# The Naked Scientists Forum

### Author Topic: At what radius to the earth would the Sun ''vanish''?  (Read 4173 times)

#### Colin2B

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##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #25 on: 28/10/2015 12:04:46 »
I am a  bit confused you have to ask what I mean by bigger, if you are 20 stone and I am 10 stone, you are bigger than me, if you are 6ft and I am 4ft you are bigger than me.
You have just provided 2 definitions of bigger. If you had asked whether one man was bigger than another Evan would quite reasonably ask what you meant by bigger.
This is a similar problem with stars as you have talked about both mass and radius.

if star had a smaller radius than our suns radius and was beyond lets say 70 ly away, we would not see it by eye, if the star was bigger and further away we would still see it?
Ok, this is better because you are being more specific. However, if you read evan's reply you will see he mentions brightness. It is this, measured as magnitude rather than diameter or mass which determines whether a star, planet, comet is visible.
You might find this chart helpful http://www.icq.eps.harvard.edu/MagScale.html

#### Thebox

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##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #26 on: 28/10/2015 12:26:40 »
I am a  bit confused you have to ask what I mean by bigger, if you are 20 stone and I am 10 stone, you are bigger than me, if you are 6ft and I am 4ft you are bigger than me.
You have just provided 2 definitions of bigger. If you had asked whether one man was bigger than another Evan would quite reasonably ask what you meant by bigger.
This is a similar problem with stars as you have talked about both mass and radius.

if star had a smaller radius than our suns radius and was beyond lets say 70 ly away, we would not see it by eye, if the star was bigger and further away we would still see it?
Ok, this is better because you are being more specific. However, if you read evan's reply you will see he mentions brightness. It is this, measured as magnitude rather than diameter or mass which determines whether a star, planet, comet is visible.
You might find this chart helpful http://www.icq.eps.harvard.edu/MagScale.html

Thank you Colin, I do want to be able to communicate properly and to be understood, the problem with messages is they can be read several ways. I consider I do have some great insight into several things, I do know though if nobody can understand them I will never be heard.

I do have to question now why science considers light magnitude before radius of a star.

If we were to experiment using a flash light at night,

Xobs=position 1

Yfl=position 2

robs pos 1 to pos 2 = 10m

di(diameter) of fl = 10cm

if dy is increased di shrinks relative to sight, eventually it will ''vanish'' past point Z. We will neither see the light or the flash light lens. Something is seemingly not right with this.
In a matter of logic , how can anyone conclude in this diagram , which circle is near and which circle is far, which circle is small by distance and which circle is large by distance?

I do not understand how science can say something is x big when there is no background for comparison.   How do we know the distance stars are not just small and close?

« Last Edit: 28/10/2015 12:38:45 by Thebox »

#### Colin2B

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##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #27 on: 28/10/2015 14:49:11 »
... I do want to be able to communicate properly and to be understood, the problem with messages is they can be read several ways. I consider I do have some great insight into several things, I do know though if nobody can understand them I will never be heard.
I agree, I think your ideas are often hidden by you trying too hard to use 'scientific' language but you often misuse it which leads to confusion. Again, keep the questions simple and on one topic. Avoid maths, if there can be a problem with a word like bigger then the symbols in maths can be a real problem if you don't use them the way everyone else does.

I do have to question now why science considers light magnitude before radius of a star.
Image you have 2 light bulbs one larger than the other but both of same wattage. At 2km they will both be tiny points of light and you won't be able to tell them apart. The same with stars, at distances of 2ly you can't differentiate size with the naked eye.
Now imagine the smaller bulb is twice the wattage of the larger one. In this case you will be able to see the smaller bulb from further away than the larger.

I do not understand how science can say something is x big when there is no background for comparison.   How do we know the distance stars are not just small and close?
Look up parallax.
If you look at a star from two points at opposite ends of the earth's orbit, it is like seeing 3d with our 2 eyes. The difference in position tells us how far away the star is by basic trig.

#### Thebox

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##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #28 on: 28/10/2015 15:08:43 »

Image you have 2 light bulbs one larger than the other but both of same wattage. At 2km they will both be tiny points of light and you won't be able to tell them apart. The same with stars, at distances of 2ly you can't differentiate size with the naked eye.
Now imagine the smaller bulb is twice the wattage of the larger one. In this case you will be able to see the smaller bulb from further away than the larger.

I am imagining the two light bulbs, except I am imagining two tiny points, however I imagine one light bulb is at 2 km and is x ''big'', and one is at 4 km and is y ''big''

So although they look like they are both at 2km, they are not.

A sort of illusion created by scaling and distance ?

each one of the A's in this diagram are a different size.

added- The A on the left is near to you, the A on the furthest right is far away from you

« Last Edit: 28/10/2015 15:19:59 by Thebox »

#### evan_au

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##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #29 on: 28/10/2015 17:51:47 »
Quote from: Thebox
How do we know the distance stars are not just small and close?
A very precise survey of the 3D position of stars in the Milky Way galaxy is underway at present.
http://en.wikipedia.org/wiki/Gaia_(spacecraft)

Quote
We will neither see the light or the flash light lens.
On a dark night, you can see the light from a flashlight from a much longer distance than you can see the diameter of the lens. At night, you can see headlights from a much longer distance than you can tell whether there is one headlight (motorbike) or two (car).

It is the same with the Sun and Stars.

We can see many stars in the sky, but only a few of them are large enough or close enough for astronomers to have constructed an image of their actual surface. It is a complex process, and more like calculating a CAT scan image than taking a traditional photograph.
http://en.wikipedia.org/wiki/List_of_stars_with_resolved_images

Quote
if star had a smaller radius than our suns radius and was beyond lets say 70 ly away, we would not see it by eye, if the star was bigger and further away we would still see it?
There are several factors that determine how visible a star is to the human eye.
- If two stars have the same temperature, the one with the bigger radius will produce more light, and will be seen from a greater distance.
- However, if you have two stars with the same radius, the one with the higher temperature will produce more light, and will be more visible.
- If two stars have the same radius and temperature, the closer one will be more visible.
- On the other hand, if you have the same star, but at two different ages in its life cycle, it has roughly the same mass, but its radius and temperature can vary dramatically. When the Sun burns all its hydrogen and becomes a red giant, it's radius will increase from the current 0.5 million km out to nearly the radius of Earth's orbit, at 150 million km. Overall, the Sun will put out over 1000 times more light than it does at present. But its temperature will drop, making its light redder than it currently is. The Sun  should still be visible to the naked eye beyond 800 light-years.
http://en.wikipedia.org/wiki/Stellar_evolution#Red-giant-branch_phase

« Last Edit: 28/10/2015 20:20:01 by evan_au »

#### Colin2B

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##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #30 on: 28/10/2015 17:57:36 »
So although they look like they are both at 2km, they are not.

A sort of illusion created by scaling and distance ?

each one of the A's in this diagram are a different size.
Agreed, all very obvious really.

#### Thebox

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##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #31 on: 29/10/2015 13:25:43 »

Agreed, all very obvious really.

Something we agree on then lol, I am impressed that you can observe X,Z as a single X axis.

#### The Naked Scientists Forum

##### Re: At what radius to the earth would the Sun ''vanish''?
« Reply #31 on: 29/10/2015 13:25:43 »