At What Altitude Can Stars Be Seen In Daylight?

[spartan45]

On 8/27/2021 at 7:39 AM, bangstrom said:

Arthur Eddington famously photographed stars appearing near the sun from the surface of the Earth during a total solar eclipse in 1919.

This is a good example of what should happen when you block the Sun in the vacuum of space. The cone of Sun light spreading out from behind the Moon continues invisible to all observers in the Moons shadow, allowing them to see the stars even near the edge of the shadow. This begs the question, why can’t stars be seen in daylight in the vacuum of space when the Sun is blocked by a smaller object such as a space craft or space station?

[MichaelBrooks]

Interesting discussion @spartan45 (albeit mostly with yourself). I'm going to throw in a thought (and my apologies in advance if this has already been discounted by any of the numerous references that you have linked but I haven't read) - is it possible that the only reason we can't see stars in space during the day is simply that the things that we can see are so bright (due to the full unfiltered reflected sunlight) that:

a) our pupils stop down to their minimum aperture, thus minimising the light reaching our retinas, so there's not enough light from dim sources such as stars.

b) only the cones in our retinas are active - the rods effectively close down under bright light conditions; normally when we look at stars at night we're doing so with the rods.

The way to test this would be to ask an astronaut to look at the daytime sky through some form of shield that blocked out all bright objects (e.g. a black tube) and wait for up to 15 minutes for his or her night vision to kick in (i.e. for the rods to build up their maximum dose of rhodopsin).

Edited August 13, 2023 by MichaelBrooks

[spartan45]

Thank you for joining the ‘discussion’ with an excellent, hard hitting, to the seat of the fire, thought:

On 8/13/2023 at 10:22 AM, MichaelBrooks said:

is it possible that the only reason we can't see stars in space during the day is simply that the things that we can see are so bright

The trouble here is that even when the cameras on the ISS have a clear view of the black daytime sky with no bright object or reflecting surface in view no stars are seen. If the reason for this is that bright reflected sunlight from objects or nearby surfaces not in camera view are hitting the camera lens then a lens collar tube / hood could be deployed. I suspect this is not done because it would not make any difference. In the visual spectrum it seems to me the daytime sky in space is black and star-less as seen on cameras and reported by what seems to me most astronauts.

I would like to see an experiment done on one of the space tourist flights using a hand held camcorder similar to the  Sony DCR-DVD handycam  ’NightShot’, super ’SteadyShot’, 20x optical zoom, the ability to disable auto for manual infinity focus, demonstrated on a post earlier of this topic. A matt black rubber hood collar fitted to the camcorder lens pressed up against the spacecraft window glass might work, but has probably already been tried..

 It may be necessary to try visual spectrum cameras adapted to see in the ultra-violet spectrum.  Ebay has lots of ‘full spectrum cameras’ advertised that are normal cameras adapted to detect the full spectrum including of course, ultra-violet. The ultra-violet telescope deployed on the Moon by the Apollo 16 astronauts to see stars in daylight under the shade of the Lunar Module and the ultra-violet telescope on the Chang’e 3 Moon Lander platform that can only observe the stars from the Moon during the 14 days of daylight using its solar panels prove that stars can be seen in daylight in the ultra-violet spectrum, while the Apollo astronauts and their visual spectrum cameras appeared unable to see them.

I asked the Hubble Space telescope, public relations officer by email; Can the Hubble ST see stars in daylight using the normal human visual light spectrum range, or does it have to resort to using the ultra-violet spectrum, (non-human light spectrum range), to see stars in daylight?

The answer I received simply informed me Hubble observes the stars 24/7, which I already knew, but I wanted to find out exactly how it overcomes the black, star-less daytime high altitude/space daylight sky. I could get no further clarity.

I’ve been fascinated by the black, star-less, daylight sky above the atmosphere for over a decade and it is very mysterious, especially when it seems to me, astronauts, professional astrophysicists and astronomers, appear uncomfortable with this topic. My curiosity remains. Thanks MichaelBrooks once again for your input.

