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Is it possible to see Morocco from the very south of Portugal, say, Faro or Lagos?

If so, which would one see more easily, Tangier or Rabat?

Both Tangier and Rabat are nearly at sea-level. The distance from Faro to Tangier is approximately 230 Km. The distance from Faro to Rabat is approximately 350 Km.

This question is based on a bet that I made with a friend. We're quite unsure about the real answer.

  • 3
    You can definitely see from Spain to Morocco. – Robert Columbia Mar 24 '18 at 11:18
  • 14
    @RobertColumbia I can also see the other bank of a river from where I am now, but what on earth does that have to do with the question? – Tor-Einar Jarnbjo Mar 24 '18 at 11:32
  • 4
    @Tor-EinarJarnbjo It seems a fair comment. Portugal and Spain are both on the Iberian peninsula. – Jim MacKenzie Mar 24 '18 at 14:22
  • 2
    I am Portuguese, live in Portugal, many times spend my holidays in Algarve and have never heard anyone even mention that possibility. I have never seen Morocco from Faro or Lagos. – Rui Barradas Mar 24 '18 at 15:35
  • 12
    There is a LOT of Spain between Portugal and Morocco. – WGroleau Mar 24 '18 at 19:42
42

What you need in order to see from country A to country B is not just the distance between them but elevation. The higher, the better. If the two countries are separated by water, then assuming ideally clear weather, what matters is whether the line of sight between the point you're standing at and the point you're trying to see dips below the surface of the ocean between them. Therefore the distance between those two points must be no larger than the sum of their horizon distances, which are a function of their elevation.

So look for mountains, not beaches.

The place in Morocco whose horizon distance reaches farthest in the direction of Portugal might be Jebel Kelti (1912 m) about halfway between Tetouan and Chefchaouen, with a horizon distance (corrected for atmospheric refraction) of 169 kilometers. I've sampled a number of hills closer to Tangier, but they are all lower and their lines of sight don't reach as far into the Atlantic.

The highest point in Algarve is Fóia at 902 m, with a horizon distance of 116 km. I'm not sure if there are any almost-as-high peaks further east in Algarve, but ultimately that doesn't matter because the distance from Jebel Kelti to anywhere in Portugal is 277 km, and the sum of the horizon distances is 285 km. There certainly isn't anywhere as high as 902 m within the few dozen square kilometers of Portuguese coastal marsh that fall inside the 285-km circle.

Thus even assuming perfectly clear air and a telescope, you can't see any part of Morocco from anywhere in Portugal. (Except possibly in the case of very unusual meteorological conditions over the Gulf of Cádiz, which might in theory enable a looming image of Kelti to appear above the horizon).

  • 1
    Thank you for your answer! It really answered to my question. But under that, I have got a sub-question, very related: How far can you see in a perfect weather and with a telescope? I'm not interested in 1 kilometer precise, but what distance we are talking about, is it 10, 50, 100, 200, 500 km? I know it depends on the elevation, but if the conditions are the best? – Jakey Mar 24 '18 at 14:42
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    Does this answer take the significant atmospheric refraction into consideration? Or do you by "ideally clear weather" mean that the entire atmosphere has been removed? – Jeppe Stig Nielsen Mar 24 '18 at 14:54
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    @JeppeStigNielsen: "Ideally clear weather" indeed assumes that the atomosphere is optically homogeneous. I couldn't on short notice find a calculator that takes refraction into account (which would depend on meteorological conditions). – Henning Makholm Mar 24 '18 at 15:00
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    @Jakey: If you're standing on the beach with water lapping on your toes, you can see about 5 km of ocean surface. From the summit of Aconcagua in the Andes (6961 m) the horizon is 300 km away. I found these numbers by googling for "horizon distance calculator", which led me to ringbell.co.uk/info/hdist.htm – Henning Makholm Mar 24 '18 at 15:04
  • Wikipedia Horizon § Effect of atmospheric refraction has a simple formula that tries to take refraction into account . Of course it depends on whether we ask for "usual" meteorological conditions or extremely favorable ones. Wikipedia also has an article Looming and similar refraction phenomena, so I guess "looming" is a term used for the extremely favorable conditions. – Jeppe Stig Nielsen Mar 24 '18 at 15:24
8

Here's a loophole to win the bet (and possibly lose a friend): If you're flying from Porto to Faro, you're in Portugal and you can see Morocco before landing in Faro. Rabat might be outside your visibility range, though.

If you stay on the ground, see @HenningMakholm's answer.

  • Was thinking exactly the same, but from the other side of view: If you're flying from Festo Porto, while you're above somewhere between Fes and Tangier, you're supposed to see the Faro or sorrounding :) – Jakey Mar 25 '18 at 13:53
0

You can calculate this yourself for any distance. There is a mental calculation formula we use in the French navy to calculate the distance of the horizon.

It’s an approximate solution, but it works fine.

D = 2.1 * (√h + √H)

  • D = distance in Nautical Miles

  • h = height of your eyes in meters

  • H = height of the object you try to see in meters (e.g. mast of a ship, lighthouse, hill)

It takes into account the refraction of the atmosphere, without it you should use 1.93 instead of 2.1.

  • 2
    An actual calculation example for Morocco/Portugal would be nice (someone already gave you a downvote, probably because you were not answering the question itself). – Jan Doggen Mar 28 '18 at 7:55

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