Unlocking Light

The key to understanding the Cosmos

Uses of Light Astronomers use light as a tool to “dissect” celestial objects

Only direct information we can get!

Collect light with various instruments

Study light to determine sources

Light Sources

Atoms or parts of the atom are the source of all light

Behavior of particles in Atom generates light

What are these particles?

Parts of the Atom

Proton

Neutron

Electron

Parts of the Atom

Atoms are building blocks of matter

Nucleus Protons – Positive Charge Neutrons – Neutral

Orbits Electrons – Negative Charge

Building Blocks

Elements-pure substances Atoms- smallest part of an element

Compound- chemically joined elements

Molecule- smallest part of a compound

Elements

Periodic Table ID’s are Atomic Number (Z) Z=number of protons Atomic Mass (A) Number of Protons + Number of Neutrons

Elements

Neutral Atoms have same # of electrons and protons

Ions have lost or gained some electrons

Isotopes have lost or gained some neutrons

Get Excited

Electrons naturally orbit in lowest energy state

Ground State If atom absorbs some energy the electron can move to a larger orbit

Excited Electron

Excited Atoms

Atoms gain energy Excited (but not ionized) atoms

Electrons move away from nucleus but are still orbiting

Excited Atom

Proton

Neutron

Electron

Excited Atoms

Electron absorbs energy to “jump up”

Electron releases energy to “fall down”

This Energy is Light!

Spectra

Light is released This is the Spectra of the atom

Unique Distinct Fingerprint for Elements and Compounds

Continuous Spectra

Rainbow No Gaps in Colors “White” light contains all colors

ROYGBIV

Emission Spectra

Dark Background

Few Bright Colored Lines

Spectral Lines

Unique for Each Element

Absorption Spectra Similar to Continuous Spectra

Dark gaps where colors are missing

Also Spectral Lines

Unique for Each Element

Kirchhoff’s Rules

Describes conditions needed to form the 3 types of spectra

Can be related to Astrophysical conditions

We can infer information from type of spectra

Rule #1

Hot, opaque light source Continuous Spectra

Light Bulb

Rule #2 Hot, transparent gas cloud

Emission Spectra

Neon Sign

Rule #3

Hot, opaque solid with a cool gas cloud between the source and viewer

Absorption Spectra

The Sun

Spectra Clues

Looking at the spectrum of a star can help us identify what elements are in it

Can also tell us about temperature and brightness

Gives clues to hidden processes within the star

Lots of Light

“Light” is any EM wave EM= electromagnetic Has both an electric part and a magnetic part

Not always “visible” to us Entire spectrum is huge

Wave Anatomy

Peak

Trough

Wavelength

Wavelength Length from one part of a wave to the next identical part

Can be measured in any length unit

Astronomers use Angstroms 1Å=.0000000001 meters (10-10m)

Frequency f

The # of waves that pass by a point in a given amount of time

# of waves per second Measured in Hertz Hz

Wavelength and Frequency Related! Long Wavelength = Low frequency

Short Wavelength = High frequency

Wavelength increases, frequency decreases

Light Waves

Wavelength x Frequency= Wave Speed

x f = c (speed of light) c is same for every light wave

So what separates them is frequency and wavelength

Electromagnetic Spectrum There is a continuous spectrum of light

Visible light (colors) are included in this

They are only a very very small part

EM Spectrum

Gamma Rays

X-rays

Ultraviolet

Visible

Infrared

Radio

← ← ← Wavelength increasing, Frequency decreasing

Energy of Light

Photons of light carry energy This energy is related to wavelength and frequency

As frequency goes up, energy goes up, since more photons are arriving

As wavelength goes up, energy goes down

Energy of Light

If you double frequency, you double energy

Or, if you halve the wavelength, you double the energy

Summary

Light carries energy Atoms make light Light allows us to dissect objects that we can’t reach

Wavelength, frequency, and energy of light are related