On Thu, 08 Feb 2018 08:06:43 +0000, Martin Brown wrote:

On 07/02/2018 17:45, Tim Streater wrote:
In article , Vortex13
wrote:

On 07/02/2018 14:02, T i m wrote:

Silly question for you ... why don't you see any stars in any of the
shots from the Roadster? Is it that it's too bright in general, even
though it looked pitch black in the background?

It's too bright in general. People asked the same Q about Apollo
moonshot pix from the Moon's surface.

Too bright for seeing any stars but Venus is doable from the ground when
it is at its brightest and maximum elongation close to midday. You just
need to stand out of direct sunlight and know exactly where to look.

The hard part is focussing your eyes at infinity.

I'd have thought focussing your eyes to infinity would be easy seeing as
how it's the result of relaxing the eye's focussing muscles used to
accommodate for close in vision. Indeed, deep thought about a problem
gives you that "Far Away Look", hence the word "consider" which literally
translates as "to be with the stars".


I'd be very surprised if you couldn't see Venus from space. Or if a
video camera didn't capture it in the same frame as a car if it was
pointed in the right direction.

The albedo of Venus is 75% which makes it stand out nicely in sunlight.

That's almost twice as bright as Earth's albedo (39% back in 1976 when
Vangelis released his space physics inspired concept album, "Albedo
0.39). Since Venus is closer to the sun, its brightness will be even
higher than that simple albedo comparison suggests.

--
Johnny B Good

On 08/02/2018 13:59, Johnny B Good wrote:
On Thu, 08 Feb 2018 08:06:43 +0000, Martin Brown wrote:

On 07/02/2018 17:45, Tim Streater wrote:
In article , Vortex13
wrote:

On 07/02/2018 14:02, T i m wrote:

Silly question for you ... why don't you see any stars in any of the
shots from the Roadster? Is it that it's too bright in general, even
though it looked pitch black in the background?

It's too bright in general. People asked the same Q about Apollo
moonshot pix from the Moon's surface.

Too bright for seeing any stars but Venus is doable from the ground when
it is at its brightest and maximum elongation close to midday. You just
need to stand out of direct sunlight and know exactly where to look.

The hard part is focussing your eyes at infinity.

I'd have thought focussing your eyes to infinity would be easy seeing as
how it's the result of relaxing the eye's focussing muscles used to
accommodate for close in vision. Indeed, deep thought about a problem
gives you that "Far Away Look", hence the word "consider" which literally
translates as "to be with the stars".

The problem is that to see a faint white speck against a bright blue sky
background you have to have an exact focus. Try it and see. It is also
quite easy to lose the thing even after you find it the first time.

Looking at a nearby con trail and transferring your gaze to the right
spot often works. Seeing a dot is much harder than you might think.

--
Regards,
Martin Brown

On 08/02/2018 13:59, Johnny B Good wrote:
On Thu, 08 Feb 2018 08:06:43 +0000, Martin Brown wrote:

On 07/02/2018 17:45, Tim Streater wrote:
In article , Vortex13
wrote:

On 07/02/2018 14:02, T i m wrote:

Silly question for you ... why don't you see any stars in any of the
shots from the Roadster? Is it that it's too bright in general, even
though it looked pitch black in the background?

It's too bright in general. People asked the same Q about Apollo
moonshot pix from the Moon's surface.

Too bright for seeing any stars but Venus is doable from the ground when
it is at its brightest and maximum elongation close to midday. You just
need to stand out of direct sunlight and know exactly where to look.

The hard part is focussing your eyes at infinity.

I'd have thought focussing your eyes to infinity would be easy seeing as
how it's the result of relaxing the eye's focussing muscles used to
accommodate for close in vision. Indeed, deep thought about a problem
gives you that "Far Away Look", hence the word "consider" which literally
translates as "to be with the stars".

Not quite correct. With nothing specific to focus on, the eye tends to
settle at a couple of metres. All pilots are taught that lookout
requires an active action of focussing on the horizon (and then breaking
the scan into a series of segments where the eye is stationary,
interspersed with re-focussing on the horizon). In the dark there's also
the problem of the blind spot.

