Astronomy Chapters 6 & 7 (Light and Matter Stuff)

Atoms

The smallest level of matter that maintains chemical identity.

Atoms are made of two main parts: nucleus + the electron orbitals.

Subatomic Particles

Protons are found in the nucleus and have a charge nature. They can create:

Gravity and electric force (+). Electric force is another force in nature.

Neurons are found in the nucleus and have no charge.

Electrons are found outside the nucleus and have charge (-).

Quarks

The building blocks of subatomic particles.

May be made of vibrating quantum cosmic strings.

Chemical Elements

The proton number in the nucleus decides the element type.

Big Bang

Creates only Hydrogen (80%) and Helium (20%), from conversion of matter into energy.

Inside Stars

Elements from Beryllium (Be) through Iron (Fe) are created in stars through nuclear reactions.

Supernovae

All elements heavier than Iron.

We're here/exist because...

A star has died.

Crab Nebula

Supernova remnant, in Taurus created in a supernova viewed from Earth in the year 1054 AD. The nebula is rich in heavy elements forged in the star's nuclear furnace during its lifetime.

The Milky Way is filled with...

Dust (heavy elements) created in supernova blasts.

Isotopes

Elements with same proton number, but different number of neutrons.

Some isotopes are unstable or radioactive. These are useful for age determinations. This is called Radioactive dating.

The Electric Force

This force is created by the charged nature of some matter.

This is sometimes referred to as the Coulomb force. This force holds the atom together.

This force also holds White Dwarf stars up against gravitational collapse.

Law of Charges

Like charges will repel, unlike charges will attract.

Electric force depends upon the amount of charge. The greater the change the more the force.

The force also weakens with distance between charges.

On the level of the small, electric force is more important than gravity.

Electric force depends upon the amount of...

Charge. The greater the change the more the force.

Electric force also weakens with...

Distance between charges.

On the level of the small, electric force is...

More important than gravity.

The force between charges can be expressed as...

F = kQ1Q2 / d^2

Where k is a universal constant much like the constant seen with gravity.

The "Qs" are the two charges.

D is the distance between the charges.

In a dead-Sun like star the fusion has ended and the matter is...

Tightly drawn together by gravity.

How to get a White Dwarf star?

In a dead Sun-like star the fusion has ended and matter is tightly drawn together by gravity.

The gravity is resisted by a crowding of electrons which exert a force by the electric force to hold the star up against its own gravity.

The result is a White Dwarf star.

Dead stars like a white dwarf or a neutron star are made of...

Very compressed states of matter.

If protons repel, what holds the nucleus of the atom together?

The Nuclear or Strong force holds the protons together.

The Nuclear Force...

It is a powerful short range force, effective only on the scale of the nucleus.

Unlike gravity and the electric force, the Nuclear Force...

Does not reach to infinity. The other two do reach to infinity though.

If Nuclear or Strong force did not exist and only gravity and the electric force did, there would be...

No chemical elements possible in the universe other than Hydrogen.

Stars shining by nuclear fusion would not be possible.

The universe would be cold and dark.

The 4 Known Forces

1. Gravity

2. Weak Force

3. Electric Force

4. Strong Force

Magnetism

Moving charges create magnetic fields.

Planetary interiors fit the bill.

Planets generate planetary magnetic fields protecting them from the solar wind and CMEs.

Stellar interiors generate fields as well. This leads to sunspots and solar flares that generate the CMEs.

Earth's Magnetosphere shields the planet from...

The outburst of deadly particles.

The Sun's heliosphere protects us from...

Cosmic rays in the galaxy.

At solar minimum, when the number of solar flares decreases...

The cosmic ray count goes up considerably.

Plasma

An excess of negative or positive charge is referred to as ionic matter or a plasma. Examples: Comets, solar wind, nebulae.

Light sometimes behaves as though it is a wave, but it also behaves...

Like a particle.

Photons

Particles of light.

Light seems to be made of...

Electric and magnetic field waves.

The two waves E and M oscillate...

Perpendicular to each other.

Light may propagate (vibrate) in a...

Higher dimension.

Both electromagnetic waves travel at light speed...

