# Finding Distances in Space

July 29, 2022

Parallax, which aids astronomers in finding distances of or between stars, has been a commonly used method for many years. This calculation system has revolutionized scientists’ ability to calculate the distances between astronomical objects, which is paramount to new discoveries, as well as for future data inputs. However, parallax can only be used to some extent, as some stars and objects are too far for this type of calculation to even work. However, astronomers have found they can use the distances of nearby stars (using parallax) to help hypothesize and find the distances of further objects. Using parallax to find the distance between multiple stars, scientists and astronomers have been able to discover the relationship between a star’s color and its intrinsic brightness, which is how bright the star would be without all the excess dust and interstellar space that distorts or becomes absorbed by the star. A quick example of this “parallax” calculation is when you’re driving on the road. Objects on the side of the road like signs, electric poles, or animals might seem to go by fast while in a moving car, yet the background like mountains and trees move by very slowly, almost acting still. This same example can be shown when using distant stationary astronomical objects and moving stars to find parallax angles.

Because it takes 12 months for the Earth to revolve around the Sun, astronomers record the position of stars every 6 months, where perspectives from Earth are opposite, and stars will seem to have moved relative to the “background” stars that are more distant. From there, scientists can check back in on stars every 6 months, record, and use a simple formula to determine the distance with simple geometry.

The Earth moves around the Sun on a 12-month cycle; the distance between the Earth and the Sun is one astronomical unit (AU). Because of this, measuring the distance between a motionless object and a star (parallax angles method) would take two astronomical units. Since one AU is around 93 million miles, astronomers can use that as a leg in a triangle, which is formed by the star, astronomical object, and Earth. This is then used to determine the longer leg/base of the triangle, which represents the distance of the star. The Earth is also at a 90 degree angle because it is at 6 months, so scientists can use simple geometry/physics to find the distances. Astronomers use parallax angles to further help them determine distance. Parallax angles are found when an astronomer focuses on a distinct, distant object close to the star, and then measures the angle between the two objects every half year. These angle measures can be helpful when determining the distance of a star and another object, or to help establish the distance of the star from Earth. Parallax angles can also inform astronomers how far away the star is without calculations; a smaller angle concludes that a star hasn’t moved much, and is therefore farther away from Earth.