Question regarding distant lighthouses

[Stefan Leahu]

Being my first post here, a small disclaimer: I'm a convinced glober, and, being a meteorologist, of course I know that flat earth doesn't compute. Living in Vendee, on the French west coast, the coastline is pretty much curved (north to south, I mean ) ) and I get a lot of chances to see the distant coastline.

So, I noticed a distant lighthouse being visible from Les Sables d'Olonne towards the south. Looking up on google maps, it turns out to be the Phare des Baleines on Ile de Re, 30 something km away. Zooming in with a Pentax X-5 , which has about 26x optical zoom and loads more crappy digital zoom, I could see it clipped by the curvature. So, in the photos, there's the lighthouse, a red light from a cell tower nearby, which is clearly verifiable with google maps&street view, and another fainter light to the right. I initially dismissed it as a ship, but it appears in photos made in different days. Looking at google maps, it seems to actually be Phare de Chassiron on Ile d'Oleron, which is 57 km away. Looking with the eye, you can just baaaaarely see it if you know where to look. A very faint, flickering light right on the horizon. Certainly doesn't catch the eye like the closer lighthouse does, but it's visible on 4 second exposures. Using the metabunk calculator, it gives me a hidden amount of 138 m, way more than the 50m of the lighthouse, using a viewer height of 9m , which is the approximate height of the ramparts of the La Chaume monastery/ whatever that is from where I took the photos. I think I'm witnessing loom of the light here, especially given the very faint nature of the light, but I'm still puzzled that it can be seen so far.

Again, as a disclaimer, this is an honest post and not some kind of flat earth bait. In one of the photos, you can also see the clouds lit up by what is probably La Rochelle, which is itself below the horizon, so no question about that. I'm just not sure of what I'm seeing and amazed that one can see that far.

So, the big one is Phare des Baleines, the red light is an antenna mast close to it and the fainter light to the east is supposedly Phare de Chassiron, 57k away. 4 second exposure, edited for contrast etc

The green light, which looked pretty white with the naked eye, I suppose to be something in the La Rochelle area. It came on periodically, but with way longer timeframes than a lighthouse.

Contrast edited photo of Phare des Baleines. The structure to the left doesn't seem to have any lights, so it isn't visible at night. I don't know what it is.

 

[Rory]

Could you take a compass bearing? Confirming to yourself that it's accurate by doing the same for the other two points you reference?

That might be a starting place: to see if you are indeed pointing at Phare de Chassiron.

Nice first post.

 

[Trailblazer]

I wouldn't be at all surprised if light could pass to you close to the surface of the sea from the lighthouse over that distance, "tunnelling" in a thin layer of colder air that bends the light rays.

 

[Trailblazer]

Contrast edited photo of Phare des Baleines. The structure to the left doesn't seem to have any lights, so it isn't visible at night. I don't know what it is.

I was going to suggest that the object on the left was the Ancienne Tour des Baleines (left in photo below), but if the photos are taken from Les Sables d'Olonne then that tower should appear to the right of the lighthouse, so the angles don't add up.

Also the refracted hidden amount should be 28 metres, which would hide virtually all of the old tower (29 metres high).

Edit: is it possible that in your daytime picture, the object on the right is actually the transmitter, and the one on the left is the lighthouse? That seems to fit better.

 

[deirdre]

photos are taken from Les Sables d'Olonne

i cant even figure out where the picture is taken from Google Earth and maps for me only show 2001.. so i'm not seeing the beach features in his pic. do you have camera coordinates?

 

[Rory]

Were they taken from Le Prieuré Saint Nicolas (Saint Nicholas's Priory) at 46.489942, -1.794633?

 

[Trailblazer]

Were they taken from Le Prieuré Saint Nicolas (Saint Nicholas's Priory) at 46.489942, -1.794633?

