# I Comparing Earth's diameter with Moon's diameter

1. Apr 28, 2016

### prashant singh

What type of geometry or tool aristarchus used to show that during lunar eclips earths diameter is 2.5 times moon's diameter and during solar eclips it tapers one moon diameter, why they add these two to get earths diameter as 3.5 times moon's diameter

2. Apr 28, 2016

### drvrm

The sun’s diameter is about 400 times larger than that of the moon – and the sun is also about 400 times farther from Earth. So the sun and moon appear nearly the same size as seen from Earth.

the size of a celestial body is usually measured by the angle subtented at the observers eye. and the angle /angular diameter depends on the distance at which the body is placed.....as an example the above statement during solar ecclipse the disc of Sun and Moon appear to be of the same size.
if you see satellite photographs- the sizes vary as the space telescopes position varies.
if you wish to see exactly the calculations of Aristarchus ...you can visit the site (many a time his geometry gave wrong figures but later got corrected) he could draw triangles in space between celestial bodies and gave arguments/calculation of sizes.