Eclipse City (APOD 2009 August 20)

[neufer]

Note how small these 0.5º eclipse images appear.
So why does this 0.5º eclipse image appear so large?

The high optical quality of the window glass can be seen in the 0.5º eclipse images at the bottom of the swimming pool as reflected off of the Pacific Place Tower on the left(; click on image to see high resolution).

Love Is a Many-Splendored Thing (1955)

Third Uncle: We shall now have tea and speak of absurdities.

[apodman]

So why does this 0.5º eclipse image appear so large?

Looks like during an eclipse the moon illusion takes the sun with it. My question is ...

http://antwrp.gsfc.nasa.gov/apod/ap080620.html
http://antwrp.gsfc.nasa.gov/apod/ap050623.html

... who moved that tree?

[bystander]

Looks like during an eclipse the moon illusion takes the sun with it. My question is ...

... who moved that tree?

I don't know, but it took them 3 years to do it.

June 18, 2008
May 23, 2005

[neufer]

My question is ...who moved that tree?

I don't know, but it took them 3 years to do it.

June 18, 2008
May 23, 2005

<<At the dissolution festival at the end of the year in the Athenian calendar, the Skira, the priests of Athena and the priest of Poseidon would process under canopies to Eleusis. They agreed that each would give the Athenians one gift and the Athenians would choose whichever gift they preferred. Poseidon struck the ground with his trident and a spring sprang up; the water was salty and not very useful, whereas Athena offered them an olive tree. The Athenians (or their king, Cecrops) accepted the olive tree and along with it Athena as their patron, for the olive tree brought wood, oil and food. After the fight, infuriated at his loss, Poseidon sent a monstrous flood to the Attic Plain, to punish the Athenians for not choosing him.>>

[apodman]

Note how the moon's path in the sky intersects the horizon at different angles throughout the year. The June moon (2008) is clearly rotated clockwise compared with the May moon (2005).

[neufer]

Note how the moon's path in the sky intersects the horizon at different angles throughout the year.
The June moon (2008) is clearly rotated clockwise compared with the May moon (2005).

When the sun rises in the far northeast the full moon rises in the far southeast.

Code: Select all

Distance  Altitude Azimuth
----------------------------------------------------------------
63.3 ER    23.079  -16.383 Up   6 18 2008  21:25:02
58.5 ER    25.035  -21.626 Up   5 23 2005  20:53:21

[JohnD]

All,

There has been a recent debate, sometimes heated, about how real was a pic taken from a window.
Here's another.

I have no doubt that the photographer took a genuine, one shot picture.
But, how and why did the glass wall of an office block produce one reflected image for each pane of glass? If that glass wall was an array of perfectly flat panes, all aligned in one plane, there should have been one image, the reflection of the sun seen by the camera as projected on the ground. There wasn't, there was one for each pane, so what distortion of the wall will produce this?

Was each pane slightly concave/vex?
The lack of perfect alignment of the reflections indicates that the wall was not flat - could that cause this?

John

[polaris]

I'm afraid I'm a bit confused by how all these images of the eclipse formed. We've seen something similiar

http://antwrp.gsfc.nasa.gov/apod/ap051014.html

when the sunlight goes through a pin-hole. But you don't see a round disk on the ground when sunlight reflects off a building or mirror on a non-eclipse day. What do you see from at this site on a non-eclipse day, little disks?

Peter

[bystander]

Note how the moon's path in the sky intersects the horizon at different angles throughout the year. The June moon (2008) is clearly rotated clockwise compared with the May moon (2005).

I know the horizontal displacement (who moved that tree) is seasonal (May vs June), but is the rotation also seasonal or is that due to precession (2005 vs 2008)?

[emc]

Relativity... As I walk down the street, I notice that I am moving faster than light reflected from the eclipse. If I stop to watch the plants grow, I notice that light is moving faster than me.

[apodman]

Note how the moon's path in the sky intersects the horizon at different angles throughout the year. The June moon (2008) is clearly rotated clockwise compared with the May moon (2005).

I know the horizontal displacement (who moved that tree) is seasonal (May vs June), but is the rotation also seasonal or is that due to precession (2005 vs 2008)?

As far as I recall, the moon has 13 or so different motions with respect to the Earth, and at least one of them produces a rocking back and forth clockwise and counterclockwise. But I think all we are seeing here is that the moon's equator is at a constant angle to its orbit and the moon's inclined orbital plane intersects the horizon at a different angle for the rising full moon of each month. So the effect I'm talking about is seasonal. I'm pretty sure the precession of the major axis of the moon's orbit is not involved, but I'm confusing myself about the precession of the line of nodes so I can't answer that one right now.

Regarding the relative positions of moon and tree, the photographer could also have been set up in a slightly different place for each photograph.

