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Perseids tonight

Discussion in 'science, nature and environment' started by DotCommunist, Aug 12, 2015.

  1. StoneRoad

    StoneRoad RIP Greebo being kinder heckling from the back!

    Saw a few last night, but gave up quite quickly, OH saw a couple of corkers. (I had driven up from Wales in some tiring traffic and we're off early to Whitby for Sunday morning so needed some shut-eye !)

    And an Iridium flare in daylight a couple of days ago ...
     
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  2. 2hats

    2hats

    A Japanese company called ALE is planning to do exactly just that with their SkyCanvas project…

    Debut at the 2020 Tokyo Olympics.
     
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  3. Corax

    Corax Read my blog you bastards.

    I'm not sure what I saw was an Iridium sat on reflection, as it was in no way a 'flare'. It was exactly what the ISS looks like in the night sky in fact - except that according to my app the ISS was over Australia at the time... :confused:
     
  4. SheilaNaGig

    SheilaNaGig Struggling and striving

    When we were kids and all through our teens, a group of grown ups who were long time friends and us kids who all grew up together would spend the summer in a big old house on a dark part of the Kent coast. When we got old enough to stay up late and entertain ourselves without adult supervision, our favourite thing to do was go out onto the sea wall after supper and share beer and tabs and take the piss out of each other for hours. In my memory, it was so normal for us to see shooting stars that we'd not even bother to remark on them unless they were particularly bright or long-tailed.

    Those years ended, and after a while I started to go camping in the summer: festivals but also wild camping. And despite my expectations of loads of shooting stars in the summer skies, I rarely did. So I thought perhaps I'd imagined the shooting stars of my youth.

    But now I realise that we were sitting out under the Perseid Shower every year :cool:
     
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  5. StoneRoad

    StoneRoad RIP Greebo being kinder heckling from the back!

    Could have been another satellite ... there are a lot up there.
    The ISS is now very bright compared to the one of the first few times I observed it, and on one of those nights, I saw one of the Shuttles dropping back (which landed safely sometime later).
     
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  6. kalidarkone

    kalidarkone Up to my knees in amniotic fluid

    I saw 3 last night! My bedroom is in the attic and I have a velux window above my bed so I just lay there.......
     
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  7. S☼I

    S☼I Fiending for knismesis

    Saw a few last night from a beach on Sicily. The number and brightness of the stars compared to home is ridiculous. And to top.it all off me and Mrs SI for the first time ever saw the "band" of the Milky Way - faint, but unmistakable.
     
    Last edited: Aug 13, 2017
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  8. Looby

    Looby Well-Known Member

    Last night we sat/laid out in my friend's garden in north Devon on the edge of Exmoor. We saw lots (and shitloads of satellites). We were out there for hours getting pissed and singing songs about space and stars which I'm sure the neighbours loved. Came in for a bit when it got cloudy about 12.30 and were planning to go out again but we were all tired and in bed by 1.30.
     
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  9. DotCommunist

    DotCommunist my world is fire and blood

    didn't see any this year. bah, curse my tired eyes. And clouds. Sposed to be an eclipse in america land soon, I don't know if that means we'll see it as well but you'd think so wouldn't you.
     
  10. 2hats

    2hats

    Sliver of a partial eclipse starting 1940BST 21 August for 48 minutes.

    NASA stream of the total eclipse from the US details here.
     
  11. nuffsaid

    nuffsaid But this goes up to 11

    So as the meteorite shower is due to the Earth going through the cloud of the Swift-Tuttle comet. Surely over time the comet will shrink as matter is released from it every time it passes round the sun - so how come we're still seeing the Perseids, shouldn't it have all dissipated by now? Recorded sightings go back to 69bc. And if the comet is on 133 orbital cycle, how come we go through it's cloud every year? :confused:

    Schoolboy errors I'm sure. Please explain.
     
  12. Fez909

    Fez909 toilet expert

    The comet is massive compared to the bits we're seeing. Each meteor is about the size of a grain of sand, and the comet is 26km in diameter.

    There's enough dust left to keep us in meteor showers for a long time :)
     
  13. 2hats

    2hats

    It will indeed shrink and has a limited lifetime.

