How far away can you see a plane?

A friend a few days ago was looking west just at sunset and saw a plane
heading west caught in the setting sun.

This was the west coast of South Wales - I assume the plane was heading
to the US at about 40,000 feet.

The plane remained visible for about 20 minutes until it eventually
faded away.

The planes must have travelled at least 150 miles in that time -
probably more.

Can anyone do the maths to confirm that a plane at that height and
distance is still in line of sight of an observer at ground level?

Thanks.
--
Les Desser
(The Reply-to address IS valid)

"Les Desser" wrote in message
...
A friend a few days ago was looking west just at sunset and saw a plane
heading west caught in the setting sun.

This was the west coast of South Wales - I assume the plane was heading to
the US at about 40,000 feet.

The plane remained visible for about 20 minutes until it eventually faded
away.

The planes must have travelled at least 150 miles in that time - probably
more.

Can anyone do the maths to confirm that a plane at that height and
distance is still in line of sight of an observer at ground level?

Thanks.
--
Les Desser
(The Reply-to address IS valid)

The relevant formula is d= 1.32 sqrt(h) where d is in miles and h is in feet
(taking refraction into account). For h = 36,000 ft, d = 250 miles to the
horizon.

So observing a plane from the ground to a distance of 150 miles seems quite
possible.

There is a good discussion of the derivation of the formula in Roy and
Clarke, Astronomy Principles and Practice.

As a passenger, from cruising altitude in clear air I have seen things 150
miles away, no problem with that.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

In uk.sci.astronomy message , Wed,
31 Dec 2008 19:40:38, Les Desser posted:

Can anyone do the maths to confirm that a plane at that height and
distance is still in line of sight of an observer at ground level?

URL:http://www.merlyn.demon.co.uk//astron-3.htm#Ele : 1.803 deg. high.
Inputs accept expressions such as 40000/5280*1.609 & 150*1.609 .

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

In article , Mike Dworetsky
Wed, 31 Dec 2008 21:54:27 writes

The relevant formula is d= 1.32 sqrt(h) where d is in miles and h is in
feet (taking refraction into account). For h = 36,000 ft, d = 250
miles to the horizon.

So observing a plane from the ground to a distance of 150 miles seems
quite possible.

Thank you - a great help, and to Dr J R Stockton for the link.
--
Les Desser
(The Reply-to address IS valid)

With lights at night, you'd likely see it longer than in the day.

"Les Desser" wrote in message
...
A friend a few days ago was looking west just at sunset and saw a plane
heading west caught in the setting sun.

This was the west coast of South Wales - I assume the plane was heading to
the US at about 40,000 feet.

The plane remained visible for about 20 minutes until it eventually faded
away.

The planes must have travelled at least 150 miles in that time - probably
more.

Can anyone do the maths to confirm that a plane at that height and
distance is still in line of sight of an observer at ground level?

Thanks.
--
Les Desser
(The Reply-to address IS valid)