Okay. I’m on a planet in deep space. I want to send morse code out in light pulses from a minuscule sun. It seems to me that this would be possible by turning the light on and off, perhaps at one-second intervals. So, two questions:
Would this work. Seems like it should, the same way it works at sea.
This is the crux of my question: what would an observer on a distant planet 90 degrees from the direction of my light beam see? Seems to me like he would see light “pulses”. If I shuttered the light beam at 1/100 of a second intervals, he should see discrete pulses 1,860 miles in length. At a distance, would that resemble the light pulses coming from a a SciFi laser gun?
Yes, you’re right. We see light when it shines in our direction — either directly from the source, or reflected off of something. So in deep space photographs, we see stars shining, and we see clouds of gas and/or dust shining by reflected light, but we don’t see light rays going in every direction from every star.
In the OP’s hypo, another problem is that both planets would probably be rotating, so even if the light pulses were reflecting off dust or something, they wouldn’t be seen as being in a constant direction.
If the source is highly collimated like a laser, you’re not going to see anything outside the beam path. Seeing any pulses would necessarily mean there’s some leakage at the source.
Exception is if there’s something in the way to scatter the light. For example, we can see the beam of a green laser pointer in a room due to Rayleigh scattering off air/water molecules.
The beam from red laser pointers generally isn’t scattered from just air but you can make those visible too if you use smoke or introduce other scatterers.
ETA: As mentioned above, that’s what nebula and other cloudy space objects are - “stuff” that scatters the light.
Sci-fi movies are sometimes inaccurate. You can’t hear sounds in space, and you can’t see a laser beam in space, unless it’s going through smoke or something (which is what’s usually happening when NOVA films lasers for pop science shows).
I guess if it were extremely powerful, it could ionize or superheat the atmosphere it goes through, and make a glowing trail that way.
Yes. Which means that Cthulhu might have destroyed the Andromeda galaxy 2 million years ago, and we would still see its light for another half a million years (it’s about 2.5 million light years away).
For your purposes, you can think of photons as bullets. If someone is shooting a very powerful machine gun at you, and it takes the bullets ten seconds to get to you, then you can’t stop ducking until ten seconds after he stops shooting.
Let me ask it this way. There is a a faint, evenly distributed dust in space, so light beams would be visible from the side. If an SOS was sent from a strong light source, at the end of the SOS would an observer from the side see three equal beams of light (each with a beginning and an end) followed by three longer beams of light, then three shorter ones?
If the light beam is bouncing off dust, it may have dissipated by the time it reaches your observer. But say the dust is only close to your observer, and the light passes through that dust cloud, yes, you’d see it just like you see a laser on a science show when they put smoke in the air. If you sent an SOS, you’d see three “dots” followed by “dashes” and “dots”. But they’d be traveling too fast for you to see the beginning and ends of the “dots”, it would probably just look like a section of dust was illuminated briefly.
A “miniscule sun” as described in the OP would emit light in all directions, turning it on and off also as described would pulse that light, so assuming that nothing was between the observer and the light source, it would be seen as a pulsing light.