chapter 10.2 radiation tells us the temperature, size, and composition of stars
TRANSCRIPT
We know about light
We know how light interacts with matter
But do we know where light come from?
And fort that matter, what is matter?
Properties of Matter (then)
Democritus (470-380 B.C)
“atoms” meaning: indivisible
All matter made up of 4 elements:fire, water, earth, air
Parts of an atom:
Nucleus proton (+ charge) neutron (no charge)
electron (- charge)
mass of proton is almost the same as mass of the neutron
mass of electron is about 1/2000 th of the mass of the proton.
If the proton and neutron were 10 cm across, the quarks & electron would be < 0.01 cm, the entire atom would be 10 km (1,000,000 cm) across.
Nuclear Densitya teaspoon of material as dense as the matter in an atomic nucleus would weigh
~ 2 billion tons!!
http://phys.org/news/2012-09-world-atomic-microscope-chemical-bonds.html
Actually seeing an atom!
http://newscenter.lbl.gov/news-releases/2013/03/07/atomic-collapse-graphene/
http://techon.nikkeibp.co.jp/english/NEWS_EN/20101105/187158/
Atoms• The kind of atom depends on the
number of protons in the nucleus.
• Most abundant: Hydrogen (H), with 1 proton and 1 electron
• Next: Helium (He), with 2 protons and 2 neutrons and 2 electrons
• Molecules: two or more atoms (ex. H2O, CO2)
We know that atoms function:
Not like a mini solar system!
But we will use the orbital model anyway:
How do atoms function? Atoms are Picky! When a photon withexactly the right energycomes along, an electronwill be kicked into ahigher orbit
The photon is absorbed,and the electron jumps to higher (excited) state.
Electron Orbits• Electron orbits in the electron cloud are
restricted to very specific radii and energies.
r1, E1
r2, E2
r3, E3
• These characteristic electron energies are different for each individual element.
Electronic Energy States
• Electrons can only have certain energies; other energies are not allowed.
• Each type of atom has a unique set of energies.• Energy level diagram.
Atoms can store energy
Ground State
Excited States
Atoms absorb/emit very specific energies of photons!
Energy levels of Hydrogen
Each element has a unique set of energy levels
Each transitioncorresponds toa unique photonenergy
Just by analyzing the light received from a star, astronomers can learn about a star’s
surface temp, chemical composition, total energy output, velocity, rotation period.
How can we use the way we know an atom worksto get information from LIGHT?
Putting refraction to work:
Different colors of visible light correspond to different wavelengths.
Spectrum (singular)
Spectra(plural)
spectrograph a device that spreads out the light from an object into its component wavelengths
spectrometer records the spectrum
Putting refraction to work:
• Emission: an electron emits a photon and drops to a lower energy state, losing energy.– The photon’s energy is equal to the energy
difference between the two levels.
Absorption: an electron absorbs the energy of a photon to go to a higher energy level.– The photon’s energy has to be equal to the energy
difference between the two levels.
It’s the missing information that’s provides THE information!
• The wavelengths at which atoms emit and absorb radiation form unique spectral fingerprints for each atom.
• These spectral lines help determine a star’s temperature, composition, density, pressure, and more.
Some light leaving the star is absorbed by atoms or molecules in the star’s atmosphere.
Makes absorption lines. Sometimes see emission lines.
electrons absorb the incoming photon and the electron jumps to a higher energy level:
absorption lines
Absorption Spectrum Dominated by Balmer Lines
Modern spectra are usually recorded digitally and
represented as plots of intensity vs. wavelength
Chemical Fingerprints
• Observing the fingerprints in a spectrum tells us which kinds of atoms are present
Energy Levels of Molecules
• Molecules have additional energy levels because they can vibrate and rotate
Energy Levels of Molecules
• The large numbers of vibrational and rotational energy levels can make the spectra of molecules very complicated
• Many of these molecular transitions are in the infrared part of the spectrum