The Naked Scientists

The Naked Scientists Forum

Author Topic: How high would a light shine from 50 miles away?  (Read 7958 times)

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
How high would a light shine from 50 miles away?
« on: 27/03/2008 19:44:01 »
Seany's post about a laser his friend bought prompted this question.

http://www.thenakedscientists.com/forum/index.php?topic=13568.0

Assuming this device really does have a range of 50 miles and was shone horizontally from the waist (say 3ft above the ground), at what altitude would the beam be 50 miles away?


 

Offline Seany

  • Neilep Level Member
  • ******
  • Posts: 4209
  • Live your life to the full!
    • View Profile
How high would a light shine from 50 miles away?
« Reply #1 on: 27/03/2008 22:47:47 »
Nice question Doc! ;) LOL
 

Offline Karen W.

  • Moderator
  • Naked Science Forum GOD!
  • *****
  • Posts: 31653
  • Thanked: 5 times
  • "come fly with me"
    • View Profile
How high would a light shine from 50 miles away?
« Reply #2 on: 27/03/2008 22:49:36 »
Yes indeed!
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
How high would a light shine from 50 miles away?
« Reply #3 on: 27/03/2008 23:04:34 »
The relevance of diegoqing's reply is...?  ???
 

Post by Seany click to view.

Offline Seany

  • Neilep Level Member
  • ******
  • Posts: 4209
  • Live your life to the full!
    • View Profile
How high would a light shine from 50 miles away?
« Reply #4 on: 27/03/2008 23:05:53 »
Shrunk
Ermm.. Like.. Because

If you buy some Nike trainers, you feel more lively and jolly and moveable.. So you jump up and down with Michael Jordan's nike shoes and you see how high the laser is..

I donno!! ;D
 

Offline Karen W.

  • Moderator
  • Naked Science Forum GOD!
  • *****
  • Posts: 31653
  • Thanked: 5 times
  • "come fly with me"
    • View Profile
How high would a light shine from 50 miles away?
« Reply #5 on: 27/03/2008 23:14:24 »
Well I think his shoes allowed me to give a good kick!! LOL!
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
How high would a light shine from 50 miles away?
« Reply #6 on: 28/03/2008 07:31:59 »
Anyone reading this will wonder what the hell we're talking about. They won't realise a post has been deleted. Well, they will now because I've mentioned it. But they won't know what it said.
 

Post by Seany click to view.

Offline Seany

  • Neilep Level Member
  • ******
  • Posts: 4209
  • Live your life to the full!
    • View Profile
How high would a light shine from 50 miles away?
« Reply #7 on: 28/03/2008 10:41:27 »
Shrunk
LOL, something about nike trainers ;D
 

Offline turnipsock

  • Hero Member
  • *****
  • Posts: 586
  • Beekeeper to the unsuspecting
    • View Profile
How high would a light shine from 50 miles away?
« Reply #8 on: 28/03/2008 11:45:40 »
It will be 0.35 of a mile, plus 3 ft.
 

Offline Seany

  • Neilep Level Member
  • ******
  • Posts: 4209
  • Live your life to the full!
    • View Profile
How high would a light shine from 50 miles away?
« Reply #9 on: 28/03/2008 12:46:11 »
It will be 0.35 of a mile, plus 3 ft.

How did you work this out? :o
 

Offline Seany

  • Neilep Level Member
  • ******
  • Posts: 4209
  • Live your life to the full!
    • View Profile
How high would a light shine from 50 miles away?
« Reply #10 on: 28/03/2008 12:46:49 »
Seany's post about a laser his friend bought prompted this question.

http://www.thenakedscientists.com/forum/index.php?topic=13568.0

Assuming this device really does have a range of 50 miles and was shone horizontally from the waist (say 3ft above the ground), at what altitude would the beam be 50 miles away?

Doesn't it also differ with the quality of the laser? Better lasers spread less than others//
 

Offline turnipsock

  • Hero Member
  • *****
  • Posts: 586
  • Beekeeper to the unsuspecting
    • View Profile
How high would a light shine from 50 miles away?
« Reply #11 on: 28/03/2008 13:35:25 »
It will be 0.35 of a mile, plus 3 ft.

How did you work this out? :o

The circumference of the earth is 360x60=21,600 miles. That is because one mile equals 1 minute of a degree.

