This file which concerns only practical aspects of the observations will inform you about the two methodologies allowing you to get the data needed to calculate the astronomical unit ( A.U.).

In fact, the results of the calculations will be mediocre if the observation is not correctly done.
To avoid confusions the calculations will be explained in another file called « Calculations of the Astronomical unit using the data from the observation ».

We invite you to read carefully this file if you want to calculate the A.U correctly.

**As a reminder:**
The astronomical unit (A.U.) is the distance Earth-Sun or 149 597 870, 691 kilometers (official value for those who like numbers, others will say approximately 150 million kilometers).

A.U. is supposed to represent the average distance separating our planet from its star.

PLEASE READ THE FOLLOWING CAREFULLY :

Observing the sun can be very dangerous, therefore the safety precautions MUST be respected, see :
http://www.venus2004.org/sinformer/n/news3366.php?langue=1
**Summary**
1 -

** Chronometrical methodology or Halley’s methodology**
2 -

** Photographic methodology **
3 -

**Material needed and advice for the observations **
4 -

**Final advice for the observations **