Giant Laser

Status: Real
image Found on Flickr: a cool picture of a giant laser beaming out of the MMT Telescope, on top of Mt. Hopkins in Arizona. The guy who took it, Filip Pizlo, says it's not photoshopped, and I'm willing to believe him, if only because when I was a grad student at UC San Diego there was a green laser beam similar to this visible in the sky over La Jolla almost every night. I never figured out where it was coming from or what the purpose of it was. It couldn't have been coming from the MMT Telescope in Arizona because that would have been too far away.

Photos Places

Posted on Tue Apr 18, 2006


It allows them to calibrate the variation in the atmosphere to the images captured by the telescope for better quality images.

Badly explained, not a hoax.
Posted by Stuart  on  Tue Apr 18, 2006  at  11:48 PM
I think it's fishy. A laser is a concentrated beam of light so it behaves a little differently then regular light. For one thing, it is pretty much invisible unless the light hits something like a wall or water and dust in the air. That's why if you go to a laser show there's usually a screen the lasers are targeted on, or lots of dry ice smoke in the air.

The problem I see with this picture is that while it is possible that there could be enough dust in the air to make the laser visible, wouldn't that make a terrible location for a telescope? After all, even if this telescope is only used for studying the atmosphere, lots of dust on the ground level will probably screw up your readings.
Posted by Guest  on  Wed Apr 19, 2006  at  12:10 AM
Could it have been photographed with some sort of a filter, showing the energy radiated by the air around the beam that's been heated up by the beam passing through it?
Posted by Accipiter  on  Wed Apr 19, 2006  at  01:28 AM
Seems pretty solid-looking for a beam of light. Plus half of the building it's coming from seems to be coated in the same green light.
Posted by Smerk  on  Wed Apr 19, 2006  at  02:04 AM
No I'm pretty sure that the lasers themselves are real, as for this particular image I'm not too sure, but it could be real. If I'm not mistaken such lasers are used in astronomy a lot, and there are some available to astronomers who use them to point out constellations. They usually project a green beam in the sky. Also there have been some issues with people using them to blind pilots attempting to land at airports (at least here in Australia).

I was pretty amazed myself when I found out about these lasers. I do not know exactly how they work, but I'm pretty sure that they are factual.
Posted by Soldant  on  Wed Apr 19, 2006  at  02:16 AM
WAIT, I just noticed this: the photo had a relatively long exposure time. The reason is because stars can be seen in the background as well as a bit of skyglow. Having done astrophotography myself, I can relatively safely say this was probably over 15 seconds in exposure length, since the brighter stars are over exposed and there are quite a number of stars visible.

This long exposure would obviously make the laser a lot brighter as well as the area inside the dome than if you were viewing it in person. Hence it looks a very, very solid neon green. In real life it may not have been so solid, it may have been more translucent, but it appears this way because of the long exposure.
Posted by Soldant  on  Wed Apr 19, 2006  at  05:35 AM
Sorry for triple posting, but: if you look closely, star trails are starting to form in the image, further evidence that it is a long exposure. I'll be quiet now.
Posted by Soldant  on  Wed Apr 19, 2006  at  05:40 AM
Green Lasers, Unlike red lasers, have a visible beam, even in semi light conditions. A laser used for scientific purposes wont be the kind you buy at radio shack or your local electronics store, this kind is large and powerful. The fact that it is the green kind especially, makes it likely you could see it like the photo shows in real life. Even the hand held pointers you can buy on ebay that are green have a visible beam. Just FYI.
Posted by Tim  on  Wed Apr 19, 2006  at  08:37 AM
Green laser pointers are becoming quite common at astronomy gatherings and star parties. They are used to point out celestial objects and as finder devices on telescopes.

Here is a website that sells them:

I can vouch for the reality of these lasers, I have a 5mw version and the beam is quite visible to the naked eye.

