Starship Asterisk*

Posted: **Fri Feb 09, 2007 4:22 pm**

Feb. 9's picture of the moon craters: To me the craters appear raised, not bowl-shaped. Is this an optical illusion?

This is the first time I've posted, but I have enjoyed this site for quite some time.

Posted: **Fri Feb 09, 2007 5:32 pm**

They do appear slightly raised, but this is typical because the force of impact displaces material upward along the crater rim. Large craters are also often flat bottomed because a significant portion of the material excavated by the blast falls back down into the crater.

You'll also notice small mountains in the center of a couple of the craters. There is a sort of splash effect, similar to a drop of water in a glass, that causes a central stream of molten/shattered rock to rise at the center of the impact, solidifying in place on its way back down.

This page has a really cool animation of a crater being modelled by computer. Explanation of the event is here

Posted: **Fri Feb 09, 2007 6:16 pm**

Thank you, Lucky. The link to the modeling site was helpful. Now when I look at the craters they do look like bowls. I think it''s my eyes!

Posted: **Fri Feb 09, 2007 6:27 pm**

daisy wrote:Thank you, Lucky. The link to the modeling site was helpful. Now when I look at the craters they do look like bowls. I think it''s my eyes!

When pictures are taken under certain lighting conditions, it is possible for your eyes/brain to recognise the craters as raised platforms instead of concave depressions.
This is more difficult to visualise in some pictures than others, which I often find to be quite a problem.
I have found that the solution is to stare at a small crater in the picture until it appears as a concave bowl, then slowly look at the larger craters around it, and the picture magically changes back to what it should be. Often however, I look away at something else, then when I look back, it has reverted to the wrong version again. Doh!
Tilting the head to either side whilst viewing the picture can also help cure this.

Posted: **Fri Feb 09, 2007 6:42 pm**

Andy, that's exactly what happened to me! Also, after looking at the animation posted by Lucky, then the craters on the moon looked like craters. I guess the brain is easily fooled by these images.

Thanks.

Posted: **Fri Feb 09, 2007 7:26 pm**

Can some one explain to me how to insert an image into my post.

Example:

"bla bla blah...... [image] ........bla bla blah"

Thank you.

Posted: **Fri Feb 09, 2007 8:39 pm**

When you type the post, there are formatting buttons above the text field. One of them says "Img." If you click that once, it will add the image tag. Then you type the url for the image, and click the button again to close the image tag.

There is also a line that shows an example, directly above the text field.

Daisy, it seems I actually misunderstood your question and answered a different one. I'm glad the animation was still helpful though.

I used to perceive craters inside out all the time, too. The shadows are the major telltale sign. If the shadow of a rock or mountain points one way, and the shadowed side of a round crater/dome feature is on the opposite side, you know it must be depression, not a protrusion.

Posted: **Fri Feb 09, 2007 8:43 pm**

I can't Martin; so I usually use a link to the image. Maybe BMAONE 23 can help you. I was just marveling how smooth the tops of these craters were;as if the crust of the moon were molten when they were made.
http://antwrp.gsfc.nasa.gov/apod/ap070209.html
Could these craters be from the creation part of the moons history?

Orin

Posted: **Fri Feb 09, 2007 11:57 pm**

Hey, I know what Daisy means....when I look at photos of carters and other planetary formations, it often looks as though I'm looking at a negative. The features that are raised appear to be sunken in the surface. This is of course a trick of the lighting and shadows, but I wonder why my eye is tricked?

I know how the features form, but why do their photos have that optical illusion?

Posted: **Sat Feb 10, 2007 8:34 am**

d2386n wrote:Hey, I know what Daisy means....when I look at photos of carters and other planetary formations, it often looks as though I'm looking at a negative. The features that are raised appear to be sunken in the surface. This is of course a trick of the lighting and shadows, but I wonder why my eye is tricked?

I know how the features form, but why do their photos have that optical illusion?

Well I'm no expert on eyes... (although I've used a pair of them for nearly 50 years

)
I understand that they are amazingly complex organs and in conjunction with the brain they are constantly trying to interpret everything they see.
This is simply a case of interpreting the light in the crater picture as coming from exactly the opposite direction than it actually does.
For myself it only seems to happen under certain lighting conditions - usually when the angle of light is on the craters is very low and the shadows are long.
Try visiting http://www.lpod.org/ if you want to drive yourself potty with it!

