Distance from the earth to the moon

Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy? I
have briefly rooted around the internet for an answer, but have not been
able find one. It's been a long time since I took physics.

catzz66 wrote:
Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy? I
have briefly rooted around the internet for an answer, but have not been
able find one. It's been a long time since I took physics.

You're going to have to define "reasonable degree of accuracy" to have a
reasonable answer. The rough distance has been known for thousands of
years. Post Apollo we can measure it to less than a foot. In between
is more or less a continuum.

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://comets.skyhound.com

To reply take out your eye

"catzz66" wrote in message

Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy?
I have briefly rooted around the internet for an answer, but have not
been able find one. It's been a long time since I took physics.

That would depend upon what you consider to be a reasonable
degree of accuracy.

In the modern era, radar signals bounced off of the Moon
would have provided a pretty good fix prior to the
installation of corner cube reflectors by the Apollo
missions.

Prior to both, triangulation with the width of the Earth
as a base would have worked well.

Newton had a pretty good idea of the distance.

On Jul 10, 9:54*am, catzz66 wrote:

Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy? *I
have briefly rooted around the internet for an answer, but have not been
able find one. *It's been a long time since I took physics.

Hipparchus (190 B.C. -- 120 B.C.) correctly determined the moon's
distance to be 30 times the diameter of the earth. (Using
Eratosthene's (276 B.C. -- 196 B.C.) value for the earth's diameter
that would have placed the moon approximately 250,000 miles away.
That sounds pretty reasonable to me. So a plausible to answer to your
question would be about 2,130 years.

Aristarchus (310 B.C. -- 230 B.C.) measured the moon's distance
earlier; but his results were far less accurate.

My source (which also gives a brief explanation of how the
measurements were made): "Asimov's Biographical Encyclopedia of
Science & Technology"

Bill Greer
To sketch is to see.
http://cejour.blogspot.com
http://www.rangeweb.net/~sketcher

"catzz66" wrote in message
...
Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy? I
have briefly rooted around the internet for an answer, but have not been
able find one. It's been a long time since I took physics.

You live under a rock..right??

Greg Crinklaw wrote:
catzz66 wrote:
Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy?
I have briefly rooted around the internet for an answer, but have not
been able find one. It's been a long time since I took physics.

You're going to have to define "reasonable degree of accuracy" to have a
reasonable answer. The rough distance has been known for thousands of
years. Post Apollo we can measure it to less than a foot. In between
is more or less a continuum.


How long the rough distance has been known is all I was really wondering
about and "thousands of years" is close enough. Thanks for your reply
and the others that followed.

"catzz66" wrote in message

Greg Crinklaw wrote:
catzz66 wrote:
Roughly how long have astronomers been able to calculate the
distance between the earth and the moon with a reasonable degree of
accuracy? I have briefly rooted around the internet for an answer,
but have not been able find one. It's been a long time since I
took physics.

You're going to have to define "reasonable degree of accuracy" to
have a reasonable answer. The rough distance has been known for
thousands of years. Post Apollo we can measure it to less than a
foot. In between is more or less a continuum.


How long the rough distance has been known is all I was really
wondering about and "thousands of years" is close enough. Thanks for
your reply and the others that followed.

The ancient Greeks did a credible job. Aristarchus (~300 BC)
estimated the size of the Moon to be 1/4 that of the Earth
by observations of the shadow of the Earth on the Moon.

Around 200 BC Eratosthenes worked out the true size of the
Earth using the angle of Sun rays at two locations. The
distance then falls out by simple geometry.

In sci.astro.amateur message , Thu,
10 Jul 2008 10:54:16, catzz66 posted:

Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy?

That's an ambiguous question.

If Pytheas had reported that, in a certain month, he had seen the Moon
pass under a certain star, and if in Rome the Moon had been seen passing
just over that star in that month, then, assuming the star to be
relatively distant, the moon's diameter could have been known to be a
little less than Pytheas' northward distance from Rome.

But that's not the same as saying that anyone actually did that at the
time.

The same can be said for other sorts of observation, for example of the
curvature of the Earth's shadow during a lunar eclipse.

Additionally, is this to be restricted to astronomers in the western
European tradition, or are Asiatic astronomers to be included?

Only in comparatively recent times has it been safe to say that
everything of interest has been measured to about the greatest accuracy
possible at the time.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

On 2008-07-10, catzz66 wrote:
Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy? I
have briefly rooted around the internet for an answer, but have not been
able find one. It's been a long time since I took physics.

Aristarchus of Samos in 270 BC estimated the distance from
the Earth to the Moon as 60 Earth radii. He did this by
timing lunar eclipses. The mean radius of the Moon's orbit
is about 60.3 Earth radii, making Aristarchus' estimate a
pretty good result.

Tycho measured the lunar parallax over the years, which is
the same as measuring the earth-moon distance in terms of
earth radii. His measurements supposedly were good to a
couple of minute of arc. You had to use telescopic sights
to get better measurements, and by the end of the 18th century
astronomers had a good handle on the earth-moon distance.

Bud

In article ,
wrote:

On 2008-07-10, catzz66 wrote:
Roughly how long have astronomers been able to calculate the distance
between the earth and the moon with a reasonable degree of accuracy? I
have briefly rooted around the internet for an answer, but have not been
able find one. It's been a long time since I took physics.

Aristarchus of Samos in 270 BC estimated the distance from
the Earth to the Moon as 60 Earth radii. He did this by
timing lunar eclipses. The mean radius of the Moon's orbit
is about 60.3 Earth radii, making Aristarchus' estimate a
pretty good result.

That was Hipparchus, a couple of generations later -- see
AstroSketcher's posting. Aristarchus' method involved measuring the
Moon's elongation at the moments of First and Last Quarter, but he
wasn't able to make precise enough measurements to get very good
results. IIRC he figured the Sun was somewhat less than twenty times the
size of the Moon, and accordingly somewhat less than twenty times as
distant.

--
Odysseus