134
(http://education.jlab.org/beamsactivity/6thgrade/tableofelements/stu01.l.html)
The number of PROTONS determines the type of element an atom is.
Isotope: Any of two or more forms of the same element whose atoms all have the same
number of protons but different numbers of neutrons.
Ion: At atom that has lost (or gained) one or more electrons.
131
The Model of the Atom
3 Questions About the Stars
What are they made of?
{
nucleus
How are they moving?
(Fraknoi, Morrison, & Wolff: Voyages to the Stars and Galaxies, 3rd Edition, Figure 4.14, Page 98)
Atoms contain 3 types of particles:
• Electron: Negatively charged particle found outside the nucleus.
• Proton: Positively charged particle found inside the nucleus.
• Neutron: Neutral particle found inside the nucleus.
Note:
The nucleus is tiny compared with the atom: Ratom 100,000 Rnucleus
The neutron is slightly more massive than the proton, and both are
much more massive than the electron. m p 1,800 me
+
Where are they located?
Light!
129
228
Today’s Lecture: An Outline
1) Properties of light.
2) Properties of thin gasses.
3) What are astronomical objects made of?
4) Brief answer to question: What is light?
Isaac Newton: 1643 - 1727
Properties of Light
138
Speed of light: 300,000 km/s, or about 186,000 miles/s.
Reflection: The return of light after striking a surface.
Properties of Light
139
Refraction: The bending of light when it passes from one
transparent medium to another.
Properties of Light
139
Refraction: The bending of light when it passes from one
transparent medium to another.
140
Properties of Light
139
Refraction: The bending of light when it passes from one
transparent medium to another.
Properties of Light
138
Speed of light: 300,000 km/s, or about 186,000 miles/s.
Reflection: The return of light after striking a surface.
Refraction: The bending of light when it passes from one
transparent medium to another.
Different colors of light refract by different amounts.
141
140
140
141
Continuous Spectrum
Dispersion: The act of separating the different colors of light through being
refracted by different amounts.
A spectrum of light composed of a continuous range of color.
Spectrum: The array of colors obtained when light is dispersed.
Spectroscopy: The study of spectra.
The Continuous Spectrum of Light
142
The Continuous Spectrum of Light
142
How to Produce
143
Heat a solid object or very dense
gas until it glows.
Examples: Lump of coal in fire;
filament of lightbulb.
Pass a continuous spectrum through
a very rarified (not dense) gas.
Example: Sunlight.
Also called absorption-line spectrum.
Pass an electrical current, or otherwise
‘excite’ a rarified gas.
Example: Gas discharge tubes.
Also called emission-line spectrum.
141
130
The Three States of Matter: Solid, Liquid, Gas
Continuous Spectrum
A spectrum of light composed of a continuous range of color.
Solid
Liquid
Gas
Today’s Lecture: An Outline
1) Properties of light.
2) Properties of thin gasses.
3) What are astronomical objects made of?
4) Brief answer to question: What is light?
144
The Spectrum of Hydrogen
Hydrogen
Bright-line (or emission-line) spectrum: A pattern of bright lines produced by a rarified gas whose
atoms have been “excited”.
Rarified: Having low density.
Mercury
Sodium
Neon
144
Neon
(Fraknoi,Morrison, & Wolff: Voyages to the Stars and Galaxies, 3rd Edition, Figure 4.11, Page 96)
Bright-line (or emission-line) spectrum: A pattern of bright lines produced by a rarified gas whose
atoms have been “excited”.
Rarified: Having low density.
The “Fingerprints” of the Elements
134
144
(http://education.jlab.org/beamsactivity/6thgrade/tableofelements/stu01.l.html)
(Fraknoi,Morrison, & Wolff: Voyages to the Stars and Galaxies, 3rd Edition, Figure 4.11, Page 96)
The number of PROTONS determines the type of element an atom is.
Isotope: Any of two or more forms of the same element whose atoms all have the same
number of protons but different numbers of neutrons.
Ion: At atom that has lost (or gained) one or more electrons.
Bright-line (or emission-line) spectrum: A pattern of bright lines produced by a rarified gas whose
atoms have been “excited”.
Rarified: Having low density.
Today’s Lecture: An Outline
3 Questions About the Stars
1) Properties of light.
2) Properties of thin gasses.
3) What are astronomical objects made of?
