

Ole Roemer and the Speed of Light - tmoretti
http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_roemer.html

======
nikcub
A solution to an accurate measurement of longitude for shipping was one of the
biggest scientific problems of the time and involved some of the brightest
minds in the world working over decades and centuries.

After losing almost 2,000 sailors and 4 Navy ships in an accident attributed
to poor navigation, the British government offered the Longitude Prize - which
was worth millions of dollars in todays money.

From Gallileo and his method of timekeeping by tracking the moons of Jupiter,
through to John Harrison and his invention of the chronometer - which ended up
winning most of the Longitude Prize - the effort that went into finding a
solution had many side effects for science and the solution opened up the
world to better navigation and the eventual colonization.

The entire story is chronicled in the book 'Longitude'[0], which was a best
seller in 1998. It is well worth a read. Wikipedia is also a good starting
point for finding out more.[1]

[0] [http://www.amazon.com/Longitude-Genius-Greatest-
Scientific-P...](http://www.amazon.com/Longitude-Genius-Greatest-Scientific-
Problem/dp/080271529X)

[1] <http://en.wikipedia.org/wiki/History_of_longitude>

~~~
carlob
Another interesting read is "The island of the day before" by Umberto Eco. A
1995 novel about the problem of longitude and time zones.

<http://en.wikipedia.org/wiki/The_Island_of_the_Day_Before>

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axomhacker
I love these kind of stories. Such stories fills me up with an immense sense
of appreciation for scientists/philosophers/thinkers from the post-middle-
ages.

Also, why I'm absolutely loving the coursera class on astronomy:
<https://class.coursera.org/introastro-2012-001/>.

If you have not peaked into it yet, the way Dr. Plesser explains concepts and
bridges them with the historical advances leaves a lasting impression. I wish
we had classes like this back in school.

~~~
notimetorelax
Sounds interesting, thank you for the suggestion. Here's the direct link to
course description:

<https://www.coursera.org/course/introastro>

Although course started a while ago they still give access to the materials is
you subscribe now.

~~~
axomhacker
Also, if you like the "Introduction to Astronomy" course, there's a follow-up
(although from a different university, Caltech) coming up: "Galaxies and
Cosmology": <https://www.coursera.org/course/cosmo>

~~~
JonnieCache
And if that isn't enough for you there's a complete series of stanford
cosmology lectures from Leonard Susskind (!) starting here:
[http://www.youtube.com/watch?gl=GB&hl=en-
GB&v=32wIKa...](http://www.youtube.com/watch?gl=GB&hl=en-GB&v=32wIKaLkvc4)

It's part of a comprehensive course in modern physics, all taught by susskind,
and all on that same youtube channel. There's classical mechanics, quantum
mechanics, the aforementioned cosmology and more iirc. He's a great teacher,
it's amazing that you can just dial up tens of thousands of dollars worth of
education like this.

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acqq
To put it in perspective, Newton's "Philosophiæ Naturalis Principia
Mathematica" was first published 11 years later.

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robolav
Adam Savage explains how light was measured in a ingenious experiment in 1849:
[http://ed.ted.com/lessons/how-simple-ideas-lead-to-
scientifi...](http://ed.ted.com/lessons/how-simple-ideas-lead-to-scientific-
discoveries)

~~~
guillaume__
Measuring the speed of light only with a cog, a piece of glass and a mirror is
so clever. The relevant part of the video starts at 4:06.

A history of measurement of the speed of light can be found there
<https://en.wikipedia.org/wiki/Speed_of_light#History>

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prezjordan
Very thorough explanation, awesome! What I'm more curious of is, how did
astronomers measure the radius of the earth and moon several hundred (1000?)
years ago?

~~~
mfn
This set of slides goes over how some astronomical measurements were made
hundreds of years ago:

[http://terrytao.files.wordpress.com/2010/10/cosmic-
distance-...](http://terrytao.files.wordpress.com/2010/10/cosmic-distance-
ladder.pdf)

~~~
hfsktr
I had known about some of this before like the eclipses being evidence of a
round earth and how the estimate for the size of earth from the well story.
From this book: [http://www.amazon.com/Theories-Everything-Illustrated-
Histor...](http://www.amazon.com/Theories-Everything-Illustrated-History-
Science/dp/0792239121)

What I found most fascinating about the explanations (I was in pre-calc at
school at the time) was the math involved. During my classes (or any math
class I've ever been in) they gave us formulas and equations but no meaning or
real world context. If they'd told us how we could use the distance and angles
to figure out what they'd figured out so long ago I think the math would have
been much more interesting and brought home the point of why it is relevant to
anything.

~~~
lifeisstillgood
And that is exactly why I want to collect all the great experiments of history
and give them to kids at the right ages to do - to calculate the size of the
earth using pencils and shadows and skyline others kids in different countries
for their measurements - it's got to stick in the brain better

~~~
bonobo
I think it's a fantastic idea. The most difficult things for me to learn were
always those which I don't know how to apply or those which I don't know where
they came from. You can't reason over something that seems like magic.

~~~
lifeisstillgood
OK - so can we start something?

