MadSci Network: Astronomy

Subject: How much light would a city add to starlight, for reading by starlight?

Date: Thu Sep 23 14:48:37 2004
Posted by Michael
Grade level: undergrad School: No school entered.
City: Tucson State/Province: AZ Country: USA
Area of science: Astronomy
ID: 1095968917.As

My friend said that he can read a map in nothing but starlight.  He makes stuff 
up all the time, so I have doubts, but it makes sense that he could just have 
good eyes.  He came back from a camping trip and said he'd done it.
I can think of three ways he's telling the truth:
1. He really does have better vision than most people.
2. The moon was out (I think it was close to the sun, on the day-side of Earth)
3. The lights from the nearby city gave him extra light.
Does number 3 make sense?
- The city is Tucson, AZ.  I don't how they measure light pollution, so I can't 
tell you how bright it is (thought you might know somebody from a telescope 
down here that could tell you).
- He would have been about 5,000 feet above the city, and 5-10 miles north of 
the city.
- He was in a valley between a couple of the lower "peaks", with one of them 
directly between him and the city.
- My thinking is that the light from the city, while not directly visible, went 
up into the atmosphere, then bounced around until some of it came back down, 
providing a significant amount of illumination.
He's not objective about anything (he attempts to refuse to be proved wrong), 
so I wouldn't be surprised if there was obvious light pollution that he didn't 
  R. Michael Starr II, A1C, USAF

Re: How much light would a city add to starlight, for reading by starlight?

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