186,000 mi/sec.

Both waves have the same...

Wavelength and frequency.

Light is the...

Fastest stuff in the universe. Light speed is detonated by C.

Wavelength

The distance between wave peaks or troughs. Wavelength is detonated by λ (lambda). Units will be that of length.

Frequency

The number of wave cycles passing an observer each second. Measured as cycles / sec or Hertz. Symbol used: f or ע (nu).

How are frequency and wavelengths related?

You can see as frequency gets greater, wavelength gets shorter. AKA Inversely promotional.

Wave Equation

C = λf

All light travels at C, but has different wavelength and frequency.

Frequency and wavelength are inversely related to each other.

The Electromagnetic Spectrum

The spectrum in order of increasing λ and decreasing f: Gamma Rays, X Rays, Ultraviolet, Visible (Right in the middle, visible to our eyes). Infrared, Microwaves, Radio

With Visible light are the familiar colors of the rainbow

Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV)

Our Atmosphere and the Spectrum

Only certain forms of light reach the ground from space, others are partially totally blocked.

The atmosphere is opaque to...

Gamma rays and X-Rays.

Portions of Radio and infrared reach...

The ground. A small portion of UV makes it. All of the visible reaches the surface.

The photons or particles of light carry...

The energy.

The energy of a photon depends upon...

The frequency of light. The greater the frequency the more the energy.

Energy equation for light

E = h f

The light with the most energy is...

Gamma Rays. What this means for astronomy is that violent high energy events will best be seen in Gamma Rays.

Radio light is least...

Energetic. Calm, cool, low energy events will best be seen in Radio.

Brightness of a Light Source

As you move away from a light source, it grows dimmer. This is particle-like behavior. Imagine a bomb-blast: A shower of particles moving out from a source.

Brightness is inversely...

Proportional to distance squared.

Brightness of a Light Source Equation

B α 1 / d2. Move twice as far away a star gets 4 times dimmer.

White Light

All colors of the rainbow are present. The full ROYGBIV blend is white.

Reflection

The color of an object reflecting white light depends upon which light is not absorbed by the body. If something looks blue, all colors except blue are absorbed by the body.

What about something white?

If something appears white, all colors are reflected, nothing is absorbed.

What about black?

All light absorbed.

Ennergy can change forms BUT...

It doesn't disappear.

Thermal Radiation

Any body that has a temperature will emit light due to the atomic motion of the matter in the body. Light emitted is heat. Perfect blackbodies will attempt to radiate everywhere in the E&M spectrum (stars).

Wien's Law

The wavelength of which a body emits most of its radiation is inversely proportional to the temperature of the body.

​​λ(max) α 1 / T

λ(max) = 3,000,000 / T

Wien's law implies the hotter an object is the...

Shorter the wavelength of light emission.

Hot objects shine...

Brightest in Gamma rays.

Cool objects shine...

Brightest in Radio.

Red stars are...

Cooler than blue stars.

Wien's law also implies that since everything has a temperature...

Everything emits light somewhere in the spectrum. Nothing physical can remain hidden in the universe.

To measure the temperature of anything in the universe:

T = 3,000,000 / λ(max)

Stefan's Law

The Amount of radiation an object emits is directly proportional to the fourth power of an object's temperature. Radioactive flux α Temperature to the 4th.

E = σT4

As the temperature of a body increases, so does the...

Amount of radiation emitted by the body. Thus, hot objects tend to be brighter.

Violet stars tend to be...

Brighter than red stars, all other things being equal.

The problem with stars is size influences...

Brightness. Larger is brighter.

The hotter a star...

Generally the brighter the star will be.

When light is passed through a prism it is dispersed into its...

Component wavelengths creating a spectrum.

Spectra Types

Continuous, Emission (or Bright Line), Absorption (or Dark Line)

Continuous

All colors are present, A continuous blend from one color to the next.

Emission (or Bright Line)

Specific wavelengths are present or lit. Most of the spectra are dark.

Absorption (or Dark Line)

Most colors are present, but dark lines or absorption lines cut through at various wavelengths.

