Starship Asterisk*

Chris Peterson wrote:

neufer wrote:I'm thinking that the magnitude -27 sun produces magnitude -2 to -7 crepuscular rays (depending on the "misting factor")
so a magnitude -13 full moon should produce magnitude +12 to +7 crepuscular rays.

The Thurso Castle "crepuscular rays" look a lot brighter than that!

Well, if the rays are the shadows, there's no problem. Keep in mind that people regularly make nighttime images under moonlight using 30-60 second exposures, and these are indistinguishable from daytime shots.

Well, if the"lunar crepuscular rays" are MOVING shadows, there IS a problem.
Clouds, including the one that you assume covers the April 8 moon,
often move quite a bit over a period of 30-60 seconds.

(Perhaps the periodic clouds that are generating the periodic
"lunar crepuscular rays" on the left are due to standing mountain wave clouds.)

Besides, if longer exposures, faster film & shorter f-stops are turning the full moon
into a 400,000 times brighter (effective) sun then why is the sky so darn dark?

I recommend that this APOD gets renamed "Moon Rays Over Thurso Castle?"
and have APOD members queried as to what they think we are seeing.

neufer wrote:I'm thinking that the magnitude -27 sun produces magnitude -2 to -7 crepuscular rays (depending on the "misting factor")
so a magnitude -13 full moon should produce magnitude +12 to +7 crepuscular rays.

The Thurso Castle "crepuscular rays" look a lot brighter than that!

Well, if the rays are the shadows, there's no problem. Keep in mind that people regularly make nighttime images under moonlight using 30-60 second exposures, and these are indistinguishable from daytime shots.

apodman wrote:

neufer wrote:I don't think that a full moon is bright enough for crepuscular rays!

Maybe not for the naked eye, but in a 3-minute exposure who knows?

I'm thinking that the magnitude -27 sun produces magnitude -2 to -7 crepuscular rays (depending on the "misting factor")
so a magnitude -13 full moon should produce magnitude +12 to +7 crepuscular rays.

The Thurso Castle "crepuscular rays" look a lot brighter than that!

neufer wrote:I defy you to pick out two "true lunar crepuscular rays" that converge on the Moon position you indicate.
I'm thinking that it is early evening of April 9 well before the full moon has risen from behind the castle near Spica.
The Thurso Castle floodlights on the hidden south east side of the castle are individually illuminating a faint sea mist

Assuming the effect is from the Moon, it would be more correct to call them crepuscular shadows. The image is confounded by the fact that the lit parts are just illuminated clouds, but that's where we try to see the rays pointing back to the Moon. It is the shadows on the clouds to the left side that could well be rayed- they come very close to pointing back to the Moon, and there's some distortion in the wide angle shot that might make estimating the vanishing point tricky.

That said, it is possible that the ray-like effect is just coincidental. But I do think the light source is the Moon, not nearby artificial lights. It would be instructive for the photographer to provide the date and time the image was taken, since that would make the analysis trivial.

(None of this should suggest that I think the photographer is trying to pull one over on us. I'm confident it is a single, unedited image, and it is certainly a beautiful shot, regardless of whether the effect is caused by true crepuscular rays/shadows or simply illuminated clouds showing motion blur from the long exposure.)

Chris Peterson wrote: I don't think it's a composite, I just think the image is being misinterpreted.
Based on the position of Saturn, the image appears to have been made on April 8, 2009.
If so, that means the sky looked like this:



So the Moon isn't below the castle wall, but behind a cloud. The rays going up and to the left are probably true crepuscular rays, while the "rays" at the center and right side of the image are actually just thin clouds directly illuminated by the Moon.

I defy you to pick out two "true lunar crepuscular rays" that converge on the Moon position you indicate.

I'm thinking that it is early evening of April 9 well before the full moon has risen from behind the castle near Spica.

The Thurso Castle floodlights on the hidden south east side of the castle are individually illuminating a faint sea mist

saturn5 wrote:The star trails follow their normal path,the crepuscular rays whether they be from the sun or moon basically radiate in a circle,you seem to think that the rays should look as though they should be following the star trails,The rays will eminate from wherever there is a gap in the clouds to allow the light to shine through,just the same as the sun,believe me its just a 3 minute exposure from a static tripod,no trickery or photoshop magic and the reason its in b&w is because of light pollution from the town.I couldn't be bothered removing the LP and i thought it looked more dramatic as a b&w.

