Starship Asterisk*

zloq, I misunderstood your previous post, and have corrected mine.


:shock:

This isn't a thin, straight, horizontal contrail high up in daylight with the sun overhead shining down. It is a nearly vertical, wide, jagged and multi-segmented rocket contrail after sunset with the sun shining up from below. This makes the shadow a cross between a crepuscular ray and a volumetric shadow, since the shadow volume does not actually include the viewer - though it does involve an accumulation of contrast through a slab-like volume for each roughly straight part of the plume. I pointed to two relevant images in my notes above where the shadow is off from the moon compared to the perfection in the apod example - for the same event - indicating the role of location and time on the alignment. Finally, I indicated that the photographer apparently changed his location in realtime during this important photo-op, and improved on the alignment of the shadow with the moon as shown by the change in the two pictures.

I have seen many jet contrail volumetric shadows in daylight similar to your picture. I have never seen a rocket launch just after sunset - but I can visualize the key differences relevant to this apod, and the role parallax would play since the bottom of the shadow is "up there" and its location in the sky is dependent on view location. I also know the direction of the shadow will depend on the time-dependent refraction of the sun as it sets - which has no analog for a jet contrail - and allows time to dial in the best alignment for a given location.

zloq

[quote="zloq"]Hmm - I think you both are missing my main point. The shadow itself was visible over a wide range of locations perpendicular to the "plane" - and those locations all had a great lookin' shadow - but it didn't go right through the center of the moon.[/quote]
Are you sure about that? My experience is that unless a contrail shadow is actually cast onto clouds, you just don't see that shadow unless you are fairly near the plane defined by the contrail and the Sun. The degree to which even humid atmosphere scatters light is just generally too small, and as you get off the plane, the shadow itself becomes planar, not linear. Certainly, this is a denser trail than typical contrails, and is more vertical. I don't think the direction matters, although the density ought to.

Could you point me again to an image that shows the shadow from well off the plane? I'm not finding it in the examples given.

Hmm - I think you both are missing my main point. The shadow itself was visible over a wide range of locations perpendicular to the "plane" - and those locations all had a great lookin' shadow - but it didn't go right through the center of the moon. The center of a given plane would have the best looking shadow - but as you move either way, the location of the shadow relative to the moon changes - and the shadow still looks pretty good. You are free to move left and right to where the shadow makes a bullseye right through the center of the moon - as shown in the apod image. It's the fact that the shadow makes a perfect bullseye that is so compelling about the image - and that's because the photographer dialed it in by changing location and choosing the exact time - since the plume, sun, and moon are all moving, and both refraction and parallax are involved. It's a dynamic scene, and what you see depends on your location and the changing solar refraction - not just the astronomical geometry.

I don't know how to make this any clearer - the same photographer has another image with a great shadow - but it's offset from the center of the moon because it was earlier and in a slightly different location. A different photographer much farther away also has a great shadow and it is way off from the center of the moon. The apod image would have been much less compelling if the shadow even slightly missed the center of the moon, but it's perfect - and that is what bothered me. It's perfect because he moved to where he needed to be, and chose the exact moment as a dynamic scene unfolded.

The contrail image above is amusing because it actually flares out at the base - as opposed to getting smaller due to perspective. A rocket contrail is different because it is roughly vertical, and it isn't straight - which means it forms many "planes" where a good shadow can appear from a wide range of locations. Additionally, the shadow in the apod image is different from a contrail because the sun has set and the earth below is in shadow. That means that the dark volume of atmosphere associated with the shadow doesn't start at the eye (as in does in the contrail example), but instead starts way up in the sky where the sun is shining. That increases the role of location and parallax in the location of the shadow relative to the moon.

In fact - I think people could plan the apod shot if they have a rocket launch around a full moon at dawn or sunset. Just be in an area where you can drive perpendicular to the plane to find where the shadow exactly hits the moon as the scene unfolds.

zloq

[quote="Indigo_Sunrise"]IMO, serendipitous image/s, indeed.[/quote]
Yes. Because, as previously noted, not only do the Sun, Moon, and plume need to be collinear (or coplanar, if you prefer), but the imager needs to be close to that plane, as well. Because otherwise, the shadow will be all but invisible.