---

The mean inclination of the lunar orbit to the ecliptic plane is 5.145°. The rotation axis of the Moon is also not perpendicular to its orbital plane, so the lunar equator is not in the plane of its orbit, but is inclined to it by a constant value of 6.688° (this is the obliquity). One might be tempted to think that as a result of the precession of the Moon's orbital plane, the angle between the lunar equator and the ecliptic would vary between the sum (11.833°) and difference (1.543°) of these two angles. However, as was discovered by Jacques Cassini in 1721, the rotation axis of the Moon precesses with the same rate as its orbital plane, but is 180° out of phase (see Cassini's Laws). Thus, although the rotation axis of the Moon is not fixed with respect to the stars, the angle between the ecliptic and the lunar equator is always 1.543°.

I'm still confused, and I have reached no conclusion as to what effect these facts have on your question and its answer. I may have opened up a bag of worms here, and I'm becoming sorry I brought up the subject. But I'm thinking I might be able to say the following safely:

"I think all we are seeing here is that the moon's equator is at a constant angle to the ecliptic and the ecliptic intersects the horizon at a different angle for the rising full moon of each month. So the effect I'm talking about is seasonal."

[geckzilla]

I'm afraid I'm a bit confused by how all these images of the eclipse formed. We've seen something similiar

http://antwrp.gsfc.nasa.gov/apod/ap051014.html

when the sunlight goes through a pin-hole. But you don't see a round disk on the ground when sunlight reflects off a building or mirror on a non-eclipse day. What do you see from at this site on a non-eclipse day, little disks?

Peter

I don't know if it reflects circles on non-eclipse days but it does help to see a photo of the face of the building to understand it. Here's one taken from the ground looking up.
http://www.flickr.com/photos/kwcpaul/3243082016/

[apodman]

I don't know if it reflects circles on non-eclipse days

Maybe Barry & Noemi can take their next vacation in Hong Kong and let us know.

[Redbone]

Note how the moon's path in the sky intersects the horizon at different angles throughout the year.
The June moon (2008) is clearly rotated clockwise compared with the May moon (2005).

When the sun rises in the far northeast the full moon rises in the far southeast.

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Distance  Altitude Azimuth
----------------------------------------------------------------
63.3 ER    23.079  -16.383 Up   6 18 2008  21:25:02
58.5 ER    25.035  -21.626 Up   5 23 2005  20:53:21

Further, the sun is high and bright in the summer while the (full) moon is only high and bright in the winter, at least in locations North/South of the equator.

1) Why are there two high tides and two low tides per day?
2) Why do we skip one tide every ~28 days?
3) Why does the high tide occur ~two hours after the moon's rise, well before the moon is directly overhead?

Edit: To fix up #3

[JohnD]

[quote="geckzilla"

I don't know if it reflects circles on non-eclipse days but it does help to see a photo of the face of the building to understand it. Here's one taken from the ground looking up.
http://www.flickr.com/photos/kwcpaul/3243082016/[/quote]

Aaaaaaaaaaaah, So!
The suns is refeklcted, niot off the rectangular building on the left, but the circular one on the right!
So thr panes are not on the same plane, but forma convex mirror that shines multiple images on the ground.
Thnak you!

John

[apodman]

The suns [are reflected], [not] off the rectangular building on the left, but the circular one on the right!

Look at this link provided in the APOD description. In fact, the multiple sun images are reflected not off the rectangular Pacific Place building on the left, not off the convex curved Conrad International building on the right, but off the convex curved Two Pacific Place building from which the photograph is taken.

So [the] panes are not on the same plane, but [form a] convex mirror that shines multiple images on the ground.

Which still doesn't fully explain why the sun reflects onto the scene below from only one spot on each pane.

1) Why are there two high tides and two low tides per day?

The tidal force of the moon pulls more strongly on what is closer. The moon pulls up water on the near side of the Earth relative to the solid Earth. The moon pulls up the solid Earth relative to the water on the far side of the Earth. This creates two tidal bulges on opposite sides of the Earth. The solid Earth rotates slightly less than once relative to these two bulges each day.

2) Why do we skip one tide every ~28 days?

The moon revolves around the Earth once every ~29 days in the same direction that the Earth rotates, so the moon crosses a given meridian on the Earth only ~28 times in ~29 days. Thus the moon rises and sets nearly an hour later every day, and thus the interval from low-to-high or high-to-low tide is somewhat longer than 6 hours, and the interval from high-to-high or low-to-low tide is somewhat longer than 12 hours. We actually never "skip" a tide; there are just slightly less than 2 (by a factor of ~28/~29) tides per day.

3) Why does the high tide occur ~two hours after the moon's rise, well before the moon is directly overhead?

It takes a while for the water (many many gallons) to move in response to the tidal pull. The Earth keeps rotating, and the water never catches up. The continents keep the tidal bulges from traveling continuously around the Earth, so instead the ocean tides slosh back and forth between the eastern and western shores. The time lag varies greatly from one ocean, shore, or inlet to another; that's why we need tide charts. Some locations are completely 90° (6+ hours) out of sync with the position of the moon, some even more. In your example, the tide isn't 4 hours early; it's 8 hours late.

