In discussing the stars in a well or chimminy, I am going to use the word mineshaft to refer to the long tube because to me that word does not imply a necessarily vertical tube, but also includes diagonal tubes.

FIRST POSSIBLE MECHANISM:

I have on quite a number of occasions viewed Venus in midday with the naked eye. (I include the planets because the average unprepared observer will describe them as stars.) The problem that I find that I have is that I can use my astronomical knowledge to figure out the approximate direction to look for Venus. It can take me several minutes of scanning the region of sky to finally see Venus. Without a reference point, if I look away for even a second, it takes as long to see Venus again as it did the first time. One method that I use is to find Venus the first time; then, while still staring at Venus, walk around until some ground attached reference is also in my field of view (the corner of a roof is sufficient) and move to a location where that chosen reference point is within a degree of Venus. Then if I look away for a minute or two, I can look back at my reference point, and need at most a few seconds to see Venus again.

This hypothesis is that the mineshaft does not allow one to see anything that could not otherwise be seen, but simply acts as a fixed reference point. Someone working in a mine taking a break looks up at the opening and looks at the tiny patch of sky they can see and has a brief impression of seeing a point of light. They then stare at it and confirm that, yes, they can see a star. If this brief impression occurred in the open, it is unlikely that an unprepared observer could replicate the observation, and if one could not, one might hypothize that one simply saw a glint of reflected sunlight off a very distant reflective object; eg, a jet too far away to be seen directly.

Complications would be that the star or planet would cross the patch of sky in a matter of minutes. Also, even for a star, the time of passage would become _earlier_ by almost 4 minutes per day. If someone unaware of this fact attempts to replicate their observation even just 5 days later, they would need to expect the entrance and exit to occur 19+ minutes earlier. If it were later, one might continue to stare at the opening even after the original time had passed in disbelief that one just simply saw things and might still be looking often enough even 12 minutes later -- the time delay for 3 days is just short of 12 minutes -- and figure out that the event occurs later each day. However, on Earth, as said before, the events occur _earlier_ each day. The average person does not know this, and so is likely with even as short as 2 or 3 days delay, not to be looking at the right time, and virtually certain not to be looking at the right time with more than 5 days delay.

Now at least with the stars (assuming that the observation can be made in the first place), one might expect a few people ignorant of the sidereal day issue might think after the failure described above to attempt to repeat the observation at the same time and date but a later year. This at least is possible. If one repeats the attempt 1 year later the events will be either 1 minute later or 3 minutes earlier. The exact value for periods longer than a single year depends on the number of leap days between the two dates. This change will very likely be less than 4 minutes, though in theory up to 8 and 2/3 minutes is possible.[*] For a planet; eg, Venus, from day to day the passage events may be affected in the reverse direction as the stars; ie, later each day instead of earlier; from year to year, no rule of thumb will help -- direct calculation is necessary. Actually, since the declination of the planets changes over time, only during short intervals will the planets pass in front of the opening of the mineshift, not every day like stars; ie, a star either passes over the opening of the mineshaft every day or not at all. [Yes, precession and proper motion means that even that last clause is not completely true over exceedingly long periods of time].

(([*]Over the interval 2096 Apr 01 to 2103 Apr 01, the change is 6.69+ minutes later. Over the interval 1903 Apr 01 to 2096 Apr 01, the change is 8.66+ minutes earlier. The formula I derived is delta=(.2425*years-leapdays)/365.2425. Negative results mean an earlier star passage, positive results a later one. (I know that I should replace .2425 by a more accurate figure -- .242190 seems a good working value --, however this means over long periods that delta grows without bound. Also the same issue that causes the differing values for the northward equinox tropical year and mean tropical year, causes the values to be slightly different for the intervals 2096 Apr 01 to 2103 Apr 01 and 2096 May 01 to 2103 May 01; even with .242190 substituted, I don't believe that my formula is more accurate than about a tenth of a second.))

In summary, under this hypothesis, on the one hand, an unprepared observer would have to be extremely lucky to observe this event. However, on the other hand, replication for a skeptical investigator would be unlikely, unless both the skeptical investigator was astronomically knowledgeable and the unprepared observer could give an accurate date and time of the observation. So one could have the situation that it is occasionally observed but nearly every time it is investigated, the observation can not be replicated.

Of course this is the least interesting of the hypotheses. If true, one could a small ring mounted on an a long bar mounted on accurate setting circles and calculate where to point the sight.

