Download 2010_02_04 LP08 Our Galactic Home

Astronomy 100
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The Lay of the Last Minstrel
Sir Walter Scott
Breathes there the man with soul so
dead
Who never to himself hath said,
This is my own, my native land!
Whose heart hath ne'er within him
burned,
As home his footsteps he hath turned
From wandering on a foreign strand!
If such there breathe, go, mark him
well;
For him no minstrel raptures swell;
High though his titles, proud his
name,
Boundless his wealth as wish can
claim
Despite those titles, power, and pelf,
The wretch, concentred all in self,
Living, shall forfeit fair renown,
And, doubly dying, shall go down
To the vile dust from whence he
sprung,
Unwept, unhonored , and unsung.
• Answer Now: Draw a picture of our galaxy.
• Goal:
– Understand how distances are calculated
– Be able to draw a picture of our galaxy
• From the side
• From the top
– Know how we know about dark matter
• Vocabulary: Distance Ladder, Parallax, Cepheid
Variables, Parsec, Proper motion, Bulge, Thin Disk,
Thick disk, Globular clusters, Halo, Dark matter,
Rotation curve, Spiral arms, Density waves,
population I, population II, “population III”
Your Cosmic Address
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6000 16th Avenue SW
Seattle
Washington
United States of America
North American Continent
Earth
Third Planet from the Sun (Sol)
Our Solar System
Orion Arm
Milky Way Galaxy
The Universe
Which Ruler Should We Use?
• What is parallax?
• What is a parsec?
• Now, can you make the Kessel Run in less than
12 parsecs?
Distance Ladder
Distance
How to Measure
Less than 30 AU = 3,000,000,000 miles
Geocentric parallax (Earth’s DIAMETER as baseline)
Lasers (reflecting off the Moon)
Radar (reflecting off the Moon or Venus)
Heliocentric parallax (Earth’s ORBIT as baseline)
Moving clusters (Pleiades)
H-R Diagram
R R Lyrae variable stars (M=0.5)
Cepheid variable stars
Brightest supergiants (M=-8)
“Normal” novae
Globular clusters (brightest at M=-10)
H II Regions (doesn’t work perfectly)
Planetary nebulae
Hydrogen clouds (measure the angular size)
Type 1 supernovae (M=-20)
Brightest galaxies in a cluster
Hubble’s measure of red shift
Galaxy brightness in the infrared
Rotational speed of the galaxy
Up to 100 pc (parsecs) = 326 ly (light years)
Up to 1000 pc (nearby in our galaxy)
Up to 10,000 pc (104 pc) (into our galaxy)
Up to 105 pc (100,000 pc) (through our galaxy)
Up to 107 pc
(far out into our galaxy
and into other galaxies)
Up to 108 pc
Up to 109 pc
(near the edge of the observable universe)
Stars Move
• Proper motion
http://apod.nasa.gov/apod/ap080606.html
Dark Matter
• Grocery Shopping.
Spiral Arms
• They’re not real.
• Proper Motion – stars do move
• Density Waves
– Traffic video
• Star formation
Traffic Video
• Population I
• Population II
• Population III
• Answer Now:
• Can you make the Kessel run in less than 12
parsecs?
• Draw a picture of our galaxy
• From the side or from the top
• Give me an analogy for how we know dark
matter exists.
• Define 1: Distance Ladder, Parallax, Cepheid
Variables, Parsec, Proper motion, Bulge, Thin Disk,
Thick disk, Globular clusters, Halo, Dark matter,
Rotation curve, Spiral arms, Density waves,
population I, population II, “population III”