[Moontanman]

21 hours ago, spartan45 said:

Thank you for joining the ‘discussion’ with an excellent, hard hitting, to the seat of the fire, thought:

The trouble here is that even when the cameras on the ISS have a clear view of the black daytime sky with no bright object or reflecting surface in view no stars are seen. If the reason for this is that bright reflected sunlight from objects or nearby surfaces not in camera view are hitting the camera lens then a lens collar tube / hood could be deployed. I suspect this is not done because it would not make any difference. In the visual spectrum it seems to me the daytime sky in space is black and star-less as seen on cameras and reported by what seems to me most astronauts.

I would like to see an experiment done on one of the space tourist flights using a hand held camcorder similar to the  Sony DCR-DVD handycam  ’NightShot’, super ’SteadyShot’, 20x optical zoom, the ability to disable auto for manual infinity focus, demonstrated on a post earlier of this topic. A matt black rubber hood collar fitted to the camcorder lens pressed up against the spacecraft window glass might work, but has probably already been tried..

 It may be necessary to try visual spectrum cameras adapted to see in the ultra-violet spectrum.  Ebay has lots of ‘full spectrum cameras’ advertised that are normal cameras adapted to detect the full spectrum including of course, ultra-violet. The ultra-violet telescope deployed on the Moon by the Apollo 16 astronauts to see stars in daylight under the shade of the Lunar Module and the ultra-violet telescope on the Chang’e 3 Moon Lander platform that can only observe the stars from the Moon during the 14 days of daylight using its solar panels prove that stars can be seen in daylight in the ultra-violet spectrum, while the Apollo astronauts and their visual spectrum cameras appeared unable to see them.

I asked the Hubble Space telescope, public relations officer by email; Can the Hubble ST see stars in daylight using the normal human visual light spectrum range, or does it have to resort to using the ultra-violet spectrum, (non-human light spectrum range), to see stars in daylight?

The answer I received simply informed me Hubble observes the stars 24/7, which I already knew, but I wanted to find out exactly how it overcomes the black, star-less daytime high altitude/space daylight sky. I could get no further clarity.

I’ve been fascinated by the black, star-less, daylight sky above the atmosphere for over a decade and it is very mysterious, especially when it seems to me, astronauts, professional astrophysicists and astronomers, appear uncomfortable with this topic. My curiosity remains. Thanks MichaelBrooks once again for your input.

The reason stars are not often seen on photographs taken in space has to do with shutter speed, and ambient light.   

[MichaelBrooks]

Thanks for the considered reply @spartan45. I am thinking that the point about the cameras on the ISS would only discount the hypothesis that I put forward if we know that those same cameras do capture a starfield at night. As per Moontanman's succinct point above, it may well be that those cameras are configured for lit conditions and won't capture a starfield at any time. If we know that those same cameras do indeed capture a nighttime starfield, then I agree that it's a valid point to consider.

However, the fact that the Hubble works 24/7 clinches it to my mind - it surely has to be down to shielding from bright light sources.

[spartan45]

On 8/16/2023 at 5:20 AM, MichaelBrooks said:

it may well be that those cameras are configured for lit conditions and won't capture a starfield at any time. If we know that those same cameras do indeed capture a nighttime starfield, then I agree that it's a valid point to consider.

All Alone in the Night - Time-lapse footage of the Earth as seen from the ISS

https://www.youtube.com/watch?v=FG0fTKAqZ5g

 The 2m29s youtube video above shows a night time star field filmed by the ISS cameras, however, it seems the video is cut as Sunrise occurs, In videos of the changeover the sudden break or camera view change makes it difficult to evaluate if the cameras used for night are the same as those for day or if the cameras simply have a day/night mode. If anyone knows how the ISS cameras cope with the day/night change over I’d like to know. 

On 8/16/2023 at 5:20 AM, MichaelBrooks said:

However, the fact that the Hubble works 24/7 clinches it to my mind - it surely has to be down to shielding from bright light sources.

Shielding from the bright light sources does not seem help astronauts or visual spectrum cameras see the stars in daylight, that’s why I’m wondering if the Hubble may have to depend on its ultra-violet spectrum capabilities for daylight viewing, although this idea is purely based on the fact that I’ve only seen star fields pictured in daylight by the Hubble or other devices capable of using the ultra-violet spectrum.