Yes, see the shape of the sea wall and the rocks:

(brightness enhanced on the night-time picture)


Zoomed out view and location: https://www.google.com/maps/@46.4896622,-1.795375,3a,90y,190.16h,74.05t/data=!3m8!1e1!3m6!1sAF1QipObAz_7twr2EeulOJXoIsqGXcm4ulxgC7pSIN5w!2e10!3e11!6shttps://lh5.googleusercontent.com/p/AF1QipObAz_7twr2EeulOJXoIsqGXcm4ulxgC7pSIN5w=w203-h100-k-no-pi0-ya333.33707-ro-0-fo100!7i9584!8i4792

Camera location is here (the dot on Google Maps is slightly wrongly placed, on the left-hand circular niche in the wall, rather than the right-hand one which is where the camera was)

 

[deirdre]

Were they taken from Le Prieuré Saint Nicolas (Saint Nicholas's Priory) at 46.489942, -1.794633?

thanks. ok my numbers (if i didn't mess up metric to what i can comprehend (miles, feet)...
elevation of lighthouse 9.1 meters

lighthouse is 46 meters

Saint-Dénis d'Oléron Lighthouses
*** Chassiron (2)
1836 (station established 1685). Active; focal plane 50 m (164 ft); white flash every 10 s. 46 m (151 ft) round stone tower with lantern and gallery, rising from the center of a circular 2-story keeper's house. Lighthouse painted....

eye height approx 7.5 meters (from where i placed him ie. guess)
=63.5 meters

curvature calculator says that is:
141 meters hidden average refraction ( 77 meters refraction variable)

77 meters= 252 feet over 35.7 miles.

*i have no idea how big the light/glow circumference itself is.

and here is @Mick West 's refraction tool, although i dont know how to use it so you're on your own to see how extreme the refraction is https://www.metabunk.org/simulating-atmospheric-refraction-and-mirages.t7881/

 

[deirdre]

just realized the lighthouse is on 2 stories, my blurb says.. so add another 5 meters ..so 136 meters, not 141. close enough

 

[Trailblazer]

The light of the nearer lighthouse appears to be almost exactly above the outer angle of the sea wall/breakwater, which agrees with the camera location:

(white line is a Google Maps great circle to the lighthouse)

 

[deirdre]

The light of the nearer lighthouse appears to be almost exactly above the outer angle of the sea wall/breakwater, which lets you pinpoint the camera location more exactly

i had him back a few feet, but same elevation really.

 

[Trailblazer]

This is another photo taken from the same location. If the tide is low then I suspect the elevation might be more than 9 metres, but it's hard to judge. Really need a photo from the beach with a person for scale:

https://www.google.com/maps/@46.489...-no-pi-0-ya122.17243-ro-0-fo100!7i5660!8i2830

Looking along the wall. Note how far down the sea is:

 

[deirdre]

I suspect the elevation might

i used google earth and when i moused over the camera spot it said 24 feet elevation.

 

[Trailblazer]

i used google earth and when i moused over the camera spot it said 24 feet elevation.

Google Maps elevation is pretty low-resolution, so near the coast it is not very accurate. It averages out over quite a wide area - I think it uses Space Shuttle radar measurements for the most part.

II found this pic which has a person stood by the wall. The person is 28 pixels high, and the height from the top of the circular rampart to the base of the rock (hard to measure exactly) is 150 pixels.

Assuming the person is 1.6 metres tall that would make the height about 8.5 metres, and then the sea is probably at least another 2-3 metres below that.

So I think the height of 9 metres above the sea is probably an underestimate.

Also that assumes the camera is placed on top of the wall. If it was on a tripod above the level of the wall that could add another half a metre or so.


Then of course there's the tidal range, which can be over 5 metres between high and low tide, and appears to be regularly 4 metres or so:

https://www.tide-forecast.com/locations/Les-Sables-dOlonne-France/tides/latest

 

[Rory]

So a time and date for the photo to see where the tide was would be useful, I guess?