[float=left][img]http://www.cloudbait.com/gallery/sky/contrailshadow.jpg[/img][/float]I observe contrail shadows all the time, and image them when I can. The only time you can see them is when you, the Sun, and the shadow are approximately on the same plane. Otherwise, you simply aren't looking through a thick enough layer of air for the shadow contrast to be significant.

Certainly, an imager can plan for a shot like this (within reason- at a launch facility, there are simply places where it will be impossible to place a camera). But catching a shadow like this without planning is the very definition of coincidental, or serendipitous.

[quote="Indigo_Sunrise"]
Your first thought was correct, zloq: it is the same picture.[/quote]

Huh? Same event, same photographer, same date, same lens, different time, different location, different foreground, different, plume, different shadow -> different (and better) picture. It is perhaps 30-60 seconds later would be my guess. Of course the distant clouds didn't change much in that time - but the plume and location of the shuttle did.

That small difference in time and location allowed the photographer to find and capture the perfect alignment shown in the later image, which is a big improvement on the earlier one, where the shadow is left of the moon. Both are much better than the earlier link I posted - which is also a "different" picture of the same event - from farther away and with a bigger miss of the moon.

zloq

[quote="zloq"]It turns out, there is another picture credited to the same photographer and at first I thought it was the same picture, but it is very different.

Here is the original APOD:

http://www.archive.org/details/shuttle_plume

and here is the other image:

http://www.atoptics.co.uk/atoptics/shuttle.htm

[/quote]


Your first thought was [b][i]semi[/i]-[/b]correct, zloq: [b][i]they are pictures of the same launch[/i][/b]. Clicking the first link you provided shows the date as 7Feb2001.
The second link listed also shows 7Feb2001 in the italicized description near the top of the page.
The foreground may have changed a bit when the photographer moved some, but even the clouds in the sky are identical.

IMO, serendipitous image/s, indeed.

:saturn:

Thanks for the comments. I think it's a rich image on many levels. For people who are still interested in the topic - I did find more info to take it even further.

It turns out, there is another picture credited to the same photographer and at first I thought it was the same picture, but it is very different.

Here is the original APOD:

http://www.archive.org/details/shuttle_plume

and here is the other image:

http://www.atoptics.co.uk/atoptics/shuttle.htm

The most obvious difference in these un-cropped versions is that the foreground is totally different. The plume is about the same, but you can tell that the second image above was taken many seconds before the first one. Also notice that this other image by the same photographer at the same event shows imperfect alignment of the shadow with the moon.

It sure looks to me like he could see the amazing shot that was possible in front of him, so he rapidly changed locations both to remove clutter in the foreground - and possibly to get a perfect alignment of the shadow with the moon. Also note that in the apod image, there is no one around him, whereas in the first image there are many people nearby. This makes me think he was somewhat unique in being near the right spot at the right time, *and* choosing to go mobile to a better aligned location where no one else was around. Since he is a nasa employee, he may have done all the shooting casually from his car - which also makes his situation unique. This last part is speculation - but he clearly did move a long way between the first and second shots - and although the shuttle is high at that point and moving slowly - there couldn't be too many seconds between them.

Anyway - it looks like the photographer showed a lot of initiative and had a good sense that he needed to move and take the shot at the right time - so a big part of the perfect shadow alignment can be attributed to the skill, intuition, and effort of the photographer - plus the fact that the alignment of the scene depends on both the view location and time, and isn't locked in by a serendipitous astronomical alignment of the moon opposite the sun that just happens to correct perfectly for all the refraction going on.

zloq

Great post zloq, that link you included was hilarious.

Sometimes I forget how many crazy/stupid/insane people there are out there... from people believing the moon landings were a hoax to people believing in "moon bases", and that's even some of the more reasonable stuff that's out there on the internet! Anyways, it's at the very least good for a laugh now and then, provided I'm not sickened by the idea of these crazies contributing to the gene pool. :-)

Overall lots of good info in here, even if it's a repeat! As shown on this page, repeats still have the ability to generate new hearty discussion. Keep up the good work APOD!

