Very simple question

How did scientists calculate the distance between earth and moon, earth and
sun etc.

Today, this can be done (in some cases, e. g. moon and venus ) by
means of laser or radar beams sent to the planet, and measuring the
time till they are reflected to earth.
Centuries ago, however, brilliant astronomers spent a lot of effort in
thinking and observation to solve this problems with geometrical
methods, starting with calculation of the distance moon-earth and
sun-earth in about the 2nd century b.c. So your question is not that
simple to answer, however, once you understand the principle of those
calculations, they indeed appear very elegant. Generally, they employ
the determination of the angles or parallaxis of sun, moon and/
planets (or moon) from different places on earth of known distance,
especially during transits or eclipses, when more accurate
measurements are possible. To get an idea, you can find explanations
and some drawings he
http://www.badastronomy.com/mad/1996/au.html
http://www.jca.umbc.edu/~george/html.../parallax.html

The attempts to determine the distance sun-earth during the venus
transit in 1761 and 1769 was, by the way, one of the first global
scientific cooperations, involving astronomic obeservations from
scandinavia to tahiti (by captain cook) . You can find some
information about this and other facts on former and next year's venus
transit he
http://www.transitofvenus.org/



"Earth Resident" schrieb im
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How did scientists calculate the distance between earth and moon,
earth and
sun etc.

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How did scientists calculate the distance between earth and moon, earth
and
sun etc.




did?

"Earth Resident" wrote



How did scientists calculate the distance between earth and moon, earth and
sun etc.

Terms to Google for are "cosmic distance scale" and "cosmic distance
ladder."

z.B.:

http://www.astro.washington.edu/labs...ce_Ladder.html

In article ,
Earth Resident wrote:
How did scientists calculate the distance between earth and moon, earth and
sun etc.

The distance to the Moon was pretty easy: it's close enough that if you
observe it simultaneously from different parts of the Earth, its position
in the sky is a little different. Knowing how far apart the observatories
are, and measuring the difference in apparent positions, you can compute
how far away it is.

Earth and Sun is a lot harder. It's too far away for the same trick to
work very well. Observational astronomy is all angles, so you can measure
*relative* distances to the Sun and the planets quite well, but unless you
can measure one of those distances by some other means, you don't know the
absolute scale of the system.

One of Captain Cook's voyages had, as its primary objective, timing a
transit of Venus (a rare event, Venus passing in front of the Sun) from
the other side of the Earth from Europe. The difference in times would
give an absolute determination of the distance to the Sun. It didn't work
too well: because Venus's atmosphere blurs things, it's hard to decide
exactly when Venus crosses the edge of the Sun.

Various other approaches were tried. The best of the pre-spaceflight ones
was that the asteroid Eros occasionally passes near the Earth, and by
looking at how much Earth's known gravity disturbs Eros's orbit in such
an encounter, you can determine how close Eros came.

Plans for planetary probes made the matter much more urgent, because they
need precision navigation, and so extra effort was put into the problem.
Shortly before the first Mariners were launched, the distance to Venus was
successfully measured by radar, reducing the uncertainty from tens of
thousands of kilometers to less than one kilometer.

To put the final icing on the cake, in the late 1970s, the distance to the
Viking landers was measured to within meters by timing signals they
received and relayed back.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

"Earth Resident" writes:

How did scientists calculate the distance between earth and moon, earth
and sun etc.

This is really a question for 'sci.astro.research', but I will answer it.

The earliest estimates of the distance to the moon was by the ancient
Greek astronomer Aristarchus [310--230 BC], who determined that the
Sun had to be at _least_ 19 times further away than the Moon,
http://galileoandeinstein.physics.virginia.edu/lectures/gkastr1.html,
http://www.astro.queensu.ca/~waugh/fallterm/qlecture5.html,
http://www.eas.purdue.edu/eas105/geos105/lecture3.html;
since the true distance ratio is about 400, this was not very accurate ---
but it was considerable better than the previously accepted value of "3."

The ancient Greek astronomer Hipparchus [190--120 BC] was able to deduce a
more accurate estimate for the distance to the Moon of 59 to 67 Earth radii
(the true value is about 60 Earth radii), from observations of lunar eclipses,
and from the Earth's diameter determined by Eratosthenes [276--195 B.C.]
(which was only about 1% off!), and observations of solar eclipses,
Hipparchus was able to estimate the diameters and distances of both the
Sun and Moon.

Later, more accurate measuremeents of the distance to the Moon used
parallax (change in apparent angle with viewpoint) to determine the
distance through trigonometery,
http://www.ifa.hawaii.edu/~barnes/ASTR110L_S03/lunardist.html;
for a high-school astronomy lab exercise that replicates this method,
see: http://www.math.wisc.edu/~rushton/scopes_kti/northstar/main.html.

Once Newton's Laws of Motion and Law of Gravitation were discovered and
Cavendish measured the Gravitational Constant, it was possible to deduce
the distances to the Sun, Moon, and all the planets from measurements of
their orbital periods plus celestial mechanics.

Moderne methods use the laser retroreflectors left by the Apollo astronauts
to measure the distance to the Moon to an accuracy of about three centimeters
(a bit more than an inch), radar can measure the distances of planets to within
a fraction of a kilometer, and the distances to space-probe transponders can be
determined to a few meters.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

"Gordon D. Pusch" wrote in message
...
"Earth Resident" writes:
How did scientists calculate the distance between earth and moon, earth
and sun etc.

Later, more accurate measuremeents of the distance to the Moon used
parallax (change in apparent angle with viewpoint) to determine the
distance through trigonometery,
http://www.ifa.hawaii.edu/~barnes/ASTR110L_S03/lunardist.html;
for a high-school astronomy lab exercise that replicates this method,
see: http://www.math.wisc.edu/~rushton/scopes_kti/northstar/main.html.

When was this?

I forget all the details, but captain cook going to the south pacific/
australia was in part to observe venus going in front of the sun (ie a
transit).

Knowing how far he was from the European observatories, and comparing the
observations of how venus passed in front of the sun gives you an absolute
distance to add to the relative distances you get from orbit data.

"Earth Resident" wrote in message ...
How did scientists calculate the distance between earth and moon, earth and
sun etc.

I'd like to suggest the book "Measuring the Universe" by Kitty
Ferguson -- http://tinyurl.com/q3jt -- for an excellent nontechnical
summary of this exact question.

eyelessgame