The Naked Scientists

The Naked Scientists Forum

Author Topic: Northern Lights & Holograms  (Read 13548 times)

Offline Tann San

  • Jr. Member
  • **
  • Posts: 44
    • View Profile
Re: Northern Lights & Holograms
« Reply #25 on: 14/12/2003 14:56:15 »
Hey thanks tweener that answered the second part.  What about gas.  Would gas or make the beam visible.  Or how about hot air.  Hot air refracts light kinda funny though doesnt it but a transparent gas in a large sealed container might not.  Maybe the gas moving would be a problem, gas moves in a vacume doesnt it.  hu.  I think I might try making one of those home holograms I've been reading about and just try some things out.
 

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 1144
    • View Profile
Re: Northern Lights & Holograms
« Reply #26 on: 14/12/2003 22:19:46 »
It depends on what gas you are talking about.  If the gas is transparent (like air, oxygen, nitrogen, methane, etc.) then, no it would not make a laser visible.  To make it visible you must have something that changes the direction of some of the photons in the beam, making them come into your eye.  Dust, water droplets (not vapor), smoke are good candidates.

The temperature of air won't really make any difference.  What you see as funny refractions in hot air are turbulent pockets of air at different temperatures.  The index of refraction changes with temperature, so the light will bend differently going through pockets of differing temperatures.  A laser passing through this turbulence would be deflected slightly so that on the "output" the spot projected by the laser would be moving around and changing size a little bit.  I doubt there would be enough scattering to make the beam visible, though there would be some very small amount.

I wish you luck with your home holograms.  Be sure to post your results!



----
John
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5339
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: Northern Lights & Holograms
« Reply #27 on: 17/12/2003 17:14:44 »
John - why does light 'bend' when passing through air of differing temperatures ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
 

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • Posts: 1144
    • View Profile
Re: Northern Lights & Holograms
« Reply #28 on: 18/12/2003 03:07:18 »
The change in temperature changes the density of the air, which changes the refractive index.  When light passes at an angle relative to the boundary of the two different air masses, the change in refractive index will bend the beam of light according to Snell's law.  Also, depending on the difference in refractive index and the angle of incidence, there may be some reflection, based on the same prinicples.  This is why you see wavy looking mirages in the heat coming off pavement or car tops in the summer.

Well, maybe you don't in the UK because you don't see the sun much. :)

I searched and found a good basic explanation here http://www.sasked.gov.sk.ca/docs/physics/u3c12phy.html


----
John
 

Offline Tann San

  • Jr. Member
  • **
  • Posts: 44
    • View Profile
Re: Northern Lights & Holograms
« Reply #29 on: 21/12/2003 00:03:52 »
Hi, I found this site which has alot of good examples and explanations

http://micro.magnet.fsu.edu/primer/lightandcolor/java.html [nofollow]
 

Offline Broca

  • Sr. Member
  • ****
  • Posts: 162
    • View Profile
Re: Northern Lights & Holograms
« Reply #30 on: 26/05/2004 01:22:43 »
Wow I just marvel at the minds in here.I have a question that is sort of along these lines and was hoping you could give me some feedback. I was told that the Northern lights are a form of the 4th state of matter, plasma. What are your views and thoughts on this.
 

Offline gsmollin

  • Hero Member
  • *****
  • Posts: 749
    • View Profile
Re: Northern Lights & Holograms
« Reply #31 on: 26/05/2004 01:36:32 »
A thread from the dead!

Yes, the auroras are caue by "plasma", meaning charged particles. The sun gives off a solar wind, which consists of many charged particles. Most of it is ionized hydrogen and helium, and electrons, because that's what the sun is made of. The particles move with some pretty high speeds. They can cover the distance from the sun to the earth in hours to days, depending on the particle. Now rapidly moving charged particles constitute an electric current, and the earth's magnetic field deflects moving charges towards the poles. So the charged particles impact the earth's ionosphere mainly at the magnetic poles. The energy of the moving charges is converted into radiation in the upper atmosphere, and we see lights.
 

Offline Broca

  • Sr. Member
  • ****
  • Posts: 162
    • View Profile
Re: Northern Lights & Holograms
« Reply #32 on: 26/05/2004 01:49:48 »
Wow, thank you for the info. I teach the kids in my 4th grade about plasma and I have a plasma ball.They love playing with that. I like making the connection to them with the Northern lights.We can see them from time to time if you go far from the light pollution.It is also a great way to teach some folklore as the Vikings thought the "lights" was the sun beating off the chest of Valkeries as they took fallen vikings to Val Hala.
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8132
  • Thanked: 53 times
    • View Profile
Re: Northern Lights & Holograms
« Reply #33 on: 30/04/2007 17:58:59 »
what I was wondering was if there was any applicability of using rainbows as holograms. 

The "Fogscreen" does use water droplets to display images , but they are not holographic:-
http://www.it-ltd.com/fogscreen.php?gclid=CK-hgNP16osCFQfnlAodMg8QQw
It only costs 62K  :o
« Last Edit: 30/04/2007 18:00:44 by RD »
 

Offline moonfire

  • Neilep Level Member
  • ******
  • Posts: 4597
  • Can't stand the heat, step away from the fire!
    • View Profile
    • http://www.m2global.com/stormdiamonds
Re: Northern Lights & Holograms
« Reply #34 on: 30/04/2007 18:08:22 »
I have seen computers with lighted keyboards projected on table and air...pretty awesome!
 

The Naked Scientists Forum

Re: Northern Lights & Holograms
« Reply #34 on: 30/04/2007 18:08:22 »

 

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