1. Mick West

    Mick West Administrator Staff Member

    I just took this photo of a contrail in the distance out of my window.

    While this is admittedly a terrible photo, what is remarkable about it is that when I looked in FlightRadar24.com, the only plane that matched was an A380 that was 115 miles away.


    The distance also matches the plane being about 1 or 2 degrees above the horizon, and me being at about 1,100 feet.

    That's probably about as far as I'm going to see from here. But I was wondering if anyone has that beat? What the farthest contrail you've seen, and been able to identify the plane?
    Last edited: Jun 23, 2016
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  2. Mick West

    Mick West Administrator Staff Member

    Likely the farthest will be those that are actually descending to or rising from the horizon. You can identify them when they get close. Like the Mystery Missile. The back of this was over 200 miles away:

    However, you can't really tell exactly where the first visible portion is. So I'm more interested in planes like in the OP, traveling perpendicular to the line of sight.
  3. MikeC

    MikeC Closed Account

    IIRC Skystef has a couple at 200 miles.......nope- not quite - his "Special contrails" page has one at 260km [161 miles] and 1 at 230, and a few at 130-180
    Last edited by a moderator: Jan 25, 2015
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  4. Trailblazer

    Trailblazer Moderator Staff Member

    I tried following a plane on FR24 and taking photos until I could no longer see it. The problem I have is that surrounding houses block the horizon - not a problem Mick has apparently! The planes usually disappear behind a rooftop when still clearly visible. The furthest I've managed to get a photo was about 95 miles.

    As for mountain lines of sight, I remember being able to see Kilimanjaro (19,341ft) from the upper slopes of Mount Kenya (about 16,000ft), a distance of about 200 miles. There's not much in between but flat plains.
    Last edited: Jan 25, 2015
  5. Mick West

    Mick West Administrator Staff Member

    I'm on a 1150 foot ridge, opposite a 1250 ft ridge a mile or two the west, so that ridge limits my view of the ultra far planes. This plane was actually going behind trees on the ridge.

    An ideal position would be high up on a mountain with very little surrounding it - or just with a clear sight line to sea level.
  6. scombrid

    scombrid Senior Member

    Aside from line of sight, atmospheric transparency plays a role in determining the distance from which a trail is visible. Back home in Virginia, like most of the eastern CONUS, haze when under summer high pressure obscures anything less than 10-15 degrees off the horizon and more than 10 or so miles distant. Sometimes you can hear thunder and not even be able to see the thunderhead that is only a few miles away despite the lack of overcast at you location.

    Meanwhile, under clear winter skies or under moist but super clear tropical air masses down here in fl I can see trails created by MIA-HOU/DFW from eastern Brevard Co. The effect is impressive at sunset. Those trails are out over the GoMex offshore of Tampa. When I'm out on the St. Johns marsh the line of sight to the horizon is fairly unobstructed. I think the distance to the trails that are right on the horizon is about 200 miles. Depends on altitude. Basically sight distance is unlimited up to the point when then curve of the earth hides the trail.
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  7. scombrid

    scombrid Senior Member

    Something that I noticed early as a child that spent a lot of time fishing from a canoe was that there were less contrails in summer and that seeing impending weather was harder in the summer. In winter you could watch the southwest sky for the first harbinger of changing weather often days before a frontal passage. In summer you were often limited to the sky immediately over head and the weather could catch you out in your slow boat.
  8. WeedWhacker

    WeedWhacker Senior Member

    "Longest Distance a Contrail is Visible"?

    IF you are a Human on the surface of the planet? Well....this planet is globe of a well-known and measurable diameter.

    Depends, then on POV ("Point-Of-View").

    "IF" (for instance) you were in the cockpit of a jet at say....35,000 feet and following another jet ahead, at 33,000 feet (you would BOTH be going eastbound, BTW!)...you might see a contrail (if it's daytime) for MANY miles.

