h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

socrates

aristotle

I think therefore I am decartes or is it descartes (the maps) seem to remember from my school days he did a lot of scientific work along them lines...
I'm racking my brains still trying to think of a greek, sure Qi actually covered this, or it could have been one of my school lessons as I remember a roof top in Alexandria and a crude spyglass polemy?

Archimedes.

He came within a gnat's pube of inventing/discovering calculus, apparently.

SCREW Archimedes?????

If the movement of Jupiter is irrelevant, presumably it's the movement of the Earth from one end of its orbit to the other we're interested - and the phenomenon of parallax - confirming that the Earth moved round the Sun* at a distance of ninety-eight million miles+. To do this he had to know the speed of light, already calculated by some old Greek guy whose name escapes me.

Hence when taken before the inquisition, Galileo toed the official geocentric line under torture, but left muttering "Eppur si muove" (still it moves!)

(*) - or, as Newton would later posit, they both moved round a common centre of gravity. Or, to get more recent, that they both moved in straight lines through a space-time curved by gravity...

(+) - I know it's ninety-three, but Douglas Himself said ninety-eight in at least one form of the Guide, and that's good enough for me.

Sorry for delay in reply. Was ill all Tuesday, and night.

Replies.

Post 20 - van smelter - no, not Ptolemy

Post 21 - Taff - no and no

Post 22 - logicus - not Descartes, too late

Post 23 - Archimedes in touching distance of Calculus! So he was, and so was our chappie! +3 DGI Pedro!

Post 24 - Taff - Nothing to do with a screw!

Post 25 - GVI - Movement of Jupiter IS irrelevant. +3 DGI. Movement of Earth is the relevance here! Another +3 DGI (I am in a generous mood!). Shooting yourself in the foot by saying a Greek guy calculated lightspeed though!!!
It is something he calculated that is in utmost relevance to our man calculating lightspeed!!



GT

I'm guessing Pythagoras calculating stuff about right angles?

PS, if this has to do with the Earth moving, then it's in relation to Earth's position compared to Jupiter. Which is, obviously, affected by .... Jupiter's movement.

Hi pedro!

Not Pythagoras. You seem to be bitten by the bug that Jupiter moves. Well, so it does. IT takes Jupiter just over 11 years to orbit the Sun. It takes Earth one year. Start thinking relative distances of Earth and Jupiter from the Sun. You are almost there. Take your time, and re-read the thread. all the clues are there.




GT

Well, a Greek whose name still eludes me calculated the Earth-Sun distance - if memory serves, it was something to do with sticks placed in the ground in different towns. He took synchronised readings to compare the lengths of the shadows - from which he was able to calculate the ratio of the (known) distance between the towns and the Sun-Earth distance.

Or maybe I've made that all up in my old, confused head.

GVI

The name escapes you!! I will give it! Eritosthenes!
Same chap measured the circumference of the Earth using a similar method.

That he provided a measurement of the distance from the Earth to the Sun is what we want! +3 DGI

So how did that fact help our man in question??




GT

Any more takers for this one???




GT

Died a death I believe.


If no more takers, will kill off Sunday night.





GT

Ok Finishing Time.

The astronomer we were looking for (which no-one seemed to pick up on)was Ole Roemer.

In 1677 he was observing Jupiter and its moons, and recording the timings of eclipses..

When he compared his timings with those in the Ephemeris he was using, he found to his consternation that his readings were off by some 20 to 22 minutes. As it said in the introduction, he had complete confidence in his clock.....

On checking the DATE the Ephemeris was compiled, he discovered that the dates of his observations were five months different. In a flash of inspiration, he realised that lightspeed must have a limit. It was not instantaneous as scientists thought.

How to calculate it??

He needed to know the Earth - Sun distance.

Fortunately for Roemer, a Greek by the name of Eritosthenes had calculated this for him in the second century B.C. He estimated it to be 180,000,000 Stadia. As Roemer had no idea the dimension of a stadia, he had to guess. This he did and declared lightspeed to be 200,000Km/Sec. Not quite right, but it brought his figures and the Ephemeris figures closer, and he was happy at that.

In 1728, using a different method to calculate Earth's orbital distance calculated lightspeed to be 301,000 Km/Sec

This was further refined by first Fizau, and then Foucault to the speed now used, 299,796Km/Sec.

Oh, yes! the astounding fact that would have earned +6??

Lightspeed was calculated 60 years before the speed of sound! The second sweep hand on a clock had to be invented first!!!!



GT

Don't you just hate it when you arrive at a thread 6 days too late and knew one of the answers?

If my memory serves me well, <./>Eritosthenes</.> got a mention in <./>Carl Sagan</.>'s TV series <./>Cosmos</.>.

Apparently, a tale had come to Eritosthenes' attention that there was a village, somewhere in southern Egypt, where the mid-day sun would fully illuminate the bottom of a deep well-shaft (I recall less well whether this was only on certain days of the year). This was deemed noteable because, in a village tens of miles to the north, with a well of similar depth, the phenomenon was never observed, whatever the time of year.

This, alone, was enough to establish that the earth's surface had a curvature and it only remained to quantify that by making measurements of the distance between the two villages (paced out on foot, through the desert - no mean feat in itself) and the difference in shadow angles (more easily done with sticks than by looking down wells, I suspect) then doing some trigenometry.

I forget the figure but Sagan commented on how many percent accurate E's calculated value for the earth's circumference turned out to be and that his lack of appreciation of the oblateness of the planet accounted for much of that discrepancy.

Not bad for someone who didn't even have the luxury of log tables.


EYG