I have gone back and forth on this image, as to how coincidental it is. A key thing is that there are many people with cameras around, so the issue isn't how rare it is for a single person to get this shot - but for *someone* to get it - and that removes a big part of the coincidence caused by the fact, as mentioned earlier, that the shadow contrast is strong due to the camera being in the plane formed by the sun and *a particular* straight part of the plume. The camera isn't collinear with the plume, which would be much rarer - it is just coplanar with a particular section of the jagged plume, and that part casts a shadow with high contrast since you are looking through the volumetric slab of shadow. A regular crepuscular ray is visible in any orientation and doesn't have this high contrast effect due to coplanar alignment.

There are many images and videos on the web with strong shadows cast just like this during a rocket launch, and an important point is how dynamic they are - changing in contrast and even orientation slightly.

There is certainly a lot of wiggle room vertically in where the moon could be to still have this effect - and that is shown by the fact that the moon is actually a fair distance above the end of the shadow. But laterally, the moon is remarkably well centered on the shadow. If that is the real moon's disk - then it looks to be centered to within 5 arc-minutes or something - much, much less than the moon's potential distance from the ecliptic - which is around 5 degrees.

I checked TheSky for the moon's phase angle at that time, and it was around 5 degrees. That's not surprising that it would not be exactly full - but what did surprise me is that it's distance from the ecliptic was 2.5 degrees. That is very far from the true anti-solar point - which would be on the ecliptic and show huge misaligment from the shadow that would have weakened the impact of the image.

Another factor not mentioned is that neither the sun nor the moon is in the true location due to refraction. The shadow is cast by the refracted sun, which is around 1/2 degree off in a normal sunset, and presumably much farther off when viewed from high up where the plume casts the shadow - because the plume is looking through much more atmosphere than a normal sunset. The moon is also offset by many arc-minutes due to its low altitude. In addition, the volume of shadow being seen isn't at infinity - but is "up there" in the sky at some range of altitudes - allowing for some lateral range of orientation due to parallax. Viewers left and right of the shadow would still see good contrast, but the shadow would be slightly shifted.

A simple question is - are there any other pictures of this event, and how good is the moon alignment? I couldn't find other images by the original photographer, and he talks as if he just took the one picture and later realized he had captured a great atmospheric shot. Unfortunately this image and others like it are associated with mystical meanings - so it's hard to find good info on the web. But I did find one other image from a different location that captures much of the phenomena - and the moon is clearly misaligned:

http://www.thelivingmoon.com/47john_lear/01archives/Soul_Catcher_Shuttle.htm

The image is about halfway down the page.

One question is just how dynamic and long-lived the shadow was. Videos of plume shadows on youtube show the contrast to be fairly dynamic, and as long as the sun is setting and the moon rising, there will be some motion of the moon relative to the shadow. This makes me think this may have been snapped at the right moment to catch it exactly aligned, where all the factors cancel the offset of the moon's location from the ecliptic. The alignment of the shadow clearly isn't guaranteed to be so good based on astronomy alone, since the image I link above shows the moon quite a ways off in comparison. The APOD image may be one of many the photographer took, and the general scene persisted for some time - but he chose the one that had the best alignment. I certainly would have been shooting constantly in such a situation - even with film.

So - I think a lot of the general alignment is guaranteed by a near sunset launch with a full moon, but additionally the astronomical parameters conspired with refraction and the changing direction and refraction of the sun as it set to bring it even closer - and then the photographer chose the best aligned version from the dynamic scene he watched. It's not surprising that things are basically aligned - but the lateral alignment of the moon with the shadow is extremely good compared to what it might otherwise have been for a different lunar distance from the ecliptic.

zloq

[quote="Jayden"]This is less of a coincidence than you may think. If the moon was to be full, then at sunset, by definition, it has to be exactly opposing the sun. Shadows will always point towards the full moon..[/quote]
The shadows point toward the anti-solar point. The anti-solar point and the full Moon only align during a total lunar eclipse. Furthermore, what appears visually to be a "full Moon" could easily be a day on either side of the actual moment of fullness, which corresponds to roughly 30° of sky. And then there is the matter of the inclination of the Moon's orbit.

However, even if you take the position that the full Moon is often fairly close to the anti-solar point (which isn't unreasonable), I don't think that's the coincidence being discussed there. The coincidence is that the Sun, Moon, launch plume, and camera were all nearly collinear at the right time. And that really is a coincidence.

