Interesting estimates

<< < (4/7) > >>

 Rigil Kent (June 14, 2013, 20:20:43 PM):
Presumably this is the molar mass ratio of Cl to NaCl, and, if so, the reason for using it is opaque to me.
True. Suddenly my calculation seems a bit opaque to me too. :-X

How much water does South Africa save every year due to people peeing in the shower?
A few million bladder-days’ worth, roughly the same amount consumed in bars and restaurants. Or do you want that in units of camel humps per kidney failure? :P

SA population is about 40,000,000 people.
Of which maybe 50% have access to a shower, i.e. 20,000,000 people.
Of which maybe 50% are prepared to urinate whilst showering, so 10,000,000 people.
Which they do maybe twice weekly. This gives 20,000,000 instances of not needing to flush a toilet per week.
Which comes to 1 billion saved flushes per year.
A toilet cistern holds maybe 8L of water.
So the annual water saving thanks to this slightly unsavoury activity comes to an estimated 8,000 megaliters per year.

Which is just over 6% of a major Eastern Cape water reserve, the Kouga dam!

Rigil

 brianvds (June 15, 2013, 03:31:02 AM):

But how long to drive to the nearest star?
??? Are you sure you calculated correctly? I get an answer that is 1/100th of that which you give — still a very long time, though.

Quite possibly - I have been battling the flu and was high on meds. Let me go check those calculations...

 brianvds (June 15, 2013, 03:42:53 AM):

But how long to drive to the nearest star?
??? Are you sure you calculated correctly? I get an answer that is 1/100th of that which you give — still a very long time, though.

Quite possibly - I have been battling the flu and was high on meds. Let me go check those calculations...

Okay, here's the new calculation:

Light travels at 300 000 km/s. So in a year, it travels 60 x 60 x 24 x 365 x 300 000 = 9 460 800 000 000 km.

Alpha Centauri is about 9 460 800 000 000 x 4.3 = 40 681 440 000 000 km from us. At 100 km/h it would take 406 814 400 000 hours to get there. Which is 16 950 600 000 days, and 46 440 000 years.

Better? I originally must have added zeros somewhere, or something - when I think now of the day I did this, I sort of see everything through a reddish fog of fever and coughing and drugs... :-)

As you say, still a rather frightful distance - as bright as the stars are, I am sometimes surprised we can see any at all. :-)
 Rigil Kent (June 15, 2013, 08:23:30 AM):
I am sometimes surprised we can see any at all. :-)
It is almost scarily amazing. And to think that you pick any star or far off galaxy and bring it into perfect focus with nothing but a stable atmosphere and a telescope. One has to marvel at the immense predictability with which light travels over even such vast distances.

Equally astounding to me is the sensitivity and range of the human eye, even in spite of it's apparent "design" flaws.

Rigil
 brianvds (June 15, 2013, 12:17:46 PM):
It is almost scarily amazing. And to think that you pick any star or far off galaxy and bring it into perfect focus with nothing but a stable atmosphere and a telescope.

Which brings me to another question I have been wondering about, and which will ft neatly into this thread of estimates. Interstellar space isn't completely empty. There is in fact a sort of interstellar "atmosphere" between us and the stars. Apart from nebulae, it is evidently not enough to blot out the stars, but how dense is the interstellar medium? How much gas is there between us and the nearest star, compared to what is in our own atmosphere?

Perhaps members with the necessary knowledge of this will want to post us some calculations and estimates. :-)