Hopeless at maths
On 30/03/2017 20:00, Mark Carver wrote:
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
It's much more than that.
A light year is 9.461*10^12 km
2.5 light years is 2.365*10^13 km.
Call it 2.5*10^13 km for ease of maths, which is 250*10^11 km.
Divide by 250 km (the distance to London) and you get:
2.5 light years is 10^11 times the distance to London. That's
100,000,000,000 or 100 billion times the distance to London.
Hairs are an irrelevant confusion. Forget them.