From that you can calculate the radius of the earth.

Then it is just a right angled triangle after that where one side is the radius of the earth, another side is 50 miles and you can calculate the length of the hypotenuse. The altitude is the difference between the hypotenuse and the radius of the earth.

A similar thing occurs when ships have to calculate at what distance they should be able to see a lighthouse.
« Last Edit: 28/03/2008 15:04:56 by turnipsock »
 

Offline ukmicky

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 3011
    • View Profile
    • http://www.space-talk.com/
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
How high would a light shine from 50 miles away?
« Reply #13 on: 28/03/2008 20:39:19 »

The circumference of the earth is 360x60=21,600 miles.

No it isn't. The equatorial circumference is 24,901 miles, and the polar circumference is 24,859 miles.

Your error doesn't inspire me with confidence in your answer  :P
 

Offline Seany

  • Neilep Level Member
  • ******
  • Posts: 4209
  • Live your life to the full!
    • View Profile
How high would a light shine from 50 miles away?
« Reply #14 on: 28/03/2008 22:42:21 »
:P
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8661
  • Thanked: 42 times
    • View Profile
How high would a light shine from 50 miles away?
« Reply #15 on: 29/03/2008 16:41:46 »
There's another complication. The air is denser at lower altitudes and so it has a higher refractive index. This means that the light bends downwards slightly.
 

Offline Pumblechook

  • Hero Member
  • *****
  • Posts: 569
    • View Profile
How high would a light shine from 50 miles away?
« Reply #16 on: 29/03/2008 17:02:48 »
If h is in meters, that makes the distance to the geometric horizon 3.57 km times the square root of the height of the eye in meters (or about 1.23 miles times the square root of the eye height in feet).   

= about 500 metres.  This is ignoring any bending and the fact that it is rarely clear enough.  A power light ot laser will help.  I saw the hills of North Wales (incl Great Orme) from near sea level at Blackpool last year at the distance is pretty well 50 miles.   
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
How high would a light shine from 50 miles away?
« Reply #17 on: 30/03/2008 08:38:57 »
Wouldn't the Earth's gravitational field pull the beam down too?
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8661
  • Thanked: 42 times
    • View Profile
How high would a light shine from 50 miles away?
« Reply #18 on: 30/03/2008 14:33:03 »
The direct effect of gravity is pretty small but the effect of the refraction is significant. If the earth's atmosphere weree replaced by SO2 which has a slightly greater refractive index, the curvature due to refraction would be roughly the same as the curvature of the earth and light would go right round (ignoring any mountains).
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
How high would a light shine from 50 miles away?
« Reply #19 on: 30/03/2008 21:08:03 »
The direct effect of gravity is pretty small but the effect of the refraction is significant. If the earth's atmosphere weree replaced by SO2 which has a slightly greater refractive index, the curvature due to refraction would be roughly the same as the curvature of the earth and light would go right round (ignoring any mountains).

Oooh... that could be fun. I could shine a torch on my own ars back!
 

Offline turnipsock

  • Hero Member
  • *****
  • Posts: 586
  • Beekeeper to the unsuspecting
    • View Profile
How high would a light shine from 50 miles away?
« Reply #20 on: 30/03/2008 23:56:41 »
The direct effect of gravity is pretty small but the effect of the refraction is significant. If the earth's atmosphere weree replaced by SO2 which has a slightly greater refractive index, the curvature due to refraction would be roughly the same as the curvature of the earth and light would go right round (ignoring any mountains).

Would that mean if the Doc fired a laser, 3ft above the ground, in an atmosphere of SO2, it would hit him in the ars back? I saw a good laser in Thunderball.
 

Offline Karen W.

  • Moderator
  • Naked Science Forum GOD!
  • *****
  • Posts: 31653
  • Thanked: 5 times
  • "come fly with me"
    • View Profile
How high would a light shine from 50 miles away?
« Reply #21 on: 31/03/2008 03:25:40 »
Anyone reading this will wonder what the hell we're talking about. They won't realise a post has been deleted. Well, they will now because I've mentioned it. But they won't know what it said.

He was spamming the site.. in a couple places.. LOL!
 

The Naked Scientists Forum

How high would a light shine from 50 miles away?
« Reply #21 on: 31/03/2008 03:25:40 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums