LIGHTGeneral Properties

By: Alex S. Marce BSEd III-B

Much of the information we get in astronomy is carried by “light”.

1. Location of light in the sky- gives position of a planet, moon or star.

2. Color- gives temperature, speed and direction of motion, chemical composition.

3. Brightness- gives distance, composition, periods of motion.

4. Size of light- gives size and distance information.

INTRODUCTION

*Adopted from Astronomy Chapter 2 handouts, Page 15

• The common term for electromagnetic radiation, usually referring to that portion visible to the human eye. However, other bands of the e-m spectrum are also often referred to as different forms of light. *(space.about.com)

• Electromagnetic radiation that can be perceived by the human eye. It is made up of electromagnetic waves with wavelengths between 4 × 10-7and 7 × 10-7 meters. Light, and all other electromagnetic radiation, travels at a speed of about 299,728 km (185,831 mi) per second in a vacuum. *(http://science.yourdictionary.com/light)

DEFINITION

- The speed of light in empty space is constant.- C = 3x108 m/s = 670 billion mph

- This finite speed has a real effect on information carried by light. it takes 11/4 seconds for light to reach us from the

moon. it takes 81/3 minutes for light to reach us from the

sun. it takes 41/3 years for light to reach us from the

nearest star.

SPEED OF LIGHT

*Adopted from Astronomy Chapter 2 handouts, Page 15

Wavelength- the distance between wave crest. The wavelength is indicated by the Greek symbol “λ”.

PROPERTIES OF LIGHT

Frequency- the number of wave crests per second passing a point.

PROPERTIES OF LIGHT

Color- is determined by wavelength ( or frequency).

PROPERTIES OF LIGHT

Spectrum- is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by analogy to many fields other than optics. *(www.wikipedia.org)

SPECTRUM AND MORE

PROPERTIES OF LIGHT

The study of light at different wavelengths is called “spectroscopy”.

Spectroscopy pertains to the dispersion of an object's light into its component colors (i.e. energies). By performing this dissection and analysis of an object's light, astronomers can infer the physical properties of that object (such as temperature, mass, luminosity and composition). *(http://loke.as.arizona.edu/~ckulesa/camp/spectroscopy_intro.html)

SPECTRUM AND MORE

PROPERTIES OF LIGHT

WAVELENTH SPECTRUM

Why do we see “visible” light?

1. Sun emits most strongly at these wavelengths.

2. Earth’s atmosphere blocks many other wavelengths.

3. Human eye efficiency detects available light.

QEUSTIONS ABOUT LIGHT

Is light really a wave?

1. Sometimes light acts like a particle “photon”.2. Sometimes light acts like a wave.3. It is really both –or neither- we just don’t have

the right words to describe it completely.

QUESTION ABOUT LIGHT

Energy carried by light depends on wavelength (color, frequency):

• Short wavelength- have more energy.• Long wavelength- have less energy.Example: 1. Blue light carries more energy than red light.2. X-rays carry more energy than radio waves.Formula: E=hc/λ

where E is the energy, λ is the wavelength, and h and c are constant numbers.