NavList:

   

Reply

> There's an interesting historical connection here. Once the distance of the
> Moon had become known (by measuring its parallax), the next question was
> "how far is the Sun, and what's the size of the Solar system?". Attempts
> were made to measure the angle between Sun and Moon, when the Moon was just
> 50% illuminated. At that moment, the angle between Earth and Sun, measured
> at the Moon, must have been 90 degrees, so by drawing similar triangles it
> should have been possible to find the ratio between the distances of the
> Sun and Moon. Unfortunately, the Sun is so much further, that the measured
> angle was also 90 degrees, an near as anyone could tell. So the result was
> that a lower limit could be set, that the Sun must be at least so many
> times the distance of the Moon, but as for measuring its actual distance,
> the only answer was "very large".

Thank you George

You are astute indeed.  In an off-list conversation with Alex, he noted that
Aristarch(us) of Samos did an experiment similar to the one you mentioned
circa 300 BC.  He was out of step with his peers as he believed the Earth
was a sphere, the Moon revolved around the Earth, and the planets revolved
around the Sun.  He had not established a distance between the Earth and
Moon, which if I understand was accomplished much closer to the present day
than to 300 BC.  He was attempting to establish a ratio of the distance
between the Earth, Sun and Moon.  You would have to approach Alex for the
details.

While the experiment itself may properly belong in a discussion of astronomy
rather than navigation, that is what started me thinking about the Moon data
in the almanac.  I usually find answers to such questions in the explanation
section of the almanac or other texts, but had no luck in this case. So I
thank you for your input.

Bill

   

Reply