How far can I (one) see?
Discussion
Toltec said:
It is the radius, i.e one AU, I have heard of having a brain the size of a planet but if you can waggle your head that far...
What I was suggesting was a baseline of around half a metre and a lateral way of looking for the answer.
False. One AU (astronomical unit) is the average distance between the earth and sun. Used only for inter-planetary distances. What I was suggesting was a baseline of around half a metre and a lateral way of looking for the answer.
Simpo Two said:
I thought they were moving apart, as in 'expanding universe'?
IIRC Andromeda is 400 light years away but this was just dragged up from some recess of the Simpo memory banks and may be wrong.
2.2 Million Light Years distant. M31's spectral lines are blue shifted meaning it is closing in on us. All other galaxy's are red shifted, the further away they are the faster their recession, in line with Hubble's constant. IIRC Andromeda is 400 light years away but this was just dragged up from some recess of the Simpo memory banks and may be wrong.
ExplorerII said:
Toltec said:
It is the radius, i.e one AU, I have heard of having a brain the size of a planet but if you can waggle your head that far...
What I was suggesting was a baseline of around half a metre and a lateral way of looking for the answer.
False. One AU (astronomical unit) is the average distance between the earth and sun. Used only for inter-planetary distances. What I was suggesting was a baseline of around half a metre and a lateral way of looking for the answer.
ExplorerII said:
2.2 Million Light Years distant. M31's spectral lines are blue shifted meaning it is closing in on us. All other galaxy's are red shifted, the further away they are the faster their recession, in line with Hubble's constant.
I think there are some other galaxies in our Local Group that are not rushing away from us as the Local Group is bound gravitationaly.Dr Jekyll said:
How many photons have to hit the eye at once for us to detect them?
That's a question I would never have thought to ask. I might go and do some research (type the question into Google). Edit: apparently between 5 and 14 photons need to reach the retina. However only 10% of the photons that reach the eye actually get as far as the retina. So that makes it something like 50 to 150 photons need to reach the eye for us to detect faint glimmer of light.
Apparently.
Edited by SpudLink on Sunday 7th December 20:25
Edited by SpudLink on Sunday 7th December 20:26
Thorodin said:
Forgive my ignorance, if the universe is expanding ie spreading is everything moving away from 'us' at the same speed? And is anything likely to come from the original centre to overtake 'us'? Wow, the more you read the less you know.
No, the further something is away from us, the faster it is receding.
If you are primed to see something,and if you have good enough eyesight, you will see it. I spoke to a scientist once who told me about experiments carried out by the RAE in the 1960s to see how far away an aeroplane could be and still remain visible to the naked eye. In the right conditions, an aircraft 60 miles away was easily visible.
Eric Mc said:
If you are primed to see something,and if you have good enough eyesight, you will see it.
Supposedly normal vision (20/20 AKA 6/6) is supposed to mean resolving about 1 minute of arc. Most people with the right spectacles if necessary can see a bit better than that, in exceptional cases half a minute.The tangent of 1 minute is .0003, implying (6/0.0003) you can see a 6 foot diameter object at about 4 miles or a 100 one at just over 60. So with the sun glinting on it an aircraft at 60 miles is plausible. But a 3 inch diameter object would only be visible hundreds feet away, a quarter of a mile at the outside. So how do you calculate the distance for a cable an inch or two thick but very very long?
Dr Jekyll said:
Supposedly normal vision (20/20 AKA 6/6) is supposed to mean resolving about 1 minute of arc. Most people with the right spectacles if necessary can see a bit better than that, in exceptional cases half a minute.
That resolution means whether you could tell if there are one or more cables, not if there is something or nothing.Example here - close to you it's obvious there are two cables per "arm", but further away you can still see wires but can't resolve whether it's one or two.
Always thought visual acuity was a function of the survival instinct. The eye will follow where it is led by various prompts, such as straight lines ie the eye will automatically follow the line and be able to assess character without the need to search for the next prompt or object. The clarity of the cable closest will be assumed to continue so although the observer may 'see' the distant line, the brain assumes the nature of it is the same. All guesswork though.
Thorodin said:
Always thought visual acuity was a function of the survival instinct. The eye will follow where it is led by various prompts, such as straight lines ie the eye will automatically follow the line and be able to assess character without the need to search for the next prompt or object. The clarity of the cable closest will be assumed to continue so although the observer may 'see' the distant line, the brain assumes the nature of it is the same. All guesswork though.
That sounds right to me. The brain has a model of how the world works, and interpretes the data receive from the eyes as continuing cable. Gassing Station | Science! | Top of Page | What's New | My Stuff