Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Rock ignites at 45,000mph over PA, NASA video, why flare up?

  1. Feb 18, 2015 #1
    From Google news,

    http://www.theregister.co.uk/2015/02/18/meteor_explodes_over_earths_beaver_in_hot_nasa_video/

    Simple question, if you play the video in the link above the light from the meteor flairs up into a very large ball of light. Why don't we continue to see a relatively small point source of light? At the very end of the video the large flair up reverts to a smallish source of light.

    Thanks for any help!
     
  2. jcsd
  3. Feb 18, 2015 #2
    It has burned up small enough to where the camera no longer can pick up the light? Nice video btw!
     
  4. Feb 18, 2015 #3
    Better stated, my question is why does the angular width of the light emitting region get so big, or is light scattered? Or is the light emitting region in the upper atmosphere that big.

    Thanks for your help!
     
  5. Feb 18, 2015 #4

    jim mcnamara

    User Avatar

    Staff: Mentor

    The kinetic energy in the meteor is converted to an incredible amount of heat. Like an explosion in slow motion. I do not know what temperatures are reached but most of the object was converted into plasma - which generates a ball of light as a byproduct. Bolides (exploding meteors) may produce an explosive sound; if they make it far enough down into the atmosphere. Try this: http://en.wikipedia.org/wiki/Bolide
     
  6. Feb 18, 2015 #5
    I kind of get that part. At its largest extent the light appears to be emitted from a very large angular region. That means either the light is emitted from a very large region or some of the light emitted scatters making it appear that the light emitting region is much larger? I guess I'm not making my self clear.
     
  7. Feb 18, 2015 #6

    jim mcnamara

    User Avatar

    Staff: Mentor

    Maybe if you thought of it as a kind of gradient phenomenon: - in a very non-dense milieu like the upper atmosphere, an excited particle from an explosion loses energy by radiating light - mostly because it cannot transfer heat to nearby atoms. They are not there.... Same explosion on the surface of the earth would be wow! but nowhere near as large a ball of light - smaller radius. Because there are way more atoms to interact with, the particle cannot not keep in motion for as long a time interval, and does not radiate as much light. Does this compute for you? Kinda like the difference in velocity: walking through Central Park at midnight versus walking through the same area of Central when there is a massive outdoor concert in progress - "Please excuse me... oops sorry.... Ow! hey make your dog let go!... didn't see you...." So, All you need at midnight is be able run faster than the person you're accompanying - to avoid muggers.
     
  8. Feb 19, 2015 #7
    Maybe it is best to estimate some numbers for the event. The camera clearly has a wide angle lens, maybe more like a fish eye lens as the field of view is almost 180 degrees. At the largest extent the light flair up is maybe 20 degrees wide, about lets say, could be more. Say at the same time of maximum flair up the meteor is at an altitude of say 20 miles. If you do the math then this implies that the light emitting region is of order 7 miles in diameter. That seems big to me. I think that the flair up seems so big because of scattered light, either in the atmosphere or in the camera?

    Thank you for being patient with me!
     
  9. Feb 19, 2015 #8
    Some of the videos of the Russian meteor event on 2/15/13 show the same effect, (video camera distortion?). As the large meteor plows into the upper atmosphere heated material spreads out with high velocity away from the meteor, but how far, meters, 100's of meters, kilometers? Lets not consider events where the meteor breaks up.

     
  10. Feb 19, 2015 #9

    russ_watters

    User Avatar

    Staff: Mentor

    Sorry I missed this/nobody answered it:
    The object remains essentially a point source, but burns-out/saturates the camera and only appears to be bigger. The same thing happens to your eyes when you look at bright stars.

    Same phenomena here:
    Horsehead-HaRGB.jpg
     
  11. Feb 19, 2015 #10
    All the stars in the photo above are basically point sources and only appear smeared out due to diffraction?

    It seems as if there are two effects going on with the video of the meteors, an actual physical width to the light emitting region (or is the light emitting region that narrow) and an effect (diffraction?) due to the camera when the light gets really bright?

    Thanks for your help!
     
  12. Feb 19, 2015 #11

    russ_watters

    User Avatar

    Staff: Mentor

    There are actually three different effects. Diffraction is one. Atmospheric refraction is the second -- that's the air spreading-out the light. The brighter the light, the more noticeable it is. Third is thermal blooming. That's the light literally heating up the camera chip and making it register light away from the center of the dot, due to the heat.

    [edit] Actually, there is a fourth in my photo above: internal reflection in the camera.
     
  13. Feb 20, 2015 #12
    From this video, starting at time 0652, the flash, at 0707 the shock - a time differential of 15 seconds.
    As a rough estimate, if the shock travels at the speed of sound, the explosion took place 3 miles up.
    Notice the camera saturation.

    Starting at 0110, one sees the meteor up to 0125, with the explosion at 0120.
    If traveling at 36,000 mph , or 10 miles per second, the video shows a travel in 15 seconds - whopping 150 miles, which is probably too high.
    Using the vertical measure from the previous of 3 miles, the horizontal distance is about 7 times that, or 70 miles.
    This is all assuming the meteor is travelling perpendicular to the line of sight, which it probably is not.

    During the explosion, at 0120, it looks darker in the middle of the flare-up where the meteor should be> I would not think that the gases and plasma given off should be travelling too much ahead, if any, of the huge hunk of rock, so the effects Russ mentioned are in play there.

    One can see in the ash trail, the cooling down of the gases. This looks to be about 1/10 of the vertical distance, so I am assuming 0.3 miles in width, or 1500 feet, or 500 meters.

    Best guestimates??
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Rock ignites at 45,000mph over PA, NASA video, why flare up?
Loading...