Many aero-med books discuss these but there are good articles he
https://www.airproxboard.org.uk/uplo...02_Lookout.pdf
http://www.cee.org/tep-lab-bench/pdf...otActivity.pdf


.... snipped

On Thu, 08 Feb 2018 15:20:31 +0000, nothanks wrote:

On 08/02/2018 13:59, Johnny B Good wrote:
On Thu, 08 Feb 2018 08:06:43 +0000, Martin Brown wrote:

On 07/02/2018 17:45, Tim Streater wrote:
In article , Vortex13
wrote:

On 07/02/2018 14:02, T i m wrote:

Silly question for you ... why don't you see any stars in any of
the shots from the Roadster? Is it that it's too bright in general,
even though it looked pitch black in the background?

It's too bright in general. People asked the same Q about Apollo
moonshot pix from the Moon's surface.

Too bright for seeing any stars but Venus is doable from the ground
when it is at its brightest and maximum elongation close to midday.
You just need to stand out of direct sunlight and know exactly where
to look.

The hard part is focussing your eyes at infinity.

I'd have thought focussing your eyes to infinity would be easy seeing
as
how it's the result of relaxing the eye's focussing muscles used to
accommodate for close in vision. Indeed, deep thought about a problem
gives you that "Far Away Look", hence the word "consider" which
literally translates as "to be with the stars".

Not quite correct. With nothing specific to focus on, the eye tends to
settle at a couple of metres. All pilots are taught that lookout
requires an active action of focussing on the horizon (and then breaking
the scan into a series of segments where the eye is stationary,
interspersed with re-focussing on the horizon). In the dark there's also
the problem of the blind spot.

Many aero-med books discuss these but there are good articles he
https://www.airproxboard.org.uk/uplo...ndard_content/
Topical_Issues_and_Themes/02_Lookout.pdf
http://www.cee.org/tep-lab-bench/pdf...otActivity.pdf


All very interesting. I guess the real problem with 'focussing' on far
away point sources of light is more to do with convergence than with
focussing per se. In dim night sky viewing, you need the use of both eyes
to mitigate the dark blind spot problem making use of both eyes correctly
converged an important requirement.

Eye convergence on distant objects can't be guaranteed by relaxation
alone, usually requiring some active trimming by muscular control.
Generally, in a sort of learned "Pavlonian" styled response, the lens
focussing muscle response takes its cue from the amount of convergence we
consciously 'dial in'.

I know from my experience with atropine drops that, my eyes lose all
accommodation powers leaving them relaxed into a state of focus at
infinity so I'm pretty sure that that bit about the eyes being in an
individually relaxed state when looking into the far distance is correct
and the corresponding convergence whilst not trimmed to precisely fixate
on a particular far and distant object when in deep thought, is
sufficient to give the outside observer, of another in deep thought, the
impression of "gazing at the stars" or the far away horizon.

However, when it comes to observing the "Morning" or "Evening" star,
namely Venus, that generally doesn't present any great difficulty with
naked eye observation since it is both very bright and discernible as a
tiny crescent, unlike the dimensionless points of light we call stars.

I have to admit that 'focussing on distance objects' relies not so much
on relaxed focussing muscles so much as on correct convergence which
almost always is a matter of some active muscle control and less about
total relaxation which usually only approximates the precise convergence
required for viewing distant objects. As you pointed out, my throw away
observation wasn't quite correct, merely just a small part of the whole
story.

--
Johnny B Good

On 08/02/2018 17:37, Johnny B Good wrote:
On Thu, 08 Feb 2018 15:20:31 +0000, nothanks wrote:

On 08/02/2018 13:59, Johnny B Good wrote:
On Thu, 08 Feb 2018 08:06:43 +0000, Martin Brown wrote:

On 07/02/2018 17:45, Tim Streater wrote:
In article , Vortex13
wrote:

On 07/02/2018 14:02, T i m wrote:

Silly question for you ... why don't you see any stars in any of
the shots from the Roadster? Is it that it's too bright in general,
even though it looked pitch black in the background?

It's too bright in general. People asked the same Q about Apollo
moonshot pix from the Moon's surface.

Too bright for seeing any stars but Venus is doable from the ground
when it is at its brightest and maximum elongation close to midday.
You just need to stand out of direct sunlight and know exactly where
to look.

The hard part is focussing your eyes at infinity.

I'd have thought focussing your eyes to infinity would be easy seeing
as
how it's the result of relaxing the eye's focussing muscles used to
accommodate for close in vision. Indeed, deep thought about a problem
gives you that "Far Away Look", hence the word "consider" which
literally translates as "to be with the stars".

Not quite correct. With nothing specific to focus on, the eye tends to
settle at a couple of metres. All pilots are taught that lookout
requires an active action of focussing on the horizon (and then breaking
the scan into a series of segments where the eye is stationary,
interspersed with re-focussing on the horizon). In the dark there's also
the problem of the blind spot.

