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PH1600: Introductory Astronomy
Lecture 3
What is this?
PH1600: Introductory Astronomy
Lecture 3: Universe Scale, and Light
School: Michigan Technological University
Professor: Robert Nemiroff
Online Course pages:
http://courses.mtu.edu/
This class can be taken online ONLY, class
attendance is not required!
You are responsible for…
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Lecture material
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Listed wikipedia entries
 But not higher math
APODs posted during the semester
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In class, iTunes, learnoutloud.com
APOD review every week during lecture
Completing the Quizzes
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Chapter 1 quiz is now due
Chapter 2 quiz is due soon
See WebCT at http://courses.mtu.edu/
Wikipedia entries (Lecture 3)
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Black body
Spectrum
Spectral line
Bohr model
Doppler Effect
4
Black Body Spectrum
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A plot of intensity versus energy
emitted by an object
The highest intensity will usually
determine the object’s color
Stars of different temperatures will
have different spectra
The spectrum can be uncovered
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Pass light through a prism
http://commons.wikimedia.org/wiki/Image:Blackbody-lg.png
Black Body Spectra
Prism (optics)
From Wikipedia, the free encyclopedia
An Iridescent Cloud Over Colorado
Credit & Copyright: August Allen
APOD: 2007 November 25
8
Stellar Spectral Types: OBAFGKM
Credit & Copyright: KPNO 0.9-m Telescope, AURA, NOAO, NSF
APOD: 2001 May 30
Absorption Lines
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Gasses absorb very specific colors
of light
Different gasses absorb different
colors
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Hydrogen atoms absorb very specific
colors that can be identified
Helium first discovered on the Sun
through its absorption lines
All the Colors of the Sun
Credit & Copyright: Nigel Sharp (NSF), FTS, NSO, KPNO, AURA, NSF
APOD: 2007 June 24
The Bohr Atom
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Outdated but useful atomic model
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Electrons orbit a central proton
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Created by Neils Bohr in 1913
Much like planets orbit the Sun
Only certain orbits allowed, called
energy levels
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Electrons falling down emit a photon
Electrons absorbing a photon get
bumped up
Bohr model
From Wikipedia: http://commons.wikimedia.org/wiki/Image:Bohr-atom-PAR.svg
Atomic Absorption and Emission Spectra
From: http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
Emission Lines
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Same colors as absorption lines
except they are bright instead of
dark
Emission nebulas typically appear
red because
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They are primarily hydrogen
Bright H-alpha emission line emitted in
the visible range (red) when an
electron falls from the n=3 energy
level to the n=2 level
The Rosette Nebula
Credit & Copyright: Robert Gendler
2007 February 14
The N44 Emission Nebula
Credit & Copyright: WFI, MPG/ESO 2.2-m Telescope, La Silla, ESO
APOD: 2006 February 13
Emission and Reflection in NGC 6559
Credit: Robert Gendler
APOD: 2001 October 23
Wisps Surrounding the Horsehead Nebula
Credit & Copyright: Star Shadows Remote Observatory
APOD: 2006 February 21
The Doppler Shift
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Heard with sound every day
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Occurs with light, too!
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Light is blueshifted – all photons are more
energetic
Source moving away from you
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Allows you to go bowling with a flashlight
Source moving toward you
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Train whistles, cars whizzing past, etc.
Light is redshifted – all photons are less
energetic
All photons always move at speed c
Signed, "A Black Hole"
Credit: B. Woodgate (GSFC), G. Bower(NOAO),
STIS Instrument Definition Team, NASA
APOD: 1997 May 16
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This Week in APOD
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Next week: Observing Stars and
Planets