LEARNATHON
III

Competition for grade 6 to 10 students! Learn, solve tests and earn prizes!

### Theory:

In our daily lives, distances are generally expressed using $$centimetres$$, $$metres$$, and $$kilometres$$. But is it possible to measure the distance between the Sun and the Earth?

Yes, astronomers measure extremely long distances, such as the distance between the Earth and a star or the distance between two stars, for space research.

In astronomy, there are two most commonly used units of distances, namely,
1. Astronomical unit
2. Light year
Astronomical unit
The distance between the Sun and the Earth changes every day since the Earth orbits the Sun in an elliptical orbit.
Perihelion is the point of the shortest distance between the Earth and the Sun.
The Sun is positioned at a distance of approximately $$147.1\ million\ kilometres$$ when the Earth is in its perihelion position.

Aphelion is the point of the longest distance between the Earth and the Sun.
The Sun is located at the farthest distance of approximately $$152.1\ million\ kilometres$$ when the Earth is in its aphelion position.

One astronomical unit (AU) is the average or the mean distance between the Earth and the Sun (which is approximately $$149.6\ million\ kilometres$$).
For example, Neptune revolves around the Sun at a distance of $$30\ AU$$. So it means the distance of Neptune from the Sun is thirty times greater than the Earth.

$\begin{array}{l}1\phantom{\rule{0.147em}{0ex}}\mathit{AU}\phantom{\rule{0.147em}{0ex}}=\phantom{\rule{0.147em}{0ex}}149.6\phantom{\rule{0.147em}{0ex}}\mathit{million}\phantom{\rule{0.147em}{0ex}}\mathit{km}\\ \\ =\phantom{\rule{0.147em}{0ex}}149.6\phantom{\rule{0.147em}{0ex}}×\phantom{\rule{0.147em}{0ex}}{10}^{6}\phantom{\rule{0.147em}{0ex}}\mathit{km}\phantom{\rule{0.147em}{0ex}}\\ \\ =\phantom{\rule{0.147em}{0ex}}1.496\phantom{\rule{0.147em}{0ex}}×\phantom{\rule{0.147em}{0ex}}{10}^{11}\phantom{\rule{0.147em}{0ex}}m\end{array}$