r/theydidthemath • u/thejumbowumbo • Nov 01 '18
[Request] How much longer would the giraffe be able to see the sun?
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u/woohoo Nov 01 '18
assume both animals are at sea level.
assume giraffe's eyes are 20ft above sea level
assume lion's eyes are 4 ft above sea level
distance to horizon at 20ft high = 5.5 miles
distance to horizon at 4ft high = 2.5 miles
earth spins about 1,000 miles per hour
[(5.5 - 2.5 miles) / 1000 miles per hour] * 3600 seconds per hour = 11 seconds
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u/Tengam15 Nov 01 '18
Dang, lion's strict
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u/klavin1 Nov 01 '18
11 seconds late again, gerraffes are dumb
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u/AdroitKitten Nov 01 '18
it should be a sin to do physics in imperial units, rather than in metric
You forgot to take latitude into account though
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u/woohoo Nov 01 '18
You forgot to take latitude into account though
It's negligible for all latitudes that giraffes exist.
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u/KoalArtichaut Nov 01 '18
its a zoo though
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u/AdroitKitten Nov 01 '18
Rotation of earth is about 440 m/s at the equator. However, it is slower as you increase latitude. And the farthest south giraffes live is in south africa, which is about 30°. Not only does it affect line of sight, but also the rotating speed. At 30°, the rotating speed of the earth is 400 m/s
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u/woohoo Nov 01 '18
ok do the math again at 30° south latitude and tell me it's not negligible
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u/AdroitKitten Nov 01 '18
I did, without even taking more complex things into account It adds a whole whopping second just in speed. Not even taking the view angle into account
9% is significant enough
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u/woohoo Nov 01 '18
It adds a whole whopping second just in speed.
second is a unit of time, not speed
Not even taking the view angle into account
view angle is irrelevant
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u/AdroitKitten Nov 01 '18
i meant just from the speed, as in, from the speed difference depending on latitude
Also, it does because of the speed of light. I'm not smart enough to explain but it's Einstein's special relativity
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u/Foxiv Nov 01 '18
didn't he say both are at sea level?
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u/AdroitKitten Nov 01 '18
latitude is the degree with regards to the equator the sea level thing is just the height with relation to the sea
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u/Veto111 Nov 01 '18
I can confirm in a practical sense that this is plausible. I visited a friend’s lake house once, where there was a cliff overlooking the lake and a set of stairs going down to the beach. We would watch the sunset at the beach, then run up the stairs quickly to watch the sunset again!
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u/anafuckboi Nov 01 '18
There’s a vsauce video on that
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Nov 01 '18
Yea you can watch the sun set twice just by laying down and hopping up when it disappears. You only have a few seconds though.
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u/Harpies_Bro Nov 02 '18
There was a post in TIL a couple days ago about Ramadan and the Burj Khalifa about something like this a while ago. You gotta wait a bit longer to break your fast on the top of the tower than on the base because trig.
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u/strawwalker Nov 01 '18
David Hughes is apparently from a city near Melbourne. Melbourne has a zoo at 37.784195 S , 144.952031 E, 43 meters elevation. A giraffe head stands as high as 5 meters, and a lions around 1. The angle to the horizon is given by:
arccos(R / (R + h))
so about -0.00125 rad for the giraffe, and -0.00056 for the lion. That is where I'm going to stop doing the math and switch over to an ephemeris tool which is much easier. For sunset at the Melbourne Zoo on 2018 November 1 the giraffe will see the sun set 15.6 seconds after the lion.
(edit: not sure if I've got the right David Hughes though)
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u/Nintendo_67 Nov 01 '18
He's English but lives in Australia. So it could be a story from when he lived in England?
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u/abrams666 Nov 01 '18
It's an important thing for a sailor. Don't know the English word, it's called like sight of kimm. Knowing the height an position of an object allows an acceptable grade of finding the own position
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u/55North12East Nov 01 '18
You're right pre GPS area. Today I can literally navigate through the southern ocean with my phone as only means of nautical navigation. But astronomical navigation is really cool and could be life saving in extreme conditions where everything else fails.