    Subsequently, IF there was some way to photograph FROM SPACE instantly (a time-travelling Star Trek Enterprise shows up, just for this specific task) then it would be yet another perspective....another "P.O.V." (wink) ;)
  9. Arbitrary

    Arbitrary New Member

    I don't have an exact idea of how far they are visible, but I remember once working out how far a contrail was from my viewpoint as a maths exercise of trigonometry at school. We worked it out to be something like 70 miles or so away though obviously, this would only be a very rough estimate given we had to completely guess the speed.

    That being said, as for mountain to mountain viewing, IIRC the 1,300m Ben Nevis - Ben Macdui are supposedly visible from each other (if you are luckier than me when it comes to the weather). This is a distance of something like 50 miles, the trouble is all the hills between makes it really hard. Certainly I've seen Nevis from other hills with distances of 30 or so miles.
  10. Trailspotter

    Trailspotter Senior Member

    I did a similar exercise a year or so ago, watching sunrise contrails in a clear sky from the top window of my house and checking them on FR24. I recall the closest to the horizon trails were some 125 miles away, over the French coast of the English Channel near Calais, but I have not kept a handy record of these observations. However, I have found recent photos that I took on December 15, 2014 at about 11:15 AM GMT.
    There is a "kinked" contrail shown by arrow that I identified at the time. It came from TAP762M flight that made a course correction near Portsmouth about 110 miles away from my location:
    TAP762M track.
    The visible part of the trail below the kink is even farther than that but probably closer than Cherbourg on the French coast.
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  11. WeedWhacker

    WeedWhacker Senior Member

    I don't know if you've seen this....KNOW that (I'm sure you do already) there is a GREAT deal of airliner traffic within the European Union, of course.

    But also.....Trans-Atlantic travels.....

    So here is just ONE example to use as a reference: (You might wish to ask any airline pilot friends for other examples...):


    Take some time to view this image.....will "take" some time for a non-pilot to absorb it all. There is a LOT to explain, and learn.

    (ETA.....when you see the term "Shanwick" this is because at one time, years ago.....there were TWO Air Traffic Control authorities in a particular bit of Oceanic airspace...."Shannon" and "Prestwick". These two ATC authorities merged, and were thence known as "ShanWick"...the radio-telephone designation, when communicated BY radio).

    BTW...contrary to what "Hollywood" portrays.....radio communication isn't how it seems, at least not in aviation.

    NO-ONE "ever" says "This is....(blah blah) calling....XYZ"

    You address the RECEIVER, by name, and THEN identify your flight number, or registration number, etc.

    Example...."Los Angeles Approach, United 347, 3 thousand" LA ATC may then say "Intercept the ILS to Runway 25 left, you're cleared for the ILS to 25 left, contact Tower".

    This is how ACTUAL radio-communication is done.
    Last edited: Jan 25, 2015
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  12. Trailspotter

    Trailspotter Senior Member

    You were lucky to have a fairly clear air in between the two mountains at the time. In 2006, in dry season we were unable to see Kilimanjaro from Tsavo West NP some 50 miles away (but saw it later from Amboseli).

    Our trip to Nepal the following year was even more embarrassing in this aspect. We were less than 30 miles away from the Himalaya highest peaks but could not see them because of the dust in the air. Luckily, in the last night of our stay, there was a light rain that cleared the air a bit.
  13. Trailblazer

    Trailblazer Moderator Staff Member

    For a scientific answer to this question, let's assume an observer at sea level and a contrail at 40,000 feet (towards the upper bounds of most commercial traffic).

    This is effectively the same as calculating the distance to the (sea level) horizon for an observer standing on a 40,000ft mountain.

    The distance d to the horizon for a person standing at height H above sea level is given by:

    d = R x arccos [R/(R+H)]

    where R is the radius of the Earth (which is 6,371km, or about 20,925,500 feet)



    d = 20,925,500 x arccos (20,925,500/20,965,500)

    = 20,925,500 x arccos 0.9980921

    = 1,292,819ft

    or about 245 miles.