Many aero-med books discuss these but there are good articles he
https://www.airproxboard.org.uk/uplo...ndard_content/
Topical_Issues_and_Themes/02_Lookout.pdf
http://www.cee.org/tep-lab-bench/pdf...otActivity.pdf


All very interesting. I guess the real problem with 'focussing' on far
away point sources of light is more to do with convergence than with
focussing per se. In dim night sky viewing, you need the use of both eyes
to mitigate the dark blind spot problem making use of both eyes correctly
converged an important requirement.

Eye convergence on distant objects can't be guaranteed by relaxation
alone, usually requiring some active trimming by muscular control.
Generally, in a sort of learned "Pavlonian" styled response, the lens
focussing muscle response takes its cue from the amount of convergence we
consciously 'dial in'.

I know from my experience with atropine drops that, my eyes lose all
accommodation powers leaving them relaxed into a state of focus at
infinity so I'm pretty sure that that bit about the eyes being in an
individually relaxed state when looking into the far distance is correct
and the corresponding convergence whilst not trimmed to precisely fixate
on a particular far and distant object when in deep thought, is
sufficient to give the outside observer, of another in deep thought, the
impression of "gazing at the stars" or the far away horizon.

However, when it comes to observing the "Morning" or "Evening" star,
namely Venus, that generally doesn't present any great difficulty with
naked eye observation since it is both very bright and discernible as a
tiny crescent, unlike the dimensionless points of light we call stars.

I have to admit that 'focussing on distance objects' relies not so much
on relaxed focussing muscles so much as on correct convergence which
almost always is a matter of some active muscle control and less about
total relaxation which usually only approximates the precise convergence
required for viewing distant objects. As you pointed out, my throw away
observation wasn't quite correct, merely just a small part of the whole
story.

Well, the correct name for the effect is "empty field myopia", which
implies it is down to focus or, possibly, cognition. Muscles can only
contract and when relaxed the ciliary muscle pulls the lens to its
thinnest (longest focal length) condition ... so I can only surmise that
either the ciliary muscle isn't fully relaxed in this state or there's
summat else goin' on.
I looked around for an explanation and stumbled over this google book,
it doesn't have the answer but is a great thing to scan through:
https://books.google.co.uk/books?id=...AAMBAJ&pg=PA71

On 08/02/2018 17:37, Johnny B Good wrote:
On Thu, 08 Feb 2018 15:20:31 +0000, nothanks wrote:

On 08/02/2018 13:59, Johnny B Good wrote:
On Thu, 08 Feb 2018 08:06:43 +0000, Martin Brown wrote:

On 07/02/2018 17:45, Tim Streater wrote:
In article , Vortex13
wrote:

On 07/02/2018 14:02, T i m wrote:

Silly question for you ... why don't you see any stars in any of
the shots from the Roadster? Is it that it's too bright in general,
even though it looked pitch black in the background?

It's too bright in general. People asked the same Q about Apollo
moonshot pix from the Moon's surface.

Too bright for seeing any stars but Venus is doable from the ground
when it is at its brightest and maximum elongation close to midday.
You just need to stand out of direct sunlight and know exactly where
to look.

The hard part is focussing your eyes at infinity.

[snip]
However, when it comes to observing the "Morning" or "Evening" star,
namely Venus, that generally doesn't present any great difficulty with
naked eye observation since it is both very bright and discernible as a
tiny crescent, unlike the dimensionless points of light we call stars.

For the avoidance of doubt I was talking about seeing Venus with the
naked eye at or around midday in a clear blue sky with the sun well
above the horizon. You need a good clear day and to stand in shadow.

I have to admit that 'focussing on distance objects' relies not so much
on relaxed focussing muscles so much as on correct convergence which
almost always is a matter of some active muscle control and less about
total relaxation which usually only approximates the precise convergence
required for viewing distant objects. As you pointed out, my throw away
observation wasn't quite correct, merely just a small part of the whole
story.

The eye's default focus is as someone else has said is a few metres away
from you if you have normal vision. You have to make an effort to bring
the distant horizon into sharp focus assuming normal vision.

If you want a serious test of visual acuity try splitting the star
epsilon-Lyra naked eye soon after dark it is a 3' arc double star -
actually a double double in a small telescope it looks like:

... :

with much bigger gap between then.

--
Regards,
Martin Brown