SECOND POSSIBLE MECHANISM:

This one involves the eye. One of the theortical limits of an optical system's resolution is caused by diffaction of the light that passes though the apature. When the human eye looks at a small bright area in a much larger dark area the pupil dilates. First, both the sky and star would become brighter simply because a larger area of incoming light is actually passing though the lens system; however, were this the only effect, the ratio of brightnesses would remain constant. But the larger apature would also mean, in theory, that the central Airy disk of the star would be smaller and brighter on the retina -- and this effect would not affect the brightness of a diffuse light source like the sky. So the _contrast_ between the star and sky should be enhanced.

I find it highly unlikely that an unprepared observer will benefit from this effect. I find it uncomfortably bright to fill my visual field with a clear midday sky under normal conditions; I expect that under these conditions that the enhanced brightness of the remaining area of sky on the retina would simply swamp the cones so badly that the increased actual contrast would be useless. However, a prepared observer could bring a set of photographic neutral density filters. The filters would not affect the brightness ratio between the star and the sky, but with the right density would eliminate the swamping effect. Indeed, with the filters in place the pupil would dilate even further, further enhancing contrast by further reducing the size of the Airy disk on the retina.

Of course, this analysis depends on the notion that diffraction is the limiting factor in the angular resolution of the eye. Not lens aberations or cone density. This also does not depend on being in a mineshaft, a tube 1 cm in diameter and 1 m in length painted matte black on the inside is the same as the mineshaft. Indeed, since the neutral density filter can be placed at the front of the tube stopping most of the light from entering the tube and potentially being scattered into the eye; the tube is a better solution than the mineshaft.

THIRD POSSIBLE MECHANISM:

This one involves a phenomenon that actually physically increases the contrast between the star and the sky. Air preferentially scatters blue light, rather higher frequencies. I first imagined this with a bright red star; eg, Betelgeuse. Particularly if the walls of the mineshaft are a dark color, the bluer light from the sky will preferentially scattered and most likely absorbed by the mineshaft walls, though a very small amount will be scattered back out of the mineshaft. This will also happen to the redder starlight, but not so quickly as it happens to the skylight. Thus the brightness contrast between the star and sky will increase.

It is virtually impossible for this effect to be of more than negligible benefit to an unprepared observer. First, if this selective scattering and absorbtion effect were increasing brightness contrast between sky and star by a more than miniscule amount, the observer would also notice that the sky had a different tint than that which is usually seen from the surface. This does happen, by the way; on very infrequent occasions the clouds can create a path that is tens of kilometers long though which there is no direct sunlight entering, but though which there is a stright line of sight to clear air which is being directly illuminated by the sun -- Observers of this meterological optical phenomenon describe this sky as having a greenish tint. Notice, however how long the path has to be for even a greenish tint to the sky, tens of kilometers. Even allowing that the white high albedo clouds inhibit the effeciency of the selective scattering, since much of the light scattered to the "wall", is then reflected back many times from wall to wall, giving it a significant chance of being scattered right back into the path, I believe that the mineshaft would have to be several kilometers long to have any real chance of even giving the sky a slightly noticible greenish tint -- To be long enough to actually have any real chance of seeing even a bright red star, there are NO _perfectly_ straight mineshafts that long.

FOURTH POSSIBLE MECHANISM:

I call the one the "smart-*** mechanism". There is one star which I can unquestionable see against the sky in a properly aligned mineshaft. However, the fact that it is less than .000016 light-years away is unquestionably the reason for this exception.

These four are the only mechanisms that I can imagine that allow one to see stars in midday in a mineshaft that one would not see on the surface.

SEEING STARS IN MIDDAY ON PURPOSE:

First, one only wants a small patch of sky to search for the star in. The tube 1 cm in diameter and 1 m in length gives one a viewing area not much larger than the Full Moon; some may want a somewhat larger viewing area -- feel free to experiment. Also, the accurate setting circles make it easy to decide that if one does not see the star, it is not because the the tube is pointed at the wrong area of sky.

Second, one wants the sides of the tube as dark as possible; paint it matte black inside. Also, the sun is likely to directly illuminate a small part of the inside of the tube near the front end, so something like a lens hood would be useful, though even an overhang or simply simply staying in the shadow of a building would be adaquate.

