The vastness of distances between planets & stars

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

12 September 2021

In 2012, I demonstrated in this column that it is not possible to make a scale drawing of the solar system (the sun and the planets) on any paper. This is because the distances between the objects are so large that, when they are scaled down to fit on the largest paper ever manufactured, the smallest planet becomes smaller than the tip of the thinnest pencil ever made!

This fact often comes as a surprise to most people mainly because we have seen many images of the solar system in books, newspapers and magazines. However, such images are grossly exaggerated. Neptune, the outermost planet, is 4.5 billion kilometers from the sun. This is about 30 times the distance from the sun to Earth (the 150 million km).

If the sun was placed at the bottom of an A4 sheet of paper and Neptune at the top, the scale of such a drawing would be approximately one centimetre representing 150 million km. In this drawing, the Earth would be just 1cm from the sun.

In this diagram, the diameter of the sun (which, in reality, is 1.4 million km) would be just 0.1mm – too small to be visible without a magnifying glass! The planet Neptune, (which is 49,000km across) would simply not be drawable. There aren’t pencils thin enough to make a 3-micrometre dot – only visible under a microscope.

Clearly, the vastness of the empty space between celestial bodies is not emphasised enough in school. Imagine this: the nearest star to the sun is about 40 trillion km away. This is almost 1,000 times the distance to Neptune. Therefore, if we used the same scale of 1cm represents 150 million km, this star would be about 300m away…. with nothing in between!

Let us close with an experiment. Place an A4 sheet of paper on the table in the landscape orientation. With both eyes open. lower your head slowly towards it maintaining full view of the paper from edge to edge. Keep lowering until the edges begin to fall outside your field of view.

Stop lowering and measure the distance between your forehead and the sheet of paper in centimetres. Multiply the measurement by 150 million km. The result is how far you would need be in order to be able view both the sun and Neptune simultaneously. Let me know your result so that I compare with mine and other readers.