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  1. #1
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    Awesome Science Stories

    Three physics students in the UK have calculated that a single spider web, if anchored properly (and big enough), could stop a four-car New York City subway train travelling at full speed - just like it does in Spider Man 2.

    Read more: Spidey Silk Can Actually Halt a Train : Discovery News

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    watched a program the other night about spiders . they were in asia some were and a spider had its web across a small lake 100 ft , but they dont no how it did it

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    Moon Rise over an Arsenic Lake

    By Phil Plait

    I sometimes wonder if aliens will have clocks.

    It seems inevitable, especially if they live on a spinning planet that orbits a star. The motions of the stars as the planet spins, the daily rising and setting of the Sun, the phases of the moon if the planet has oneóall these movements fit together like the gears of a clock, ticking away in patterns that seem obvious once you notice them.

    They happen here on Earth, and if you keep your eyes openóand skywardóyou canít help but see them. And sometimes the hands of that celestial clock align, producing wonderful things. Photographer Jeff Sullivan was able to snap a picture of just such a wonderful thing:


    The full Moon rising over Mono Lake, California.
    Image credit: Jeff Sullivan, used by permission.


    I love this shot. Itís got so much going on! Sullivan took it on Jan. 26, 2013 just after sunset. The full Moon was rising, as it must just after sunset: For the Moon to be full, it has to be opposite the Sun in the sky, so we see the fully lit face of our satellite. If itís opposite the Sun, then it rises at sunset and sets at sunrise. He even made a very cool time lapse video of it (the shaking is due to the wind):


    Thatís wild. But thereís more. The pink band across the top of the photo is called the Belt of Venus, and we'll get to that in just a moment. But perhaps more interesting is the dark horizontal band just above the horizon in the photo and in the video. Some people see it and think itís just the sky getting darker as the Sun sets. Thatís kinda sorta true, but itís more than that. Itís actually the shadow of the edge of the Earth on the sky!

    On a hazy day, have you ever seen the shadow of a cloud or mountain stretch across the sky? Particles in the air are lit by the setting Sun, but if the cloud or mountain blocks the Sun, some particles are shadowed, and appear darker. If conditions are right, this happens on a much grander scale, with the horizon of the Earth itself blocking the Sun.

    This drawing I made might help:


    A brilliantly-drawn diagram showing the setting Sun and the shadow of the Earth projected on the sky.
    Image credit: Phil Plait


    When the Sun is just below the horizon (on the left, west), air above your head is still lit up. But air far enough to the east (to the right) sees the Sun below the horizon, blocked by the Earth. That air is dark, so when you look to the horizon opposite the Sun you see a broad band of dark sky. As the Sun sets further, the top of the band creeps upward. Eventually the sky darkens completely once the Sun is far enough below the horizon. This is the same reason we have twilight, by the way. Without an atmosphere, the sky would darken the instant the Sun dips below the western horizon.

    Since this dark band is to the east, and the Moon was full and rising in the east as well, it appears to be inside the dark zone. Pretty!

    Thereís an irony here, too. Technically, the Belt of Venus is the pinkish band just above the top of the Earth's shadow line, and not the dark band itself. Itís name may come from that glow, referring to the girdle worn by the goddess VenusóIíve seen that etymology bandied about, but Iím not sure itís true. Anyway, the irony is that the planet Venus can never be in that part of the sky. Venus orbits the Sun closer than the Earth, so, due to geometry, can never appear more than about 45į away from the Sun. Since the Belt is opposite the Sun, 180į away, Venus can never be in it.

    And one more thing, since I canít resist. Sullivan took this shot at Mono Lake, California. If that sounds familiar, that may be because it was the epicenter of the ďarsenic lifeĒ brouhaha in 2012, when scientists claimed they had found bacteria that could metabolize arsenic; a claim that was later shown to almost certainly be wrong. It was fun for a while though.

    Sullivan took lots of pictures when he was at Mono Lake, and theyíre all quite lovely. Go take a look. And of course the Belt of Venus itself is a fascinating thing to see in person, especially if you watch it over a few minutes and see it slowly move upwards. All you need is a good sunset and a clear view to the east. Give it a try! Thereís a lot going on in the sky all the time, if you just go out and look up.


    The Belt of Venus: Moon rise into the Earth's shadow

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    They probably have clocks, but might not regard time as a property of the universe, a dimension, but a construction of a mind trying to make sense of what is going on.

