Mount Wilson Laser Tag



(from emails of accomplice late in Nov. '03)


        Thanks for running the Mt. Wilson towercam!  It's a wonderful service to the community, and has saved us many a foggy day in Pasadena (we can check conditions up top before deciding to go hiking ...)  Plus we get reminded to go look at the latest EIT shot ...

        We thought you might like to know about a little experiment we did recently.  The cam was pointed south towards Pasadena, and we fell to arguing about exactly *where* in the field of view *we* were.  Then we fell to arguing about whether we would be able to see a laser pointer if we pointed it up at the webcam.

        Well, I think this picture speaks for itself:


      Alignment was difficult - we got lucky just after twilight and then spent quite some time fiddling with binoculars and a night-vision scope before seeing that image.  Here's what our end looked like:


Just in case somebody wants to know, the laser pointer is rated at 5mW.  We figure the beam diameter after six-and-a-half miles is about 20 feet -- there was no chance of harming the camera; and the beam probably isn't even visible during daylight ...

        Thanks again for running the Mt. Wilson towercam!


           - nick


(there's me aiming the laser... here's the reply from the hill...)



>We used a green 532nm green laser pointer because a 5mW green
>*looks* much brighter than a 5mW red (at 635nm, typically)

>the camera seemed to be producing images about every 6
>minutes (despite what the towercam page says!)

Thank you for the information!  Amazing that such a small laser can accomplish so much!  <stuff omitted...>

Regarding the Mount Wilson Towercam, it actually does snap an image every 4 minutes but because the program which uploads the image to UCLA is separate from the program that controls the camera, the Web-based image delay can be as much as 8 minutes.  Also, client's web browsers do not always reload a fresh image (as they should) adding yet another delay in the apparent spacing of the images.

The camera has a set exposure of about 1/2000 second during the day, but at night (4:30 pm these days) it switches over to automatic exposure.  This can be as long as 16 seconds on a dark night, but when looking toward the city lights (and with the moon up) the exposure was probably more like 6-8 seconds.

I went through the archives and located 4 images that show the laser and I have attached them here.  In my humble opinion, the one taken at 00:08 seems to be the best.