I'm willing to take the photographer at his word.

Fair comments Chris, and very plausible. I'm delighted with the way you've added the sky representation to the image. Well done! Regards.

starfinder wrote:So, why do I think it is a composite?
A: the Moon is way, way too far south of the ecliptic...

I don't think it's a composite, I just think the image is being misinterpreted. Based on the position of Saturn, the image appears to have been made on April 8, 2009. If so, that means the sky looked like this:



So the Moon isn't below the castle wall, but behind a cloud. The rays going up and to the left are probably true crepuscular rays, while the "rays" at the center and right side of the image are actually just thin clouds directly illuminated by the Moon.

Art, could be city lights (though Thurso is rather small - population around 9000), except that the image's author specifically states "moon rays@Thurso Castle"; BTW image was uploaded to flickr on 11th April 2009. The Castle is about a mile NE of the Town centre. Based on Leo's orientation the camera was pointing a little E of S which means it was pointing away from the brightest lights of town. This is a sparcely populated part of the world - largest city is Inverness 80 miles to south, ie way over the horizon.

I agree with apodman (who replied as I was writing this!)

Re your comment - is full moon bright enough for crepuscular rays? The exposure was 3 minutes long - plenty long enough to show features not visible to the eye.

I still think the Moon's in the wrong place and image is a composite. Regards.

neufer wrote:I don't think that a full moon is bright enough for crepuscular rays!

Maybe not for the naked eye, but in a 3-minute exposure who knows?

---

I looked at a map. Offhand, the town of Thurso looks a little too close to be the source of light rays. And (if north is up on the map), light coming from Thurso would say the shot is to the southwest, whereas the angle of Leo looks like a shot to the south or southeast, and moonrise should be east or southeast. So I'm still at a loss for a satisfactory answer.

apodman wrote:

starfinder wrote:the Moon is way, way too far south of the ecliptic. The ecliptic is roughly the (straight) line joining Regulus (right most vertex of the 5 pointed star described by apodman with Saturn, correctly identified as the bottom most vertex) and extended along that line in both directions. I say roughly because Saturn is currently 2degrees N of the ecliptic plane and Regulus is about 1/2 degree N of same. The Moon's orbit is inclined 5.1 degrees to the ecliptic plane which means that the Moon cannot be more than this amount N or S of the line of the ecliptic in the sky, irrespective of your location on planet Earth. (For scale purposes the bright star immediately above Regulus is eta Leonis which is close to 5 deg from Regulus). By assuming the rising Moon is at the intersection of the crepuscular rays out of frame I estimate that the Moon is fully 30 deg S of the ecliptic, deep in the constellations Crater or Hydra. There might be some strange optical foreshortening effect taking place which puts the Moon higher in the sky than suggested by the rays, but the relative positions of the stars in Leo are correct and do not support this.

http://www.hawastsoc.org/deepsky/leo/leo.html

Your point looks valid. I'm not willing to reach a conclusion yet. So what do we have here, crepuscular rays from city lights beyond the horizon?

That would be my guess...Thurso, itself, presumably... or the castle itself:


I don't think that a full moon is bright enough for crepuscular rays!

Art (purporting to be truth) Neuendorffer

starfinder wrote:the Moon is way, way too far south of the ecliptic. The ecliptic is roughly the (straight) line joining Regulus (right most vertex of the 5 pointed star described by apodman with Saturn, correctly identified as the bottom most vertex) and extended along that line in both directions. I say roughly because Saturn is currently 2degrees N of the ecliptic plane and Regulus is about 1/2 degree N of same. The Moon's orbit is inclined 5.1 degrees to the ecliptic plane which means that the Moon cannot be more than this amount N or S of the line of the ecliptic in the sky, irrespective of your location on planet Earth. (For scale purposes the bright star immediately above Regulus is eta Leonis which is close to 5 deg from Regulus). By assuming the rising Moon is at the intersection of the crepuscular rays out of frame I estimate that the Moon is fully 30 deg S of the ecliptic, deep in the constellations Crater or Hydra. There might be some strange optical foreshortening effect taking place which puts the Moon higher in the sky than suggested by the rays, but the relative positions of the stars in Leo are correct and do not support this.

http://www.hawastsoc.org/deepsky/leo/leo.html

Your point looks valid. I'm not willing to reach a conclusion yet. So what do we have here, crepuscular rays from city lights beyond the horizon?

saturn5 wrote:the reason its in b&w is because of light pollution from the town.I couldn't be bothered removing the LP

In what direction is the town located?

