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Fireball Spotted over Northeastern USA

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Re: Fireball Spotted over Northeastern USA

#61

Post by LASR »

alexpotato wrote: post #45
FPGAhacker wrote: post #31

Earlier quoted context omitted.

Do meteors ever hit the atmosphere at low speed?

While the odds of what I'm about to describe are astronomically (pun intended) low, I can see the following occurring: - earth moves in its orbit - meteor is moving in a straight line - that line is perfectly parallel to a point on the earth's orbit - the earth and the meteor basically link up and the speeds match so precisely that the meteor just goes into orbit

For this to happen, it must have a low-enough potential energy to begin with. Otherwise, it will just shoot out the other side of the orbit.

In that case, most likely a meteor was already in orbit, and we just didn't know about it.

Re: Fireball Spotted over Northeastern USA

#62

Post by zerocrates »

daggersandscars wrote: post #56
swores wrote: post #36

Earlier quoted context omitted.

" the UK gets an average of 30-50 tornadoes a year. That’s more tornadoes per land area than anywhere else in the world (except – weirdly – the Netherlands.) " https://www.bbc.co.uk/programmes/articles/3QTh1mRGDNg16cDYHg... I too would've said we never get them here, apart from remembering one big one in the news I think in or near Birmingham...

Citation needed. Oklahoma averages over 50 per year and is 2/3rds the land area of the UK.[0] [0] https://www.weather.gov/oun/tornadodata-ok-monthlyannual

I assume the stat is actually that the UK gets more per unit of area than any other country except the Netherlands.

Re: Fireball Spotted over Northeastern USA

#63

Post by titzer »

IIAOPSW wrote: post #60
alexpotato wrote: post #45

Earlier quoted context omitted.

While the odds of what I'm about to describe are astronomically (pun intended) low, I can see the following occurring: - earth moves in its orbit - meteor is moving in a straight line - that line is perfectly parallel to a point on the earth's orbit - the earth and the meteor basically link up and the speeds match so precisely that the meteor just goes into orbit

You haven't accounted for the massive gravity well that is the sun. The difference in potential energy from infinity to the radius of Earths orbit is GMm/r. Set that equal to momentum (.5mv^2) and you get sqrt(2GM/r). Plug in the numbers and you'll see you can't really have a meteor that stumbled in from outside the solar system with a similar velocity to Earths orbit by the time it came down to Earths orbit. Put ano…

Orbital mechanics is considerably more complex than this because there are several over massive planets orbiting the Sun. Granted, the odds are very low of getting kicked into a trajectory that will just barely kiss Earth's orbit (at the right time), but it can happen. Not everything orbits in a conic. Also, extrasolar meteors are probably a lot more rare than the above comment would suggest.

Re: Fireball Spotted over Northeastern USA

#64

Post by roywiggins »

alexpotato wrote: post #45
FPGAhacker wrote: post #31

Earlier quoted context omitted.

Do meteors ever hit the atmosphere at low speed?

While the odds of what I'm about to describe are astronomically (pun intended) low, I can see the following occurring: - earth moves in its orbit - meteor is moving in a straight line - that line is perfectly parallel to a point on the earth's orbit - the earth and the meteor basically link up and the speeds match so precisely that the meteor just goes into orbit

It has happened. Such orbits are not stable, due to the moon and sun's influence.

https://earthsky.org/space/2020-so-mini-moon-asteroid-or-spa...

Re: Fireball Spotted over Northeastern USA

#65

Post by titzer »

digitalsushi wrote: post #59
anamexis wrote: post #55

Earlier quoted context omitted.

It's not immediately obvious to me – why would escape velocity also be the minimum speed at which an object could enter the atmosphere?

Indeed. What if the object was traveling at the same speed as Earth as it revolves around the Sun, and their paths intersect at a very acute angle? That is to say, they met at a traffic 'zipper' ... Could an object collide with earth at a lower speed?

Yes, but it is rare because most objects in such orbits tend to either be gobbled by Earth right away, settle into L2, L3, or L4, or enter a high orbit.

Re: Fireball Spotted over Northeastern USA

#66

Post by roywiggins »

IIAOPSW wrote: post #60
alexpotato wrote: post #45

Earlier quoted context omitted.

