Fireball sound and location

[acey]

I saw the fireball on Friday night (21 Sep) at 10.56pm, and at 11.00pm I heard a deep, distant rumbling that appeared to come from the east or south-east: the direction in which the object had first appeared. Question: did I hear the fireball as well as see it?

My watch readings indicated a minimum time delay of 4 minutes and maximum of 5 minutes. Assuming the speed of sound to be 340m/s this would be a distance of 81.6km to 102km.

I estimated the fireball to be about 35 degrees above the horizon when due south but I first saw it as it was breaking up (having been startled to look at the sky by the initial brilliant flashes) and judging by its path across the sky its initial elevation would have been higher. Also one must allow for observer error, so suppose an elevation of 30 to 50 degrees above horizon at moment of break-up.

Then (from simple trigonometry) the object at time of break-up had an altitude of approximately 40-80km and a horizontal distance of 65-90km due east or south east of my observing location (which was roughly 40km north-west of Newcastle). This would place it out at sea, somewhere off the coast between Blyth and Hartlepool.

On a news report I heard it said that the object was 80 miles up (130km approx), about twice as high as my estimate. I don't know how that figure was arrived at. Apart from observer error, my estimate could be criticised because the speed of sound varies with altitude: at 80km it would be 280m/s (according to the 1976 Standard Atmosphere calculator http://www.digitaldu...scalc/index.htm), but since the speed decreases with altitude this would bring my estimate down rather than up. On the other hand, it could be the case that the supersonic boom was emitted only once the object was sufficiently low in the atmosphere, and that this occurred some time after break-up.

In any event, I think I heard it as well as saw it.

[Stu]

Plenty of variables which are pretty hard to estimate but given you heard it a significant time after the event (not simultaneously) and in the same direction, it seems quite likely that it was the sonic boom from the meteor/space junk you heard, excellent stuff

Stu

[LukeSkywatcher]

Good stuff. I was wondering if anyone had heard a sonic boom. No reports of one apart from this.

[mikeyscope]

In addition to my observation here...

http://stargazerslounge.com/topic/162818-fireball-tonight/#entry1645338

I didn't really take it on board at the time but after the last fragments disappeared over the horizon I checked the time....by my watch the time was exactly 11.00pm, I then went back to what I was doing before the fireball...re-balancing the mount after changing the mount plate over, it was during this I heard at least two distant but distinct bangs to the south behind me with a short rumble 3-4 secs duration...the time on my watch was exactly 11.05pm though wasn't counting odd seconds.

As we can often hear artillery from the firing ranges in Northumberland I was uncertain if that's what I was hearing but saying that these sorties are always prolonged around an hour or more...this was the only bang that night, the air was almost still with heavy dew & dead quiet...was thinking to myself could it really be heard around 5mins after the event?

Mike

[Epicyclus Dave]

Hi Mike .

We were up the hill between yarrow and ettrickbridge and saw the green light enter the atmosphere then slowly coast across the sky breaking up as it went , initially we thought it was heading for Carlisle at that point the lead and bigest chunk broke into many pieces and started to follow the curve of the earth heading in Ireland direction & beyond.

I was frozen to the spot with jaw wide open thinking maybe hiding behind the car would save us :D .

I returned back to the telescope doing M31 subs and about 5 mins later heard "boom boom" then a fading rumble, very strange.

Dave.

[astronymonkey]

Hi Acey,

I too heard a boom but only 20 seconds or so after fragmentation. Im on teesside and calculated the distance of only 15km away and 15km above the ground which seems low I know but puts this as somewhere between Darlington and barnard castle , only 25km from Harlepool.

Astronymonkey

[allcart]

with all the info you have relating to speed of sound etc, (mathematic stuff) you must be able to calculate the speed of the fireball. If you saw it at 11pm, then heard the sonic boom 5 mins later, how fast must the fireball have been travelling. Did it look that fast? and is it feasable that the sound could take 5mins to reach you?

[Stu]

It's quite possible. Sound travels at roughly 1200 kmh in air, at sea level I guess. Not sure what happens to it as the atmosphere thins.

5 minutes at this speed is around 100 km if my back of fag packet maths is correct.

I think objects tend to start to burn up at around 80 to 120 km above the earth. Taking into account the horizontal distance between the observer and the object, 5 mins sounds quite reasonable. Think how long you get between lightening and thunder if it is quite a distance away, this would have been significantly further away, and louder.

Stu