[ASTR 111] Chapter 5 - Light and Matter

Power

Rate of energy flow, measured in watts

Watts

1 watt = 1 joule(s)

Diffraction grating

Piece of plastic or glass etched with many closely spaced lines

Emission

Matter emits energy in the form of light

Absorption

Matter absorbs radiative energy

Transmission

Light passing through

Reflection/scattering

Light bouncing off matter

Wavelength

Distance from one peak to the next

Frequency

Number of peaks passing by any point each second

Cycles per second

Units of frequency for a wave; describes number of peaks of a wave that pass by a given point each second. = hertz

Speed of waves

Tells how fast a wave’s peaks travel

Field

Describes strength of force that a particle would experience at any point in space

Electromagnetic wave

Synonym for light, consisting of waves of electric and magnetic fields

Speed of light

Speed at which light travels; 300,000 km/s

Photons

Individual particle of light, characterized by wavelength and frequency

Electromagnetic spectrum

Complete spectrum of light, including radio waves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays

Electromagnetic radiation

Another name for light of all types

Visible light

Light we can see, with a wavelength range 400 - 700 nm

Infrared

Has wavelengths between radio waves and visible light

Radio waves

Has very long wavelengths and low frequencies; longer than infrared

Microwaves

Has wavelengths in the range of micrometers to millimeters; considered as subset of radio waves

Ultraviolet

Has wavelengths between visible light and x-rays

X-rays

Has wavelengths between ultraviolet light and gamma rays

Gamma rays

Has very short wavelengths; shorter than x-rays

Atoms

Basic units of chemical elements, composed of nucleus with protons and neutrons, surrounded by electrons

Element

Substance made from individual atoms of a particular atomic number

Protons

Positively charged particles built from 3 quarks

Neutrons

Particles with no electrical charge, built from 3 quarks

Electrons

Negatively charged particles; the distribution of these within an atom gives the atom its size

Nucleus

Compact center of an atom made from protons and neutrons

Electrical charge

Fundamental property of matter described by its amount and positive or negative charge

Atomic number

Number of protons in an atom

Atomic mass number

Combined number of protons and neutrons in an atom

Isotopes

Forms of an element that have the same number of protons, but different number of neutrons

Molecules

Combination of 2 or more atoms held together by chemical bonds

Chemical bond

Interactions between electrons that hold the atoms in a molecule together

Vaporization

Atoms or molecules escape into gas phase from liquid or solid phase

Molecular dissociation

Molecule splits into its component atoms

Ions

Atoms with positive or negative electrical charge

Ionization

Stripping one or more electrons from an atom

Plasma

Gas consisting of ions and electrons

Pressure

Force per unit area pushing on an object

Energy levels

Possible energies of electrons in atoms

Energy level transitions

Electron rising or falling to a different energy level

Spectroscopy

Process of obtaining spectra from astronomical objects

Continuous spectrum

Spectrum of light spanning a broad range of wavelengths without interruption by emission or absorption lines

Emission lines

Bright band of single color, superimposed on a fainter or completely absent rainbow of light; occurs when viewing light through a diffraction element

Absorption lines

Dark band on an otherwise bright rainbow of light, occurs when viewing light through a diffraction element

Molecular bands

Tightly bunched lines in an object’s spectrum, produced by molecules

Thermal radiation

Spectrum of radiation produced by opaque object, dependent on the object’s temperature

Law 1 of thermal radiation

Each square meter of a hotter object’s surface emits more light at all wavelengths

Law 2 of thermal radiation

Hotter objects emit photons with a higher average energy

Blueshift

Doppler shift where spectral features are shifted to shorter wavelengths, observed when object moves toward observer

Redshift

Doppler shift where spectral features are shifted to longer wavelengths, observed when object moves away from observer

Rest wavelengths

Spectral feature’s wavelength in the absence of any Doppler shift or gravitational redshift