Hi all. Although this is my first post on this forum, a forum covering what I consider to be the best astronomical image site on the web, I am not a newcomer to astronomy having enjoyed over 40 years of active "service". For a long time I've had a problem with art purporting to be truth. By truth, in the context of imaging, I mean an image that represents what the camera's sensor recorded during that single exposure. Of course the sensor may well have captured more than what the eye saw (this is true of most astronomical imagery) and there may be aberrations that distort and blur, but the result is still a representation of the distribution of photons that struck the sensor during the exposure. Over the years I've had fun taking many double exposures on film and digital media, but I consider the results to be art rather than truth and have always indicated this to avoid misleading the viewer. With the advent of image processing programmes, such as Photoshop, the sky is now the limit in what can be done, and is done, to manufacture images. "Don't worry, I'll photoshop that out later" is becoming an all too common expression these days! And we all know about airbrushing of publicity photos of models and movie stars!

This image is a beautiful and evocative one capturing some of Scotland's grand historical architecture with some pretty sky subject matter in the background, but IMHO it is not true. If it is true then it has captured an impossible deviation of the Moon from its orbital path around the Earth (wouldn't that be something?). In my opinion it is a composite and please dispute this if you think I'm wrong. I'm not saying there was deliberate intention to deceive, but it has, according to the posts in this thread, and those who have "digged it", but there was no acknowledgement of it being a composite image. The description certainly suggests that it was a single shot and I believe the image would have far less impact on the readership if it was correctly described as a composite.

So, why do I think it is a composite?

A: the Moon is way, way too far south of the ecliptic. The ecliptic is roughly the (straight) line joining Regulus (right most vertex of the 5 pointed star described by apodman with Saturn, correctly identified as the bottom most vertex) and extended along that line in both directions. I say roughly because Saturn is currently 2degrees N of the ecliptic plane and Regulus is about 1/2 degree N of same. The Moon's orbit is inclined 5.1 degrees to the ecliptic plane which means that the Moon cannot be more than this amount N or S of the line of the ecliptic in the sky, irrespective of your location on planet Earth. (For scale purposes the bright star immediately above Regulus is eta Leonis which is close to 5 deg from Regulus). By assuming the rising Moon is at the intersection of the crepuscular rays out of frame I estimate that the Moon is fully 30 deg S of the ecliptic, deep in the constellations Crater or Hydra. There might be some strange optical foreshortening effect taking place which puts the Moon higher in the sky than suggested by the rays, but the relative positions of the stars in Leo are correct and do not support this. Also, the patch of sky to the left in the Castle Tower's window is brighter than the surrounding sky, suggesting that something is not quite right there.

Apologies for the long-winded description....

Please be assured, I have no problem at all with composite images as long as they are acknowledged as such. There are many stunningly beautiful and evocative composites out there. But please, let's not confuse art with truth (or science)!

To Jerry and Robert, Editors of APOD - keep up the good work! Thank you.

apodman wrote:The world's tallest equilateral pentagonal building stands at Baltimore's inner harbor.

Baltimore World Trade Center:

• Floor Count: 32 = 2^5
  
  Height: 405 ft = (5/3) 3^5 ft

---------------------------------
_Angels and Demons_ Script

Langdon: I became fascinated with 503, trying everything to find meaning in the number-numerology, map references, latitudes. For many years the only clue seemed to be 503 began with the number five... one of the sacred Illuminati digits.
---------------------------------

http://math.bu.edu/DYSYS/FRACGEOM2/node7.html wrote:
<<The Fibonacci Sequence: The ideas in the previous section allow us to show the presence of the Fibonacci sequence in the Mandelbrot set. Forget for the moment about the rotation numbers and concentrate only on the periods of the bulbs (the denominators). Call the cusp of the main cardioid the ``period 1 bulb.'' Now the largest bulb between the period 1 and period 2 bulb is the period 3 bulb, either at the top or the bottom of the Mandelbrot set. The largest bulb between period 2 and 3 is period 5. And the largest bulb between 5 and 3 is 8, and so forth. The sequence generated (1, 2, 3, 5, 8, 13,...) is, of course, essentially the Fibonacci sequence.>>

http://tinyurl.com/qnqq9q

The flying star makes a great asterism. Too bad Saturn will eventually move on.