    This ignores atmospheric refraction, which bends light to follow the earth's curvature slightly, and so extends the range to the horizon. A good rule of thumb to account for this is to multiply R by 1.2, to 25,110,600ft.

    If you do this then you end up with a distance to the horizon of 1416399 feet, or about 268 miles.

    So theoretically you could see a contrail from over 250 miles away, but atmospheric haze at the horizon (and the very small size of the trail at this distance) would make that impossible in the real world.
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  14. Trailblazer

    Trailblazer Moderator Staff Member

    Yes, it was early in the morning and there was an inversion, with cloud cover on the plains and clear air above. I don't have any photos to prove it unfortunately, as I only had a wide-angle lens and it didn't show up.

    Here's a pic from another trip, though, showing the layers of distance haze quite nicely. Mount Taranaki from Mount Ngauruhoe, in New Zealand: straight-line distance 85 miles, and plenty of detail visible.

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  15. Mick West

    Mick West Administrator Staff Member

    Just got the exactly same thing again today.

    Again this is just above the ridge line. I think this contrail easily has to be visible from somewhere in the Sierras, 50-100 miles behind me.
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  16. Trailspotter

    Trailspotter Senior Member

    Well, the illumination probably is a key factor here. Contrails near horizon have the highest contrast at sunrise and sunset, when they are illuminated by the Sun being just below horizon. Can you see a contrail in this location in a different time of the day?
  17. Trailblazer

    Trailblazer Moderator Staff Member

    Same flight number. If this is a daily flight at the same time of day, get yourself out there on a hiking trip before sunset gets too much later!
  18. Mick West

    Mick West Administrator Staff Member

    I've seen them pretty close to the horizon, but not that close. That view is just out my office window at home, so I'll keep looking (right now it's a bit cloudy). But yes, illumination is key to visibility at long distance, hence the post-sunset photos.
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  19. Jay Reynolds

    Jay Reynolds Senior Member

  20. Mick West

    Mick West Administrator Staff Member

    And that's not accounting for atmospheric distortion, which probably adds another 50 miles. Although of course the atmosphere also blocks light, so it would have to be pretty special conditions and a big contrail.
  21. Trailspotter

    Trailspotter Senior Member

    To address the title question I tried available data. Having searched Flickr for the sunset and sunrise photos taken in the past week in costal areas, I selected results picturing probable contrails close to the horizon. I narrowed my selection down by checking the availability of original EXIF and information on the photo locations. These locations then were looked at FR24 for the possible flight identification. My best result so far came from this photo taken at Fort Walton Beach, Fl on 25-Jan-2015 at 12:09 UTC (06:09 CST):

    It is a zoomed image (Focal Length in 35mm format is 145 mm that gives horizontal FOV being about 14° and the contrail elevation above the horizon being 1.0°). In the photo album, there is a wide angle (63°) photo with the same contrail taken a few minutes later:

    The candidate flight for this contrail, FFT711, has been identified with FR24 and verified by displaying the flight track from FlightAware on Google Earth:
    Ft Walton Beach FFT711 trail.
    At the time of the photo the plane was about 185 miles away from the camera location:
    185 miles.

    The KMZ file including FFT711 flight track is attached.

    Attached Files:

    Last edited: Jan 29, 2015
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  22. cloudspotter

    cloudspotter Senior Member

    At what altitude?
  23. Trailspotter

    Trailspotter Senior Member

    34,500 ft according to FlightAware tracklog, at the end of climb to 36,000 ft.

    There is a couple of wide angle pics in the album taken more than a minute before the zoomed image. In the original size images, there is a tiny brighter spot in the area where the plane was supposed to be at the time.
    If the guy had taken pictures with a better camera or zoomed his iPhone 5s in that area a bit earlier, it could have pushed up the distance record by another ten miles:rolleyes:
    Last edited: Jan 30, 2015
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  24. Trailblazer

    Trailblazer Moderator Staff Member

    This is why I love this site!
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  25. scombrid

    scombrid Senior Member

    Wow. Thanks for quantifying what I attempted to convey with anecdote further up thread.

