework only.
> Usually due Thursdays > Posted about a week in advance of due date> More information when first assignment is given
• You need a scientific calculator for homework & tests
Class format
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• Your course work will be weighted as> 15% for each of 2 mid-term tests (30%)> 10% for each of 2 interlude projects (20%)> 20% Homework> 5% PollEV> 25% Final Exam
Basis of Grade
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• Poll Everywhere is an instant response system.> You can use it with any web device like a smart
phone, tablet or laptop.> During class, I will ask various types of questions
(multiple choice, true/false or even opinion)> Points are assigned as 2 points for a correct answer, 1
point for an incorrect answer and 0 points for no answer. Opinion questions count 1 point.
> The final average will be calculated using 90% of the total possible points. This will allow for missing about 4 days of class.
> You must sign up for PollEv. The cost is free.
Poll Everywhere
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• This course is a 'College 200' course> 'College' courses are the new curriculum> Entering freshmen and sophomores fall under this
new curriculum> This course meets the 'old' GER standard for juniors
and seniors.
Interludes
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For the College 200 requirements, we will spend two one week interludes 'reaching out' to other fields outside of astronomy. This semester, we will look at the space race and at SETI
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• The lab (Physics 177) is a separate course> There is a separate manual for the lab. (online and in
the bookstore). You also need a planisphere • See http://physics.wm.edu/~labs/astro• The first lab is the week of September 4-8• Labs meet in Small 133
Please note that the lab is a separate course
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Are we ready for the fun stuff… ?
Any Questions?
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To understand the universe, astronomers use laws of physics to construct testable theories and models
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What is Science?• The 1st law of science
> For every observable effect, there is a physical cause
> First used in an argument by Anaximander of Melitus 2650
years ago (Pythagoras’s mentor)
• What constitutes a scientific hypothesis?
> It must have predictive power
– i.e. predict something that allows it to be tested
> If not, it is just a belief
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Scientific method
Develop Hypothesis
Make new prediction
Make new observation
Consistent?
Yes?
No?
Revise Hypothesis
Can fix Hypothesis?
no
Yes?
Start again
Yes
no
Can't tell
Yes
Yes
no
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If the hypothesis is repeatedly verified then is can be come Theory, Law, or Model
Develop Hypothesis
Make new prediction
Make new observation
Consistent?
Can’t tell? Yes?
NO
Revise Hypothesis
Can fix Hypothesis?
No Start again
YESYES
NO
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● If it withstands tremendous experimental scrutiny then it will become generally adopted by the scientific community
● Theory or Law applies to a repeated verified hypothesis
● What do we call it? ● Law is usually a mathematical statement● Theory is a verified relationship that is usually a concept stated in
words● Model is a set of concepts to that can explain a system
– Often used to explain a set of approximations to gain some conceptual insight
● Rules that are not always followed …● e.g. theory of general relativity is very mathematical
Theory, Law, or Model ?
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• It is fundamental in science that each theory be tested repeatedly to ensure its veracity
• How is this done in astronomy? > We only have one Universe and can’t rerun the
“experiment”> It’s an observational science …
• The answer is we need to keep making new, better, observations to continue to test theories> This naturally leads to newer and better instruments in
astronomy so the field can to continue to develop. New technology
• As we go along, try to figure out what evidence we have to uphold the ideas we’re learning about, how theses ideas might have been disproved
• Remember, we don’t know it all yet. Some of the ideas developed in this class may still turn out to be wrong!
Testing hypothesis in Astronomy…
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Our Star, the Sun
18Planets Orbiting the Sun
19The Sun and Planets to Scale
By exploring the planets, astronomers uncover clues about the formation of the solar system
21Stars like Grains of Sand
By studying stars and nebulae, astronomers discover how stars are born, grow old and die
22The Orion Nebula – Birthplace of Stars
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The Crab Nebula – Wreckage of a Supernova in 1064
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Astronomers use angles to denote the positions and apparent sizes of objects in the sky
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• We use a short hand common in computers for scientific notation
● "6.2 times 10 to the 8th power" ● 620,000,000● 6.2*10^8 instead of all the zeros!!!● 6.2×108 the way you see in print● 6.2e+8
• The last is the easiest to type for email and valid for written work too● 0.0015● 1.5×10-3
● 1.5e-3
Scientific notation
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• Math example(2.002 × 105) × (3.011 × 10-7) = ?
= 2.002 × 3.011 × 105 × 10-7
= 6.028 × 105-7
= 6.028 × 10-2 or 0.06028 (either are valid answers)
• Points… > Multiplication can happen in any order
(before addition)> Multiplication of “numbers to powers” … just add the
exponents
Scientific notation: math
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• Based on the idea of powers of ten> Units are some power of ten different from each
other• Uses a set of standards for definition
> They have changes over the years> Meter was 10,000,000th of the distance from the North Pole
to the equator> Now it’s defined as the distance light travels in
1 / 299,792,459 of a second
The metric system
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10 -1 = deci (d)
10 -2 = centi (c)
10 -3 = milli (m)
10 -6 = micro (μ)
10 -9 = nano (n)
10-12 = pico (p)
10-15 = femto (f)
10-18 = atto (a)
10-21 = zepto (z)
10-24 = yocto (y)
101 = deca (da)
102 = hecto (h)
103 = kilo (k)
106 = mega (M)
109 = giga (G)
1012 = tera (T)
1015 = peta (P)
1018 = exa (E)
1021 = zetta (Z)
1024 = yotta (Y)
Names for the powers of 10
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• Treat units like variables in a fraction both for a formula & converting units
• FormulaDistance = velocity X time
d= v t = 5.5m/s * 10 s = 55m
• Unit conversion 10 hours (10h) → seconds 10 hr x 60 min/hr x 60 s/min
= 36,000 s
• If your units work then you probably didn’t make an algebra mistake!
Unit analysis and unit conversion
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Base Units in the SI System
All units in the metric system can be 'reduce' to a combination of 4 base units. The base uses are the meter, kilogram, second and coulomb (for electricity which we will not need).
The meter we have defined earlier
The second used to be defined by the motion of the Earth. Now it is defined by atomic clocks using the frequency of atoms.
The kilogram is defined by a piece of metal preserved outside of Paris. Scientist are working on a new standard for mass since this is the only base unit that requires a physical object.
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• Astronomical Unit (A.U.)> Average distance between the Earth & the Sun> 1 AU = 1.5 × 108 km
= 150,000,000 km
(or roughly 93,000,000 miles )
Need a new unit for planetary distance scales…
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• LIGHTYEAR (LY)> A light year is the distance light travels in one year
• Speed of light: 3.0 × 108 meters/second• One year has 3.16 × 107 seconds • d = v t = (3.0 × 108 m/s) × (3.16 × 107 s)• 1 LY = 9.46 × 1015 m
(That’s roughly 6 trillion miles)
Need a better unit for interstellar distances
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We define the “parsec” or “pc” as the distance that causes 1 arcsec of parallax
1pc = 3.26 ly1pc = 3.09×1013 km1pc = 2.06×105 AU
• We can then use a measured parallax to find distance> The measured parallax (p) should
given be in arc seconds> The distance of an object (d) is then
given in 1 parsec or 1pcPage 36
An arc second is the size of a penny at 2.5 miles
sec
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arcpc pd