4) Brief answer to question: What is light?
129
What are they made of?
How are they moving?
Where are they located?
Light!
Continuous Spectrum
146
7
Bright-Line Spectrum (Hydrogen)
Star: A sphere of gas shining under
its own power.
144
The Spectrum of Hydrogen
Hydrogen
Hydrogen
Sun’s Spectrum
Bright-line (or emission-line) spectrum: A pattern of bright lines produced by a rarified gas whose
atoms have been “excited”.
Rarified: Having low density.
Joseph von Fraunhofer (March 6, 1787 – June 7, 1826)
145
Dark-line (or absorption-line) spectrum: A pattern of dark lines superposed on
an otherwise continuous spectrum.
143
Continuous Spectrum
146
Continuous Spectrum
146
Dark-Line Spectrum (Sun)
Bright-Line Spectrum (Hydrogen)
Kirchoff’s 3 Laws of Spectral Analysis
Bright-Line Spectrum (Hydrogen)
147
Joseph von Fraunhofer (March 6, 1787 – June 7, 1826)
145
1) A luminous solid, liquid, or hot, dense gas emits light of all colors,
producing a continuous spectrum.
2) A rarefied luminous gas emits light of certain colors only, producing an
emission-line spectrum.
3) If a continuous spectrum is passed through a rarified gas, the gas will
absorb certain, specific, colors, so that those colors will then be missing
(or diminished) in the otherwise continuous spectrum. This produces an
absorption-line spectrum.
(Fraknoi,Morrison, & Wolff: Voyages to the Stars and Galaxies, 3rd Edition, Figure 4.18, Page 102)
Dark-line (or absorption-line) spectrum: A pattern of dark lines superposed on
an otherwise continuous spectrum.
148
The Solar Spectrum: Elements Identified
(http://education.jlab.org/beamsactivity/6thgrade/tableofelements/stu01.l.html)
7
1
Orion (the hunter)
Betelgeuse
1
Star: A sphere of gas shining under
its own power.
Lecture 1: The Takehome Message
12
149
• The Universe is, evidently, a very big place.
• When we look OUT into space, we look BACK in
time.
• Stars are distant suns.
• Stars evolve: they are born, they live, and then
they die, sometimes by exploding.
We know what types of atoms
make up an astronomical
object by studying its
SPECTRUM.
3 Questions About the Stars
129
How to Produce
143
Heat a solid object or very dense
gas until it glows.
Examples: Lump of coal in fire;
filament of lightbulb.
What are they made of?
Pass a continuous spectrum through
a very rarified (not dense) gas.
How are they moving?
Example: Sunlight.
Also called absorption-line spectrum.
Pass an electrical current, or otherwise
‘excite’ a rarified gas.
Where are they located?
Example: Gas discharge tubes.
Also called emission-line spectrum.
150
The Orion Nebula: A Star-Forming Region
Type of spectrum produced:
150
The Orion Nebula: A Star-Forming Region
Type of spectrum produced:
Continuous?
Absorption?
Emission?
Emission!
3 Questions About the Stars
129
What are they made of?
Today’s Lecture: An Outline
1) Properties of light.
2) Properties of thin gasses.
3) What are astronomical objects made of?
4) Brief answer to question: What is light?
How are they moving?
Where are they located?
151
152
Basic difference between
particles and waves:
What is LIGHT?
152
152
Basic difference between
particles and waves:
Basic difference between
particles and waves:
Particles: energy localized,
in a packet.
Particles: energy localized,
in a packet.
Waves: energy spread out.
152
152
Basic difference between
particles and waves:
Basic difference between
particles and waves:
Particles: energy localized,
in a packet.
Particles: energy localized,
in a packet.
Waves: energy spread out.
Waves: energy spread out.
Is light a wave or a particle?
Is light a wave or a particle?
Answer: Neither…or, actually,
both! Depending
on the experiment, light
sometimes behaves like a
wave, and sometimes like a
particle.
153
Lecture 11: The Takehome Message
We know what types of atoms
make up an astronomical
object by studying the
emission lines (“bright lines”)
and/or absorption lines (“dark lines”)
in its spectrum.
(Fraknoi,Morrison, & Wolff: Voyages to the Stars and Galaxies, 3rd Edition, Figure 4.2, Page 87)
Wave: Energy being transported through a medium.
Medium: The substance through which a wave is traveling.