    That short contrail way in the distance low to the horizon is comparable to what we often see in the western sky from the east coast of Florida just after sunset when the conditions are right.
  26. WeedWhacker

    WeedWhacker Senior Member

    Title of thread is "What's the Farthest Distance a Contrail is Visible at?".

    To be clear, this discusses viewing a contrail that has been made in the atmosphere (which may occur at various heights above the Earth's surface) as viewed presumably by a person ON the surface.

    For a pilot? Well....once aloft, the ability to observe (in daylight conditions) increase, depending of course on contrail formation altitude, and the altitude of the observer. (THIS is why pilots generally understand the lack of 'fact' of so-called "chem"trails. We have --perhaps-- a 'unique' perspective, comparatively).

    BUT? This thread is likely attempting to quantify what can be viewed by those ON THE GROUND...(keeping in mind, please, that various parts of this planet's "ground" have variations above "Mean Sea Level" (AKA...a mean 'average' "Zero" to define for all of aviation).

    Estimating contrail heights, from one's location ON the Earth's surface?....already WELL covered at contrailscience.com/

    For example: http://contrailscience.com/?s=estimate+height&searchsubmit=
    Last edited: Jan 30, 2015
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  27. Trailblazer

    Trailblazer Moderator Staff Member

    It's just gone sunset here and a few minutes ago I managed to get a photo of a plane about 125 miles away. It's British Airways flight 95 which was heading away from me towards Canada, so I had a great view of the sunlit contrail all the way.


    At the time I took this photo, the plane had gone a few miles past Brecon (visible right on the flight path in Wales in the screenshot below), which is 118 miles from me as the crow flies.


    I probably could have tracked it another few miles before it disappeared, but the oven timer went off :)
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  28. Mick West

    Mick West Administrator Staff Member

    What! Have you no sense of priorities! :)

    It does look like it would have been visible quite a bit longer. It's rather boring watching contrails so far off though, as they hardly move. But you could have set a new world record.

    Your location reminds me of the photos I used here:

    It's hard to convey to people just how far away contrails usually are. at least 80% of the planes you might see leaving a contrails will not get closer than 10 miles to you.
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  29. Trailblazer

    Trailblazer Moderator Staff Member

    My daughter wouldn't have been too impressed. "I know your dinner is burnt but daddy is taking photos of planes again..."

    And actually I came back upstairs two or three minutes later and it was no longer visible. I think it had passed into shadow - my photo was taken 14 minutes after local sunset at the plane's location.

    I'll see if I can beat it with a plane a little earlier relative to sunset some time...
    Last edited: Feb 6, 2015
  30. Trailspotter

    Trailspotter Senior Member

    I also have watched and photographed contrails today for 15 minutes after the sunset. Unlike @Trailblazer, I have had no distractions at the time. The 65x zoom was of great help in picking up the lowest trails. My line of view to the horizon is obstructed by the Cambridge city centre, but its landmarks have provided accurate headings for the flights identification.

    The farthest (almost 190 miles) was the lowest of the three trails in the same line of view:
    All three planes were over Wales at the time (17:03 UTC)

    The runner up (178 miles) was over the English Channel near Exeter (17:15 UTC):

    The third place (155 miles) was also above Wales (17:11 UTC):

    I've made more pictures of these and other trails to document the directions of each flight.

    PS As the EZY7181 flight track has become available from FlightAware, a more accurate measurement on Google Earth has given the runner-up distance of 185 miles. The leader's flight track is yet unavailable, as the BA115 flight is still in progress.

