Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Longest Lines of Sight on Earth

beyondhorizons.eu

Post reply on HN
Print view View original

121–130 of 164 posts

Re: Longest Lines of Sight on Earth

#121

Post by jrimbault »

nerdponx wrote: post #119
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?

Put him on a plane, window seat.

Re: Longest Lines of Sight on Earth

#122

Post by Scarblac »

utoku wrote: post #81

Reminds me of a habit I have which made me end up on tops of mountains occasionally. I guess the algorithm can be called "observable ascent": 1. Look around 2. Find a relatively close high spot that is visible 3. Plan and climb on top of it 4. From the peak, find the next highest spot visible 5. Repeat Also works for other topologies.

This fails in countries that are simply too flat (the Netherlands).

Re: Longest Lines of Sight on Earth

#124

Post by madcaptenor »

YZF wrote: post #57
kovek wrote: post #42

Earlier quoted context omitted.

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.

The version I got, in a tech company interview, was how much longer would you need to make the rope to allow a cat to go under it. They were basically just look for 2 x Pi x Cat in this case.

The "multiply by 2pi" version of this problem is the one where you have to lift the rope by a cat's height all around the entire earth. So if you have an army of southern-hemisphere cats and they need to get to the northern hemisphere, but you have cunningly put a rope around the equator because you don't want dogs to invade, how much extra rope do you need to lift it to just let in the cats but not the dogs?

(I'm assuming all cats are shorter than all dogs.)

Re: Longest Lines of Sight on Earth

#125

Post by chrisseaton »

seanmcdirmid wrote: post #73
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.

Ya, these also can totally be gamed with the right amount of prep.

So why doesn't everyone pass the interview?

Either they can't be gamed, or they select for people who can at least be bothered to do the work to game them.

Re: Longest Lines of Sight on Earth

#127

Post by pimlottc »

dwightgunning wrote: post #110
burkaman wrote: post #34

Earlier quoted context omitted.

.eu suggests this website was not created by native English speakers.

Since when does the TLD imply the native language of the website creator? Also the .eu TLD, which is a country-TLD for the European Union, consider that the UK (still in the EU), along with Ireland and Malta have English as an official language [1]. 1. http://www.nationsonline.org/oneworld/european_languages.htm

I think it's quite reasonable; the tld suggests the location/nationality, which suggests the language. It's not ironclad, but it's implied.

Those three english-speaking countries (UK, Ireland and Malta) make up roughly 13.7% of the total population of the EU; when the UK leaves, it will drop down to around 1.1%.

Re: Longest Lines of Sight on Earth

#128

Post by elcapitan »

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.

Wasn't it renamed to Denali anyway? ;)

Re: Longest Lines of Sight on Earth

#129

Post by Aardwolf »

a12jun wrote: post #17
Doradus wrote: post #15

Earlier quoted context omitted.

Depends on the elevation of the horizon.

How so? You mean due to sea level?

You would want at least a mountain on (or "behind" instead of "on", with its tip sticking out) the horizon as well. You could see a distant 6km high mountain from another 6km high mountain much farther, than flat horizon from an 8km high mountain (mt Everest)

Re: Longest Lines of Sight on Earth

#130

Post by mannykannot »

davidmanescu wrote: post #93
liuhenry wrote: post #85

Earlier quoted context omitted.

The answer to the first interpretation is considerably less than twice the height of the cat, and I think it's an interesting result as well: Assuming a 0.3 meter high cat, you only need ~0.12mm of extra rope (about the width of two sheets of paper) to be able to pull it up at a point and let the cat through.

Follow-up question - after extending the rope by 0.12mm and pulling it up to allow the cat to pass under it, how far away are each of the two points where the rope lifts off the ground?

That would be the same as the 'how far away is the horizon' calculation at the top of this thread, right? (assuming weightless rope.)
Post reply on HN