Observatories use them in a process called "adaptive optics" as described in a previouse post. Large aperture telescopes using adaptive optics can almost completely negate atmospheric effects (called 'bad seeing') and obtain higher resolution images of dimmer objects than the Hubble Space Telescope. The main advantage the HST now is that it can see parts of the spectrum that are filtered out by the atmosphere.
Posted by Blondin  on  Wed Apr 19, 2006  at  09:09 AM
I used to live and work in San Diego (Mira Mesa) and I remember the laser light show above La Jolla. If I recall correctly it was part of the San Diego Tech Center art program. Part of the same program that funded the big red tubes that were visible from the 805 and Miramar road. Anyway, there were 3 or 4 separate beams that danced around for several hours every night for about a year. Very visable from all of northern San Deigo.
Posted by danny boySD  on  Wed Apr 19, 2006  at  10:42 AM
check out or do a search for "adaptive optics" on if my link didn't post correctly.

There's a thin layer of a specific type of gas in the atmosphere that glows when hit with a laser and creates a holographic, artificial "star" that can be used in calibrating a telescope to compensate for atmospheric interference.

"An alternative is the use of a laser beam to generate a target (a Laser guide star, LGS) in the atmosphere. LGSs come in two flavors: Rayleigh guide stars and sodium guide stars. Rayleigh guide stars work by propagating a laser, usually at near ultraviolet wavelengths, and detecting the backscatter from air at altitudes between 15-25 km. Sodium guide stars use laser light at 589 nm to excite sodium atoms in the mesosphere and thermosphere, which then appear to "glow". The LGS can then be used as a wavefront reference ..."
Posted by intjudo  on  Wed Apr 19, 2006  at  11:49 AM
Lasers are used to measure the distance to the moon and compute how fast it's moving away from Earth. That could be what this is.
Posted by Ian  on  Wed Apr 19, 2006  at  05:19 PM
The first time a read about these green lasers was when they were first tested over cities to calibrate the effects of dust on the beam of light.
I'm not sure about the power of the lasers at that time, but the light would only be visible to the naked eye when there was enough dust (hence the long exposure time).

I don't think they are the kind of lasers that can reach to the upper layers of the atmosphere, most likely they are used to filter out the effects of small particles on observations.
Posted by FrostBird  on  Thu Apr 20, 2006  at  06:41 AM
While I was in the USAF and stationed at Wright-Patterson Air Force Base, they had a lab in area 'B' (the R&D area of the base) that was a tall building that shot a laser straight up into the atmosphere. It also had a large vacuum chamber at it's base for objects necessary to the experiments run there. I know about it as I went through this building often to reach our MARS repeater located at the top of the building. These lasers are located at all kinds of research facilities in the world. Nothing secret or unusual....
Posted by Jim Phelps  on  Thu Apr 20, 2006  at  07:03 AM
"I used to live and work in San Diego (Mira Mesa) and I remember the laser light show above La Jolla. If I recall correctly it was part of the San Diego Tech Center art program." Spot on, dannyboy SD...I'm a San Diego native (47 years) and I remember the laser show in UTC quite fondly. It was generated from the top of a bank building across from Sears at UTC (yes, it was an art installation) and one evening, late, the artist gave my friend and I a private show where he went nuts with it reflecting it off the mirrors set up in the parking lot and changing the colors - so, yes, that photo is quite possible - and beautiful!
Posted by SDNative  on  Mon Apr 24, 2006  at  10:52 PM
McDonald Observatory in south Texas has done lunar range finding with a green laser since the early 1970s. They bounce the beam off of reflectors left there by the Apollo missions for the purpose of determining the exact distance to the moon.
Posted by justme  on  Thu Apr 27, 2006  at  10:02 PM
"Use the force, Ronald." :down:
Posted by Anguirus  on  Thu Jun 15, 2006  at  01:26 PM
Its effect rocks!
Posted by green lasers  on  Fri Jul 18, 2008  at  11:33 PM
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