Radiation, Spectroscopy, and Telescopes Chapter 3, 4, 5 Radiation, Spectroscopy, and Telescopes

Chapter 3: Radiation- Outline 3.1- Information from the Skies 3.2- Waves in What? 3.3- The Electromagnetic Spectrum 3.4- The Distribution of Radiation 3.5- The Doppler Effect

3.1 Information from the Skies Galaxies- even close ones like Andromeda (3 million light years away)- are much to far away to study by space travel or probes

3.1 Information from the Skies Light and Radiation Scientists use the laws of physics, as we know them on Earth, and interpret the electromagnetic spectrum emitted by objects

3.1 Information from the Skies Radiation is any way in which energy is transmitted through space from one point to another without the need for physical connection Electromagnetic is energy carried in the form of rapidly fluctuating electric or magnetic fields

3.1 Information from the Skies Visible light- is a part of the electromagnetic spectrum that our eyes are sensitive too (we can see!) invisible parts of the electromagnetic spectrum include: radio, infrared, ultraviolet, x- rays and gamma rays

3.1 Information from the Skies Wave Motion All types of electromagnetic radiation travel in the form of waves A wave is a way in which energy is transferred without physical movement of material from one location to another

3.1 Information from the Skies Waves are characterized by the speed at which they travel, and the length of their cycle Wave period is how many seconds it takes for the wave to repeat itself wavelength is the length of an individual wave cycle

Frequency- the number of crests or cycles passing per given time frequency= 1/wave period

Wavelength and wave frequency are inversely related Doubling the frequency halves the wavelength wave speed= wavelength x frequency

Diffraction and Interference Diffraction- is the deflection, or “bending”, of a wave as it passed a corner or moves through a narrow gap Interference- the ability of two or more waves to reinforce or cancel each other out

3.2 Waves in What?? Waves of radiation differ from water, sound, or any other wave that travel through a medium- radiation does NOT need a medium

3.2 Waves in What?? Electric Field- extending outward in all directions from any charged particle Determines the electrical force exerted by the particle on all other charged particles in the universe The strength of the electrical field decreases with distance

3.2 Waves in What?? A particle changing position causes associated electrical fields to change, in turn changing the fields on other charges If we measure the change in the force on these other charges, we learn about the original particle- information about the particle’s state of motion is transmitted through space via a changing electric field This disturbance in the particle’s electrical field travels as a wave

magnetic field- must accompany every changing electric field They govern the influence of magnetized objects on one another

When the charged contents of a star move around, their electric fields change, and we can detect that change The “rippled” response is how we detect the radiation

Electromagnetic waves move at the speed of light- 299, 792.458 km/s Light we see from the Andromeda galaxy left that object 3 million years ago- around the time the first known human ancestors were on Earth We know nothing about how Andromeda exists today, or even if it is still around

We observe the universe as it WAS not as it IS

3.3 The Electromagnetic Specturm The opacity of the Earth’s atmosphere- the extent to which it absorbs radiation- varies greatly with wavelength Only radio waves, some infrared wavelengths, and visible light can penetrate the atmosphere and reach the ground from space- all other waves must be used from satellites

3.3

3.4 The Distribution of Radiation The temperature of an object is a measure of the speed with which its particles move The intensity of radiation of different frequencies emitted by a hot object has a characteristic distribution, called a blackbody curve, that depends only on the temperature of the object

3.4 The Distribution of Radiation Wien’s Law: wavelength at which the objects radiates most energy is inversely proportional to its temperature Stefan’s Law: the total amount of energy radiated is proportional to the fourth power of the temperature

3.5 The Doppler Effect Doppler Effect- the motion-induced change in the observed wavelength of any wave

3.5 The Doppler Effect Blue-shift- radiation measured by an observer situated in front of a moving source- blue= shorter wavelength shift Red-shift- radiation situated behind the source- red= longer wavelength shift

Chapter 4: Spectroscopy- Outline 4.1- Spectral Lines 4.2- The Formation of Spectral Lines 4.3- Molecules 4.4- Spectral-line Analysis