Third, one wants as little other light getting to the eyes as possible and preventing the pupil from reaching maximum dilation; add a rubber lens cap to the eye end of the tube, cover one's head with a thick dark cloth, and wear a dark eyepatch over the non-observing eye. Also, this is another advantage to being in the shadow of a building. More elaborate systems can be imagined.

Fourth, choose one's stars for a given day and time based on several considerations. On a clear day, skylight is dimmest at the zenith. Also, the least absorbtion of starlight occurs at the zenith. The polarization of skylight is at a maximum about 90 degrees away from the sun; this generates a arc-shaped prefered region. (Of course, this assumes that, as noted in the next step, one uses a polarizing filter.) Of course, if the zenith is 90 degrees away from the sun, then the sun is on the horizon; this is no longer midday, though there is something to be said for trying to observe when the sun is only 30 degrees above the horizon rather than 75 degrees. Finally, give preference to red stars. A red filter will also be used below; also the color contrast will be stronger, even if one does not use a color filter.

Fifth, one wants preferential absorbtion of skylight. A polarizing filter will not affect the color of the star, though it needs to be rotatable, so that it can be made perpendicular to the sky polarization -- this may require shortening the tube somewhat or fabricating a system for rotating the polarizing filter remotely. The bluer component of skylight is polarized less than the redder component, and is already brighter in the first place, add a deep red filter.

Sixth, one may still find that the skylight is too bright; add a appropriate neutral density filter.

Seventh, of course, one wants a day with high transparency to the atmosphere and no thin high clouds in the area one is trying to observe stars in. This increases the polarization and blueness of skylight (making the filters even better) and reduces the initial brightness of skylight (always helpful), and increases the brightness of the stars (always helpful) -- less absorbtion means more light gets to ground level.

Eighth, low sun altitude helps, but too low and it's not midday anymore. In records, include either date and time and observer coordinates of actual star observation or attempted star observation -- probably a good idea in any event, but also sun altitude can be calculated from that information --, or actual sun altitude.

Ninth, high altitude should help; ie, if one is on a high mountain, one is above part of the atmosphere -- same enhancements as in the seventh point.

Tenth, somewhat in contradiction to the ninth point, if one can be in the shadow of a near high mountain the sun altitude can still be quite high and at least part of the volume of the sky above one is now in shadow and contributes much less to the skylight. Ideally, if one can have a building or other obstruction that is in the shadow with one on the other side of one the once-reflected sunlight from the distant background land does not reach one's eyes and helps improve point three.

Eleventh, a high altitude object that can block sunlight from you would be slightly useful. Some ballons can be somewhat propulsive, by choosing which sides the hot air is vented on at the top. Also a propeller mounted to the side of the basket could allow one to hold position against the wind; though, I know the actual enginnering would be more complex.

Twelvth, the ultimate extension of point eleven is a partial (or even total) solar eclipse; while interesting, like very low sun altitude, is not keeping in the spirit of observing stars in midday -- any solar eclipse is to be noted and fraction of sun's disk covered to be calculated.

Thirteenth, the ultimate assistance is, of course a large telescope. Magnification is limited by seeing; apature is limited, I believe, by the fact that when the telescope's exit pupil exceeds one's eye's entrance pupil, part of the apature is being wasted. Placing the filters on the end of the telescope and using the other techniques should still allow one to push the limiting magnitude even further.

Fourteenth, if one would also be interested in seeing the stars on a screen in real time, one could go down in to the deeper near infrared. The red filter might even be opaque to visible light and only transmit infrared. For a reflector, ideally only the eyepiece would need to be replaced with one designed for infrared. A refractor might have to be designed from scratch. Of course, one needs to obtain the infrared camera, as well. A cheaper, though less efficient, approach would be old-style infrared film cameras; perhaps the reduced quantum efficiency would not be a limiting factor in this application.

Fifteenth, digital image processing, even in visible light, might also push the limiting magnitudes further than the system could otherwise do.

OK, any other ideas, other than building, buying, or renting a space vehicle?

Sorry, also meant to ask if anyone knew of any other, at least plausible on the surface, mechanisms for seeing stars in daylight in a mineshaft.

Well, besides having someone whack you hard on the head. Yes, you, or at least I, can see stars from a blow to the head; I had always assumed that the cartoon representations of stars moving around the head of characters hit in the head were just a silly representation of the pain or dazedness, but no, I was extremely surprised to first discover from personal experience in my mid-twenties that one can really see stars from a blow to the head. I assume that the impact of the brain to the inside of the skull triggers initial random nerve firings, which then drift causing the perception of colored points of light that drift around.

I tried, but I saw no stars.

It's cloudy out.

__________________
Fields of Space

LOGIC, n.
The art of thinking and reasoning in strict accordance with the limitations and incapacities of the human misunderstanding.

In the Year 2525.

"One small step for (a) man. One giant leap for mankind".

If an astronaut doesn't need good grammar, niether does you.

Host of Seraphim

I have succeeded in seeing Venus during daylight but never a star. As a boy I heard it was possible to see the stars from the bottom of a well, and have attempted to confirm such while at the bottom of other structures (not wells) and did not succeed in seeing anything other than a blue patch.

Nevertheless, the idea that an open sky can saturate the eyes and thereby reduce visual acuity or contrast seems reasonable to me, but I am reasonably certain a vision expert could easily explain the mechanism.

-Veeger

Are you arguing that one should be able to see stars from the bottom of a well through one of these three mechanisms (discounting the fourth)? If so, the evidence is against the argument no matter what mechanism is hypothesized - the sky is just too darned bright:

http://www.astronomycafe.net/qadir/q241.html
http://www.snopes.com/science/well.asp
So the simple experiment in the first reference would duplicate effects from bottom of a well, (to no avail) and the second reference makes the point that at the bottom of a well or mineshaft the sky is VERY bright and washes out everything else. In fact this makes stellar observation even harder, not easier.

I am tempted to ask if you actually read the whole text. The first mechanism is really ignorance of the average person. It seems logical that if I can see Venus in the midday (when it is near maximum elongation from the sun and maximum brilliance) by simply looking in the right direction and shading my eyes from the sun -- I have even simply used my hand --, then I should be able to see Venus at the bottom of a properly aligned mineshaft, if only for the period of time it take Venus's apparent position to cross the small visible region of sky. A straight mine shaft 2 meters in width and 100 meters long would ideally give me a visible area about 1 degree wide. A star or planet;eg, Venus, would take about 2 minutes to cross this region.

The effects of absorbtion (3rd proposed mechanism) are simply much too small over a mere 100 meters to either help or hinder my attempted observation of Venus.

The sharpening of the diffraction limit (2nd proposed mechanism) can not hinder and may help my attempted observation of Venus.

The swamping effect (discussed in the commentary on the 2nd proposed mechanism) could hinder my attempted observation of Venus, but could easily be countered by placing a high-quality photographic neutral density filter just in front of my eye.

Unfortunately I do not have access to a mineshaft of any type at this time and do not expect to have access at any time in the near future, so I can not do what I would like to be able to say that I have done:

Find a number of mineshafts with a view of the sky. Measure the angle to the horizontal and true direction of the line of sight. Measure or calculate the size of the region of sky that can be observed. Determine the latitude and longitude coordinates. Use algorithms for the apparent position, magnitude, and elongation from the sun of Venus; to determine a set of dates and times when Venus would pass though the visible regions of sky for each mineshaft near its times of maximum elongation and magnitude. Use this schedule to determine when to be at the bottom of particular mineshafts on particular days and times. Actually be at the bottom of these mineshafts with a watch set by a standard time service and a set high-quality photographic neutral density filters on calculated dates and times.

I have no doubt that if the weather is such that an observer standing just outside the mineshaft could see Venus with the naked eye and no unusual problems intervene (eg, a lot of dust suspended in the air in part of the mineshaft) that I would be able to see Venus at the bottom of the mineshaft. There is a fair chance that I would not even need any of the neutral density filters.

Of course, if I don't need the neutral density filters, then one has to admit to the possibility of the scenario described in the 1st proposed mechanism: a person ignorant of the fact that a apparent star-like object; ie, Venus, can be seen in midday even without a mineshaft gets extremely lucky and happens to look up the mineshaft at exactly the right time -- this not only has tight requirements on alignment, but also requires the weather conditions to be quite good -- and sees Venus and then proceeds to conclude that a mineshaft can allow one can see at least some stars in midday that could not be seen otherwise. I don't consider this mechanism to be particularly interesting because it is the boldfaced clause that is false; the only significant effect of the mineshaft was that (by luck) it acted as a sighting reference for the observer. This is the meaning of: If true, one could a small ring mounted on an a long bar mounted on accurate setting circles and calculate where to point the sight.

What I find interesting about the 1st; 2nd; and, of course, 4th proposed mechanisms is that their effects can be duplicated without a large mineshaft; any one who knows how Foucault mirror testing works could design both of the proposed duplicators: a small ring mounted on an a long bar mounted on accurate setting circles, and a long thin tube with a internal surface that is as non-reflective as one can make it.

If I presently had the resources, I would build both projects and actually try them out. One advantage of these proposed projects is that they can be moved to point to any location in the sky; so, if the geometry were just right, I could test Jupiter, Mars, Sirius, and Betelgeuse in a single day, without having to move any more than needed to rotate the device. With a mineshaft the direction is fixed for a particular mineshaft, and even if one were lucky enough to have two passes in the same day over different mineshafts; I have climb back out of one, travel to the other one and descend down it. And the chances of two passes in a single day over a single mineshaft -- remote.

Notably, even if both projects turned out to be a complete failure (except for Venus, of course), I could still use them to make Venus much easier for me to find in midday. Use the calculations to determine where to point the device and then instead of having to search a large area of sky to determine if I can see Venus under the given conditions, I could look at the small area pinpointed by the device and know that Venus should be very nearly at dead center. Indeed, add a fixed-rate sidereal drive and I should be possible to track Venus for at least a couple of hours; if it is like one model I have seen with a variable-rate control so that the rate can be adjusted to track the sun or moon, then the rate can also be calculated and the device will accurately track Venus all day.

As for the third proposed mechanism, NO human being has ever seen stars at the bottom of a mineshaft/etc even marginally helped by this mechanism -- mineshafts/etc do not exist that are both long enough and straight enough for the third proposed mechanism to have even a marginal effect.

So, the 1st and 2nd proposed mechanisms can be fairly easily duplicated on a small scale. If it is determined that the 1st proposed mechanism does not work for anything but Venus. And that the 2nd proposed mechanism fails to even improve the naked eye observed contrast of Venus with the sky. Then, it being already established that the 3rd propose mechanism is irrelevant to any actual cases of looking at the sky at the bottom of a mineshaft/etc, then it can safely be said that a mineshaft does not allow one to see some apparent star-like objects -- this phrasing is so as to include the planets -- in midday that could not be seen otherwise be seen in midday.

The section labeled SEEING STARS IN MIDDAY ON PURPOSE, basically says forget the mineshaft question (because as we have established, the mineshaft is not necessary), I just want to want to see as many different astronomical objects as possible during daylight.

Obviously, using a total solar eclipse, using a telescope, using a camera which can use wavelengths and integration times that your eye can not, and using digital processing; particularly in combination, are the most effective ways of doing so.

While being able to image magnitude 15 stars with a camera and digital processing even through a large aperture telescope during a very long total solar eclipse would be an very interesting accomplishment, I find that I also want to see the stars directly and that I would be interested in exploring how far I can go without using the larger aperture and magnification of a telescope. As far as the total solar eclipse, I would have to either be older than Methuselah or have a time machine to ignore the main show and attempt to see 5th magnitude stars during the totality of a solar eclipse.

So the other suggestions are ideas I have to try and see astronomical objects other than Sol, Luna, and Venus during the daytime. Go ahead and use the tube so that one can know that; eg, Sirius is at the center of this quite small field of view, whether or not it is visible, rather than questioning whether or not one can't see Sirius because one is not looking in exactly the right direction or because the current setup and conditions simply will not allow it.

The polarizing and red filters seem an obvious way to increase contrast; knock down the sky brightness as much as possible while trying to affect the starlight as little as possible. Go to the Himalayan peaks to get above as much atmosphere as possible, so that the skylight will be dimmer, more polarized, and more blue; so that after filtration the skylight will be even darker than after the filtration at sea level. Also, putting the same types of filters on the objective end of a large-aperture telescope, should allow one to see more stars in daylight though the telescope.

So, my query breaks down in to two questions. Are there mechanisms that I have not described in the first part that even a snowball's chance in Hades of allowing one to see a apparent star-like astronomical object at the bottom of a mineshaft/etc? Are there improvements to toys and methods that I would like to someday build/acquire/attempt, admittedly expensive toys, described in the second part that I have not mentioned, other than leaving the earth's surface; eg, stratospheric balloons, high altitude jets, or going to low earth orbit? I hope this clarifies my query.