From APOD 2009 May 6 (with mouse over photo for labels):



That still leaves the question why the small point of light just to the right of the castle does not have a long continuous streak like many of the other objects. Perhaps it was interrupted by a small cloud or patch of haze during the exposure. Dimmer objects are more easily blotted out than brighter objects. You can see that many of the objects have a streak that is dimmer toward the right end, one object at the far left of the photo has a strong interruption in the middle of the streak, and one object in the lower right has a streak that is dimmer toward the left end. Also, the streak of the object just to the right of the castle may be slightly washed out by the light of the moon ray. Just guessing. You can see more detail in the variations in each streak in the large photo at full size.

Saturn is streaked,it is the lowest of the "bright starts"

I am a brand new viewer. Please excuse any errors.
In the APOD with Thurso Castle, why isn't Saturn streaked like the stars?

neufer wrote:Yeahrr..but noww I'mm shhtuck in herre...

Anish Kapoor: Turning the World Inside Out wrote:

One more reason they don't let you take flash pictures in the museum.

---



The world's tallest equilateral pentagonal building stands at Baltimore's inner harbor.



You are looking straight up one of the five corners of the building at two mirrors mounted together. A light shines straight up the channel and is reflected into two sky beams by the mirrors. Together, the five lights and the mirrors project 10 sky beams roughly parallel to the ground spaced around the compass in 10 directions. Okay, it looks like four mirrors, so maybe there are two per beam, or maybe it's just two mirrors with a four-point mounting; I never climbed up there to look.

This is unnecessary light pollution, pure and simple. Astronomers and anyone who enjoys the night sky should consider it evil.

But that's not my point, and this is:

I used to live midway between two of the beams and not very far away. If I faced toward the source, I could see the beams in the sky above me converging to a point at their source and spreading apart as they headed my way. If I turned around and faced away from the source, a funny thing happened - instead of continuing to spread apart as they got farther from the source, the beams got closer together again. Even for an experienced sky observer familiar with the rules of spherical geometry, this was a freaky sight. Not a strange phenomenon, not an optical illusion, just the way the sky is shaped from a point perspective. It turns out spherical geometry isn't just for crepuscular and anti-crepuscular rays on the celestial sphere on a cosmic scale - it works on a small scale, too. So let's not be too hard on anyone who has trouble mentally aligning the curves in the sky.

apodman wrote:To do it right, use a globe to represent the celestial sphere. The parallels of latitude represent the paths of the stars. Pick a nice tropical location like Tahiti to represent the position of the moon. Draw straight lines emerging from Tahiti in all directions which will follow great circles and meet on the other side of the globe. You will see that the rays you drew north-south are perpendicular to the parallels of latitude (star trails). You will see that the lines you drew east-west diverge from the parallel of latitude. Now tilt the globe, get inside it, and you're there.

Yeahrr..but noww I'mm shhtuck in herre...

The image above is three lines I superimposed on the APOD from 2007 December 8.

The yellow line starts off parallel to the star trails but diverges.
The green line is perpendicular to the star trails.
The red line intersects the star trails obliquely.

The three lines (which represent rays from the unrisen moon) converge at a point below the horizon (which represents the position of the unrisen moon). The three lines should actually be shown as slightly curved in projection themselves, but the straight lines are close enough to make the point and I didn't want to take all day to make the illustration.

To do it right, use a globe to represent the celestial sphere. The parallels of latitude represent the paths of the stars. Pick a nice tropical location like Tahiti to represent the position of the moon. Draw straight lines emerging from Tahiti in all directions which will follow great circles and meet on the other side of the globe. You will see that the rays you drew north-south are perpendicular to the parallels of latitude (star trails). You will see that the lines you drew east-west diverge from the parallel of latitude. Now tilt the globe, get inside it, and you're there.