 

[deirdre]

Then of course there's the tidal range, which can be over 5 metres between high and low tide, and appears to be regularly 4 metres or so:

all of which knocks off about 40 feet from my numbers.. so a bit over 200 feet showing about the average refractive index.

 

[deirdre]

well a bit less than 200 actually as light is an area, unlike a building. and judging by that Balatane thread the cone can get pretty large : )

 

[Rory]

Line of sight for the distant lighthouse:

Looks like it agrees with the image in the OP as far as alignment with the rocks goes.

 

[Rory]

To see the very top of a 50m structure 57.44km away one would have to be 61m about sea level, according to the curvature calculator.

But is seeing the light the same as seeing the structure?

On the wikipedia page for the Phare de Chassiron it reads:

Today the lighthouse lamp operates with a 250 watt metal halide bulb, allowing its eight light beams to be visible up to 52 kilometers away in clear weather.

https://fr.wikipedia.org/wiki/Phare_de_Chassiron

It also says it flashes every 10 seconds.

 

[deirdre]

But is seeing the light the same as seeing the structure?

On the wikipedia page for the Phare de Chassiron it reads:
Today the lighthouse lamp operates with a 250 watt metal halide bulb, allowing its eight light beams to be visible up to 52 kilometers away in clear weather.

https://fr.wikipedia.org/wiki/Phare_de_Chassiron

Content from external source​

that might just be pure wattage (like if youre up high enough to see the lighthouse), there is another tower next to it that probably has a red light too, but we can't see it in the pics maybe because it is too dim.

But i think "yes" as far as a light would be different than a structure, remember the Lake Balatan lasar? it diffused quite a bit.

 

[deirdre]

oops i did save a pic of the red light

 

[Stefan Leahu]

The night photos were taken on 16 december. Photo data shows 18:32 , but I'm not entirely sure if it has been edited for winter daylight saving time. Around an hour&half or two after high tide that day. Yep, the photos were taken from the Prieure St Nicolas. Not exactly on that outward rampart, since it's difficult to set up the tripod there, but a few meters from it anyway. Both the daylight photos and the night ones were taken relatively close to high tide, since my main goal is ship spotting when I go there and the big ones only come in during high tide. I intend to take a few photos from the sea wall as well; but sea conditions didn't allow that so far , as it's often swept by waves . When I took the photos, the tripod was on the outer wall, unextended, since I'm lazy. Probably not more than 4 feet above that plateau.

This is the phare des Baleines and the radio mast, seen from the south. Thinking of it, the low structure does look like the old tower, so perhaps we're dealing with an alignment issue on Google Earth over those distances. Or it's something higher farther away, on Ile de Re or even in the port of La Rochelle


Edit: I don't know how they measure range for the lighthouses, but from most of the seawall/pontoons there, you're looking down on the ships, or at most eye level at high tide. Of course, if it's not the relatively big cargo ships which I guess can see over the city when they come in .

Edit 2: I've always thought the red light in the photos comes from a radio mast close to Phare des Balienes, the closer lighthouse. Unlike the faint light on the right, which is barely visible, the red light is not visible at all to the naked eye. Or at least I can't see it, no matter how much I try. And I've tried not looking directly at it etc.

 

[Rory]

I think given that the line of sight is pointing right at the Phare de Chassiron, and the Phare de Chassiron is a lighthouse with a powerful white light, and the light in your photo is white...

It's the Phare de Chassiron - and maybe the wikipedia entry needs updating to say "its light can be see up to 57km away".

 

[deirdre]

I think given that the line of sight is pointing right at the Phare de Chassiron, and the Phare de Chassiron is a lighthouse with a powerful white light, and the light in your photo is white...

I agree. i looked briefly over the rest of the island and the right edge of the first island, but there doesnt seem to even tall buildings on them.

 

[deirdre]

I've always thought the red light in the photos comes from a radio mast close to Phare des Balienes, the closer lighthouse.

I agree.