[quote="Jayden"]

This is less of a coincidence than you may think. If the moon was to be full, then at sunset, by definition, it has to be exactly opposing the sun. Shadows will always point towards the full moon..[/quote]
Shadows will always point towards the [b][u]eclipse position[/u][/b] somewhere very near the horizon.

The full moon is well above both the horizon and the eclipse position.

This is less of a coincidence than you may think. If the moon was to be full, then at sunset, by definition, it has to be exactly opposing the sun. Shadows will always point towards the full moon..

I thought I would mention that the "this photogenic coincidence" link in the explanation brings up a "No records matched your query" in the NASA website.

Are my aged eyes deceiving me, or do I detect a hint of a 'green flash' at the uppermost illuminated segment of the vapor trail ?

Remarcable resemblance to a recent APOD starring the Pelican nebula and its star forming pillars. So cool I need an ice cold one

[quote="Beyond"]Chris, i noticed the -shadow-into-the-round-rainbow-picture comes from Wiki-pedia. Have you ever seen a round one like that yourself?[/quote]
Yes, I've seen the Brocken spectre both with and without an associated glory. The most spectacular was last summer, filming a documentary at Pisgah Astronomical Research Institute in North Carolina. We were up on a mountain in a light fog, and the camera lights cast amazing Brocken spectre shadows. I just didn't have any pictures handy, which is why I used the Wikipedia image.

Chris, i noticed the -shadow-into-the-round-rainbow-picture comes from Wiki-pedia. Have you ever seen a round one like that yourself?



[img2]http://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Brocken-tanzawa.JPG/640px-Brocken-tanzawa.JPG[/img2]

According to http://science.ksc.nasa.gov/shuttle/missions/sts-98/mission-sts-98.html liftoff was Wednesday, February 7, 2001, 6:13 p.m. EST. The status report indicates that the launch occurred at sunset, but there are three sunsets, if my memory still works: civil, nautical and astronomical. The shadow appears to begin shortly before throttle-down, maybe 45 seconds after launch. It might be fun to calculate a graphical depiction of the event.

[quote="Tszabeau"]Why does the shadow narrow and seemingly focus itself? My own shadow spreads the further away from me it is. I guess the penumbra narrows and the umbra widens, if given enough distance?[/quote]
Whether the ubmbra spreads or not depends on the relative sizes of the source and shadowing body, and their separation. Any shadow that is being cast away from the observer by the Sun will generally be seen getting smaller in the distance, because of the vanishing point effect. You should see this with your own shadow, as well- it may get larger in terms of its physical size, but it should still look smaller to you as it is cast into the distance. I posted this image in the weather discussion a while back- shot from horseback with the Sun directly behind me.

[attachment=0]IMAG0138p.jpg[/attachment]
The [url=http://en.wikipedia.org/wiki/Brocken_spectre]Brocken spectre[/url] phenomenon is perhaps an even better example, as the shadow is cast into the air, just like the shadow of the Shuttle's plume.

[img2]http://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Brocken-tanzawa.JPG/640px-Brocken-tanzawa.JPG[/img2]

The shadow in today's APDO is a cousin to the common crepuscular and anticrepuscular rays, which appear widest when closest (overhead), and narrowest at their most distant (the solar and antisolar points).

Why does the shadow narrow? Totally perspective. It's actually a linear feature but appears to taper just like railroad tracks appear to converge.

As I've observed often with contrails, to see the shadow, your eye also has to be in the plane defined by the Sun and the contrail. In this case what's forming the shadow is that linear stretch just before the sharp upper kink. The shadow is cast on aerosols in the atmosphere. Only if you're looking exactly along the shadow plane is there a high enough density of shaded aerosols to see easily.

Why does the shadow narrow and seemingly focus itself? My own shadow spreads the further away from me it is. I guess the penumbra narrows and the umbra widens, if given enough distance?

credits for Pat McCrackens

[quote="Henk-Jan"]This apod is the same as two apods before.
[url]http://apod.nasa.gov/apod/ap070603.html[/url]
[url]http://apod.nasa.gov/apod/ap010219.html[/url][/quote]
Repeats come on Sundays! No biggie! :wink: