The Study of Light

The Electromagnetic Spectrum  includes gamma rays, X-rays, ultraviolet light, visible light, infrared radiation, microwaves, and radio waves.  the arrangement of electromagnetic radiation according to wavelength.

The Nature of Light  Sometimes light behaves like waves, and other times like particles – it’s commonly referred to as a wavicle.  In the particle sense, light is thought to consist of small packets of information, called photons.  In the wave sense, you can use an analogy to waves on the ocean.

Wavelength and Frequency Two important terms for light are wavelength and frequency. ©Wavelength (λ)is the distance from one wave crest to the next. ©Measured in nanometers (nm) ©1 nm = 1 x m = m)

Wavelength and Frequency  Frequency (f) is measured in cycles per second = Hertz (Hz)  Number of waves that pass a given point in 1 second  Look at this animation: /amplitude.asp?strReferringChannel=resources &strReferringPageID=tcm: /amplitude.asp?strReferringChannel=resources &strReferringPageID=tcm:  What is the relationship between wavelength and frequency?

Speed of Light  All waves in the electromagnetic spectrum travel at the speed of light = 3 x 10 8 m/s.  The speed of light is a FUNDAMENTAL CONSTANT OF THE UNIVERSE.  Wavelength, frequency, and the speed of light are related by: Speed = wavelength x frequency Or v = λf

Example: The radio station WMMR broadcasts at a frequency of 93.3 MHz (93,300,000 Hz). How long is one radio wave emanating from WMMR? –c = λf… so λ = c/f –λ = (3.0 x 10 8 m/s) ∕(93,300,000 Hz) –λ = 3.21 m

Example 2: Microwaves are short-length radio waves. A typical microwave has a wavelength of 3 mm. What is the frequency of a typical microwave? c = λf f = c/λ f = (3.0 x 10 8 m/s) ÷ m f = 1.0 x Hz

Visible Light  Visible Light is the narrow band of electromagnetic radiation that we can see.  It consists of a range of waves with various wavelengths. Visible Spectrum ColorWavelength Red 700 ‑ 650 nm Orange 649 ‑ 580 nm Yellow 579 ‑ 575 nm Green 574 ‑ 490 nm Blue 489 ‑ 455 nm Indigo 454 ‑ 425 nm Violet 424 ‑ 400 nm

Invisible Light Invisible light refers to the portions of the EMS that humans cannot see with the unaided eye –Includes Radio waves, Microwaves, Infrared, Ultraviolet, X rays, and Gamma Rays –Radio, Micro-, and Infrared Waves all have wavelengths LONGER than red –UV, X and Gamma Rays all have wavelengths SHORTER than violet

Light and Energy Light is actually a form of energy The amount of energy contained in the light is based on the frequency of the light –Higher frequency light has more energy –E = hf (h = Planck’s constant = 6.6 x Js)

Example: How much energy is contained in Infrared light (f = 3 x Hz)? E = hf E = 6.6 x x 3.0 x E = 1.98 x J How about UV light? (f = 1.0 x Hz)? E = 6.6 x x 1.0 x E = 6.6 x J

Formation of Spectra  An absorption spectrum contains dark lines.  A continuous spectrum is an uninterrupted band of color (all the colors of the rainbow.)  An emission spectrum contains bright lines.

Spectroscopy  Spectrometers are in use in the laboratory, in the field, in aircraft (looking both down at the Earth, and up into space), and on satellites.  Spectroscopy is the study of light as a function of wavelength that has been emitted, reflected or scattered from a solid, liquid, or gas.

Types of Spectroscopy  There are as many different types of spectroscopy as there are energy sources! Here are just a few examples: o Astronomical Spectroscopy Energy from celestial objects (such as stars) is used to analyze their chemical composition, density, temperature, and other characteristics. o Infrared Spectroscopy The infrared absorption spectrum of a substance is sometimes called its “molecular fingerprint.” Frequently used to identify materials. o Raman Spectroscopy Raman scattering of light by molecules may be used to provide information on a sample's chemical composition and molecular structure.

Application to Earth Studies  This is a mineral map, where each color is the identification of specific minerals through imaging spectroscopy analysis.

Application to Earth Studies  The plot above shows how data from a Raman spectrometer can be used to identify the chemical composition of minerals.

Application to Earth Studies  Astronomers study stellar spectra in order to determine the chemical composition of stars. Every star in the sky has its own unique spectra making its identification kind of like finger printing stars.