    Swift-Tuttle has a mass of around 10^17 kg. It’ll lose something like 10^11 kg on each passage (I don’t have the current figure for it but that is the value for Halley’s Comet so lets go with that). So that would last some 10^6 passages ie over 133 million years. Note that most of the Perseid fireballs are little bigger than a grain of sand (10^-9 kg ie micrograms) so it can afford to shed a lot of material, feed spectacular showers and keep trucking for some time yet.
     
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  14. nuffsaid

    nuffsaid But this goes up to 11

    But what about going through the cloud every year if it's only on an orbit of once every 133 years, surely the cloud would dissipate well before it returns.
     
  15. Fez909

    Fez909 toilet expert

    According to Wiki, the cloud has been there for 1,000s of years.

    Where would it go? The cloud is also in an orbit, so when the sun melts a bit of the comet, it breaks up, but the particles have still got momentum, so will carry on orbiting....until we smash into them every August :cool:
     
  16. 2hats

    2hats

    It does gradually spread out, gravitationally perturbed (though solar radiation pressure does rearrange some of the lighter material). Then every 133 years the parent comet repopulates the trail of debris. That’s why the precise date and peak varies form year to year and why after a recent passage a meteor storm is often observed (the classic being 55P/Tempel–Tuttle which re-seeds the Leonid shower every 33 years or so and has yielded some spectacular meteor storms - I saw the last one back in 1999, from the UK, and it was truly spectacular).

    This week’s Sky At Night programme covering the Perseids (and meteors in general).
     
    Last edited: Aug 14, 2017
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  17. nuffsaid

    nuffsaid But this goes up to 11

    Hmm..I suppose so, because it happens, but I'd like to see a graphic (.gif) showing the orbit of the cloud and Earth's. I would have thought the cloud having momentum as you say would move outside of the Earth's orbit. I understand with the comet coming back it forms another cloud in the same spot, but surely the cloud would keep moving, is it just on a loop that keeps it in sync crossing the Earth's orbit every August? Surely the cloud would want to follow the trajectory of the comet and so end up moving outside of the inner solar system, and so the Perseids would reduce over several years, (to zero), then reappear after the next fly by, for a few more years?
     
  18. 2hats

    2hats

    [​IMG]
    The trail of ‘debris’ (increasingly being laid down well before arrival in the inner solar system and then decreasingly so well after) is co-moving with the parent body and largely stays along the same orbit, though gradually spreading and twisting out from that over time (over many millions of years a lot of material will end up along most if not all of the orbital path of the comet - see previous lifetime estimate). Jupiter plays a fairly major role in putting kinks into the trail of material and that will result in apparent outbursts (as seen on Earth) from time to time.
     
  19. nuffsaid

    nuffsaid But this goes up to 11

    Ah, that's better, so yes along the orbital path of the comet there will always be a certain amount of debris due to successive flybys that in time string out along the orbit and we pass through it each year!! I am Patrick Moore (1.1) and I claim my £5. I didn't actually realise the orbital path truncated the inner solar system, I thought it was on the same plane, that makes more sense in constantly passing through a ring of debris then.

    So, about this Dark Matter...?
     
  20. 2hats

    2hats

    Generally: Short period comets (<200 year orbits) tend to come from the Kuiper Belt and are largely constrained to orbit in the plane of the ecliptic (ie same plane as all the planets plus or minus a bit) given the Kuiper Belt is likewise. Longer period comets (>200 year orbits) come from the Oort Cloud so they tend to have widely varying, random inclinations to the ecliptic (since the Oort Cloud is spherically distributed).

    Swift-Tuttle is however highly inclined yet in a relatively short period orbit (~133 years). Aphelion is around 50AU which suggests it originated around Kuiper Belt distance (nowhere near the Oort Cloud which is at least 40 times further out). Interestingly it is in a 11:1 resonance with Jupiter (which perturbs the debris trail and nucleus) though has only been so for a few thousand years and may only remain so for a few thousand more. It could be that this interaction is the source (in part) of the unusual orbital eccentricity for an object of this origin.
     
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