Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

Laser into the night sky, How far am I seeing it?

Joined
Mar 19, 2014
Messages
49
Points
8
I have a 5mw green pointer and 1.7w+- 445nm pointer. When I shine them both into the night sky they both seem to go on until a certain point. The point is the same with the both of them. How far is it?
I have a theory that its the intersection of a straight line from my eye versus a straight line from my hand but that doesnt seem correct because the distance seems the same when I mount it in a tripod.

I am sure there is some scientific name for this and explanation
 





Joined
Jan 22, 2014
Messages
464
Points
28
Well I think they can see laser pointers from the space station? Not saying there is a visible beam seen from up there but visible light has made it that far and further, it just keeps going and going and going until every last photon has been blocked or
by something, mind boggling awesomeness is the scale of the Universe!
 
Joined
May 14, 2013
Messages
3,438
Points
0
Yes that's right, that 1.7W 445nm would be easily visible from the space station if you were to shine it directly at them, and that's over 310 miles at its closest. The 5mW green would quickly become too dim, I don't know but I doubt it would be visible from a mile away even pointed straight at you but I could be wrong, it depends a lot too on atmospheric conditions.

Alan
 
Joined
Aug 14, 2013
Messages
2,655
Points
63
I don't know enough about the atmosphere to say for sure, but dirt water vapor in the air are what make the
beam more visible. As you get higher, the air becomes less dense, and probably cleaner, and drier. That
would make the beam appear to stop when in actuality it is moving on even more unimpeded. You just
can't see it because there is nothing to bounce or turn it back down to your eyes. Again I don't know for
sure because I have no way to test it, but I'm guessing that in a vacuum a laser beam would be much
more difficult to see because there is nothing for it to interact with.
 
Joined
May 14, 2013
Messages
3,438
Points
0
Yes in a vacuum the beam is not visible, unlike in Sci-Fi movies. I frequently make a ionic/colloidal silver solution and I use a 5mW 635nm to provide a visual indication of the particulate silver content. When I begin with distilled water there is no beam visible when shinning it through the distilled water but as the silver content reaches only a few parts per million the beam becomes very visible.

Alan
 
Joined
May 6, 2013
Messages
178
Points
0
I think the only way to answer that question is with two people: one shining the laser up, and someone else standing on a high hill or small mountain some distance away looking horizontally towards the beam. When your eyes are close to the source of the beam, the perspective lines make it impossible to judge.
 
Joined
Jan 7, 2007
Messages
6,309
Points
83
Consider that the atmosphere with all it's dust etc ends up there to go to a vacuum
where the beam becomes invisible. The beam goes on to become nothing, considering
all the stuff it encounters coupled with beam expansion.
The visible beam appears to end at the edge of our atmosphere.
HMike
 
Last edited:
Joined
Feb 24, 2014
Messages
1,425
Points
83
The star wars program started by president regan struggled with making lasers strong enough to destroy a missile in flight. the atmosphere does some crazy things to laser light but the navy has a missile defense system that uses 8 different lasers to accomplish this its all over the web look it up
 
Joined
Jan 7, 2007
Messages
6,309
Points
83
300 feet+ is clean and dry? WOW --
We get towering Q's here going to over
25,000 feet. Storm clouds, moisture.
I have encountered corn husks in the air
at 1,500+ feet AGL while flying my old Piper...
I even punched a Cumulus cloud at 10,000' once
HMike
 
Last edited:
Joined
Mar 19, 2014
Messages
49
Points
8
The 300 foot aerosol layer seem about right. Both the 5mw green and the 1+w 445 seem to viaually end at the same spot in the night sky
 
Joined
Dec 10, 2013
Messages
1,343
Points
83
I think the only way to answer that question is with two people: one shining the laser up, and someone else standing on a high hill or small mountain some distance away looking horizontally towards the beam. When your eyes are close to the source of the beam, the perspective lines make it impossible to judge.

Would you even see it though, unless it was a laser tens of watts in power?
 
Joined
May 6, 2013
Messages
178
Points
0
Would you even see it though, unless it was a laser tens of watts in power?

It depends on the distance. In my home town, roughly square-shaped and 7 miles on a side, we have four hills that are more than 900 feet high, 13 more that are over 500 feet high, and a whole bunch in the 200-500 foot range. From the top of one these hills, the bottom could be anywhere from 2 or 3 blocks to maybe a mile. I'm pretty sure a 50mW greenie would work with higher hills, 5mW with the smaller ones.
 
Joined
May 6, 2013
Messages
178
Points
0
It is surprisingly hard to see a laser when you are looking at it "side on".

I agree that viewing angle makes a huge difference. When trying to see a hard-to-see beam, it's a question of how small you can make it in your field of view. Looking down the beam really helps. On the other hand, if you want to see how far it's going, something like 90 degrees would be ideal. Since that would diminish brightness, the question becomes what can be done to compensate, besides a more powerful laser.

Distance: looking out the window of a tall building, have someone across the street shine the laser straight up. Then have the person go half way down the block so you can get a better view.

Darkness: get as far away from light pollution as possible

By the way, I've never heard of a 300-foot aerosol layer. There's a stratospheric aerosol layer called the Junge layer. Just from my own observations, there does seem to be a lot more mist and dust at very low elevations.
 
Joined
Jan 7, 2007
Messages
6,309
Points
83
OK - I yield. My experience fails to
globule warming stuff..... But I occasionally
wash my plane in a fair weather Q. Takes
about 10 seconds. :)
HMike

Is that 300' AGL or ASL ???
 
Last edited:




Top