Starship Asterisk*

Colors of Mercury

Explanation: The colors of the solar system's innermost planet are enhanced in this tantalizing view, based on global image data from the Mercury-orbiting MESSENGER spacecraft. Human eyes would not discern the clear color differences but they are real none the less, indicating distinct chemical, mineralogical, and physical regions across the cratered surface. Notable at the upper right, Mercury's large, circular, tan colored feature known as the Caloris basin was created by an impacting comet or asteroid during the solar system's early years. The ancient basin was subsequently flooded with lava from volcanic activity, analogous to the formation of the lunar maria. Color contrasts also make the light blue and white young crater rays, material blasted out by recent impacts, easy to follow as they extend across a darker blue, low reflectance terrain.

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http://photojournal.jpl.nasa.gov/catalog/PIA16850
http://photojournal.jpl.nasa.gov/catalog/PIA16852
http://photojournal.jpl.nasa.gov/catalog/PIA16853

http://asterisk.apod.com/viewtopic.php?t=30640#p193380

Much better than I can see from here!!!

:---[===] *

Typo -- from by ????

Thanks; I've let TPTB know.

This is a gorgeous image!

http://photojournal.jpl.nasa.gov/catalog/PIA14233

The color base map is composed of WAC images taken through eight different narrow-band color filters and will cover more than 90% of Mercury's surface at an average resolution of 1 km/pixel (0.6 miles/pixel) or better. In contrast to the imaging conditions best suited for seeing surface topography, the highest-quality color images of Mercury's surface are obtained when both the spacecraft and the Sun are overhead and shadows are limited. The eight different color filters of the WAC that are used to create the color base map have central wavelengths of 430, 480, 560, 630, 750, 830, 900, and 1000 nm. The images acquired through these narrow-band filters are combined to create color images that accentuate color differences on Mercury's surface. As an example, this image was created by using three images acquired as part of the color base map with the central wavelengths of 1000, 750, and 430 nm displayed in red, green, and blue, respectively.

Wikipedia tells me that the visible spectrum for humans is 390 - 700nm, so this image extends to either side of what our eyes can see. Is that correct?

I'm still battling with understanding how astro-photography gets the images that it does.

Edit: - I read the numbers incorrectly. COULD anyone explain how this image is made?

Margarita

Earth has earth, does Mercury have mercury?

Thanks for the links bystander! and the spin!

emc wrote:Earth has earth, does Mercury have mercury?

And does Mars have candy?

orin stepanek wrote:

emc wrote:Earth has earth, does Mercury have mercury?

And does Mars have candy?

All I ask is that we keep to the inner solar system...

M

MargaritaMc wrote:Wikipedia tells me that the visible spectrum for humans is 390 - 700nm, so this image extends to either side of what our eyes can see. Is that correct?

I'm still battling with understanding how astro-photography gets the images that it does.

Edit: - I read the numbers incorrectly. COULD anyone explain how this image is made? :roll:

An image- any image- is really just a big array of numbers. Every pixel, under the hood, is one or more numerical values. With multispectral images like today's- that is, an image with data collected at different wavelengths (typically using filters that pass only specific wavelength ranges), each pixel is represented by a single numerical value for each wavelength observed. These values correspond to intensity- the more signal acquired at that wavelength range, the larger the number.

Almost all display devices are based on a color mapping system using red, green, and blue as primaries (printing methods usually use cyan, magenta, and yellow). So turning the data collected by a camera into an image for our eyes is simply a matter of mapping the numeric values at each pixel into a color, i.e. a specific ratio of red, green, and blue. There are many ways of doing this. For an image with only a single value per pixel, the most common is to assign that value directly to the red, green, and blue channels, which gives a grayscale image. For data with two values per pixel, it is common to map the values to two of the primaries, and construct the third from the sum or difference of the two values. For data with three values per pixel, the most common strategy is simply to directly assign each to its own primary. When there are more than 3 spectral data channels, as in today's APOD, some sort of mathematical transformation is applied, which converts multiple input values to three output values, one for each primary. For instance, you could take the value from the longest wavelength channel, and apply it directly to red. You could take the next shorter, and assign it to "yellow", meaning a mix of red and green. The next could be just green. Next, cyan, by mixing some into green and some into blue. And so forth. There are many ways of doing this- if you do a search on color theory, there are many good articles online.

Thank you, Chris. That is very helpful - the (now obvious) fact that every pixel is a representation of a number was light dawning for me. I think my experience doing water colours (and colour wheels in that medium) was/is actually a handicap in seeing what happens when, presumably, any photograph is taken digitally?
M
PS. I now have the Wikipedia article on Color Theory open in another tab.

On reading on about Additive colour, I see that it isn't only a property of the digital age.
http://en.m.wikipedia.org/wiki/Additive_color#section_1

For his experimental work on the subject, James Clerk Maxwell is sometimes credited as being the father of additive color.[2] He had the photographer Thomas Sutton photograph a tartan ribbon on black-and-white film three times, first with a red, then green, then blue color filter over the lens. The three black-and-white images were developed and then projected onto a screen with three different projectors, each equipped with the corresponding red, green, or blue color filter used to take its image. When brought into alignment, the three images (a black-and-red image, a black-and-green image and a black-and-blue image) formed a full color image, thus demonstrating the principles of additive color.[3]

Margarita

Another wonderful APOD image. Thank you.

Bet you an ice cold one Pluto is going to look the same, little darker and cooler. I really do hope New Horizons crashes into it with cameras rolling, a la Ranger. edited for spelling, lively keyboard today.

APOD Robot wrote: Colors of Mercury

Mercury's large, circular, tan colored feature known as the Caloris basin was created by an impacting comet or asteroid during the solar system's early years. The ancient basin was subsequently flooded with lava from volcanic activity, analogous to the formation of the lunar maria. Color contrasts also make the light blue and white young crater rays, material blasted out by recent impacts, easy to follow as they extend across a darker blue, low reflectance terrain.

This got me wondering... Does Mercury's location (so close to Sol) cause significantly greater impacts due to the higher impact velocities (relative to the rest of the planets)? I would imagine that it certainly does given that energy is proportional to the square of velocity. Many of the rays visible in today's image extend over a large part of the planet. Has anyone done a histogram of impact energy as a function of orbit diameter? (Of course impact frequencies would need to be equalized due to different planetary diameters...)

Note similar colors of our moon in a slightly adjusted APOD image from Feb 16 2006
http://img16.imageshack.us/img16/8641/m ... edlerk.jpg

pferkul wrote:Note similar colors of our moon in a slightly adjusted APOD image from Feb 16 2006
http://img16.imageshack.us/img16/8641/m ... edlerk.jpg

By the methods used, most bodies will look similar, since essentially what is being done is to take whatever the recorded color range is and boosting its range and saturation to produce something that maximizes our visual sensing abilities. But looks can be deceiving: there is very little in common mineralogically between the lunar and mercutian surfaces.