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

2. 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. 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

4. 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

6. 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

7. 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

8. 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

9. 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

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

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

12. 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

13. 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

14. 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

15. 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

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

17. 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

18. 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

19. We observe the universe as it WAS not as it IS

20. 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

21. 3.3

22. 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

23. 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

24. 3.5 The Doppler Effect
Doppler Effect- the motion-induced change in the observed wavelength of any wave

25. 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

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