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

Buy Site Supporter Role (remove some ads) | LPF Donations

Links below open in new window

FrozenGate by Avery

Keeping a small dot over one mile distance

srow said:
Yes, but I've got to study it first. The moon is an extremely interesting topic to me and I'm gasping to get onto it. When you look at the moon with a clear sky it shines so bright it's very hard to believe that it is just reflecting light from the sun. If you held a grey rock up to a bright light would it really shine like the moon do you think? Of course, flat earth theory says that the moon is a self illuminating and not reflecting the suns light.
Click to expand...

Self illuminating moon? wow, i mean really wow. you do understand that the only reason you see anything is because of reflected light, right?
 





BowtieGuy said:
Check this Link out for some interesting ideas on that subject. If you want, skip to - "Part 2 - Why does the beam from a green laser appear to "end" in the sky as compared to just going on forever?", that's where the pertinent info. starts. Interesting reading at the very least.
Click to expand...
I got this from your link:-

"We transmit high-power laser beams in the zenith on many occasions and observe the same optical effect you describe. The cause of this is the enhancement of aerosols (atmospheric particles) in the planetary boundary layer (PBL) which causes enhanced scattering of the laser beam back to your eyes. Above the PBL, which can be very low at night (<100 m), the amount of aerosols is very low compared to within the PBL, and as a result the scattering of the laser beam appears to end abruptly at the top of the PBL. More sensitive detectors, such as we use in Lidar, can continue to sense the scattering from aerosols and molecules well above the PBL demonstrating that the beam does not just stop there. If you are interested, you can see from our airborne lidar images that are posted on our web site (NASA Langley Lidar Applications Group) how the aerosols (and scattering) vary across the atmosphere."
Click to expand...
This doesn't explain why laser beams appear to end abruptly when they are fired horizontally. It talks about the PBL being the boundary at which the laser ends abruptly but that would only account for when the laser is being fired vertically and not horizontally. Perspective explains why the laser ends so abruptly. The vanishing point caused by perspective is abrupt like an exact cut off point beyond which is invisibility. What a perfect example of perspective and shows exactly what happens at the horizon. I never thought lasers and flat earth theory had so much in common.
 
srow said:
Yes, but I've got to study it first. The moon is an extremely interesting topic to me and I'm gasping to get onto it. When you look at the moon with a clear sky it shines so bright it's very hard to believe that it is just reflecting light from the sun. If you held a grey rock up to a bright light would it really shine like the moon do you think? Of course, flat earth theory says that the moon is a self illuminating and not reflecting the suns light.
Click to expand...

Atoms are required to go into a higher energy state before they emit a photon, which, of course, requires energy. The moon is not nearly massive enough to induce nuclear fusion, so if the moon is self-illuminating then where is the energy coming from?

Also, it wouldn't shine like the moon, because the sun is much brighter than a flashlight. It would reflect about the same percentage of light though.
 
What shape do you believe the earth to be then, srow? A disc, an infinite plane, a cylinder?
 
Can we all just stop now? This isn't real. Nobody is this naive. Nobody, at this point in human history, is dumb enough to ignore the scientific, mathematical, observational and countless other forms of proof that the Earth is spherical. So please srow, do your experiment so you can come back here and make excuses why the results you get are flawed.
 
paulys55 said:
Can we all just stop now? This isn't real. Nobody is this naive. Nobody, at this point in human history, is dumb enough to ignore the scientific, mathematical, observational and countless other forms of proof that the Earth is spherical. So please srow, do your experiment so you can come back here and make excuses why the results you get are flawed.
Click to expand...


You'd be surprised ... :(
 
The topic of keeping a beam tight over distance is a good one.

We could ignore the premise and talk about the technical aspect.

One might ponder why a laser diode with a lens in front of it that can focus bigger and smaller cant produce as tight of a point at distance as we want.

Well have you ever held a magnifying glass over a white piece of paper on your desk and moved it up and down in line with your overhead light source until you can see an image of the light above you?

What determines the size of that image?

Now take that paper and move it to half the distance between your desk and the light source and focus to an image again....it's not the same size image...hmm :thinking:

Well any lens has a focal length for the point source based on it's shape and the smaller the point source is the tighter/smaller your focused image will be.

At twice that focal length the focused image will be twice as wide and twice as tall, making it 400% the area and 1/4 the energy density.

Now if you expand your point source of light and use a wider lens with a longer focal length then you can extend the distance that you produce the 1st size focal picture. But your beam will be wider to start.