Posted: **Sat Feb 10, 2007 6:25 pm**

If they don't look like craters, then yes, you are seeing a very common optical illusion - which the folks posting the images could easily avoid. I wish they would. See the post: Mesas / Plateaus on the Moon again (APOD 9 Feb 2007)

Posted: **Sat Feb 10, 2007 10:32 pm**

Seeing things in 'reverse' on such pictures is common. Much of our 'seeing' is processing in the eye and brain, that relies on familiar cues and light direction. When those are absent, we cannot 'see' things as they are.

A famous illusion relies on this - as in the staircase on this page: http://wilstar.com/science/optical_illusions.htm
Or
more sophisticated, Escher's prints: http://www.meridian.net.au/Art/Artists/ ... r/Gallery/

The animation linked to by lucky shows how, in this situation, rock flows like water. Compare that animation with this highspeed film of water dropping into water: http://courses.ncssm.edu/hsi/splashes/P ... -29-01.htm

This site shows an even cleverer, and beatiful, way of watching craters form:
http://cre.ations.net/creation/the-time-fountain

John

Posted: **Mon Feb 12, 2007 1:49 am**

Martin wrote:Can some one explain to me how to insert an image into my post.

You'll need to host the image on a web server of your choice; as far as I know this board does not provide space for images.

Once you've done that, the easiest way is to press the [ Img* ] button while posting, which gives you an

tag. Or you can type the tags yourself.

For example, the text...

Code: Select all

[img]http://ncarboni2.home.att.net/Moon_Hypersaturated_Thumbnail.jpg[/img]

...produces the inline image...

Hope this helps.

-Noel

Posted: **Mon Feb 12, 2007 4:44 pm**

Thanks for the input guys -I understand now -I cannot insert an image directly it has to be linked in from a website/URL.

So I guess I just host the image somewhere and then URL the "address" ----wait thats not the same is it -what the hell is a URL -lol

I once hosted an image of the horse head and I posted the web address in here. That is not the same is it? so in that example what is the image URL? How do I find the URL of an image? Man I feel like an amateur again

Posted: **Mon Feb 12, 2007 5:22 pm**

Martin wrote:Thanks for the input guys -I understand now -I cannot insert an image directly it has to be linked in from a website/URL.

So I guess I just host the image somewhere and then URL the "address" ----wait thats not the same is it -what the hell is a URL -lol

I once hosted an image of the horse head and I posted the web address in here. That is not the same is it? so in that example what is the image URL? How do I find the URL of an image? Man I feel like an amateur again

Martin I found this searching the net; http://www.cockatielcottage.net/postingtut.html
I'm not sure I'm going to try it yet.
Orin

Posted: **Mon Feb 12, 2007 6:07 pm**

Martin wrote:Thanks for the input guys -I understand now -I cannot insert an image directly it has to be linked in from a website/URL.

So I guess I just host the image somewhere and then URL the "address" ----wait thats not the same is it -what the hell is a URL -lol

I once hosted an image of the horse head and I posted the web address in here. That is not the same is it? so in that example what is the image URL? How do I find the URL of an image? Man I feel like an amateur again

Well, this is a bit OT, but just in case you're not joking...
URL means "Uniform Resource Location"
This is the web address.
http means hyper text transfer protocol
www means world wide web
Then the domain name and sub domain folders etc etc until you get to the file type - eg html (hyper text mark-up language)
Contrary to popular belief 'Internet' actually refers to the email and newsgroup system, rather than websites per se, but as it's now in popular usage, anything goes I guess.
Although a lot of people now seem to be using "Interweb" to describe the whole online experience.

The URL of anything on the web is the address that appears in your browser address box. So you just copy and paste to add a link.
And the image tags to show an image in your post - if you don't use the image tags all it does is link to the relevant URL
Works for me anyway.

Posted: **Wed Feb 14, 2007 2:47 pm**

I was going to pipe in on the "raised craters" effect to say that this kind of illusion happens with other things too, but the whole links to illusions and Escher beat me to it.

I noticed a similar effect in some photos I took of Mayan relief carvings from Mexico. They would flip back and forth between inner and outer carvings on the photos where as, of course, in person they did no such thing. Partly this is due to losing the direction of light cue, but it also has to do with rendering 3-D objects (even relatively flat ones) in a 2-D plane. Our stereoscopic vision deals with ambiguity in shading cues in real life objects by relying on other cues. When all you have is a flat rendition of the same thing (as in a photo), your visual perceptual system is missing some of those other cues that would anchor the view to be one way or the other. So, they can flip.

It's also interesting that the ability to perceive the flip varies greatly among individuals. Some see it, some don't.

Starship Asterisk*

Craters are an optical illusion?

Craters are an optical illusion?

Craters appearing in reverse

craters are an optical illusion

Re: craters are an optical illusion

Yes, it's a common optical illusion.

Uniform Resource Location