by neufer » Sat Jun 22, 2013 12:04 am
geckzilla wrote:Fritz Stumpges wrote:
One thing I question about this series of photos is that the sun appears to be setting (or rising in some place in the south) at too straight of a path to have occurred on the solstice? It looks like the pictures were taken approximately 5 minutes apart and so this should have occurred over 80 minutes or so. Even allowing for refraction close to the horizon straightening out the last few frames a little, this path is far to straight for a solstice...it's more like an equinox.
Such a curve would be subtle.
It is clearly curved (i.e., concave)
slightly upwards as one would expect
both at summer solstice & with refraction.
http://cseligman.com/text/sky/moonillusion.htm wrote:
<<To many people, the Moon appears much larger when rising or setting than when it is higher in the sky. This effect is particularly pronounced when the horizon appears far away. In reality, the Moon's image is actually SMALLER when it is on the horizon, than when it is higher in the sky; as a result, this phenomenon is an illusion. No explanation of the Moon Illusion has general acceptance, but this page (when revised and completed) will hew to the following theory:
Things seen at large distances appear smaller than nearby things (that tiny lion sitting over there is probably just as big, but further away than that huge one, hungrily eyeing us). Almost everyone is aware of this "perspective" effect; but not as many are aware that our brain automatically corrects for the effect, to a certain extent -- that is, things that are further away look smaller than nearby things, but not as small to our brain as on our retinas. For reasons to be discussed below, which are more or less obvious without discussion, the horizon appears further away than the sky appears high, so when the Moon is on the horizon it appears further away, and our brain "adjusts" the image sent to it by our eyes, to tell us that it is really larger than what we see.
I favor this theory because (1) when we look at distant mountains, they appear larger than in snapshots taken at the same place and (2) on planetarium domes, showing the Moon and Sun at their correct size makes them look much smaller than they do in the sky. In the planetarium, we can tell that the images are much closer to us than in the sky, and even though they are the right size on our retina, they look far too small to our brains. (At LBCC, we have to show the Moon and Sun four times their correct size to approximate their appearance in the sky.) This seems to be corroborated by the fact that constellations also look smaller on the planetarium dome than in the real sky, even though their angular size is actually the same.
A series of images taken by astronaut Don Pettit from the International Space Station, showing the full moon "setting" on April 16, 2003 (the "setting" being caused by the orbital motion of the Space Station). As a celestial object's light passes through our atmosphere it is bent, or refracted, making it appear thigher than it really is. As the object nears the horizon, the amount of refraction rapidly increases, so as the Moon sets, its lower limb is "lifted" more than the top, making the Moon appear vertically squashed (but leaving its horizontal width unchanged). Scattering of light by the atmosphere, greater at shorter wavelengths than longer ones, also makes the Moon look redder as it descends. The same phenomena are observable on the Earth, but because the setting Moon is "below" the Space Station, the effects are doubled, compared to the view from the ground. (Don Pettit, Les Cowley, ISS, NASA)>>
[quote="geckzilla"][quote="Fritz Stumpges"]
One thing I question about this series of photos is that the sun appears to be setting (or rising in some place in the south) at too straight of a path to have occurred on the solstice? It looks like the pictures were taken approximately 5 minutes apart and so this should have occurred over 80 minutes or so. Even allowing for refraction close to the horizon straightening out the last few frames a little, this path is far to straight for a solstice...it's more like an equinox.[/quote]
Such a curve would be subtle.[/quote]
It is clearly curved (i.e., concave) [u]slightly[/u] upwards as one would expect [u]both[/u] at summer solstice & with refraction.
[quote=" http://cseligman.com/text/sky/moonillusion.htm"]
[float=right][img3=""]http://cseligman.com/text/sky/spacemoonset.jpg[/img3][/float]
<<To many people, the Moon appears much larger when rising or setting than when it is higher in the sky. This effect is particularly pronounced when the horizon appears far away. In reality, the Moon's image is actually SMALLER when it is on the horizon, than when it is higher in the sky; as a result, this phenomenon is an illusion. No explanation of the Moon Illusion has general acceptance, but this page (when revised and completed) will hew to the following theory:
Things seen at large distances appear smaller than nearby things (that tiny lion sitting over there is probably just as big, but further away than that huge one, hungrily eyeing us). Almost everyone is aware of this "perspective" effect; but not as many are aware that our brain automatically corrects for the effect, to a certain extent -- that is, things that are further away look smaller than nearby things, but not as small to our brain as on our retinas. For reasons to be discussed below, which are more or less obvious without discussion, the horizon appears further away than the sky appears high, so when the Moon is on the horizon it appears further away, and our brain "adjusts" the image sent to it by our eyes, to tell us that it is really larger than what we see.
I favor this theory because (1) when we look at distant mountains, they appear larger than in snapshots taken at the same place and (2) on planetarium domes, showing the Moon and Sun at their correct size makes them look much smaller than they do in the sky. In the planetarium, we can tell that the images are much closer to us than in the sky, and even though they are the right size on our retina, they look far too small to our brains. (At LBCC, we have to show the Moon and Sun four times their correct size to approximate their appearance in the sky.) This seems to be corroborated by the fact that constellations also look smaller on the planetarium dome than in the real sky, even though their angular size is actually the same.
A series of images taken by astronaut Don Pettit from the International Space Station, showing the full moon "setting" on April 16, 2003 (the "setting" being caused by the orbital motion of the Space Station). As a celestial object's light passes through our atmosphere it is bent, or refracted, making it appear thigher than it really is. As the object nears the horizon, the amount of refraction rapidly increases, so as the Moon sets, its lower limb is "lifted" more than the top, making the Moon appear vertically squashed (but leaving its horizontal width unchanged). Scattering of light by the atmosphere, greater at shorter wavelengths than longer ones, also makes the Moon look redder as it descends. The same phenomena are observable on the Earth, but because the setting Moon is "below" the Space Station, the effects are doubled, compared to the view from the ground. (Don Pettit, Les Cowley, ISS, NASA)>>[/quote]