While the odds of what I'm about to describe are astronomically (pun intended) low, I can see the following occurring: - earth moves in its orbit - meteor is moving in a straight line - that line is perfectly parallel to a point on the earth's orbit - the earth and the meteor basically link up and the speeds match so precisely that the meteor just goes into orbit

You haven't accounted for the massive gravity well that is the sun. The difference in potential energy from infinity to the radius of Earths orbit is GMm/r. Set that equal to momentum (.5mv^2) and you get sqrt(2GM/r). Plug in the numbers and you'll see you can't really have a meteor that stumbled in from outside the solar system with a similar velocity to Earths orbit by the time it came down to Earths orbit. Put ano…

Near-earth asteroids periodically wander into temporary orbits around the Earth and then wander off.

https://earthsky.org/space/2020-so-mini-moon-asteroid-or-spa...

Re: Fireball Spotted over Northeastern USA

#67

Post by teraflop »

anamexis wrote: post #55
jacquesm wrote: post #38

Earlier quoted context omitted.

11.2 km/sec at a minimum. (Earth's escape velocity!)

It's not immediately obvious to me – why would escape velocity also be the minimum speed at which an object could enter the atmosphere?

Even if an object is moving in a parallel orbit to Earth's around the sun, if you "zoom in" to the point where it enters the Earth's sphere of influence, the influence of the sun is relatively small. It's roughly as if Earth and the object are free-falling together in empty space, with a small relative velocity. And Earth's escape velocity is the same velocity that would be reached by a stationary object "dropped" from infinitely far away. So relative to the Earth it will accelerate and hit the atmosphere with at least escape velocity.

(This is only an approximation, but it's a pretty good one because there's such a large difference between Earth's mass and the sun's.)

Another way to look at this is to simply observe that Newtonian physics is time-symmetric (neglecting effects like friction that dissipate energy). If you have a trajectory that arrives at the edge of Earth's atmosphere with a certain velocity, you can reverse it to get a trajectory that leaves with the opposite velocity (i.e. equal speed).

Re: Fireball Spotted over Northeastern USA

#68

Post by andrewstuart »

I saw a meteor once when I was a kid. I was on the beach and it streaked across the sky and exploded into a bunch of other things that streaked a little further and faded out.

I never really told anyone because it seem so preposterous that I wasn't really sure I had seen it at all.

It was well out over the over the ocean a number of kilometeres and up very high - zero chance it was fireworks and there weren't ny on that night anyway.

Re: Fireball Spotted over Northeastern USA

#69

Post by AYBABTME »

vba616 wrote: post #57
FPGAhacker wrote: post #31

Earlier quoted context omitted.

Do meteors ever hit the atmosphere at low speed?

Yes, relatively speaking. First likely hit I found: "Meteors enter the atmosphere at speeds ranging from 11 km/sec...to 72 km/sec ... The wide range in meteoroid speeds is caused partly by the fact that the Earth itself is traveling at about 30 km/sec (67,000 mph) as it revolves around the sun. On the evening side, or trailing edge of the Earth, meteoroids must catch up to the earth’s atmosphere to cause a meteor, an…

I wonder, if a meteor was moving very slowly (relatively) and basically just gently falling to earth, if we'd notice.

Re: Fireball Spotted over Northeastern USA

#70

Post by OJFord »

swores wrote: post #36
OJFord wrote: post #29

Earlier quoted context omitted.

I had an experience a bit like that, but with mini-tornadoes, somewhere along the M11 in the UK (Essex I think, but perhaps the edge of Cambs). I recall looking it up afterwards and it seemed to be 'a thing', though none of the news examples I found from various years before the event were anything like as extreme - tens and tens of them, well-formed. A truly bizarre 'what is happening' experience for me - before tha…

" the UK gets an average of 30-50 tornadoes a year. That’s more tornadoes per land area than anywhere else in the world (except – weirdly – the Netherlands.) " https://www.bbc.co.uk/programmes/articles/3QTh1mRGDNg16cDYHg... I too would've said we never get them here, apart from remembering one big one in the news I think in or near Birmingham...

But also:

> the area from Berkshire into London had the highest likelihood of a tornado - one every 17 years.

What I saw was probably your UK annual 30-50 in a single small area all at once! Not huge, but many.

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