How do they measure the distance of a star?
The distance of a star may be given as its parallax angle. This angle is at the top of an immense celestial triangle. Like all triangles it has three sides and an angle at each corner. However, it has two equal sides. When you know the base line of such a triangle and the angle at each end of it, you can figure its other two sides and the angle at the top. The orbiting earth can provide you with a base line for a triangle big enough to measure the distance of a star. The star is photographed in relation to a background star. six nigths later it is photographed again, to show a different relative position. Meantime the earth has passed to the opposite side of its orbit. Your base line is the diameter of the earth’s orbit. The measuring line to your star begins midway on the base line and ends at the parallax angle at the top of your immense triangle.
