Why is it that we cannot observe light beaming off of a star at right angles

Question

We understand that there is a speed of light which travels in a light year.

We also understand that light waves are emitted off a star and move out in all directions... So why is it that we cannot observe light being emitted at a right angle off of a distant star - like our sun which beams DAYLIGHT, why doesn't the sky light up at night (the affected matter should glow, wouldn't the Big Bang also glow)?

Does a light wave traveling in a static universe thin out or does it impact at a lesser molecular level?

(or no pun intended, does the intensity fade with the strength of radiation)...

Is light a one-way-road - okay, now I've confused myself...

Answer 1

You actually touch on a few interesting concepts;  I think all you need is a little fine-tuning to your understanding.  

Let's start with the notion of seeing light that is traveling at a 90º angle relative to the line from us to the light source.  We can only see light that enters our eyes and strikes our retinas.  Light traveling in any direction other than directly into our eyes is therefore unobservable to us.

Think of it this way.  Stand in a room and turn on the light switch.  You will of course be able to see everything in the room, but what you're really "seeing" is the light bouncing off of those objects.  Furthermore, you only see the light that happens to bounce off of those objects and directly into your eyes.  In reality, there is a LOT of light bouncing around in the room that you don't see, simply because the path of the light doesn't intersect your retinas.  Also, there are frequencies of light that you couldn't see even if they DID intersect your retinas, like UV and IR light.

The same is true with stars: they emit light in all directions equally, but you can only see the light that happens to intersect your retinas.

It's a common error made in science fiction movies; the heroes and villains are locked in a laser-gun battle, and you can clearly see the laser beams from the side as they whiz through the air.  In reality, you can only see a laser if it's shining directly in your eyes (and that's a very, very bad idea), so the laser beams fired from sci-fi laser guns would be invisible to a third-party observer.  But I guess that wouldn't make for a very interesting movie, would it?

So what about sunlight?  When the Sun is up, it seems that the whole sky is illuminated, which makes it seem like you're seeing sunlight from an odd angle.  Actually, you're seeing blue light that is scattered by the molecules in Earth's atmosphere.  If the Earth had no atmosphere (or if you went to the Moon), you would see no blue sky.  Instead, the sky all around the Sun would look as black as the space between stars.

Of course, that doesn't get us off the hook as to explaining why the sky is dark between stars.  The supposed dark sky paradox, also known as Olbers' Paradox, says that if the universe is infinite and static, then every line of sight should terminate at the surface of a star (albeit incredibly distant stars), and the night sky should be incredibly bright with the light of infinite stars.

Of course, we know that the number of stars in the universe isn't infinite.  Also, the finite age of the universe puts a limit on the number of stars whose light has had time to reach us.

As for the light emitted by the Big Bang...it's still there.  It's very, very low in energy (as you would expect of light that has been "cooling off" for more than 13 billion years), and it's no longer visible to the human eye; in fact, it stopped being visible long before there were eyes to see it.  It persists as microwave radiation that makes the temperature of space about 3ºC above absolute zero.

I hope that helps.  Good luck!

Answer 2

  The sun is a disc so light is emitted at all angles,a star,because of it's distance is a single point of light so light from that point,the light we see is emitted at ninety degrees from the surface,sort of like a laser beam emitter.

Answer 3

Well, you might see the light from the laser.  That's why amateur astronomers buy powerful $100 green flashlights (called lasers).  You point the thing at the object you want others to find, like a passing airplane (just kidding - amateur astronomers are interested in stars and such) and the light from the magic wand bounces off water vapor and dust in the air.  The green line is quite visible.

And, light from an explosion in space can bounce off of gas and dust too.  Say you have a supernova.  The light from it goes out in all directions.  The stuff that makes it to your eyes also gets there first - that was the shortest path.  But most of it didn't get to your eyes (which is a good thing).  Some of it went out and struck a gas and dust cloud that was, say, 50 light years away.  It might have been at an angle 90 degrees from the supernova and you.  It might have been at another angle.  But with a sensitive camera and a big light bucket telescope, the light reflected off the cloud can be imaged.  They call this a light echo.

For example, we know that in 1987, a supernova went off in the Large Magellanic cloud.  That's when the light first got to us.  So a few years later, people went looking for a light echo.

It's not just great big nebulae that reflect.  All of space can have gas and dust - just less of it.  And the LMC has a bit more than the Milky Way.  But it's been done here too.

Answer 4

So much that can be said on this subject on which I would not feel comfortable as it can get quite deep. I can only suggest you read 'David Deutch's - Fabric of reality. It explains this.

Light can be seen as a wave or as individual particles