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Old March 30th 17, 07:00 PM posted to
Mark Carver
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Posts: 7,543
Default Hopeless at maths

On 30/03/2017 19:39, Bill Wright wrote:
I'm hopeless at maths, but I'm trying to get something across to an
intelligent child. So, if the distance from here to London (250km) is
represented by the thickness of a hair (0.2mm) how far is a light year?
It doesn't have to be a hair; it could be anything familiar and small.

It's 2.5 million light years to the Andromeda Galaxy; that's what we're

Speed of light, 299,792,458 m/s

Number of seconds in a year

60 x 60 x 24 x 365 = 31,536,000 seconds

Therefore in one year light travels 31.536 x 10^6 x 299.792458 x 10^6

= 9.4542547 x 10^15 metres

So in 2.5 years

2.3635637 x 10^16 metres

2.3635637 x 10^13 km

So 2.3635637 x 10^13 km / 250 x 10^3 = 9.4542548 x 10^7

Therefore if a human hair represents 250km, it's 94.5 million hairs to

Please replace invalid and invalid with gmx and net to reply.