    PPS As the BA115 flight track become available, the distance to the plane at the time of the photo (17:03 UTC) is confirmed as 189 miles. However, I've taken a few more pictures of its trail, with the last one after 17:04 pushing the distance up to 204 miles.
    Last edited: Feb 6, 2015
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  31. Trailspotter

    Trailspotter Senior Member

    I'm putting the photo of the BA115 trail (in the bottom left corner) that is visible at the distance beyond symbolic 200 miles in a separate post.
    The long trail in the middle probably belongs to CKS977 and a short one above to FR842 (RYR26MN).
    Screen shot 2015-02-07 at 00.24.39.
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  32. WeedWhacker

    WeedWhacker Senior Member

    We are seeing (now) with FlightAware and other "real-time" sources of actual flight tracking technologies (THESE airplanes "mostly" nowadays use GPS as part of their navigation protocols...)...

    It's getting easier and easier to identify flights...and THEIR contrails.

    When it comes to the subject of this thread? When on the ground, the ability to "view" what is in the sky above will vary considerably. There are MANY threads here (and many resources on Google, too, that discuss this). A solid foundation in science education is a "starting point"....but, only a 'beginning'.
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  33. Trailblazer

    Trailblazer Moderator Staff Member

    Yes, as both I and @Trailspotter noticed, yesterday was a very good day for long-distance trail watching here in the UK. A nice cold clear arctic airmass gave really good visibility.
    I don't think I'll be rivalling 200 miles though, as there's a house and trees immediately to my west blocking the view.
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  34. Efftup

    Efftup Senior Member

    i thought i would upload some photos I took here today.
    sadly I only have a £100 Compact camera with a 5 x optical zoom.
    These are probably no more than about 50 miles away or so. I was having a lot of trouble reconciling wirth what the FR24 app on my phone was telling me with the FR24 website. Also I had to double check the map and discovered my road is not as North to South as I though it was. so the first photo where the house is parallel to me must therefore be approx WSW from my position.
    Having then identified a load more planes I didn't photograph based on the FR24 data cos there was so many in relative positions it was fairly easy to work out, I could definitely see which plane was over Cardiff (43 miles) and the furthest away was over LLandovery (89miles).

    Based on a further plane which was over Cerne Abbas (56 miles) at the time, I would suggest that the more South West to South planes would have been a similar distance. If someone trustworthy like Trailblazer wants to PM me, I will be more willing to give better details as to my location.
    all my Mile distances are based from this website: http://www.distancesfrom.com/ and I just typed in Bristol so they aren't really THAT accurate.
  35. WeedWhacker

    WeedWhacker Senior Member

    Only limited by the power of your optics...and of course, the curvature of the Earth's surface....IF your viewing location is ON the surface of this globe.

    Seen from various other heights? Well......
  36. Trailblazer

    Trailblazer Moderator Staff Member

    Not up there with some of the distances above, but this shot even shows the separation of the trails, and is taken from between 105 and 110 miles away: a Lufthansa MD11 north of Cardiff, taken from Hampshire.

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  37. Trailblazer

    Trailblazer Moderator Staff Member

    I forgot to add this screenshot showing the distance of the above photo. Taken at 19:06 UTC on April 18.

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  38. steve holmes

    steve holmes Member

    I doubt that was the plane. If you could see that trail (how wide was it likely?) what other things the same width ought you see that far away? (It'd take a telescope to see anything that far away besides the coast range mountains)
    More likely to me, it proves that there's trails out there that you can't identify.
  39. Mick West

    Mick West Administrator Staff Member

    No it's identified correctly. It was in the correct spot, moving at the correct speed, and it was at 39,000 feet, well above the mountains. It was more visible because of the setting sun. I'm at about 1,000 feet altitude here.

    And I essentially DID have a telescope. A long lens (800mm equivalent) and then cropping in photoshop.

    I've seen them consistently from here (my office window faces West). A few hours ago (at 2PM) I saw KAL18, although I was not able to get a good photo due to distractions. It's an A380, so leaves about the thickest trail out there.

    In this case it was closer