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Longest Lines of Sight on Earth

beyondhorizons.eu

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Re: Longest Lines of Sight on Earth

#111

Post by dwightgunning »

kbenson wrote: post #32

Mt. McKinley (6.194 m.) What country uses '.' as the thousands separator but speaks English? Or is this someone mixing their native language thousands separator with English? Or is there some weird interaction between country and language that makes this the preferred, or at minimum an acceptable standard form? I'm actually hoping it's one of the latter options, that would be something new to me.

Use of a decimal point for separating thousands is prevalent The Netherlands where English is fairly commonly spoken.

I see it all the time.

Re: Longest Lines of Sight on Earth

#112

Post by newman8r »

URSpider94 wrote: post #61
jdironman wrote: post #53

Earlier quoted context omitted.

Laser powered ISPs anyone? I kid, but is this a possibility?

This exists already, from some pretty serious telecom companies, for distances of a few miles. The problem is that, in optical wavelengths, there's too much absorption and scattering in the atmosphere - fog, rain, storms, smog, smoke - that can disrupt the signal. But, in radio frequencies, this is how the microwave tower communications network works -- it's line-of-sight from tower to tower. https://www.wired.com/20…

Nice article, now I need to plan a hiking trip to see one of the old towers.

wikipedia mentions that the longest microwave link is ~200 miles, but it's 2GHz and from the 1970s. I wonder what the limits for higher frequencies might be.

Re: Longest Lines of Sight on Earth

#113

Post by rmc »

4ad wrote: post #106
rmc wrote: post #88

Earlier quoted context omitted.

FYI OSM doesn't (really) store elevation data. Individual mountain peaks are often mapped, and tagged with the elevation. But OSM doesn't store land contours like that. There are some free, open, datasources for that, like SRTM[1], ASTER[2] (and maybe OpenDEM[3], but I don't know what that's like) [1] https://wiki.openstreetmap.org/wiki/SRTM [2] https://wiki.openstreetmap.org/wiki/ASTER [3] http://www.opendem.info/

So how are these contour lines being generated? My hike of a few months ago: https://www.gaiagps.com/datasummary/route/67dcc2001bea9e9e39... Also, if OSM doesn't store elevation data, then why do you need a GPS tracker with a barometric sensor in order to map for OSM?

> So how are these contour lines being generated?

It depends on the people make the map.

That map uses Thunderforest's Outdoor style[1]. The person running that company is a long time OSM contributor, but that isn't "from the OpenStreetMap project". I suspect they are using SRTM data to generate countour lines in addition to OSM to create the map

> why do you need a GPS tracker with a barometric sensor in order to map for OSM?

You don't? You can map for OSM without needed a GPS tracker. You can just trace things from the aerial imagery, or add local features from memory ("There's a post office at that road junction", "the speed limit of this road is 40 kmph").

[1] https://www.thunderforest.com/maps/outdoors/

Re: Longest Lines of Sight on Earth

#114

Post by oblio »

cheeseprocedure wrote: post #40
kbenson wrote: post #32

Mt. McKinley (6.194 m.) What country uses '.' as the thousands separator but speaks English? Or is this someone mixing their native language thousands separator with English? Or is there some weird interaction between country and language that makes this the preferred, or at minimum an acceptable standard form? I'm actually hoping it's one of the latter options, that would be something new to me.

TIL there's quite a few countries that use the decimal point as a thousands separator: https://en.wikipedia.org/wiki/Decimal_mark#Examples_of_use

Those "quite a few countries" account for about 50% of the world's population, I think :p

Re: Longest Lines of Sight on Earth

#115

Post by oblio »

polymatter wrote: post #38
ianai wrote: post #37

Earlier quoted context omitted.

Pretty sure England does.

Londoner here. Nope, we use a comma as a thousands separator. I believe some European countries use a period though.

https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/De...

TL;DR: All of them, except for... you guessed it ;)

Re: Longest Lines of Sight on Earth

#116

Post by codfrantic »

KozmoNau7 wrote: post #91
yread wrote: post #82

The link in the "done" column doesn't work - it should point to https://beyondhorizons.eu/2016/08/03/pic-de-finestrelles-pic... It's a report how they made an actual photograph of a sunrise over 443km far. Quite amazing! BTW if you ever get the chance to go up Mt. Canigou, go for it. Since it's the first big mountain in Pyrenees from the east you have really spectacular views and it's not that difficult to hike up th…

There's something utterly awe-inspiring about huge distances, especially if you're simply not used to viewing objects at those scales. I live in a country where the highest point above sea level is ~171m. Walking in the Scottish highlands was a transcendental experience for me.

You must be Danish, I though us Dutch had it bad (320 max) I guess we do go below sea level more which also makes this calculation more difficult :)

I do agree on the utter amazement of visiting less flat places :)

Re: Longest Lines of Sight on Earth

#117

Post by jnbiche »

kovek wrote: post #42
btilly wrote: post #25

You can actually work out roughly how far away the horizon should be surprisingly easily. Just use the fact that if R is the radius of the Earth and you are at height h, then from you to the horizon to the center of the Earth back to you is a right angled triangle with one side of length R and the hypotenuse of length R+h. Therefore the distance to the horizon is sqrt(2Rh+h^2) which is roughly sqrt(2Rh). The Earth is…

I had this question worded differently asked to me when I interviewed to do an undergrad at Cambridge. If you have a rope that is wrapped around earth and you lift it off the ground as much as possible, and you see that it is 10km above the ground, then how long is the rope? I was not able to answer that question right away, and their hint to draw it helped a lot. I did not end up getting accepted.

To be clear, they gave you the radius of the earth here, if you didn't already know it by heart? Otherwise, I'm not getting how you could solve this problem (assuming they didn't give you the angle that the arch formed, for example).

Re: Longest Lines of Sight on Earth

#118

Post by erispoe »

pm215 wrote: post #95
BurningFrog wrote: post #70

Earlier quoted context omitted.

Sure, but it also filters for people like me, who have seen this problem at least a dozen times.

When I did my university entrance interview (for maths, at Cambridge) the interviewers were clear that they expected that some subset of candidates would have seen the problem before, and some wouldn't -- for those in the first set they'd get them to quickly go through the problem and move onto the later parts which would be new to them; for those in the second set they'd provide sufficient guidance to let the candid…

But how do you know it's a new problem? You can always fake a little struggle and thinking your way to the solution for a problem that you know the answer already.

Re: Longest Lines of Sight on Earth

#119

Post by nerdponx »

btilly wrote: post #25

You can actually work out roughly how far away the horizon should be surprisingly easily. Just use the fact that if R is the radius of the Earth and you are at height h, then from you to the horizon to the center of the Earth back to you is a right angled triangle with one side of length R and the hypotenuse of length R+h. Therefore the distance to the horizon is sqrt(2Rh+h^2) which is roughly sqrt(2Rh). The Earth is…

How can I use this calculation to convince my flat-earther cousin that he is wrong?
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