In the case of a river, think of a standing wave in a river rocking from the upstream tidal limit to the ocean end and driven by the ocean water level; picture the tidal waters from the ocean not actually making it way up a river themselves, but the water coming from upstream piling up when the level downstream is high and flowing out when the level downstream is low. I once lived over 100 miles north of NYC on the Hudson River and we had tides right up to the first lock on the Erie Canal. Now I live near Washington, DC which is way up the Chesapeake Bay and then way up the Potomac River from the ocean, and we have tides past both Beltway crossings right up to Great Falls. All of these tides are completely out of sync with the visual position of the moon.

Additionally, when the moon is not new or full, the vector component of the tidal force contributed by the sun is either ahead of or behind the component contributed by the moon, which also changes the lag time forward or backward as we go through a lunar month.

[Chris Peterson]

So [the] panes are not on the same plane, but [form a] convex mirror that shines multiple images on the ground.

Which still doesn't fully explain why the sun reflects onto the scene below from only one spot on each pane.

The Sun is not being reflected from one spot on each pane, but from each pane as a whole. Each window pane is essentially acting as an individual pinhole lens (it doesn't matter whether you have an aperture or a small reflector, the optics are the same). The horizontal (or circumferential) dispersion of images occurs because each pane is at a slightly different angle (from the cylindrical building). The vertical (or radial) dispersion occurs because each row of windows is isolated from the next by a wide, non-reflective band. Without the separators, you'd not get proper images- it would be like you had a slit camera instead of a pinhole camera- something that doesn't work very well. The pattern around the building would look like spokes rather than a radial array of spots.

[NoelC]

Makes you wonder... What would life be like (if there was life at all) without the moon?

Chris beat me to the explanation. The reflected crescents are much larger than the original windows.

I looked very closely at the subject APOD image and I believe it to be quite genuine. I can only guess the designers of the building intended for the windows at Two Pacific Place to send out these wonderful solar reflections, though perhaps not anticipating the eclipse.

Some images of the area I found online showing the curved buildings...

http://upload.wikimedia.org/wikipedia/c ... 26_Two.jpg
http://www.pacificplace.com.hk/images/e ... omplex.jpg
http://farm4.static.flickr.com/3549/329 ... b2af_b.jpg

-Noel

[JohnD]

BUT, but, but but,

This circular building may be considered as a convex mirror, with many parallel light beams striking it.
The mirror would cause the reflected beams to diverge.
The points at which the beams strike a plane in front of the mirror would not be equidistant, but spaced further apart, the further they are from the central beam.
So will the building.
Yet the reflected images are seen as a regular grid.
Impossible, surely?

For instance, see the video of light beams being reflected from a convex mirror on this website: http://www.wfu.edu/physics/demolabs/dem ... ideos.html the tenth tiem down.
It can be clearly seen there that individual beams are varying distance apart on a plane in front of the mirror, growing further apart the more they are distant from the central beam.

I've seen the dappled shade beneath a tree transformed during an eclipse into a pattern made up of sun images.
If you had a perforated plate, not the leaves of a tree, that would produce an array of equidistant images of the partly occluded Sun.
But the above effect is from reflection, and should cause diverging rays.
Sorry, but I grow more sceptical about this picture.

JOhn

[apodman]

The pattern spacing looks good to me, but I'm disturbed by the uniformity of the vehicles. Does Chinese law allow only red and white paint in Hong Kong?

[geckzilla]

The pattern spacing looks good to me, but I'm disturbed by the uniformity of the vehicles. Does Chinese law allow only red and white paint in Hong Kong?

Hong Kong taxis.

[apodman]

Hong Kong taxis.

I suppose in any major city the ratio of taxis to private vehicles is higher than in the countryside. I was just saying there's barely a private vehicle in the whole picture. (I'm calling the white van with the moon roof a delivery truck.) There is a white car on the highway on the left, and a couple of dark cars in the far upper right, but you really have to look for them.

I'm not really complaining about the color scheme; after all, look at the ubiquitous standard in Mexico:

[geckzilla]

Well, parking is very hard in any big city, so people just take a taxi instead of having to deposit their car somewhere and get charged a lot of money. So they line up in the taxi lane ready to take anyone who pops out of the building. Haven't ever lived in a metropolis before?

[apodman]

Haven't ever lived in a metropolis before?

You would ask Jimmy Olsen such a question? I've seen the curb lane at airports and train stations, too. When my little sister lived in NYC, she parked her car in NJ and only visited it on weekends. Is that alternate-side-of-the-street parking working out for you as well as it did for Oscar and Felix? Do they still do it that way in the land of starless skies?

[geckzilla]

I... I don't know! Too many questions!