---

(Solar) Crepuscular Rays Over Utah:
http://antwrp.gsfc.nasa.gov/apod/ap050831.html

(Solar) Anticrepuscular Rays Over Colorado:
http://antwrp.gsfc.nasa.gov/apod/ap081116.html

(Solar) Anticrepuscular Rays Over Florida:
http://antwrp.gsfc.nasa.gov/apod/ap060917.html

(Solar) Anticrepuscular Rays Over Horseshoe Canyon:
http://antwrp.gsfc.nasa.gov/apod/ap030226.html

(Solar) Sunrise Cloud Shadows Over Everglades:
http://antwrp.gsfc.nasa.gov/apod/ap020227.html

Bill - Australia wrote:Are the crepuscular rays radiating from the position of the unrisen moon?

Yes.

Bill - Australia wrote:If so, why are the star trails perpendicular to the crepuscular rays?

The rays indeed converge on the unrisen moon, so their orientations have everything to do with the moon's position and nothing to do with the moon's direction of travel. The rays radiate in all directions from the moon, and only one opposed pair of them running north and south (with one ray of the opposed pair being below the horizon) is perpendicular to the stars' direction of travel. We can expect the moon to be rising at a low angle to the horizon at the high latitude of Scotland, parallel to the stars' paths (allowing that the paths are curved in this flat picture of a spherical sky shot through a lens).

Bill - Australia wrote:... the star trails would be expected to run from the observer towards the rays' radiant.

This is not logical. You are saying the stars should be heading directly toward or away from the current position of the moon, which is not the case (except for stars at the moon's declination and the one opposed pair of rays east and west along that line which are not really in the picture - and even then the ray which follows a great circle would diverge as it crosses the sky from star trails that don't follow a great circle). And trails only run directly from the observer when the observer and stars are all on the equator; the moon would have to be on the equator that night too for a ray to line up with those star trails, and still there would be rays that crossed the trails of all the other stars.

BMAONE23 wrote:It would seem likely that the star trails would progress from east to west and that the moon beams would rise out of the east and into the west.

One moon beam would rise out of the east and into the west parallel to the star trails and the Earth's rotation. The other moon beams would radiate at other angles to the north and south of that one, but if extended across the sky they would all converge again at a point in the west at the opposite point in the sky from the moon's position. Even the one beam that emerges westward from the moon parallel to the star trails would diverge from the star trails as it crosses the sky (because it follows a great circle while that star trails don't).

Saturn5, I see your point. Given that the earth rotates from west to east (counterclockwise when viewed fron the north pole) which causes the moon to rise in the east. It would seem likely that the star trails would progress from east to west and that the moon beams would rise out of the east and into the west.
Given that the image was taken in Thurso Scotland which sits above 55deg N, the Moon would have a more southerly track. Since you would look SSE toward the moon, It does stand to reason that the Moon Beams would cast about 45deg accross the star track.

saturn5 wrote:The star trails follow their normal path, the crepuscular rays whether they be from the sun or moon basically radiate in a circle, you seem to think that the rays should look as though they should be following the star trails, The rays will eminate from wherever there is a gap in the clouds to allow the light to shine through, just the same as the sun, believe me its just a 3 minute exposure from a static tripod, no trickery or photoshop magic and the reason its in b&w is because of light pollution from the town. I couldn't be bothered removing the LP and i thought it looked more dramatic as a b&w.

• --------------------------------------------
  . Macbeth > Act III, scene V
  
  HECATE: Great business must be wrought ere noon:
  . Upon the corner of the MOON
  . There hangs a vaporous drop profound;
  . I'll catch it ere it come to ground:
  . And that distill'd by magic sleights
  . Shall raise such artificial sprites
  . As by the strength of their illusion
  . Shall draw him on to his confusion:
  --------------------------------------------

The star trails follow their normal path,the crepuscular rays whether they be from the sun or moon basically radiate in a circle,you seem to think that the rays should look as though they should be following the star trails,The rays will eminate from wherever there is a gap in the clouds to allow the light to shine through,just the same as the sun,believe me its just a 3 minute exposure from a static tripod,no trickery or photoshop magic and the reason its in b&w is because of light pollution from the town.I couldn't be bothered removing the LP and i thought it looked more dramatic as a b&w.