Unlike the faint light on the right, which is barely visible, the red light is not visible at all to the naked eye. Or at least I can't see it, no matter how much I try. And I've tried not looking directly at it etc.

the Phare des Balienes red light is not visible to the naked eye either?

 

[Stefan Leahu]

Not by my eyes, at least. The lighthouse is clearly visible hough, flashing periodically. The Phare de Chassiron light, honestly t looked like it was clipped by waves or something. Visible, but intermitently

 

[deirdre]

Visible, but intermitently

Chassiron (2)
1836 (station established 1685). Active; focal plane 50 m (164 ft); white flash every 10 s. 46 m (151 ft) round stone tower with lantern and gallery, rising from the center of a circular 2-story keeper's house. Lighthouse

it's a strobe light. it only flashes every 10 seconds according to this site anyway https://www.ibiblio.org/lighthouse/bsc2.htm

836 (station established 1685). Active; focal plane 50 m (164 ft); white flash every 10 s. 46 m (151 ft) round stone tower with lantern and gallery, rising from the center of a circular 2-story keeper's house.

 

[LMR]

@Stefan Leahu well, there is a way how to know exactly what you see. You need a quadcopter. When it reaches ~100-200 meters, you will see all object because visible horizon will be behind all objects you see.

 

[Stefan Leahu]

Actually, I got one of those FPV drones for Christmas. Especially got one with the screen integrated on the controller; since viewing on a phone means crappy range and quality, usually. It worked precisely once, when I checked the range by leaving the drone on the ground and walking away with the controller. Then it wouldn't pair again. Like ever, regardless of what I tried. But it's not the topic for this

Took a few more photos one day from Puits d'Enfer, a rocky outcrop a few miles south of Sables d'Olonne, on the coastal road. The closer one, Phare des Baleines, is visible even with the naked eye. I can also confirm that the further one is indeed a strobe. You can clearly see the further one, Phare de Chassiron, is mostly below horizon.

These are the structures visible on the closer island. Not visible in thie photo, but you can actually see trees on the coast more to the left, which taper out as you pan to the south. A clear example of curvature.

And to the right is Phare de Chassiron, the further one. You can see how it looks stubby, because only the top is visible.

 

[LMR]

@Stefan Leahu
1) Could you title (name) all these objects and label the distance to them? (just put some text on the photos).
2) What altitude and distance of the observer in these last photos?

 

[deirdre]

1) Could you title (name) all these objects and label the distance to them? (just put some text on the photos).

just quick if your wanting a quick layout...

my bottom photo is reversed, taken from the back of the lighthouses. In his new pic the closer island is all the things to your left. And the black and white lightouse (on the further island) is circled in yellow.
The names are to funky to remember off the top of my head so i'm not labeling them.

 

[Stefan Leahu]

Yep. Pretty much everything except the yellow thing should be on the closer island. I have video of both the strobing lighthouse and the closer Phare des Baleines, so no doubt about that. I'll upload it when I have time. I went today to Les Sables, trying to photograph the moonrise. No luck, since it was cloudy.
But I did take some new photos from basically the same spot at the Prieure St. Nicolas. Turns out, at true high tide, Phare de Chassiron isn't visible. So yeah, it's really at the limit of visibility.

Edit/ In the photos from Puits d'Enfer, the distances are slightly lower. Phare de Chassiron is at about 53 km away, the closer one I assume is also a few km closer. The height of the plateau was around 7m, according to Google Earth, but it varies depending on the tide.

 

[Ray Brown]

What was your exact vantage point at Puits de' Enfer? I don't think Chassiron light structure is visible at that distance. Maybe "loom" of light might be. When direct light is obstructed by waves it's called blinking. It's appearance as it becomes visible over horizon. Also, I'm trying to determine where the greenish light to left in second photo. I thought it might be approach lights for La Rochelle airport but it's too far. Also may be town sky glow or soccer field lights or such.