This formula is useful to calculate the stars' distance.
We use two points of observation to measure the distance to an object (in our case a star) by observing how it appears to move against a background. We make two observations of the same star on opposite sides of the Earth's orbit, we would have a separation of 2 astronomical units, or AU*. With this we taka an angle (α) between the star's two apparent locations. And we can sense that by cutting α in half, we get a right triangle where one leg is the distance between the sun and the other star. So we have: 1/2α=p. And we can use tan p to find the distance to that star (as we can see in the imatge).
(*) AU is an astronomical unit, and means "the average distance from the Sun to the Earth".
Imatges
Here we can see the first deduction (1st formula)
Now, we see how we calculate d (distance)
Finally, we see the whole deduction without formulas
