3 ms·

How huge is a 1mm beam when it hits the moon (and visa-versa) ? I wonder if wolframalpha can tell me... Actually, I don't even know how to ask it the proper q

by ck2 13y ago

How huge is a 1mm beam when it hits the moon (and visa-versa) ? I wonder if wolframalpha can tell me... Actually, I don't even know how to ask it the proper question. Can anyone make this formula work in wolfram? http://laserpointerforums.com/attachments/f51/17952-calculate-expansion-laser-beam-schematic_laser_beam.jpg http://laserpointerforums.com/attachments/f51/17952-calculat... update: I think I figured this out as ((λ * L) / d)* 2 (((630nm in meters)*(380000km in meters)) / (1mm in meters)) * 2 Which would be a nearly 500km wide for a 1mm beam on earth from a red laser at 630nm The shortest wavelength laser I can find online is experimental violet at 400nm which would make a 300km beam on the moon.

colanderman 13y ago
Depends on the focal length.
femto 13y ago
The width of the beam is determined by diffraction, caused by the finite aperture of the laser: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp.html http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp.htm...
wyager 13y ago
Even if the laser is extremely low divergence (maybe NASA is using some huge gas laser or something), atmospheric effects will still cause significant widening of the beam.
- deleted 13y ago
  [deleted]
DanBC 13y ago
Have you seen this "What If?" post by xkcd? http://what-if.xkcd.com/13/ http://what-if.xkcd.com/13/ It doesn't talk about the size of the beam as it hits the moon, but it's interesting noodling none-the-less.
- ck2 13y ago
  The end of that had me in tears. I think I like the "what-if" section more than the comics! Gems like Unfortunately, the laser energy flow would turn the atmosphere to plasma, instantly igniting the Earth’s surface and killing us all. and another article It's a shame humans wouldn't live this long, because at this point, something really neat would happen.
  - b_emery 13y ago
    That one links to this: http://what-if.xkcd.com/8/ http://what-if.xkcd.com/8/ which devolves into a hilarious analysis of 'how to get 7 billion people out of Rhode Island'.
    - ck2 13y ago
      I remember reading that one and the hilarious part is, it is not how it is supposed to start off. He seems at first disappointed other sites have attempted to answer the original question, so in his own wonderful style he tries to solve the other weird engineering aspects of it. He seems cut from some of the same cloth as Douglas Adams but with advanced math knowledge.
      - b_emery 13y ago
        Agreed, he must be one of the 10 most creative people on earth.
noselasd 13y ago
Somewhere on a cover event when they launched LADEE, someone asked that, which they answered the receiver had to be within a spot with a (radius or diameter, I can't remember) of 3 km on earth

by ck2 13y ago

colanderman 13y ago

Depends on the focal length.

femto 13y ago

The width of the beam is determined by diffraction, caused by the finite aperture of the laser: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp.html http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp.htm...

wyager 13y ago

Even if the laser is extremely low divergence (maybe NASA is using some huge gas laser or something), atmospheric effects will still cause significant widening of the beam.

deleted 13y ago
[deleted]

DanBC 13y ago

Have you seen this "What If?" post by xkcd? http://what-if.xkcd.com/13/ http://what-if.xkcd.com/13/ It doesn't talk about the size of the beam as it hits the moon, but it's interesting noodling none-the-less.

ck2 13y ago
The end of that had me in tears. I think I like the "what-if" section more than the comics! Gems like Unfortunately, the laser energy flow would turn the atmosphere to plasma, instantly igniting the Earth’s surface and killing us all. and another article It's a shame humans wouldn't live this long, because at this point, something really neat would happen.
- b_emery 13y ago
  That one links to this: http://what-if.xkcd.com/8/ http://what-if.xkcd.com/8/ which devolves into a hilarious analysis of 'how to get 7 billion people out of Rhode Island'.
  - ck2 13y ago
    I remember reading that one and the hilarious part is, it is not how it is supposed to start off. He seems at first disappointed other sites have attempted to answer the original question, so in his own wonderful style he tries to solve the other weird engineering aspects of it. He seems cut from some of the same cloth as Douglas Adams but with advanced math knowledge.
    - b_emery 13y ago
      Agreed, he must be one of the 10 most creative people on earth.

noselasd 13y ago

Somewhere on a cover event when they launched LADEE, someone asked that, which they answered the receiver had to be within a spot with a (radius or diameter, I can't remember) of 3 km on earth