# Odległość do Słońca

## A burning question

Pamiętasz Arystarcha z Samos? Był on greckim astronomem, który zasugerował że Ziemia krąży wokół Słońca (Model heliocentryczny). Odpowiedział również na fascynujące pytanie: Jak daleko leży Słońce?
Zdał sobie sprawę że możemy wyliczyć odległość do słońca względem odległości do księżyca. He noted that the sun, moon, and earth form a right triangle (right angle at the moon) during the first and last quarter moons.
A quarter moon occurs when the moon appears to be half illuminated from our vantage point. When the moon is seen to be exactly in the first quarter phase the sun-moon-earth angle is exactly 90 degrees. This means a line drawn from Aristarchus’ position to the moon and from the moon to the Sun formed a right angle.
Aristarchus simply needed to calculate the angle x. That is equal to how far he would have to tilt his telescope between the moon and sun (if telescopes had been invented yet). He calculated this angle as 87 degrees, though the true value is closer to 89.83 degrees (a difficult measurement to get right with the naked eye!).
We already know the distance to the moon is 384,400 km. Finally we have all the information needed! We apply the cosine function to find the hypotenuse of the triangle which is the distance to sun:

### sun distance = 129,556,058 km

This is estimate off by 13.3% which is quite good for a rough approximation. Compare this to the actual value:

### Average distance to the Sun: 149,600,000 km

This is the basis for the astronomical unit (abbreviated as AU) which is based on the Earth-Sun distance.

### 1 AU = 149 597 871 km

Challenge question: How could we measure the size of the sun using this new information?
hint: we need to review similar triangles. Let's do that now!