What is the peak wavelength of light emission for a star with surface temperature of 6000 kelvin?

T = 3,000,000 / 6000 = 500 nm. Peak wavelength of light emission is 500 nm. 

What is the difference in radiative flux leaving a body that is 4 times hotter than another?

4^4 = 256 times hotter.

What happens to the wavelength of light emitted by a body as it triples in temperature?

The wavelength of light emitted by a body as it triples in temperature decreases/becomes shorter as the body becomes hotter.

If an observer moves 10 times further away from the sun than Earth's orbit, by what factor will the brightness of the sun change?

The brightness of the sun will change: 10^2 = 100.

Why do different atoms have different lines in their spectra? 

Because they have different numbers of protons and electron arrangements.

What is the wavelength of maximum intensity and the total energy emitted by a celestial object at absolute zero?

Wavelength max = 2.9 x 10^6 / T, T = 0, no energy emitted.

Celestial object A has a temperature of 60 K, and celestial object B has a temperature of 600 K. Which object emits the shorter wavelength of maximum intensity? Which objects have the least total energy emitted?

Object B has a shorter wavelength of maximum itensity. 
The least total energy emitted is object A.

What kind of spectrum does a neon sign produce? Describe this process. What colors are associated with a neon sign?

Emission spectra. The colors associated with a neon sign includes all colors of the visible spectrum possible. Depends on the gas used for colors.

Which kind of spectrum is produced by a white household incandes-cent lightbulb?

Continuous Spectrum is produced by a white household incades-cent lightbulb.

Why does the Doppler effect detect only radial velocity?

It produces compressions and stretches in light and sound waves. The direction of the object is told by variations. The doppler effect is useless because transverse motion doesn’t compress or stretch waves.

If a star has a surface temperature of 20,000 K (2.00 3 104 K), at what wavelength will it radiate the most energy? Is this star cooler or hotter than the Sun?

Radiates the most energy at wavelength: 3x10^6/20,000 = 150 nm.

This star is hotter.

If you double the temperature of a blackbody, by what factor will the total energy radiated per second per square meter increase?

If you double the temperature of a blackbody, T^4 = 2^4 = 16.

The amount of energy is proportional to the temperature to the fourth power.

If one star has a temperature of 6000 K and another star has a temperature of 7000 K, how much more energy per second will the hotter star radiate from each square meter of its surface?

(7,000^4) / (6,000^4) = 1.85

The hotter star radiates 1.85 energy per sec. more.

Basic Components of Matter

Quarks, Protons, Neutrons, and Electrons.

Nature of light and its components are…

Wavelength, Frequency, and Speed.

Kirchoff’s Laws

Law 1: A HOT DENSE GLOWING OBJECT emits a CONTINUOUS spectra.

Law 2: A HOT LOW DENSITY GAS emits an EMISSION spectra.

Law 3: A COOL LOW DENSITY GAS absorbs light at wavelengths specific to the gas.

The Sun’s complex spectra shows the presence of many…

Shows the presence of many elements.

Creation of the Continuous Spectra

Since everybody in the universe has a temperature, everybody must radiate light. The light is generated through agitation of the atoms and molecules within the substance.

The hotter the object the more radiation emitted and the shorter the wavelength of peak emission (Wien’s and Stefan’s laws). 

Creation of Emission and Absorption Spectra

Occur at the level of the atom specifically they are formed as the result of the electrons changing their orbital distances from the nucleus of the atom. 

The Bohr Model of the Atom

The electrons of atoms for each chemical element will be found orbiting at specific distances from their atomic nucleus.

NO TWO elements have the same distance.

The physical distance between orbitals corresponds to a specific level of electron energy, since the electron is attracted to the positively charged nucleus.

The only way the electron can overcome the Coulomb force attraction is to gain energy, much like a rocket burns fuel to leave Earth orbit. Ladder analogy.

The only way the electron can overcome the Coulomb force attraction is to..

Gain energy, much like a rocket burns fuel to leave Earth orbit. Ladder analogy.

A ladder has a unique and specific distances between rungs. This is true with electron orbitals in the atom as well.

Electron orbits are…

Unique and specific for each element.