  5. #5
    Have you got any cheese Thetyim's Avatar
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    Quote Originally Posted by kingwilly
    Three physics students in the UK have calculated that a single spider web, if anchored properly (and big enough), could stop a four-car New York City subway train travelling at full speed
    Well they are only 45 years too late.
    I learnt that spiders web had a greater tensile strength than steel when I was at school.

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    I didn't know that about atmosphere, thought it was the clouds only reflecting light. It's a lovely planet we live on. Need to take better care of her.

    Quote Originally Posted by Rainfall
    They probably have clocks, but might not regard time as a property of the universe, a dimension, but a construction of a mind trying to make sense of what is going on.
    Think it would depend on seasons. Aren't seasons caused by a wobble from a prior collision ?Or is that gryroscopic precession. Oh dear I am forgetting my education,
    any way ; other planets might not.

  7. #7
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    Quote Originally Posted by Thetyim
    I learnt that spiders web had a greater tensile strength than steel when I was at school.
    Yes, but not necessarily enough to stop a train.

    Quote Originally Posted by Hypatia
    Aren't seasons caused by a wobble from a prior collision
    Not quite.

    The earth is tilted by about 6 or 7 degrees, that tilt faces towards and faces away from the sun at different times of the year, which allows the seasons to occur. (not because of distance, but because of the variation of the amount of atmosphere that the Sun's radiation must pass through.

  8. #8
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    Einstein's theory passes deep space test
    Stuart Gary
    Friday, 26 April 2013


    The unusually tight orbit of the white dwarf and pulsar allowed scientists to confirm Einstein's general theory of relativity
    (Source: European Southern Observatory/J. Antoniadis (MPlfR))

    A bizarre stellar system made up of two dead stars 7000 light-years away has put Einstein's famous general theory of relativity under its most extreme test yet.

    An international team of scientists discovered an unusually heavy neutron star that spins 25 times each second orbited by a white dwarf companion once every two and half hours.

    Observations of the system, dubbed PSR J0348+0432, produced results consistent with Einstein's theory, scientists report in the journal Science.
    Lead author, Dr John Antoniadis, of Germany's Max-Planck-Institute, and colleagues used radio and optical telescopes to search for subtle changes in the system.

    "I was observing the system...looking for changes in the light emitted from the white dwarf caused by its motion around the pulsar," says Antoniadis.

    "A quick on-the-spot analysis made me realise that the pulsar was quite a heavyweight. It is twice the mass of the Sun, making it the most massive neutron star that we know of and also an excellent laboratory for fundamental physics."

    The large mass of the neutron star (the extremely dense dead corpse of a star far more massive than the Sun) and the closeness of its white-dwarf companion (the dead core of a Sun-like star), made the system an ideal candidate to test Einstein's general theory of relativity.

    "We thought this system might be extreme enough to show a breakdown in general relativity, but instead, Einstein's predictions held up quite well," says Dr Paulo Freire, also of the Max Planck Institute.

    The general theory of relativity, which Einstein published in 1915, explains gravity and the effects of mass on the fabric of space-time.

    It expands on his special theory of relativity which explains light and the electro-magnetic force.

    Antoniadis and colleagues were able to measure the decay of the two stars orbits as gravitational waves carried off energy from the system.

    By very precisely measuring the time of arrival of the pulsar's radio pulses over a long period, they determined the rate of decay and the amount of gravitational radiation emitted.

    Had competing theories been correct, the rate of orbital decay would have been different.

    Relativity theory vs quantum mechanics

    These findings improve our understanding of relativity according to Dr Paul Francis of the Australian National University Mount Stromlo Observatory.

    "Quantum mechanics is very well laboratory tested...to 20 decimal places," says Francis.

    "Whereas relativity is not all that well tested because it's so hard, not having a black hole in your laboratory, which is probably a good thing!"

    "It's only been tested to about two decimal places, [so] people have been rather unsure about how good relativity was. But this has added another decimal place to it and it still looks like Einstein's theory is working."

    The findings also support the use of general relativity based templates for future gravity wave detectors.

    Researchers using such instruments hope to detect the gravitational waves emitted by events such as dense pairs of neutron stars and black holes spiralling inward toward violent collisions.

    Gravitational waves are extremely difficult to detect and even with the best instruments, physicists expect they will need to know the characteristics of the waves they seek, which will be buried in quantum noise from their detectors.

    "The fact that this is giving more confirmation that relativity is working pretty well implies that the gravity waves will be out there at the strength people are predicting," says Francis.

    "Therefore the next generation of gravity detectors should be able to find them."

    xxx.xxx.xx

  9. #9
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    cool, I dont really understand most of it, but I love it nonetheless!

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