Who made first Sun-Earth distances calculations?
Michael Boschat
Reply to;
From: Daniel Flath <fl...@bianya.crm.es>
here is a question that has stumped me for years -
literally. i have been tring to
document exactly when, how, and by whom with references the
first
scientifically sound measurement of distance
from earth to sun was made. one idea i heard was that this
happened in late 1700s by observing closely orbits of
earth crossing asteroids. another was in same time period but
had to do with measurements during total solar eclipse. there
was some ancient stuff done too with simultaneous shadow lengths
at two places on earth but perhaps that does not count because
it was not accepted into the common science tool kit. if you
have any ideas where ic ould look i would really appreciate it.
thanks.
dan flath
Bill McClain
[Restricted to sci.astro.amateur]
Michael Boschat <andr...@atm.dal.ca> wrote:
According to Arthur Berry's _A Short History of Astronomy_, G.D. Cassini
in the 1670s derived a value of 87 million miles. He used contemporary
observations of the horizontal (that is, earth-based) parallax of Mars.
The ancients had tried a similar technique by observing the moon, but
were hampered by poor instrumentation and derived much smaller values.
Berry hints that Cassini's math was unsound, meaning he was lucky to get
a pretty close value.
-Bill
Robert Casey
Fred Hoyle (who gave us the name "Big Bang") wrote a book _Astronomy_ in the
mid 1960's. A history of astronomy. There was a transit of Venus across
the Sun, and people went to various far points on the Earth to observe
the paths Venus made across the Sun. Different sites would see slightly
different paths. Triangulation methods were used to get a value of
Earth to Sun of about 75 million miles. About 20% off.
This was done about 2 centuries ago.
Stephen Tonkin
Michael Boschat <andr...@atm.dal.ca> writes
>Reply to;
>
>From: Daniel Flath <fl...@bianya.crm.es>
>
>here is a question that has stumped me for years -
>literally. i have been tring to
>document exactly when, how, and by whom with references the
>first
>scientifically sound measurement of distance
>from earth to sun was made. one idea i heard was that this
>happened in late 1700s by observing closely orbits of
>earth crossing asteroids. another was in same time period but
>had to do with measurements during total solar eclipse. there
>was some ancient stuff done too with simultaneous shadow lengths
>at two places on earth but perhaps that does not count because
>it was not accepted into the common science tool kit. if you
>have any ideas where ic ould look i would really appreciate it.
The simultaneous observation of shadow lengths was Eratosthenes -- the
places were Alexandria and Syene (now Aswan). He did this in order to
estimate the size of the Earth. One of the errors was the distance from
Alexandria to Syene -- the officials who measured these distances were
paid "by the mile" as it were, so many distances were over-estimates.
Civil Servants don't change!
Aristarchus of Samos (as opposed to Aristarchus of Samothrace) estimated
the distance of the Sun by observing the angle between the Sun and Moon
when the latter is at exactly half phase -- sometime in the 3rd Century
BC, possibly around 265BC.
--
Stephen Tonkin : UK Amateur Telescope Making Pages
<s...@aegis1.demon.co.uk> : <http://www.aegis1.demon.co.uk/atm.htm>
Alice or William Ferris
Dan Flath wrote...
>here is a question that has stumped me for years -
>literally. i have been tring to
>document exactly when, how, and by whom with references the
>first
>scientifically sound measurement of distance
>from earth to sun was made.
It is interesting to note that ancient astronomers had the mathematical
knowledge to determine the Earth-Sun distance but their tools were not
accurate enough for the task.
Eratosthenes measured the polar circumference of the Earth to be roughly
39,300 km, accurate to within 2% of today's modern measurements. Aristarchus
compared the angular size of the Earth's shadow with the angular size of the
Moon during lunar eclipses to determine that the Moon was approximately
one-fourth the size of the Earth, again quite accurate by today's standards.
Both men made their measurements in the third century BC.
Aristarchus attempted to measure the Earth-Sun distance by measuring the time
the Moon takes to go from its new phase to first quarter and from full to
third quarter. Knowing the difference between these intervals would allow
him to use geometry to determine the Earth-Sun distance. The 12 hour
difference between the two intervals led him to miscalculate the Earth-Sun
distance by a significant margin--the actual time difference is about 30
minutes. That having been said, Aristarchus' geometry was perfect. If he
had had the proper tools, he would have achieved a fairly accurate result.
As it was, Aristarchus determined the Earth-Sun distance to be 7 million km,
quite a substantial distance back then.
Bill Ferris
Madison, WI
BEN
> Reply to;
>
> From: Daniel Flath <fl...@bianya.crm.es>
>
> here is a question that has stumped me for years -
> literally. i have been tring to
> document exactly when, how, and by whom with references the first
> scientifically sound measurement of distance
> from earth to sun was made. one idea i heard was that this
> happened in late 1700s by observing closely orbits of
> earth crossing asteroids.
Unlikely, since no asteroids were discovered until the 1800's. And I
don't believe any earth-crossing asteroids were discovered until the
20th century.
