Size of the Solar System

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Can we say that Kepler in the early 17th century was the first person to know the distance from the earth to all the known planets?
One of his laws:The square of the orbital period is proportional to the cube of the radius(actually the semi-major axis). So he new Saturn was about 900 million miles from the earth, Jupiter about 400 million miles away. Was he the first? Copernicus didn't know. Brahe?.
By the time Newton was born the size of the Solar System was well known among European astronomers.
 

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By the time Newton was born the size of the Solar System was well known among European astronomers.
The solar system extends all the way through the Ort Cloud, about half the distance to the next nearest star. They didn't know THAT.
 
  • #4
russ_watters
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I'm not sure what you consider the edge of the solar system, but if it is the bow shock, that's a tiny fraction of the distance to the nearest star.
 
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Chronos
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Redbelly98
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The thread title is rather misleading. The OP is really asking who first knew the distances from the sun to the known planets. As in whatever planets were known at the time -- I guess this would mean the planets out to Saturn.
 
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cepheid
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Kepler knew the relative distances between planets, but I'm not sure if he knew any absolute distances. Had they figured out a way to measure the length of 1 AU at that point?
 
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davenn
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relating to all this ... this statement... "At the great distances of the Oort Cloud, comets can be affected by the gentle gravitational tugs of nearby passing stars. The passing stars tug on the comets, "perturbing" their orbits, sending some of them into the inner solar system" from the page ... http://www.astronomynotes.com/solfluf/s8.htm chronos listed above, and other printings I have seen over the years, has always irked me

nearby passing stars ?? are there stars closer than the Alpha Centauri system passing by that we have never seen ?
or.... can the Alpha Centauri trinary system at 4.3 lightyears affect objects in the Oort Cloud ?

Dave
 
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Chronos
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Agreed, although we could just now be seeing comets perturbed by rogue stars passing by a many thousands of years ago.
 
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Can we say that Kepler in the early 17th century was the first person to know the distance from the earth to all the known planets?
One of his laws:The square of the orbital period is proportional to the cube of the radius(actually the semi-major axis). So he new Saturn was about 900 million miles from the earth, Jupiter about 400 million miles away. Was he the first? Copernicus didn't know. Brahe?.
By the time Newton was born the size of the Solar System was well known among European astronomers.
In the late Middle Ages they had a sufficient idea of the distances to estimate that Jupiter and Saturn were bigger than the Moon. But past that the distances were hazy. In Ptolemy's geocentric model the sphere of stars was estimated to be about 20,000 Earth radii away. Thus Earth was just a tiny speck in an immense and perfectly working system of moving nested spheres, in their mechanistic model. The Greeks didn't believe truly empty space was possible and couldn't imagine action-at-a-distance forces, so they imagined a bunch of cosmic gears made of invisible material supported the planets and the celestial sphere.
 
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Can we say that Kepler in the early 17th century was the first person to know the distance from the earth to all the known planets?
There is not really a "first person".
The Earth-Sun distance (astronomical unit, AU) was measured with increased accuracy, starting around 17th century, using the transits of Venus and Mars.
Older estimates were made even in ancient times but not very close, I think.

The relative distances were known during Kepler times. It's not clear for me if he knew about the first modern absolute measurements.

Based on Kepler law, is sufficient to measure the absolute value of the AU and then all the other planetary distances can be found as absolute values.
 

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