A photon checks into a hotel. The desk clerk asks, “Do you

need help with your luggage?”

The photon replies, “I don’t have any. I’m travelling light.”

(get it?)

The Electromagnetic Spectrum

AKA--- LIGHT!

Big Questions:

• What is light?• Why do scientists study light?

Image from My NASA Data website

Properties of EM Waves: Wavelength

The distance between peaks or troughs of a waveMeasured in nanometers (nm) or angstrom (Å)Each type of EM radiation (and each color of visible

light) has a different wavelength

Properties of EM Waves: FrequencyThe frequency is measured by the number of

waves (or cycles) that pass a given point in one second.

Measured in Hertz -- Hz

0 1 sec

15 Hz

3 Hz

Energy and Wave Properties

Figure 1.

Short wavelength : High frequency =

High ENERGY

Figure 2.

Long wavelength : Low frequency =

Low ENERGY

All EM Waves travel at the speed of light- 300,000 km/sFrequency and Wavelength are inversely proportional

Electromagnetic Radiation

• EMR has properties of both a wave and a particle– Photons are the elementary particles of

electromagnetic radiation of all wavelengths– Photons can travel through the vacuum of space

• All types of EMR carry energy

Studying light

• By studying light energy at different wavelengths along the electromagnetic spectrum, astronomers can learn about:– An object’s size– An object’s temperature– The amount of energy an object is producing– The elements found in that object– An objects speed and direction relative to Earth– The interstellar matter between that object and Earth

Doppler Effect

• A change in wavelength as a result of a shift in the frequency of sound waves or electromagnetic radiation.

• Can show the direction a celestial object is traveling in relation to Earth

Doppler Effect video explanation

• https://www.youtube.com/watch?v=h4OnBYrbCjY

Red Shift

• Radiation emitted by objects moving away from earth is stretched or shifted to the RED end of the spectrum- RED SHIFT

EARTH

Blue Shift Objects such as stars and galaxies moving

toward Earth seem to have their wavelengths of radiation squeezed and the frequency increased- Blue Shift

EARTH

Doppler Effect Simulation

• http://astro.unl.edu/classaction/animations/light/dopplershift.html

Spectroscopy

Spectroscopy

• Spectroscope- a tool that disperses a ray of light into its constituent colors

• Astronomers can learn about a celestial object by studying the wavelengths, intensities, and patterns of its spectrum

Spectroscopy• When looked at through a spectroscope, every gas gives off a

different spectrum of colors, just like every person has a different fingerprint.

• When astronomers use a spectroscope to look at stars, they can determine what type of gases the stars are made of by the color of the lines in the spectrum they see.

• Astronomers can tell the temperature of a star by studying the intensities of the lines in the spectrum.

• The thickness of the lines tell astronomers about the rotation speed, density, magnetic field and gas turbulence of the star

Continuous Spectrum

• An unbroken band of colors, such as a Rainbow

• Shows the size, temperature, and life expectancy of a star

Emission or Bright Line Spectrum:

• An unevenly spaced series of lines of different colors and different brightness

• Determined by the chemical make up of an object

Dark line or absorption spectrum

• A series of dark or absorption lines that appear on the continuous spectrum

• Show the make up of cooler gases in the universe

Big Questions:• What is light?• Why do scientists study light?