How to imagine the distances between stars

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

18 October 2020

In April 2012, I showed that it is impossible to make a scale drawing of the solar system. That is; using the thinnest pencil ever made (0.2mm) to represent the smallest planet (Mercury, diameter = 4,800km), the last planet (Neptune; 4.5 billion km from the sun) would be almost 200 metres away. There is no factory in the world that makes paper wide enough to fit that orbit!

In this scale, the 1.4 million-km diameter of the sun is reduced to a sphere measuring 6cm (slightly smaller than a tennis ball) and the Earth is dot of just 0.6mm. The largest planet, Jupiter would be a large dot 6mm across.

Interplanetary distances are large, but they are miniscule when compared to those between stars. The nearest star to the sun is about 4.5 lightyears away. That is, its light takes 4.5 years to reach us.

At 300,000km per second, light from the sun takes about 8.3 minutes to reach the Earth. At that speed, it covers about one billion kilometres in one hour. That is, sunlight takes about 4.5 hours to reach the last planet, Neptune.

In one day, light travels about 26 billion kilometers and, in one year, about 9.5 trillion km. Thus, in 4.5 years, the distance travelled is about 42 trillion km. This is how far away the next star is from the sun.

If this distance was drawn in the same scale as the one where Neptune is 200 metres from the sun, where would this star be located? Well, in such a drawing, one metre represents 22.5 million km; so, 42 trillion km would be represented by 1,870,000m. That is, 1,870km!

Stop: That’s too far away. In this scale, if the sun was in Nairobi, the next star would be in Asmara in Eritrea! Imagine that: So, let us change it by drawing the sun as a 0.2mm dot. In that case, the 0.2mm now represents 1.4 million km.

In this scale, 1mm represents 28 million km, so, at 42 trillion km, the farthest planet would be 16cm from the sun, while the next star would drawn about 6km away. In the new drawing, if the 0.2mm sun dot is at Nation Centre in Nairobi, the next star would be at the Drive-In Cinema on Thika road!

But how small is 0.2mm? Well; this dot “.” is about 0.3mm in diameter. Now imagine the sun reduced to that size…