PHYS 005 Lecture Notes - Lecture 6: Windows Xp Visual Styles, Galactic Center
5 Jul 2018
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Session 6- Shape & Size of the Milky Way
Reading- Ch. 5 Sect. 9, Ch. 23 Sect.2, 3
Shape of the Milky Way
●Hard to tell what the milky way looks like
○We only travel within
the milky way
○Look at other galaxies
■Spiral w 2 arms
■Barred w 2 arms
■Eliptical
■Irregular
■Smudge
●Why does it look like a ribbon?
○William Herschel (1785)
■We’re inside a disk (plate)- when you look around yourself it looks like a ribbon
●Where are we in the milky way?
●** if we are in the middle, there are the same number of stars around
us
●** if we are offcentered- more stars on one side
■Conclusion: we are the center of the galaxy
●Kapteyn (early 20th century)- SAME CONCLUSION
●1930 Trampler
○You can’t see candle anymore bc something gets in the way of your vision
○Remote star clusters were dimmer
■Usually have same type of bright, young stars -> space is not empty; something
blocking vision
●Attenuation
of luminosity of stars due to dust btw us & star- extinction
○Herschel & Kapteyn weren’t counting stars around the galactic center (where dust is)
Globular clusters- act like moons of milky way
●Groups of around 100,000-1 million stars packed into compact sphere
●Above & below disk of stars in milky way
○No dust & gas (extinction)
1912 Henrietta Leavitt-discovered cepheid stars
●Pulsate periodically, longer the pulse, brighter they are
●Shapley found 2nd family of pulsating stars- RR Lyrae
○Cepheids usually found outside
galaxies, RR lyrae found inside
○Need RR lyrae to determine distances fr us
■Common in globular clusters
■** only thing that makes RR lyrae dimmer
is the further they are away fr the star
●NO EXTINCTION AT ALL
○****Also found that globular clusters form a circle around milky way
Document Summary
Session 6- shape & size of the milky way. Hard to tell what the milky way looks like. We only travel within the milky way. We"re inside a disk (plate)- when you look around yourself it looks like a ribbon. ** if we are in the middle, there are the same number of stars around us. ** if we are offcentered- more stars on one side. Conclusion: we are the center of the galaxy. You can"t see candle anymore bc something gets in the way of your vision. Usually have same type of bright, young stars -> space is not empty; something blocking vision. Attenuation of luminosity of stars due to dust btw us & star- extinction. Herschel & kapteyn weren"t counting stars around the galactic center (where dust is) Globular clusters- act like moons of milky way. Groups of around 100,000-1 million stars packed into compact sphere. Above & below disk of stars in milky way.
