Welcome Back Physics 1411 A3 Introduction to Astronomy

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Welcome BackPhysics 1411 A3Introduction to
Astronomy

• For those who are new my name is
• Mr. Kris Byboth you may call me
• Mr. B. if you would prefer
• Note 3

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Write down these questions on a blank page. Write
down your best guesses for the answers.

• 1. What is the closest star to Earth?
• 2. What is the brightest star in the sky?
• 3. On what horizon do stars rise? Set?
• 4. How many stars are there?

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Answers to the Questions

• What is the closest star to Earth?
• The Sun!
• Proxima Centauri is the second closest star.

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Proxima Centauri
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• What is the brightest star in the sky?
• The Sun!
• The star Sirius is the second brightest star.
• On what horizon do stars rise? Set?
• East
• West

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• How many stars are there?
• Approximately 10 billion trillion stars

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Charting the Heavens

• The Foundations of Astronomy

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Objectives
Students will begin to develop an understanding
of the range of distance and time scales used to
talk about the physical history of the universe .
  Students will be able to use orders of
magnitude and scientific notation to represent
large and small numbers. Students will be able to
make simple conversions between scales and
systems of measurement. Students will be able to
recognize how selected usage of units and prefix
combinations can make using large or small units
easier. Students will learn to set the site
location data on The Sky software.  
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Our Place in Space

• While the Earth is a very special place to us.
  It is the only place we know for sure there is
  life . It is not the center of the Universe
  anymore than everywhere is.
•  
• The text says we inhabit no unique place. But
  actually the fact that we inhabit this place
  makes it unique. We had better take care of it
  until we can find another .

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• What is more accurate to say is the laws of
  science are not different here than anywhere
  else. We are justified to assume that what we
  find out about the rules of the universe can be
  applied to anywhere and with corrections for
  changes in conditions to any when.
•  

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Chapter 1 The Scale of the Universe

• Its Big.
• Astronomy is the study of the Universe. The
  universe is the totality of all space, time,
  matter, and energy .
•  We study everything and every when, from the
  smallest to the largest, from the beginning to
  the end.

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Earth from Space
Once the whole universe as we know it.
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Earth Moon System

Each of the illustrations In the textbook
represent a step of 100X in magnification. Im
using figures from more than one source.
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Our Sun
Our sun looks small, but is enormous compared to
earth. At 93 million miles( 1 A.U.) even light
takes eight minutes to get here.
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AU
1 Astronomical Unit is 1.5 x 1011 m or 93,000,000
miles. Venus is at 0.7 AU
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Solar System
Mars 1.5 AU Jupiter 5.2 AU Saturn 9.5
AU Uranus 19 AU Neptune 30 AU Pluto 39 AU
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Nearest Stars
This represents a distance of 1 million AU. For
distances to stars the AU is no longer
reasonable. Itd be like measuring the distance
to Dallas in inches. Well use light years and
parsecs for really large distances.
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Each step is a factor of 100
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Galaxies
Galaxies have more stars than there have been
people. Without telescopes we can see only one
galaxy outside our own. This one is NGC
4414. Galaxies range from 1500 to over 300,000 ly
in diameter. Our Milky Way visible disk is 75,000
ly. Galaxies may contain over 100 billion stars.
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Galaxy clusters
At a millions of light years from earth galaxy
clusters contain galaxies bound by gravity
orbiting one another.
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2. Below Clusters form superclusters and these
form long filaments and walls outlining voids.
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1. Above A representation of our local cluster.
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Giant Steps
This slide shows the scales larger than a
man. We also study the universe on the
microscopic scale.I.e. atoms and nuclei.
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Use of multipliers
Distances vary from the size of the theoretical
granularity of space ( 10-39 m), to quarks, to
nuclei ( 1 Fermi or femto , 10-15 m) , to atoms (
1 Angstrom, 1010 m)to people ( 1m), to cities
( km s, 103 m) to planets ( 1000 s kms, 106 m )
to solar systems ( 1 A.U.)
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Distance from time
A Light Year distance rate x time 1
ly 3 x 105 km/s x 86,400 s/day x 365 d/yr
10 trillion km or 6 trillion
miles. the Earth is 1/20 light second
across.The sun is 8 light minutes away. The
science fiction movies slow c down . In movies
you can see the light energy travel..to be
accurate youd see the object illuminated or
not. You wouldnt see the path either unless dust
was present in large amounts.
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Video notes are required
Great detail is not required. Write something
of interest from the videoavoid the urge to
bullI do look at these. POWERS OF TEN
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Scientific Notation
  Physical quantities have a quantity (number)
and a quality (units). The large range of values
we discuss are more easily handled by using
scientific notation. In scientific notation
numbers are expressed with only those we are sure
of ( called significant digits) as a number
between 1.ddd and 9.ddd followed by a power of 10
multiplier then the units.
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Avagadroes Number   602,300,000,000,000,000,000,0
00 becomes the more familiar 6.023 x 1023
particles/mole   and the mass of a proton    
0.000 000 000 000 000 000 000 000 001 67
kg becomes 1.67 x 10-27 kg  
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• Some skill (and editorial freedom) allows the use
  of prefixes to make writing values easier to read
  and/or cheaper to print.
• i.e. 1,350,000 km is also 1.35 Gm (gigameters)

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Metric prefixes
These are the most commonly used metric prefixes.
You are expected to be able to use these. See
p.497.
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Metric units
The quality,i.e. type of measurement is given by
the unit. Lengths, distances are in inches, feet,
kos, bligdorfs,.. Metric units are most useful.
Kmeny7_at_aol.com
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Prefix-unit combinations

• We usually chose a prefix-unit combination or
  scale unit consistent with the scale of the
  universe we a talking about.
• Small things. fm, nm, Angstroms
• systems Solar A.U.
• Distances to stars in our galaxy, ly, kpc
• Distances to galaxy clusters.. Mpc, millions of
  ly.
• SeedsSee Appendix A, pp 497

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Conversions..using unit factors
Multiplying anything by the number one does not
change its value. One may not look like 1.
Anything divided by its equivalent is the number
1. 6/(42) 1 12 inches 1 foot so 12 inches/1
foot 1 also. Any defined equality can become
unity,1. EOC problem 2 If a mile equals 1.609 km
and the moon is 2160 miles in diameter what is
its diameter in kilometers.
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Astronomy Picture of the Day A Star Cluster in
the Rosette Nebula
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Astronomy Picture of the Day Your Home The Milky
Way Galaxy

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  The Motion of the Moon
Unlike the Sun the Moon really does orbit the
Earth. Its position changes about 12o per day
or about a distance equal to its own diameter in
an hour.   The Moon undergoes changes in its
appearance called phases. One full cycle is
called a month, about 29 days.
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One sidereal month is the time it takes to
complete one revolution wrt the stars is 27.3
days. A synodic month is about 29.5 days due to
the motion of the Earth, Moon system about the
Sun.
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ECLIPSES   The orbit of the Moon around the Earth
is inclined slightly to the orbit of the
Earth-Moon system around the Sun. On occasion the
Earth, Moon and the Sun are in a straight line
resulting in the possible observation of an
eclipse. This can only happen during a New or a
Full Moon. When the Earth blocks the Suns light
from the Moon we see a Lunar eclipse, during a
Full Moon.  
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When the Moon (during a New Moon), blocks the
light to a part of the Earth a Solar eclipse can
be seen from the shadow regions on the
Earth.   Eclipses can be full or partial
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Angular momentum is conserved so the orientation
of the Moons orbit remains the same wrt the
universe as a whole
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