Look at the beam that comes out of a dpss 532nm crystal, it is needle thin, but to get a decent beam over a distance there is first a little GRIN lens or gradient index lens, it's basically a double concave that expands that needle thin beam so it can be focused over a longer distance and maintain the appearance of an infinite beam, that beam diameter is actually expanding, it just looks like a tiny beam because of our visual perspective.

Just like a street light looks so much bigger when it's laying on the ground.

Anyway if you want to measure over distance by the outside edge of any laser beam you will not get accurate results, you must measure from starting center to your ending center.

p.s. You can build a telescope of lenses to shrink your beam smaller to start, but any laser beam is always either expanding or contracting over distance by some amount.
 
Last edited:
I dunno, I don't think we should ban him yet. He hasn't contributed anything, but he hasn't abused or harmed anyone either. We should also wait until we're 100% sure he is a troll before banning, we don't want to ban an innocent (albeit close-minded) n00b.
 
H2Oxide said:
Aye.

This is a science(ish) forum and he is providing no hard evidence to back up his claims.
Click to expand...

Yeah I'm shocked at the nitpicking of evidence. For example this thing with the snipers. Who sees snipers on a regular basis anyway? wtf

Gabe said:
I dunno, I don't think we should ban him yet. He hasn't contributed anything, but he hasn't abused or harmed anyone either. We should also wait until we're 100% sure he is a troll before banning, we don't want to ban an innocent (albeit close-minded) n00b.
Click to expand...

Yeah I guess so. It's really up to the mods to ban anyway. I figured this isn't going to get better any time soon lol
 
Hahahhahah, just found this thread and it has made my day! People believing in a flat earth....
 
srow said:
Yes, but I've got to study it first. The moon is an extremely interesting topic to me and I'm gasping to get onto it. When you look at the moon with a clear sky it shines so bright it's very hard to believe that it is just reflecting light from the sun. If you held a grey rock up to a bright light would it really shine like the moon do you think? Of course, flat earth theory says that the moon is a self illuminating and not reflecting the suns light.
Click to expand...

Ok, so please answer this:
Have another look at my lunar eclipse photos, if the moon is self illuminating then why do we see the earth's shadow come across the face of the moon during a lunar eclipse, pray tell?

:)
 
The fact that you can see the grey rock in direct sunlight means a significant amount of light is being reflected back at you. The reason the moon looks so bright, is because it is juxtaposed against the black void of space. It's not actually that bright, you can rarely see the moon in the light of day.


A grey rock hit by direct sunlight when everything else is devoid of light would actually look very bright. Project a white laser on a grey rock in a deep cave and you'll see what I mean. Next time you read a book on your classic Kindle also note how bright grey can be in direct sunlight, against the contrast of black letters.

Anyway, no point debating a flat earth'er. As long as you're not trying to teach kids or anything, you can believe the moon is a giant jelly bean for all I care. :pop:

As for the topic of banning, come on. You shouldn't ban people for having different ideas, even if they're comical. I support open forums. He's not harming/scamming anyone, he should be able to share his ideas and we should be able to laugh at them.
 
Last edited:
Akiyama said:
The fact that you can see the grey rock in direct sunlight means a significant amount of light is being reflected back at you. The reason the moon looks so bright, is because it is juxtaposed against the black void of space. It's not actually that bright, you can rarely see the moon in the light of day.


A grey rock hit by direct sunlight when everything else is devoid of light would actually look very bright. Project a white laser on a grey rock in a deep cave and you'll see what I mean. Next time you read a book on your classic Kindle also note how bright grey can be in direct sunlight, against the contrast of black letters...
Click to expand...
Actually, the moon really is "that bright".

From the film days of photograph, many professional photographers used the "sunny 16" rule to determine exposure when we didn't have an exposure meter at hand, or were too lazy to use one. That rule said when shooting a scene in bright sunlight if you used an aperture of f16, then the shutter speed on the camera would be the reciprocal of the film ISO. That means that if your film was ISO 200 then you could shoot at f16 with a shutter speed of 1/200 sec.

This rule applied pretty well to shooting the full moon too. Day or night you could get good detailed shots of the moon at that "sunny 16" or equivalent exposure. Sometimes some photogs liked to open up one stop from that exposure but basically the moon behaves just like any earthbound object when determining exposure in sunlight.

Ed
 
You must log in or register to reply here.


Back
Top