# Laser pointers and airports question **URL:** \ **Category:** Factual Questions\ **Created:** [December 19, 2006, 9:21pm UTC](https://boards.straightdope.com/t/laser-pointers-and-airports-question/384836 "2006-12-19T21:21:39Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![BwanaBob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bwanabob/32/2985_2.png) [@BwanaBob](https://boards.straightdope.com/u/BwanaBob)\ **Post date:** [December 19, 2006, 9:21pm UTC](https://boards.straightdope.com/t/laser-pointers-and-airports-question/384836/1 "2006-12-19T21:21:39Z")
Well I just got a Class IIIa green laser pointer (for astronomy use). Rated at less than 5 mW. I understand there are restrictions as to its use near airports. Problem is the FAA site is a horrific morass of info; I cannot tell if my unit is restricted/illegal to use where I live ( I am within 10 nautical miles of an airport). They somehow expect you to know the beam divergeance of your unit. No info like that was provided with the unit. Only its class. So am I out-of-luck? I don’t want to be arrested because I pointed out Betelgeuse to my kid. Any astronomer dopers out there that have better info? Thanks ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [December 19, 2006, 9:26pm UTC](https://boards.straightdope.com/t/laser-pointers-and-airports-question/384836/2 "2006-12-19T21:26:45Z")
Manufacturers often list the divergence of the beam in its specs. If the data didn’t come with your unit, you can check on-line for its specs. Heck, contact them and ask about use near airports. If you know the beam size, you can work out its divergence – the smaller the beam, the larger the divergence. You can assume TEM[sub]00[/sub] mode. ---
**Author:** ![MrSquishy](https://avatars.discourse-cdn.com/v4/letter/m/b9e5f3/32.png) [@MrSquishy](https://boards.straightdope.com/u/MrSquishy)\ **Post date:** [December 19, 2006, 10:39pm UTC](https://boards.straightdope.com/t/laser-pointers-and-airports-question/384836/3 "2006-12-19T22:39:33Z")
[QUOTE=BwanaBob] Well I just got a Class IIIa green laser pointer (for astronomy use)… [/QUOTE] Do tell! How do you point out stars with a laser pointer? I mean, I’m guessing the little green dot doesn’t show up on the star itself (or not for a long time, anyway). This sounds cool, and I have a friend interested in astronomy who needs a Christmas gift… ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [December 19, 2006, 10:43pm UTC](https://boards.straightdope.com/t/laser-pointers-and-airports-question/384836/4 "2006-12-19T22:43:43Z")
[QUOTE=MrSquishy] Do tell! How do you point out stars with a laser pointer? I mean, I’m guessing the little green dot doesn’t show up on the star itself (or not for a long time, anyway). This sounds cool, and I have a friend interested in astronomy who needs a Christmas gift… [/QUOTE] The high-powered green laser pointers are bright enough that they’ll visibly reflect off dust particles in the air, allowing you to “point” really, really far. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [December 19, 2006, 10:45pm UTC](https://boards.straightdope.com/t/laser-pointers-and-airports-question/384836/5 "2006-12-19T22:45:10Z")
For astronomical demonstration use in front of an audience, you also need a cloud/fog/smoke-generating machine. That makes the beam nice and visible. Oh. Wait… ---
**Author:** ![JCorre](https://avatars.discourse-cdn.com/v4/letter/j/3da27b/32.png) [@JCorre](https://boards.straightdope.com/u/JCorre)\ **Post date:** [December 20, 2006, 1:38am UTC](https://boards.straightdope.com/t/laser-pointers-and-airports-question/384836/6 "2006-12-20T01:38:26Z")
There’s also [this](http://www.thinkgeek.com/gadgets/lights/8a39/) laser pointer (Class IIIB 10mW). You should be able to see its beam when pointing out stuff in the nighttime sky.