But you are on the right track. Basically you need something close
enough to show a detectable parallax from different places on the
earth. Then, if you know the true scale of one heliocentric orbit,
you know them all, by Kepler's laws. Transits of Venus were used
for such purposes in the 1700's.
> there
> was some ancient stuff done too with simultaneous shadow lengths
> at two places on earth but perhaps that does not count because
> it was not accepted into the common science tool kit.
The classical measurements by Eratosthenes et al. were fully accepted
but tell you only the size of the earth, not the distance to the sun.
That's a much tougher problem.
In ancient times people realized that a finite distance to the sun
implies that an apparent first-quarter or last-quarter moon will not
happen when the sun-earth-moon angle is exactly 90 degrees, but some
smaller angle. However the method is difficult to apply in practice,
and gave only lower limits.
Ben
Robert Casey
In article <oOAKOJA8...@aegis1.demon.co.uk> Stephen Tonkin <as...@aegis1.demon.co.uk> writes:
>Aristarchus of Samos (as opposed to Aristarchus of Samothrace) estimated
>the distance of the Sun by observing the angle between the Sun and Moon
>when the latter is at exactly half phase -- sometime in the 3rd Century
>BC, possibly around 265BC.
>
number did he get? I imagine he would not be able to determine an
distance, only declare that the Sun can be no closer than X distance
and also must be very large. Minimal size of the Sun probably would
be determined to be no smaller than about 2/3 the diameter of the
Moon's orbit. As anything smaller would show a measurable deviation
from 90 degrees angle of a half Moon to the Sun. Quite possibly,
this conclusion might be regarged as absurb, and be thrown out.
Helps when you know the real answer.........
Lloyd Johnson
>But you are on the right track. Basically you need something close
>enough to show a detectable parallax from different places on the
>earth. Then, if you know the true scale of one heliocentric orbit,
>you know them all, by Kepler's laws. Transits of Venus were used
>for such purposes in the 1700's.
Was that why Captain Cook sailed to Tahiti?
http://michele.gcccd.cc.ca.us/~ljohnson/johnson.html
Lloyd Johnson
>Aristarchus of Samos (as opposed to Aristarchus of Samothrace) estimated
>the distance of the Sun by observing the angle between the Sun and Moon
>when the latter is at exactly half phase -- sometime in the 3rd Century
>BC, possibly around 265BC.
But, he found that the sun was 20 times as far away as the moon when
in fact it was more like 400 times as far away. Nice attempt though.
http://michele.gcccd.cc.ca.us/~ljohnson/johnson.html
Tim Gillespie
Michael Boschat wrote:
>
> Reply to;
>
> From: Daniel Flath <fl...@bianya.crm.es>
>
> here is a question that has stumped me for years -
> literally. i have been tring to
> document exactly when, how, and by whom with references the
> first
> scientifically sound measurement of distance
> from earth to sun was made. one idea i heard was that this
> happened in late 1700s by observing closely orbits of
> was some ancient stuff done too with simultaneous shadow lengths
> at two places on earth but perhaps that does not count because
> have any ideas where ic ould look i would really appreciate it.
>
>
> dan flath
If by "scientifically sound" you mean using principles that, performed
using properly precise equipment and measurements would yield the
correct result; then the first to do so was Aristarchus. I believe his
measurements were flawed, and he cauculated a result that was 'way too
low, but his principle was sound, and had his measurements been more
accurate, he would have arrived at the correct figure. I am not sure
when this was, certainly several hundred years BC, but it would be easy
enough to look up.
Tim
Michael Dworetsky
In article <4vvd5j$2...@News.Dal.Ca> andr...@atm.dal.ca (Michael Boschat) writes:
>Reply to;
>
>From: Daniel Flath <fl...@bianya.crm.es>
>
>here is a question that has stumped me for years -
>literally. i have been tring to
>document exactly when, how, and by whom with references the
>first
>scientifically sound measurement of distance
>happened in late 1700s by observing closely orbits of
>earth crossing asteroids. another was in same time period but
No, this was not done until the present century.
>had to do with measurements during total solar eclipse. there
No, I think you mean the transit of Venus.
>was some ancient stuff done too with simultaneous shadow lengths
>at two places on earth but perhaps that does not count because
>it was not accepted into the common science tool kit. if you
This was how Erastosthenes measured the size of the Earth.
>have any ideas where ic ould look i would really appreciate it.
>
>thanks.
>
>dan flath
>
>
Try to find a book on the history of astronomy, Dan. The following is an
outline of material I gleaned from several sources, including my 1889 Edn
of Young's General Astronomy.
The earliest attempt to measure the solar distance was done by
Aristarchus, who tried to use the times of apparent dichotomy (first and
last quarters) of the Moon. If the Sun is not extremely far away, the
angle between the two points in the sky will be less than 180 degrees, and
from the angle measured one could deduce the relative distance of Sun and
Moon. The method fails because of the elliptical orbit of the Moon, and
other effects, but the value obtained later by Hipparchus, 19 times the
distance of the Moon, was undisputed for many centuries, until Kepler
showed that Tycho's observations of Mars did not permit the distance to be
so small, and it had to be at least 3-4 times further than Hipparchus'
value.
