What is Forward-Scatter?

This is the vanity site and creative outlet for astronomer Mark Showalter.

"Forward-scatter" is the term for light that hits a particle but then keeps going in nearly the same direction. Think of glare on a windshield or a thin crescent moon. The opposite is backscatter, where light bounces off something and comes back toward the source. Think of a full moon, or your own reflection in a mirror.

I have no idea. Your tax dollars at work. See the Federal Standard 1037c home page for other gems. It takes a full page to define "fax".

This amazing picture was taken by NASA's Cassini spacecraft as it was looking back toward the Sun while passing inside Saturn's shadow. In other words, the Sun was eclipsed by Saturn's disk. The surrounding ring system glows due to the forward-scatter of sunlight by tiny dust grains. This is my own version of a NASA press release image.

This is a quasi-scientific and extremely crude way of describing the different functions of the two hemispheres of our brains. In the most general terms, our left hemispheres emphasize language and reasoning, while our right hemispheres emphasize images and emotions. See the Wikipedia article for more information.
 
As someone who spends a lot of time reasoning about images, I find that photography for the pure joy of it is a pleasant creative diversion.

Short answer: Yes, they are really images.
 
Longer answer: The way that our eyes respond to light is completely different from the way that a digital camera's detector responds to light. And both of these are also different from the way film responds (or may I say responded?) to light. So at best, any image is just a crude approximation to what the eye might have seen.
 
Every image on this or any other site has been manipulated in some manner. In my photography, I am an avid and unrepentant user of Adobe Photoshop™ and Apple Aperture™, as well as other image processing tools. However, usually my goal is to make the image look as much as possible like what my eye saw when I pushed the shutter release on my camera. If I have done something more to the image, I'll say so.
 
My mantra is, "What would Ansel do?" Ansel Adams was both a master of the camera and a master of the darkroom. If he were alive today, I think he would be using all the digital tools at his disposal to go from a negative raw digital file to a photographic print displayed image. He would just be doing it better than anybody else.

The purpose of a scientific image is very different. The standard in science is that another investigator, given the same data, could reach the same conclusions that you have reached. Every bit as much image manipulation goes on, and possibly much more, but every step must be recorded, explained and justified. So no, I do not remove dust specks (and/or add moons) to my astronomical images. Or if I do, I say so and explain why.
 
That being said, however, astronomers have much less reason to show an image that looks "real". The human eye responds to a very narrow band of the spectrum of light. All those other wavelengths that we can't see contain real information. In astronomy, we often make images that intentionally look "unreal", because they enable us to convey information that our eyes could never possibly see.
 
As a kid, I wanted to play with X-ray glasses. As an astronomer, I can. And infrared and ultraviolet glasses too.

These are images taken by telescopes and spacecraft, which I have manipulated to try to meet two goals simultaneously. First, I want them to show something interesting and truthful about the universe. But second, I also want them to please the eye and to engage the "right brain" as works of art. Hubble meets Picasso.

Short answer: I thought it looked cool.
 
Longer answer: When a ray of light enters a raindrop, most of the light gets focused into the forward direction. In effect, the raindrop acts like a tiny magnifying glass. This is one aspect of the phenomenon called "forward-scatter". Small and nearly transparent particles tend to forward-scatter, whereas large and opaque objects (think the Moon) tend to backscatter instead. This is one of the phenomena I study in planetary rings; we can learn a great deal about ring particles and other distant surfaces by studying how they scatter light.

Answer #1: Some rays of light get bent (refracted) as the enter a raindrop in such a way that they undergo an internal reflection, meaning that they bounce of the inside of the sphere. Those rays come out in a completely different direction, usually about 138° away from the direction they were going when they entered. Because different colors of light bend a little bit differently as they cross into and out of the raindrop, this produces a rainbow. See the Wikipedia article if you want to know more.
 
Answer #2: I liked the symbolism of one colorful (gay perhaps?) ray of sunlight going off in a completely different direction instead of marching in lockstep with the others.

Nope.*
 
* But you never know....