32
$\begingroup$

In the question How to make a green LED as visually bright as a 0 magnitude star? I worked out that a 100 mA green LED with a 10° half-angle 18 kilometers away would be as bright as a 0th magnitude star. So a 5 mW laser pointer with a miliradian divergence could potentially be seen even farther away, or at least photographed.

Question: Has anyone in space seen or photographed a laser pointer from Earth?

Note I'm asking about a laser pointer, not some high-powered laser used to bounce off of the Moon, or a powerful searchlight. Something that you can hold in your hand.

$\endgroup$
33
$\begingroup$

Don Pettit mentioned a an experiment set up with the San Antonio Astronomical Scociety who pointed both spotlights and a blue laser pointer at the ISS, pictured below in a 5-10 second exposure:

enter image description here

I believe, but don't quote me on this, that the laser pointer was seen while the spotlight was not (with the aperture used). This is a picture from the ground, probably a short exposure (seeing the trail on the ISS). This was not an official experiment, rather one he set up with a friend who wanted to test a theory.


In addition to this, a picture of what the laser from the incident on March 4, 2012 can be seen in this tweet, also by Don Pettit, as Tristan previously mentioned, and would look approximately like this:

enter image description here

If you like cool, seemingly odd, but ultimately insightful experiments I highly suggest looking through his tweets and clicking into his blogs. He does many random experiments which have garnered him scientific patents and entries in research papers.


Quotes from an airspace article:

Early Sunday morning, at 01:27 our time, the San Antonio Astronomical Association, an amateur astronomy group, succeeded in flashing the space station with a one-watt blue laser and a white spotlight as we passed overhead. This took a number of engineering calculations. Projected beam diameters (assuming the propagation of a Gaussian wave for the laser) and intensity at the target had to be calculated. Tracking space station’s path as it streaked across the sky was another challenge. I used email to communicate with Robert Reeves, one of the association’s members. Considering that it takes a day, maybe more, for a simple exchange of messages (on space station we receive email drops two to three times a day), the whole event took weeks to plan.

Another photo of the light, from this source (I am unsure if they are the same image):

enter image description here

Note: This is all paraphrased from a talk he gave at NEAIC, so if it's wrong please correct me.


@DarrelHoffman pointed out that:

Should be noted that a 1 watt laser is far more powerful than the one you buy to tease your cat. At least in the US, the most powerful one a normal person can legally buy is only 5 milliwatts...

It was a 1 watt laser pointer.

$\endgroup$
  • 4
    $\begingroup$ This is cool and new to me. Pettit was (is) quite a character. $\endgroup$ – Organic Marble Jul 9 at 20:29
  • 3
    $\begingroup$ @OrganicMarble did you see his space-cup ;)? $\endgroup$ – Magic Octopus Urn Jul 9 at 20:31
  • 7
    $\begingroup$ When getting briefed on the Orbiter fuel cell system, he told us that liquid oxygen is light blue in color, and he knows because he had some in his garage. $\endgroup$ – Organic Marble Jul 9 at 20:34
  • 1
    $\begingroup$ @organicmarble That's hilarious! Did he just keep it on hand? I wonder how much it costs to sustain -300F for periods of time in a garage. $\endgroup$ – Magic Octopus Urn Jul 9 at 20:55
  • 2
    $\begingroup$ Should be noted that a 1 watt laser is far more powerful than the one you buy to tease your cat. At least in the US, the most powerful one a normal person can legally buy is only 5 milliwatts... $\endgroup$ – Darrel Hoffman Jul 10 at 13:23
9
$\begingroup$

This has happened at least once, on March 4, 2012, there was an experiment to do just that.

YouTube: ISS FLASH PROJECT (lower your volume first)

$\endgroup$
  • $\begingroup$ "This becomes complicated when highly collimated light from lasers are used, since the beam diameter at our orbital distance is about one kilometer, and this spot has to be tracking us while in the dark." Quite the steady hand! update: Annotation in the video says the laser is mounted on a telescope. $\endgroup$ – uhoh Jul 9 at 17:03
  • $\begingroup$ This event is the same as the one in Magic Octopus Um's answer. $\endgroup$ – Camille Goudeseune Jul 10 at 20:14
  • 1
    $\begingroup$ @CamilleGoudeseune he posted this first, I augmented it with pictures. $\endgroup$ – Magic Octopus Urn Jul 10 at 22:23
  • $\begingroup$ (Mostly because I didn't know they were the same event when posting and discovered slowly it was). $\endgroup$ – Magic Octopus Urn Jul 12 at 19:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.