Question

How many light years are there from Earth to Pluto?

Answer 1

Hint: You recall that the value is found to vary in between a certain range. Mostly probably you may happen to find the value to be in astronomical units. You could simply convert that value by first converting it in terms of light minutes and then in terms of light years and thus you’ll get the required answer.

Complete solution:
In the question, we are asked to find the distance of Pluto from Earth in light years. Along with their respective position in their orbit the distance between Earth and Pluto is seen to vary between 28.6 and 50 in astronomical units. You may recall that 1 astronomical unit is known to be the average distance between sun and earth. This value is found to be about 8.3light minutes. So, we see that,
$1A.U\to 8.3l\min $

Therefore,
$33.8A.U\to 33.8\times 8.3=280l\min $

But we are asked to find the distance in light years. Light year is known to be the distance that light is found to travel in one year.

You may recall that one year has 24 hours and each hour has 60 minutes, so,
$1day=24\times 60=1440\min $
Also, there are 365 days in a year, so,
$1\min \to \dfrac{1}{365\times 1440}yr$
$\Rightarrow 280l\min =\dfrac{280}{365\times 1440}lyr$
$\therefore 280l\min =0.0005ly$

Therefore, we found the distance between Earth and Pluto to be $0.0005ly$.

Additional information:
Astronomers used parallax method to find the distances such as these. For finding the distance to a star, astronomers observe them from different places along the orbit around the sun. Now the technology has seen a drastic change that it is much easier to find such distances.

Note:
The variation in the distance between planets is due to their position in their orbit with respect to the sun. The core reason behind this is the elliptical orbits of planets. Though Pluto is no more considered a “planet”, we could say that this reason is valid for it. We have taken the average distance between Pluto and sun as it is almost the same as the distance from the earth.