cosmolog

weight watchers

Over a heap of eggs and bacon, sluiced down with a mug of tea, Pedro explained how to count the number of stars in our galaxy having first ascertained the respective weights (or masses to be more accurate) of the Sun and the Milky Way.

In the middle of a cafe, in eyeshot of the tabloid Sun and a confection display within which lurked several chocolate Milky Ways, while adding pounds to my own mass, Pedro's precise formulation of galactic dimensions found a banal terrestrial counterpart.

Without going into the precise details - some of the finer points of which now escape me - one starts by employing parallax to work out how far away the moon is. Then by a cunning series of calculations, each building on the results of the previous, one ends up with the mass of the sun and it's distance from the galactic centre. This can be substituted into an equation, G * Mass of the Milky Way * Mass of Sun / distance of sun from galactic centre squared, to neatly deduce the mass of our galaxy. Approximately 10 to the power 41 kilograms.

That's 100,000,000,000,000,000,000,000,000,000,000,000,000,000 kilograms.

If one makes the assumption that every star is, on average, the mass of the sun, then dividing the above figure, the mass of the entire galaxy, by the mass of the sun one finds approximately how many stars there are in the Milky Way.

100,000,000,000 stars.

Among all this wonderful mathematical deduction were other wonders, how to work out the distance of a star, how the transit of Venus allows us to calculate the distance to the sun . . . the universe provides the clues, becomes the lab, to explain itself.

Posted by Jem Finer at July 7, 2004 6:59 PM