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Domain: aspsky.org

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Comments · 9

  1. Re:Interesting, but.. by jmh_az · · Score: 5, Informative · on How Spirit Takes Pictures
    It extracts data by looking at the return levels at the various wavelenghts of the filters, among other things. With image processing software like IRAF you can get an amazing amount of information out of an image. Also, conventional comsumer CCD cameras use one CCD device with a RGB patterned color filter literally painted onto the face of the CCD to get red, green and blue. High-end cameras use three CCD's with seperate filters in front of each imaging device and splitter prisms to direct the light. Since things like weight and complexity are issues when building spacecraft, they accomplish the same thing as the high-end cameras here on earth by using one CCD and a filter wheel. This approach also allows them to do other things, such as take images through polarizers, or have magnification if they need it, and all in one camera package. And, last but not least, these cameras are tested and calibrated to within an inch of their lives before they ever leave the ground, so the researchers know exactly what the dark current (electronic noise), flat field (pixal responsiveness across the entire CCD) and defect characteristics for the CCD are. This information is then used to subtract out a lot of the noise and imperfections, leaving as much of the original data for analysis as possible. That analysis is the stuff of research papers like this one.

    Hope that was useful.

  2. Re:How was the ice supposed to survive anyhow? by hubie · · Score: 1 · on Lunar Polar Ice Not Present
    I believe that if your temperature and pressure are low enough, you'll get very slow (if any) sublimation. See the H2O phase diagram here. In that figure if you are down at point "D" you basically stay in the solid phase.

    The example you mention with freezer ice is a bit contrived. You don't need low pressures there because the freezer, by design, is condensing out the water vapor which forces the ice/air interface to not be in equilibrium (the water vapor does not have the opportunity to refreeze because the freezer removes it).

  3. Re:I�m surprised. by FTL · · Score: 4, Funny · on NASA Ames Research To Close Largest Windtunnels
    > However, no software is perfect.

    I don't know, my "Hello World" program seems to be bug free. Be careful with sweeping generalisations.

    Isnt the surest way of knowing how an object will behave in the wind is to run it through a wind tunnel? After all, consider sending a probe to mars. What if the parachute checked out OK in a computer simulation, but doesn't apply to real physics because of some bug?

    Computers can do cute things like simulate the parachute in a Martian atmosphere. Which might be kind of handy given that the air density on Mars is 1% of Earth.

    For the simple stuff, there are wind tunnels. For everything else, there's computers.

  4. Re:Double-edged sword of nature by cervo · · Score: 1 · on Total Solar Eclipse at Ceduna, South Australia

    Viewing the eclipse is dangerous. Here is a dated article about the solar eclipse, most relevant is the material towards the bottom of the page on how to build A Projection Camera or a Solar Filter to view the eclipse safely. Furthermore there are other methods discussed above on viewing the eclipse safety. It also states the Sun causes the eye damage and emits the radiation, not the eclipse.

    This article would seem to indicate that the sun does not emit more radiation as eluded to by other posts during the eclipse, but rather it is dangerous because you can look at it longer. If you stare at the normal sun your eyes start to hurt from the brightness, and you either close them or turn away after a short time. During the eclipse it isn't as bright so you can keep looking and the normal radiation emitted by the sun is exposed to your eyes for longer. This is from the black part that your eyes can fixate at. This is also the partial eclipse when part of the sun is still exposed.

    Additionally the topic of eclipses was discussed not too long ago on slashdot here And there are comments on the same thing of the eclipse burning the retina and so fourth. Consensus seems to be that the sun is no more dangerous during the partial eclipse, but we just look at it more than usual because it is an eclipse.

  5. -1, Pedantic by LMCBoy · · Score: 5, Informative · on Warcraft III Gone Gold

    Of course, the Sun is actually white, almost by definition. People think it's yellow because they usually see it when it's low in the sky near the horizon, which causes its color to be significantly reddened
    by its long path length through the gas and dust of our atmosphere.