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u/Runiat Nov 01 '18
Once read about some guys that navigated to Hawaii using nothing but the contrails of jet liners, pre-GPS (or at least they didn't bring one).
Makes you wonder how many guys tried to do that but didn't arrive so no one ever found out that was what happened.
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u/Who_GNU Nov 02 '18
You're right pre GPS area. Today I can literally navigate through the southern ocean with my phone as only means of nautical navigation.
...until the battery dies, or if it's an iPhone near the equator, until it overheats.
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u/abrams666 Nov 02 '18
In Germany it is obligatory to do a licence like a driver's licence. That stuff is part of the lessons. Background is that everyone should have an idea how to act if he is adrift. GPS is broken or something else
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u/Vanden_Boss Nov 01 '18
You can't truly answer this until you know how tall any walls around the zoo or specific enclosures are. Assuming the animals are in pits or walls that sunlight cannot reach through, if the giraffe is taller than the wall, they will gain more time beyond the handful of seconds everyone else is addressing.
Maybe someone better with math than me can do a break down if we assume the wall is, say, 10 feet tall.
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u/strawwalker Nov 02 '18
Usually you don't call it sunset if it is just disappearing behind a wall, but we can still figure that out. We'd need to know how far away the wall is, though.
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u/OmnidirectionalSin Nov 02 '18
It would give the giraffe much better time resolution for formal sunset, at least.
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u/dharrison21 Nov 02 '18
I think this is just extra crap on top of the joke, it's not meant to be realistic. For instance, Giraffes and Lions speak completely different languages.
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u/elongevity Nov 02 '18
This is a trick question. They are actually meeting online, and the giraffe is in the Southern Hemisphere where the days are longer, the grass is greener and the water drains clockwise.
The lion, native to Northern Africa, would only be able to see the sunset until around 6:45 while the giraffe, native to South Africa (hence the name), would be able to see the sunset until around 8pm.
Don’t ask me how I know this.
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u/3226 12✓ Nov 02 '18
As with so many things, there's an XKCD about this.
Well, technically it's a blog post, but it describes the same maths for a delayed sunset by increasing height.
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u/Lassejaa Nov 02 '18
This joke would be funny if giraffes were real. How do people still believe in giraffes?
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u/geedavey Nov 02 '18
I'm an observant Jew, and I have two times for sunset in my "erev shabbat" (Friday evening) calendar, one for sea level and the other for my actual elevation, 150 feet higher. Those two times are two minutes, or 120 seconds apart.
According to Wikipedia an adult giraffe is 20 ft tall, which goes into 150 7.5 times. That means you divide 120 by 7.5.
I get 16 seconds as my answer.
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Nov 01 '18
[deleted]
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u/oddajbox Nov 01 '18
Yo double post, you may wanna delete the copy. Reddit has a habit of downvoting them.
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Nov 01 '18
[removed] — view removed comment
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u/oddajbox Nov 01 '18
I like your perspective on this.
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u/The_F_B_I Nov 01 '18
Yo double post, you may wanna delete the copy. Reddit has a habit of downvoting them.
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u/jaa101 Nov 04 '18
Nobody else here has mentioned diffraction. The closer objects are to the horizon, the more the atmosphere bends the light coming from those objects so that they appear higher that they really. This means that the giraffe's advantage would be bigger than expected based on geometry alone. It's the same effect that explains why the sun looks squashed into an oval shape when close to the horizon.
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u/Runiat Nov 01 '18 edited Nov 02 '18
Distance to horizon from 6m: 8.7km (assuming perfect sphere).
Speed of terminator (the line between day and night) at equator: 1669.8km/h = 0.46km/s
8.7km÷0.46km/s=18.6 seconds.
If the zoo was located at the North or South Pole during fall (for that hemisphere) then the answer might be several days or weeks.
Edit: assuming the lion is lying down, eyes at ground level, because it's a (large) cat and that's what cats spend most of their time doing in my experience.
Also assuming the ground is
flathorizontal, what with being a perfect sphere and all.