<https://github.com/lifeisstillgood/importantexperiments4kids>

I think I can get support for something like this from STEMAmbassadors of the
UK. I shall see.

Comments?

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vishal0123
For those who don't know, a more accurate calculation of speed of light was
done in ancient india and had been mentioned in rigveda:
<http://www.hitxp.com/articles/veda/light-speed-rigveda/>

~~~
yread
Looking at the imprecision of vedical units of time and length the range of
what the speed could be is pretty big <http://en.wikipedia.org/wiki/Yojana>

But I have to admit it's still stunning that the people had an idea that light
travels that "slow" as opposed to infinitely fast.

EDIT: also it seems the calculation for time is wrong, wiki says "30 Kālas are
one Muhūrta" and not 30.3 <http://en.wikipedia.org/wiki/Muhurta>

EDIT 2: Perhaps they learned that light has finite speed from the Arabs who
knew already in 11th century thanks to the "first scientist"
<http://en.wikipedia.org/wiki/Alhazen>

~~~
kaka189
Vedas are much much older than 11th Century
(<http://en.wikipedia.org/wiki/Vedas>)

~~~
yread
Yes, but the precise number appears only in the commentary from 14th century

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bjornsing
Our little startup started it's life at Ole Römers väg (Ole Roemer's road) in
Lund, so I've looked up a few versions of this story. The one I like the best*
has a more dismal tone: Ole discovered the finite speed of light, but was
outmaneuvered by Jean-Dominique Cassini who had a complex theory based on
tables. I sometimes use it when I want to explain how important it is to try
and see past "social truth" to find the real one.

I can's say which version is more accurate, but there's a scientific
inaccuracy in the OP that makes me a bit skeptical of the author: The distance
between Jupiter and the Earth will have no impact on how long Io is hidden
behind Jupiter. It's the _change_ in distance been Jupiter and Earth from when
Io disappears behind Jupiter to when it reappears some minutes later that will
affect the timing.

So IMHO the illustration in the OP is wrong, the timing will be approximately
the same in position 1 and 2. Position 2 should be moved so that it is at the
far right (or left) of Earths orbit.

(*) <http://www.pbs.org/wgbh/nova/physics/ancestors-einstein.html>

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lmm
Arrgh. The original, better title had stood for at least four hours, and was
the name under which I knew the discussion.

Is there any kind of site/extension that displays hacker news, but gives
stories the titles they were originally submitted under? If not I guess I'll
do it myself.

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imglorp
I'm a little unclear on how was the +/- 11 minutes variation measured
throughout the year? Huygen's clocks lost about 15s/day, which would give them
around an hour and a half a year.

source: [http://www.americanscientist.org/issues/pub/huygenss-
clocks-...](http://www.americanscientist.org/issues/pub/huygenss-clocks-
revisited)

~~~
ef4
If you're always measuring from the same longitude, you don't need to rely on
a clock. You can take measurements of the stars and get a very precise local
time.

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redwood
Love this: "He later served as mayor and prefect of police of Copenhagen and
ultimately as head of the State Council."

A real renaissance (or post-renaissance) man! I love imagining a scientist
heading up a bunch if police!

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rimantas
Is there a book with collection of stories like this?

~~~
Avalaxy
I was just about to post this, but 'A short history of nearly everything' by
Bill Bryson has a LOT of these stories. It explains how we determined the
circumference and the weight of the earth, the distance to the moon and the
sun, etc.

In fact the whole book is about this, it explains all the important scientific
breakthroughs from the past and how we've gotten to them.

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lectrick
The NOVA series was good, for anyone curious.

[http://www.amazon.com/NOVA-Lost-Sea-Search-
Longitude/dp/B000...](http://www.amazon.com/NOVA-Lost-Sea-Search-
Longitude/dp/B000XBPDXK/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1355505396&sr=1-2-catcorr)

------
lectrick
Loved this. Interesting how it was an accidental discovery based on a
different pursuit at the time. That is almost a trope of life itself...

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Pr0
Very impressive!

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maeon3
What I take away from these stories is not how to calculate the speed of
light, but how to discover things previously not known. Observe something on
the edge of what is known, (the orbital period of IO), take better
measurements than ever before (creating new measurement technologies), observe
unexplained phenomenon (the annual increase/decrease in the orbital period of
IO), and apply tried and true mathematical principles: (given the distance
between planets, and the observed orbital period, solve for speed of light).

It's this process that will answer other unanswered questions in our physics
engine, another one for example being whether or not photons degrade, or if it
is possible to remove the higgs boson from matter, rendering it with no mass.

~~~
gus_massa
The Higgs bosons don't live inside the matter, so it's not possible to remove
them.

It's more complicated, and difficult to explain without a few algebra and
physics study years, but let's try with another broken analogy:

The Higgs field is like an invisible background. When the particles bounce
against this background the effective effect is that the particles have
apparent mass. Sometimes, the particles create bumps in the background; these
bumps can move and they are the Higgs bosons.

It's (probably) not possible to remove the background to make the particles
"lighter".

(The equations are so clear, the analogy explanations are so confusing. :( )

