Radiation in Astronomy I. Electromagnetic Radiation (EM) Energy travels through space as EM. $ Electromagnetic – radiation has an electric field and a magnetic field.

Homework: Pg 74 Review and Discussion (1-14) complete sentences and Problems (1-7) showing work – due Tuesday 10 October

l = wavelength EM travels in waves. Wavelength is distance from crest to crest.

Electrically charged particles give off an electric field which is stronger the closer you are to it. As the particle vibrates, it causes the electric field to change. This causes the wave.

A magnetic field is associated with every changing electric field A magnetic field is associated with every changing electric field. Therefore Magnetic fields exert forces on moving electirc charges. Electric fields are perpendicular to their accompanying magnetic fields = Electromagnetic waves.

Wavelength (l) varies from one type of EM to another Wavelength (l) varies from one type of EM to another. YET, ALL EM travels at the same speed (c). C = l f Frequency ( f ) = How often the crest of a wave passes a given point in a given amount of time. C = 300,000 Km/Second

Frequency ( f ) is measured in Hz (cycles per second) or wavelengths per second. As wavelength increases, frequency decreases, and visa versa. C = l f

ELECTROMAGNETIC SPECTRUM ranges from high-energy, short wave gamma rays to long wave, low energy AM Radio waves. AM – Short wave – FM – TV – Radar – Microwave – IR -Visible – UV – X-rays – Gamma radiation

Know these in order from largest wavelength to smallest.

- X-rays Ashley Should Fly To Russia Making It Visible Under eXtreme Gamma rays - AM radio waves - Short Wave radio - FM radio - Television waves - Radar waves - Microwaves - Infrared - ROYGBV - Ultraviolet - X-rays Yeah, gamma rays!

Interference: Diffraction is the deflection (bending) of a wave. Ability of two waves to cancel each other out or reinforce each other.

The two waves cancel each other out, leaving a completely unmoving string due to destructive interference.

Radiation NEEDS NO MEDIUM TO TRAVEL THROUGH (like sound waves do * Radiation NEEDS NO MEDIUM TO TRAVEL THROUGH (like sound waves do.) Space is empty! * Electrically charged particles exert an ELECTRICAL force on every other charged particle in the universe.

1. l (wavelength) determines the EM SPECTRUM FACTS: 1. l (wavelength) determines the type of EM radiation. 2. Visible light only makes up the small range of 400 nm (nanometers) to 700 nm. * Our eyes detect from 400-700nm which we call the visible spectrum. - Red frequency = 4.3 x 1014 Hz - Violet frequency = 7.5 x 1014 Hz

Bluer light has shorter waves, yet, travels at the same speed Bluer light has shorter waves, yet, travels at the same speed. So, which has the higher frequency, red or blue? blue

Our Sun as seen by our eyes in the visible spectrum. Our Sun as seen in the X-ray spectrum.

Opacity – The extent radiation is blocked by a material through Opacity – The extent radiation is blocked by a material through. which it passes. Our Atmosphere is OPAQUE to ALL but: RADIOWAVES (1 cm–10meter l ) Some INFRARED And VISIBLE light (400 – 700 nm)

Water (H2O), Oxygen (O2), O3 (ozone) and CO2 (carbon dioxide) block (reflect or absorb) most radiation from entering the Earth. H2O and O2 absorb many radio waves H2O and CO2 absorb Infrared O3 blocks U.V., X- and gamma- rays. Ions in the ionosphere reflect longer radio waves (short and AM)

All objects emit radiation! 1. Blackbody – Any object that absorbs radiation hitting it and then reemits the same amount of energy it absorbed. 2. Temperature: The measure of the amount of MOTION OF PARTICLES in an object.

3. INTENSITY: The AMOUNT of radiation given off in an instant. More waves given off makes it Shorter wave lengths are due to the fact it is

* As TEMPERATURE INCREASES in an object, the FREQUENCIES & INTENSITIES of radiation emitted from that object INCREASE. Wavelengths get shorter as temperature increases.

Zero Kelvin = -273 oC or -459 oF Kelvin is: oC + 273. Absolute zero is the total lack of any energy – it gets no “colder” or less energetic.

A blackbody curve represents the intensity of radiation emitted by any heated object. The wavelength (l) of “peak” emission is related to temperature. Total amount of energy given off also increases as temperature increases.

Wien’s law – Relates TEMPERATURE to most intense (peak) WAVELENGTH. The “hotter” the object, the “bluer” or shorter the wavelength it’s radiation.

* As Temperature increases, TOTAL AMOUNT OF ENERGY RADIATED BY THE OBJECT INCREASES EXPONENTIALLY. This is shown by Stefan’s law: F = sT4 “F” is Total amount of energy emitted per meter of an object surface area, or “flux.” “T” is temperature in Kelvin. “s” (sigma) is Stefan-Boltzman constant = 5.67x10-8 w/m2K4

Stefan’s law states: Total Energy radiated is proportional to it’s temperature to the fourth power, or F a T4 So, if object “A” is twice (2x) as hot as object “B”, how much more energy does it give off? l/ / F = s (2x)4 F = s (x)4 = (2) 4 = 2x2x2x2 (1)4 1x1x1x1 = 16x more energy

Doppler Effect – only occurs in RADIAL MOTION (direct line between observer and object.) Any other motion (across the line of sight) is called TRANSVERSE motion. Defined as the change in the apparent frequency of a wave as observer and source move toward or away from each other.

To determine the speed of recession of an object (how fast it is moving away) the following equation is used: Apparent l = 1 + recession velocity True l wave speed

Blue shift (Doppler effect) means light is moving toward us from a distant object, making the wavelengths shorter, so the light seen appears “bluer.”

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