How many stars / galaxies ?

[Bazile]

Astronomers estimate that there are x million
stars in our galaxy and x million galaxies

Obviously you cannot count them - so what ever the estimated figure is - might not it be 10/20/30 etc times the figure ?

Isn't it therefore just a GUESSTIMATE ?

[Bazile]

oops - Billions , even

[ll_billym]

The calculated figure is (or should be) expressed as the number of stars/galaxies in the VISIBLE universe. It is impossible to know how many more there are that we cannot see.

The figure is calculated by taking a photo with a telescope of small parts of the sky. The number of galaxies in the photos are counted and their brightness is used to work out how many stars are in them. That figure is then multiplied by the mumber of these parts (photos) it would take to cover the whole sky.

So there is some actual counting (of the galaxies) and some esimation (of the number of stars in a particular galaxy, and the assumtion that the photos taken are typical of the sky as a whole) so ultimately it is an estimate and I am unsure of the error margin but I would guess it is nowhere near 10 times.

And the definition of an "estimate" is a probable figure, not an exact one so nobody is saying that they actually know.

[donslot]

Bare this in mind...
There are more stars out there than there are grains of sand on all the beaches of this world. That's all I need to know.

[Teddio]

A typical galaxy contains 10000000000stars and there are an estimated 10000000000 galaxies.
Therefore the number of stars in the observable Universe is 100000000000000000000 (10 to the power of 20) The uncertainty in this is of the order of 500% but whatever the actual figure is, it is really big!