How do we obtain detailed information about the Universe? Chapter 3 Radiation How do we obtain detailed information about the Universe?

Electromagnetic Radiation Radiation – any energy emitted that travels through space from one point to another without the need for any physical connection Electromagnetic – the energy that is carried in the form of rapidly fluctuating electric and magnetic fields.

Types of electromagnetic radiation radio and microwaves infrared waves visible light ultraviolet radiation x-ray radiation gamma ray radiation

All types of electromagnetic radiation travels through space in the form of waves. Waves – a way in which energy is transferred from place to place without physical movement of material from one location to another. In wave motion, the energy is carried by a disturbance of some sort which occurs in a distinctive repeating pattern. Waves

Wave Properties Wavelength – the number of meters needed for the wave to repeat itself. Wave period – the time needed for the wave to repeat itself. Amplitude – the maximum height from an equilibrium position. Frequency - the number of waves to pass a point in one second of time

Wave Properties Wave Frequency and period are reciprocals of each other. Wave frequency = 1 / wave period Frequency is expressed in Hertz. 1 Hz = 1 wave / second

Speed of radiation All electromagnetic radiation travels at the speed of light, 300,000 km per second. Wave speed = wavelength x frequency The larger the wavelength, the lower the frequency.

Visible Light White light is a mixture of colors, red, orange yellow, green, blue and violet. White light can be passed through a prism and separated into a spectrum.

How do waves move through space? Information about the particles' state of motion is transmitted through space via a changing electric field. This disturbance in the particle's electric field travels through space as a wave.

Electric Field around a charged particle Like charges repel Unlike charges attract Electric field represented by a series of field lines. If a charged particle starts to vibrate, its electric field also moves, affecting other particles around it.

Magnetic Field Any moving electrons cause an object to have a magnetic field. Lines of equal points of magnetic force encircle the object. Electric and magnetic fields act perpendicular to each other in space.

The Electromagnetic Spectrum

Powers of Ten The link below will take you to a site where you can experience the powers of ten and maybe get a perspective on how it works. http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html

The Distribution of Radiation All macroscopic objects emit radiation based on their temperature. The hotter the object—that is, the higher its temperature—the faster its constituent particles move and the more energy they radiate.

Blackbody Spectrum The Planck Curve illustrates schematically the distribution of radiation emitted by any object. The curve peaks at a single, well-defined frequency and falls off to lesser values above and below that frequency. Note that the curve is not shaped like a symmetrical bell that declines evenly on either side of the peak. The intensity falls off more slowly from the peak to lower frequencies than it does on the high-frequency side. This overall shape is characteristic of the radiation emitted by any object, regardless of its size, shape, composition, or temperature.

The Radiation Laws The blackbody curve shifts toward higher frequencies (shorter wavelengths) and greater intensities as an object’s temperature increases. Even so, the shape of the curve remains the same.

Wein's Law From studies of the precise form of the blackbody curve we obtain a very simple connection between the wavelength at which most radiation is emitted and the absolute temperature (that is, the temperature measured in kelvins) of the emitting object. Wavelength of peak emission is inversely proportional to the temperature.

Stefan's Law It is also a matter of everyday experience that, as the temperature of an object increases, the total amount of energy it radiates (summed over all frequencies) increases rapidly. The total energy emission is directly proportional to the fourth power of the temperature.

Astronomical Applications Nothing natural on earth emits very short wavelengths of radiation. Most x-ray and gamma ray wavelengths are only given off by astronomical objects like our sun.

Doppler Effect The apparent change if wavelength of radiation given off by an object due to motion of the object or of the observer. If the object is moving away from the observer, the light shifts towards the red end of the spectrum. If the object is moving towards the observer, the light shifts toward the blue end of the observer.

Trifid Nebula in Infrared

Trifid Nebula in Visible Light

Trifid Pillars and Jets

Eta Car in Infrared

Crab Nebula in Radio Wavelengths

Crab Nebula in X-Ray Radiation

Crab Nebula in Visible Light

Trifid Nebula in Infrared Light