[AZ-Observing] Re: [EVAC] Astronomy Survey

My answers in bold, blue below each question.  What is the purpose of the test?
Cheers,

/Bob
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  ----- Original Message ----- 
  From: Chuck 
  To: evac@xxxxxxxxxxxxxxxxxxxxxxx 
  Cc: AZ Observing 
  Sent: Thursday, January 22, 2004 9:41 AM
  Subject: [EVAC] Astronomy Survey


  I have been asked to do a survey for a group of science and astronomy 
teachers in secondary and lower grades locally for use in their classrooms.  If 
you are willing to participate please review and respond off list with a brief 
answer representing your own interpretation to each of the questions below.  

  If not interested then merely delete.  Thanks!

  INTRO: Light is a common aspect of our daily lives. During the daytime, the 
sun provides light. We can also use lamps and other light sources for 
additional lighting. At some point in your life, you may have asked the 
following question "What is light?" We are interested in your current 
fundamental answer to this question. 

  QUESTION 1: What is it about light that makes it different colors (that is, 
what makes blue light blue and red light red)? 

  The wavelength of light contains the color information.  The longer 
wavelengths are towards the red end of the light spectrum, the short 
wavelengths are towards the blue-violet end of the light spectrum.

  QUESTION 2: Consider the following three examples of light: light from the 
sun, light from the lamps overhead, light from your hand right now 

  2a. How do you think these examples of light are the same? 

  They are the same because they are all comprised of photons, the basic form 
of light, no matter what the light source, or it's type.

  2b. How do you think these examples of light are different?

  The light from the sun is called natural light, because it is not man made, 
and comes from a source which we do not control, and is ultimately generated 
from nuclear fusion reactions in the core of the Sun.  The light from the lamp 
is called artificial light, because it comes from a man-made source and can be 
turned off or on at will, and is usually due to either thermal, chemical, or 
electric exitation of electrons and the subsequent loss of energy by those 
electrons in the form of a photon .  The light from your hand is reflected 
light and the light source can be either natural (SUN) or artificial (Lamp) as 
the hand does not generate the light and therefore is not a light source.

  QUESTION 3: You may have heard of light that is "invisible." Examples of this 
are infrared light and ultraviolet light. What about light makes it 
"invisible"? (Try to encourage an answer that is detailed and more than 
'because we can't see it')

  The human eye is sensitive to only a narrow band of the electromagnetic 
spectrum, of which light is a part.  This means that electromagnetic radiation 
(light) with a wavelength longer than the eye's lower wavelength cut-off can't 
be detected, or is said to be invisible to our eyes.  In like manner, 
electromagnetic radiation (light) with a wavelength shorter than the eye's 
upper wavelength cut-off can't be detected, or is also said to be invisible to 
our eyes.   The human eye is most sensitive to yellow-green light, which occurs 
at about a wavelength of 5600 angstroms, which is about the middle of the 
"visible" light spectrum for the human eye.

  QUESTION 4: Do you think infrared light is really light, even though you 
can't see it? Explain your answer; if you think it is something other than 
light, what is it?  

  Infrared light is indeed light, just at a long enough wavelength that puts it 
below the lower wavelength cut-off of the human eye.  It is associated with 
heat, which is yet another form of energy, sometimes referred to as thermal 
energy.  Most all objects emitting thermal energy, also emit infrared light, 
invisible as it may be to the human eye.

  QUESTION 5: Stars are very far away and yet we can see them in the night sky. 
Describe how starlight travels through space. 

  Starlight travels through space in a straight line unless perturbed by either 
a gravitational field, is absorbed by another object, or its direction is 
changed by reflecting off of an object in its path. The eye has a threshold 
such that if the density of light (enough photons per square centimeter) 
reaches our eyes then we shall be able to see it because it takes some minimum 
photon density to trigger the light receptors in our eyes.  If that photon 
density is too low, then we will not be able to "see", or detect, the 
starlight.  Stars of magnitude 6.5 to 7 magnitude, and brighter, generally can 
be seen by the human eye.  Stars of higher magnitude (dimmer) generally do not 
have a high enough photon density reaching our eyes for us to be able to "see" 
(detect) them.

  QUESTION 6: Which travels faster, a radio wave or a light wave? Explain how 
you know the answer to this question.

  Both are forms of electromagnetic radiation, and theoretically have the same 
velocity in free space - approximately 186,000 miles per second.

  Please respond privately to astrogeoc@xxxxxxxx

  Thanks to those who took the time from your busy schedules.

  Chuck Crawford
  Earth/Space Scientific Research Institute, inc.




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