The first really useful scientific method was devised by Halley, who
suggested (1716) that observations of transits of Venus from different
known latitudes on the Earth could give an accurate value for the
astronomical unit. Halley did not live long enough to see his method
applied at the transits of 1761 and 1769, but the second of these gave
values within 3 per cent or so of the modern accepted value (the first was
not well enough observed).
Various other planetary methods were used in the following century. In
1862 Foucault determined the speed of light accurately enough to apply it
to the problem through observation of the constant of aberration (the
apparent shift in stellar positions due to the motion of the Earth around
the Sun) and derived a more correct distance.
The use of close approaches by asteroids for this purpose did not occur
until the 20th century, using observations of the asteroid Eros.
Hope this helps!
--
Mike Dworetsky, Department of Physics | Haiku: Nine men ogle gnats
& Astronomy, University College London | all lit
Gower Street, London WC1E 6BT UK | till last angel gone.
email: m...@star.ucl.ac.uk | Men in Ukiah.
Tim Gillespie
Obviously others have adequately answered this question. My news server
is obviously slow. Please excuse the redundancy.
Tim
Stephen Tonkin
R. Klappal
joh...@mintaka.sdsu.edu (Lloyd Johnson) wrote:
>http://michele.gcccd.cc.ca.us/~ljohnson/johnson.html
Sir Thomas Heath reports ("Aristarchus of Samos: The Ancient Copernicus", Dover
Books, ISBN 0-486-24188-2) that Thales (approx 624BC to 547BC) attempted
calculations concerning the size of the sun. Translation difficulties make it
unclear as to how good his answers were--1/30 of an hour..24 hours/day gives 1/2
degree. The problem is that it is not clear if they were using a 24 hour day or
a 12 hour day. If it was a 12 hour day, you get a 1 degree size for the sun.
There is also evidence that Thales was working with Egyptian techniques and that
the Babylonians and/or Chinese had made these detrminations 1000 years earlier.
Anaximander (~610 - 546BC) estimated that the sun was the same size as the
Earth, and that it was 28 diameters away; the moon was 19 diameters away.
Aristarchus is credited with being the first to have systematically tried to
compute it and to have his calculations survive. The earlier research reports
we get are second, third, ... hand.
kla...@xnet.com
41N48' 88W15'
================
A new civilization is emerging in our lives, and
blind men everywhere are trying to suppress it.
A. Toffler
================
Stephen Tonkin
"R. Klappal" <kla...@xnet.com> writes
>Anaximander (~610 - 546BC) estimated that the sun was the same size as the
>Earth,
Worse than that, Anaxagoras was exiled from Athens for claiming that it
was bigger than the Peleponese peninsular!
Heraclitus of Ephesus thought it was a foot in diameter.
Michael Dworetsky
In article <500plc$f...@sjx-ixn3.ix.netcom.com>
Yes, indeed it was. The Royal Society was given 4000 pounds by the king
to fund several expeditions to locations suitable for observing the
transit, and the astronomers went along. Now, would you rather have been
on the shores of Hudson's Bay, or in Tahiti? Both were sites for
observing the transit. This was, incidentally, one of the first
astronomical uses of the newly developed Dolland achromatic crown/flint
glass doublet lenses and this accounts for much of the success of the
work.
Cook's ship was named Endeavour.
pyotr filipivich
Stephen Tonkin <as...@aegis1.demon.co.uk> writes:
:>Robert Casey <wa2...@netcom.com> writes
:>>What sort of
:>>number did he get?
:>I haven't a clue!
"Myriads & Myriads" according to Sagan of Patmos. :-)
tschus
pyotr
--
py...@halcyon.com Pyotr Filipivich here, Nikolai Petrovich in the SCA.
People don't learn from History. Most of them don't even learn from
Current Events.
R. Klappal
Stephen Tonkin <as...@aegis1.demon.co.uk> wrote:
>Heraclitus of Ephesus thought it was a foot in diameter.
>--
>Stephen Tonkin : UK Amateur Telescope Making Pages
><s...@aegis1.demon.co.uk> : <http://www.aegis1.demon.co.uk/atm.htm>
Heath says that Heraclitus was a big step backwards; so big that "...he scarcely
needs mention in a history of astronomy except as an illustration of the
vicissitudes, the ups and downs, through which a science it its beginning may
have to pass."
Rich
PATRICK DIJUSTO
Lloyd Johnson (joh...@mintaka.sdsu.edu) wrote:
: >But you are on the right track. Basically you need something close
: >enough to show a detectable parallax from different places on the
: >earth. Then, if you know the true scale of one heliocentric orbit,
: >you know them all, by Kepler's laws. Transits of Venus were used
: >for such purposes in the 1700's.
: Was that why Captain Cook sailed to Tahiti?
Exactly. At Edmund Halley's suggestion....