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  1. Mick West

    Mick West Administrator Staff Member

  2. Trailspotter

    Trailspotter Senior Member

    Could it be just dust particles or similar drifting with the airflow much closer to the camera?
     
  3. Trailblazer

    Trailblazer Moderator Staff Member

    I don't think dust particles would be in focus in this type of shot. A telephoto lens wouldn't have the necessary depth of field.
     
  4. Whitebeard

    Whitebeard Senior Member

    Many species fly at night, and many migrate at night. Its hard to tell from the footage if they are small song birds a 100ft or so up or large geese or the like at altitude. And because we haven't got a location its not possible to place the shot on any species know areas of distrubution or migration route..

    Having said that, they are not in formation, and most species that fly at higher altitudes tend to use the familer V formations when flying in groups. Smaller birds that fly in flocks at lower levels just bustle along in loose groups. So going by the footage I would lean more towards a sparrow or songbird size bird rather than a swan, goose, heron etc...

    Another posibility is that they could just as easily be bats. Bats tend to group rather than formate, and do the straight line bit when going between roost and hunting area.
     
  5. Trailblazer

    Trailblazer Moderator Staff Member

    According to the page linked in the OP, the video was shot in Rome, Italy, on July 29.

    In my completely unprofessional opinion, it looks like a mass release of balloons drifting in the wind.

    The moon was just east of south in the sky, so the objects were heading roughly southwards.

    upload_2018-9-4_16-27-6.


    The wind in Rome at that time was from the north.

    upload_2018-9-4_15-59-42.
     
    Last edited: Sep 4, 2018
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  6. Trailspotter

    Trailspotter Senior Member

    "Drifting in the wind" is what it looks like. I had filmed similar drifting of plant seeds across my telephoto shots, but balloons will do too. Here are a couple of my photos of a mass release of balloons in Rome taken in 2011:
    IMG_0564. IMG_0571.
     
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  7. Mick West

    Mick West Administrator Staff Member

    I was thinking that the meandering meant birds, but the balloons does seem more likely now. Anyone got a good video clip of balloons with fixed camera I could do the trails thing with?
     
  8. deirdre

    deirdre Moderator Staff Member

    I see wings. bats?

    upload_2018-9-4_13-4-20.
     
  9. Mick West

    Mick West Administrator Staff Member

  10. deirdre

    deirdre Moderator Staff Member

    no, I see flapping. but wouldn't your path vary depending on what angle the birds or bats are flying? and maybe distance of the birds/bats?
    Do we know what 'altitude' the top of the moon is at to the camera view?

    add: also how long does it take for the moon to travel across the screen like we see? that video can't be real time right? or can it be?
    although it looks a bit jumpy, is the moon's movement just the camera moving?
     
  11. Mick West

    Mick West Administrator Staff Member

    Here's a difference track for a soaring vulture, camera pointing straight up (in my back yard). Much lower, but shows something of a meandering path.
    Soaring turkey vulture.

    I sat my phone on a chair for 30 minutes, pointing straight up
     
    Last edited: Sep 4, 2018
  12. Mick West

    Mick West Administrator Staff Member

    It's never straight overhead in Rome.
     
  13. Trailblazer

    Trailblazer Moderator Staff Member

    The moon takes about 2 min 20 sec to move its own diameter across the sky, so yes, the video is in real time. (Leading edge of the moon appears at about 0:36, and trailing edge at 2:56)

    (The Earth's rotation, 360 degrees in 24 hours, makes the background stars appear to move 15 degrees per hour across the sky from east to west, or 1 degree every 4 minutes. The moon travels in the opposite direction, west to east, relative to the stars, which means its apparent east-to-west motion across the sky is slightly slower than that of the background stars.)
     
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  14. Trailblazer

    Trailblazer Moderator Staff Member

    From that star chart I posted earlier (Link here but you need to set the time and date to the right values) the moon's altitude was about 29 degrees above the horizon.
     
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  15. deirdre

    deirdre Moderator Staff Member

    I did frame by frame a balloon release video and the camera glitches/focus issues does make a few balloons appear to flap.. so .. now I'm accepting the balloon idea too.
    upload_2018-9-4_17-35-19.
     
  16. Trailspotter

    Trailspotter Senior Member

    If so, the angular speed of the dots is about 0.035° per second. For the objects drifting in the wind with the speed of about 2 metres per second this would give the distance to them being about 3000 metres. At this distance, a typical balloon with the diameter of 0.25 m would have the angular diameter being about 0.005°, or one hundredth of the Moon diameter (about 0.5°), that roughly corresponds to the relative size of the dots.
     
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  17. Robert Sheaffer

    Robert Sheaffer New Member

    See if this sounds right: based upon my own measurements of the dark objects on my screen, and assuming that the diameter of the lunar disc is 30', then each of the objects is approx 9" of arc. This is .156', or .0026 deg, whose tangent is 4.53 E-5. Assuming an object size of 200mm (a typical balloon), its distance from the camera would then be about 4.4 km. Since the moon was at 29 deg altitude, whose sin is .48, the altitude of the objects above the ground would be about 2.13 km.