### Photons

A star a bazillion miles away send photons zipping out in every direction, and no matter where you are, some of them hit your eye (e.g. if you move an inch over you're not going to be in an "uncovered" area).

Think about that.

DF
March 6th, 2007 5:20pm

I think the republicans created photons so they can convertly be used by terrorists and then later to attack them.

The universe must be bound then. Or each star must produce an infinite amount of photons per second.

strawberry snowflake
March 6th, 2007 5:37pm

" Or each star must produce an infinite amount of photons per second"

Is this something that Al Gore and the democrats are pushing. Damn global warming.

Good weed up there in Canada?

zed
March 6th, 2007 5:47pm

>The universe must be bound then. Or each star must produce an infinite amount of photons per second.

I don't know much about astrophysics, or even photons for that matter, but really think of the number of photons to cover that 3D surface area at such a distance, continuously.

DF
March 6th, 2007 5:55pm

There is a precise mathematical term for that number of photons. It is "quite a lot".

bon vivant
March 6th, 2007 5:57pm

Well, I do think it's more like "one Gazillion!" -- but even that is WAY below "Infinite".

SaveTheHubble
March 6th, 2007 6:01pm

This is why it's such a big deal whether neutrinos have mass or not...

WTF?! They do have mass? I haven't been keeping up... Wow,

at least 0.05 eV, but no more than 0.3 eV.

Ward
March 6th, 2007 6:57pm

This is proof that people really don't comprehend large orders of magnitude. 10^26 just doesn't help w/ day-to-day comparisons...

>>> The Sun's luminosity is 3.83e26 W

>>> So let's say that 40% of the Sun's energy is emitted at a wavelength of 550 nm (which is pretty reasonable).

Not sure where they got this, but probably close enough.

>>> The energy of a 550 nm photon is E=hc/lambda=3.6e-19 J.

>>> So the number of photons emitted at 550 nm is roughly: 3.82e26 J/s * 0.4 / (3.6e-19 J/photon)= 4.2e44 photons/s.

Here's a better rough estimate:

The Sun generates about 4x10E26 Watts.

The surface area of our telescope is 0.03141 square metres.

200 light years. (work out the area yourself A = 4*pi*r*r)

Energy in a photon = 3.97x10E-19 Joules (800nm)

Photons in a Joule = 2.52x10E18

100 Watts = 2.52x10E20 photons per second.

Jiggle the sums, and the number of photons that reach my telescope is about 700,000 photons per second.

Ward
March 6th, 2007 7:20pm

How many if your telescope is 10 light years away from the star?

strawberry snowflake
March 6th, 2007 7:23pm

And to think, all those photons and we STILL have to use photomultipliers in space telescopes...

no label
March 6th, 2007 8:20pm

There might be 700,000 of them per second, but a photon is *really* small.

interesting thought.

$--
March 7th, 2007 4:16am

it's amazing that flickr can store that many, when you think about it.

$--
March 7th, 2007 4:16am

Ah, you see, the trick is that Flickr stores each photon only once and then just uses it for different pictures!

Is that a second's worth of photons in your pants, or are you just happy to see me?

JoC
March 7th, 2007 10:36am

We should outlaw photons.. those sneaky bastards are always up to no good.

So the further you get from something, the more limited the precision of imaging could be.

e.g. If we had the most amazing CMOS-sensor ever, and it was 10 gazillipixels, but we fed it through the aforementioned lens super zoomed in to some far off star, we aren't going to see surface details because there just aren't enough photons coming in.

DF
March 7th, 2007 2:47pm

hence my conclusion that if

> no matter where you are, some of them [photons] hit your eye

is true, then either stars produce infinitely dense beams of light, or the universe is bound (aka, you can never move out of a beam of light from a star ... the finite density of the spread is greater than the size of the universe).

strawberry snowflake
March 7th, 2007 3:20pm

>>no matter where you are, some of them [photons] hit your eye

That doesn't require infinite density of photons. It just requires infinite time between photons hitting your eye.

In other words, given finite density, given random emission direction, a photon from a star will eventually come by and hit your eye, you just might have to wait a while.

bob's your uncle
March 7th, 2007 4:13pm

ok good point. I read the OP as saying that you could move over an inch and there would be light there from said star. Ie, that upon moving over one didn't need to bring popcorn, some beef jerky and wait an *infinite* amount of time to see the star.

But yes, that works too.

strawberry snowflake
March 7th, 2007 7:12pm