Question

How many AU are there between the sun and pluto?

Answer 1

Hint: You could first introduce Pluto. Then, you could give the known value of the required distance in the commonly used units of distance, like kilometers and miles. Then, you could give the reason for taking the average value for this. Then you could define an AU and then express the required distance in AU.

Complete answer:
In the question we are asked to find how many astronomical units are there in between the sun and Pluto. Pluto is the dwarf planet that is present on the Kuiper belt.

The distance of Pluto from the sun in kilometers is known to be 5.9billion km. In miles, it is found to be 3.67 billion miles. But we should know that this is an average value. This is because the orbit in which Pluto revolves around the sun is elliptical and thus the distance between planets varies during the revolution. At the closest point which is called the perihelion Pluto is known to be at a distance of 4.44billion km from the sun. Now, for the farthest point called the aphelion, the distance between them is found to be 7.38billion km.

We know that astronomical unit (AU) is another unit that is commonly used by astronomers to measure such distances. 1AU is defined as the average distance between earth and the sun which is about 150million km. In astronomical units, the perihelion and aphelion of Pluto is found to be at 29.7AU and 49.3AU from the sun respectively.

So, on taking the average we get the distance between them as 39.5AU.

Therefore, we found that there are 39.5AU in between sun and Pluto.

Note:
Astronomers once used parallax methods to find the distances such as these. In this method, for finding the distance to a star, astronomers have to observe them from different places along the orbit around the sun. Now the technology is so developed that it is much easier to find such distances.