  6. nothing new by lanclos · · Score: 1 · on The End Not As Near As We Thought

    I don't have any sources, but this is not a new theory in any way... astronomers and astrophysicists have a rather good understanding of angular momentum and its application, and have maintained for some time that the Earth would not be completely enveloped by the outer layers of our sun as it goes into a red-giant phase.

    As others have pointed out, the natural life-cycle of the sun will sear all life from the surface of the Earth long before any potential engulfing happens (as if it was the engulfing that mattered; the outer layers of a red giant are extremely thin, much more tenuous than our atmosphere). We'll experience some kind of runaway greenhouse effect something like a billion years before the sun enters the red giant phase... and our galaxy will collide with Andromeda before the sun goes belly-up.

    One of our hopes for preposterously-long-term survival, as researched (with a smile on his face and a glint in his eye) by Greg Laughlin (et al.), is for the Earth to be caught by a wandering type-M star and pulled out of the solar system.

    But really now... we're talking billions of years, here. It's fun to think about, but calling it "news" (especially "breaking news") is a pretty harsh misnomer.

  7. Re:The diameter and mass figures seem screwy by Anonymous Coward · · Score: 1, Informative · on Black Hole Sans Donut Puzzles Astronomers
    According to the Schwarzschild formula (Rs = 2GM/c^2), the radius of a black hole is about 3 kilometers per solar mass. So a 3 billion solar-mass black hole would have a radius of about 9 billion kilometers. That's about 50% larger than the radius of Pluto's orbit, hence the "approximately" in your quoted statement.

    What you're neglecting is the fact that a black hole is not necessarily more dense than a star. In fact, a sufficiently large black hole is less dense! For instance, a black hole of ~100 million solar masses only has an average density near that of water. It's not just how dense it is, it's how much of it you've got. Take a bucket of water, and it won't form a black hole. Take 100 million solar masses worth of buckets of water all next to each other, and they will

    (I got the last example from this nice page discussing black hole myths at the bottom.)

  8. Re:Unfortunately, we're just at the beginning... by Shoden · · Score: 2 · on How To Handle A Killer Asteroid
    I generally agree with your line of reasoning, but I just wanted to point out that an object "several AU away" wouldn't reach us any time soon... at the very least not in the next few centuries.

    I have to disagree with this, and will use the following well know example to illustrate why:

    Halley's Comet has an orbital period of approx 76 years. It's perihelion is 88 million kilometers, and it's aphelion is 5.2 billion kilometers.

    An astronomical unit (AU) is 149,604,970 km.

    That means that Halley's Comet is at it's furthest distance from the sun (aphelion) is about 34.75 AU away from the sun, and 33.75 AU from us (assuming both the Earth and Halley's Comet are on the same side of the sun).

    Now, I think that 34 counts as 'several', and it only takes half of Halley's orbital period to travel that distance, or 38 years... not centuries as you stated.

  9. Re:Read the frigging article! by tesserae · · Score: 2 · on Jupiter Moon Ganymede May Have An Ocean
    When it gets cold enough, water ice is a bit different from what you're familiar with -- it behaves more like your "geologic crust" than something you can skate on. In the extremely cold conditions of the outer Solar System, water ice (and other volatile ices, too) are very much structural materials; they work just fine as the crust of a planet or a moon. There are even "geologic" processes akin to plate tectonics which can operate with volatile ices replacing the rock that Earth uses.

    In this case, the ocean might be similar to Earth's mantle in function: the still-frozen crustal ice floats on it, much as the Earth's low-density continental and lithospheric rock "floats" on the denser, plastic mantle.

    Just one more comment. It may be that some of the outer Solar System objects (Pluto and Charon, plus some of the outer-System moons) have no "geologic crust" in the sense of a separate rock component: they may be nothing more than large "dirty" snowballs which never differentiated. They would still have a "surface", however...

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