The Cosmic Perspective Chapter 5: Light and Matter

Measurement of Light and Matter

measured with special instruments attached to telescopes. We can learn the chemical composition of distant objects as well as their different temperature, how fast they rotate , and whether they are moving away or toward us.

-It carries information

Radiative energy

energy that light carries

color

basic property of light

spectrum

prism split into rainbow of light, basic colors are red, orange, yellow, green, blue, and violet

defraction grating

hard piece that reflects rainbow of colors

Ex: dvd's, cd's

white

when red, orange, green, blue and violet are reversed in equal portions

black

when there is no light and no colors

Emission

process by which matter emits energy in the form of light

absorption

a process where matter absorbs radiative energy.

Transmission

process in which light passes through matter without being absorbed

Reflections

Process where matter changes, the direction of light. (Light bounces in the same direction) The direction of a reflected beam depends on direction of incident

Scattering

when reflection is random.

ex: projection screens

vision

brain interprets messages the light carries

Newton's Prism Experiment

Newton placed a second prism in front of the light and one color showed. It light came from a prism the second prism would have produced another rainbow of color, it didn't

He discovered colors are not a property of the prism but are part of the white light itself.

wavelength

is the distance from one peak to the next (or trough to the next)

Particles

are separate objects - things

Waves

are patterns, revealed by interaction with particles

Frequency

number of peaks, passing any point each second - measured in cycles per second (Hertz, Hz)

Speed

how fast energy travels from one place to another

speed= wavelength x frequency

- The shorter the wavelength the higher the frequency, the more energy.

Electric magnetic spectrum

The complete spectrum of light, including radio waves, infrared light, visible light, ultraviolet light, x rays, and gamma rays.

Gamma rays

carries more energy, shortest wavelength

electric magnetic wave

are light waves that travel with vibrations of both magnetic and electric fields

Photon

An individual particle of light, characterized by a wavelength and a frequency.

light

is a particle and a wave

- light consists of individual photons characterized by wavelengths

visible light

light our eyes can see

Infrared light

Light with wavelengths that fall in the portion of the electromagnetic spectrum between radio waves and visible light

radio waves

longest wave length light, no noticeable effect on our bodies, can make electrons move up and down in an antenna

microwaves

wavelengths of light that fall near the border between infrared and radio waves, where wavelengths range from micrometers to centimeters

ultraviolet

light with wavelengths somewhat shorter than those of blue light because it lies beyond the the blue (violet) end of a rainbow

-carry enough energy to harm cells in our skin.

x-rays

light with shorter wavelengths

-have enough energy to penetrate through skin and muscle but can be blocked by bones or teeth

element

identified more than 100 of these, fire, water, earth, and air are not among these.

Some of the more common ones are hydrogen, helium, carbon, oxygen, silicon, iron, gold, silver, lean, and uranium

nucleus

found in the center of an atom

-contains most of the atom's mass because protons and neutrons are each about 2k times as massive as an electron

electrons

a smeared out cloud that surrounds the nucleus and gives the atom it's apparent size

- has an electrical charge that is precisely opposite that of a proton so it has a negative charge (-1)

electrical charge

properties of an atom depend on this. It is a fundamental physical property that describes how strongly an object will interact with electromagnetic fields.

- Is the basic unit of positive charge (+1)

neutrons

are electrically neutral, meaning they have no charge.

Atom

Consists of nucleus made from protons and neutrons, surrounded by a cloud of electrons.

atomic number

the number of protons in an atom

Atomic mass number

combined numbers of protons and neutrons in an atom

isotopes

contains same number of protons but different numbers of neutrons

molecules

atoms that are combined

compounds

molecules with two or more atoms

chemical bond

Interactions between electrons that hold the atoms in a molecule together

Example: hydrogen and oxygen atoms are held together in a molecule of h2o

Sublimation

The process by which molecules escape from a solid

Evaporation

Process by which molecules escape from a liquid

Molecular dissociation

When molecules split into pieces.

Example: as temperature rises molecules move faster and collisions become more violent at high enough temperatures collisions become so violent that can break the chemical bonds holding individual water molecules together.

Ions

Atoms with a positive or negative electrical charge.

Ionization

Process of stripping electron from atoms

Example: ionization turns what was once water into a hot gas consisting of freely moving electrons in positively charged ions of hydrogen and oxygen

Plasma

Type of hot gas in which atoms have become ionized

Sometimes referred to as the fourth phase of matter because of its charged particles interaction with light

Pressure

Is the force per unit area pushing on an object's surface

Evaporation of water molecules

Balanced in part by molecules of water vapor in Earth's atmosphere returning to the ocean the rate at which these molecules return is directly related to the pressure created by water vapor in the atmosphere

Atom's containment of energy

1) By virtue of their mass the possessed mass-energy mc2

2) Possesses kinetic energy by virtue of their motion

3) They contain electrical potential energy that depends on the arrangement of their electrons and their nuclei

Energy level transitions

Electron can rise from a little energy level to a higher one or fall from a higher level to a lower one

- can only occur when an electron gains or loses the specific amount of energy separating the 2.

Spectroscopy

the process of obtaining spectra from astronomical objects

Continuous spectrum

When rainbow spans a broad range of wavelengths without interruption

Emission line spectrum

The spectrum of bright lines, bands, or continuous radiation characteristics.

Absorption line spectrum

A spectrum that contains absorption lines.

Thermal Radiation (Black Body Radiation)

The spectrum of radiation produced by an opaque object that depends only on the object's temperature.

Law One of Thermal Radiation

Each square meter of a hot objects surface emits more light at all wavelengths.

Example: when a poker is still relatively cool it emits only infrared light which we cannot see. As it gets hot it begins to glow with visible light and includes more brightly as it gets hotter

Law two of thermal radiation

Hotter objects emit photons with a higher average energy , which means a shorter average

Example: the color of a hot poker demonstrates this.

The Doppler effect

If an object is moving toward us the light waves bunch up between us and the object so its entire spectrum is shifted to shorter wavelengths.

Blueshift

A Doppler shift in which spectral features are shifted to shorter wavelengths, observed when an object is moving toward the observer.

Redshift

Longer wavelengths of visible light or rather when an object is moving away from us its light is shifted to longer wavelengths

Rest wavelengths

Wavelengths that are stationary.

Power

The rate of energy transfer measured in watts.