How far away is that airliner...?

[Stroppalot]

Okay, here's the scene:

It's early morning, the sky is crystal clear. You look up, and cruising along at 37,000' (or whatever), you see a dinky little airliner, blatting it's way across the skies, leaving 4 contrails for miles behind it. You keep watching the 747 or whatever it happens to be.

Ten minutes later, you can still see it in the distance, many many miles away.

What I want to know is : HOW FAR AWAY WOULD IT BE?

(I know there are in infinate number of variables which would affect the answer, like atmospheric quality, light, blah blah blah - I'm just after a rough answer)

[Evanelpus]

SPOTTER ALERT, SPOTTER ALERT

[Stroppalot]

Yeah, yeah... I asked for that.!

[Desk Driver]

I'm guessing after 10 minutes anywhere between 75 - 90 miles. Depending on lots of things?



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You fly em we'll fill em!

[Evanelpus]

Stropp

You took that on the chin like a man, congrats.

[Lawyerboy]

Actually I have to confess, although I don't own an anorak and haven't yet spent a day on top of any airport car parks, that I've often wondered the same thing. Looking up and seeing a chemtrail, just how far might that little speck be?

[Desk Driver]

Well am I right???

Someone tell me!

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You fly em we'll fill em!

[below_the_line_please]

It really depends on your eyesight!

Assuming that the 747 was at cruise speed and altitude, I would hazard a guess at between 70 and 100 miles, as has already been pointed out.

[angels]

Hey! What's wrong with plane spotting??
I wouldn't class myself as an anorak and yet when I lived in Hong Kong some four years ago it used to be great fun to take my (then three year old) up to Kai Tak and stand on the top of the car park watching you guys performing split-arse turns over Kowloon.
I must admit though, after 30 minutes, it would be off to the bar for sustenance.

[Icarus]

Let's make a few assumtions here;
1. The aircraft is cruising West to East and is therefore likely to be at 37000' (B747).
2. The aircraft is directly above your head when you first spot it.
3. A B747 typically cruises at 8nm per minute.
4. We shall assume 'still air'.
5. We shall ignore the curvature of the Earth.

Therefore;
When you first spot the aircraft it is 37000' away from you.
After 10 minutes the Aircraft is 487805'(or 92.3 statute miles)away from you by line of sight.

[Use of Pythagorus' Theorm where -
1 Statute mile = 1nm x 38/33
1 Statute mile = 5280 feet.]

[This message has been edited by Icarus (edited 17 March 2001).]