Explore the Whole Night Sky – Interactively

2 Responses to Explore the Whole Night Sky – Interactively

1. Carol says:

   July 29, 2011 at 7:56 pm

   Could you help me with a cosmology question? I have heard people say that there are more stars in the universe than there are the grains of sand “on the beach”. What size is the beach and are the grains of sand coarse or fine? Or does the saying go “all the grains of sand on all the world’s beaches,” something I simply can’t believe to be true.

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   • David says:

     July 29, 2011 at 8:01 pm

     Lets star(t) “close to home” and see the number of sand grains we need to represent our galaxy.

     There are (very) roughly 50 to 100 billion stars in our Milky Way galaxy.

     1,000 grains of (Carmel Beach) sand is about a foot long. (Your sand may vary).

     1,000 grains of sand by 1,000 grains of sand on a flat surface = 1 million grains of sand. (a square foot)

     Now put the vertical dimension of 1,000 grains high = 1 billion grains of sand. (one cubic foot) 1 Billion grains of sand is a cube only ~ 1 foot on a side.

     That means you only need about 50 (for 50 billion stars) cubic feet of sand (a cube about 3 feet on a side) to represent each star in our galaxy.

     Not very big is it ?

     Lets call that – One cubic “sand-galaxy.”

     You can keep this for reference —

     “You could easily fit a galaxy of sand in a car.”

     Even if you double that (to represent 100 billion stars) – you could still fit that in most cars.

     Next, there are several “estimates” (all less than fully convincing) of the number of galaxies visible from here – again (very) roughly 50 to 100 billion to maybe a trillion galaxies.

     So next, lets see how big a cube of one billion “sand-galaxies” is.

     Surprisingly its a cube of sand only a fifth of a cubic mile in size ~ about 3,000 feet on a side ( ~ 2.7 billion cubic feet).

     That 3,000 foot wide cube of sand represents one billion galaxies. So lets call it a “one billion galaxy sand-cube.”

     Lets use Carmel Beach for an educated guess.
     Its pretty close to a mile long and in the summer lets make an estimate of maybe 100 feet wide and 30 feet deep. That comes to ~16 million cubic feet.

     So we’d need about 1,000 Carmel Beaches to make a “one billion galaxy sand-cube.”

     If we counted all the sand in Carmel Bay – we’d probably get enough for a whole “one billion galaxy sand-cube.”

     For the next step lets get another reference point.

     To represent the 50 to 100 to 1,000 billion galaxies – you just multiply the “one billion galaxy sand-cube” by 50, 100 or 1,000. Again, really not that much more (not that many beaches).

     Even the biggest estimate of a trillion galaxies “only” needs 1,000 cubes of sand about 3,000 feet on a side (billion galaxy sand-cubes).

     I think there are probably that many cubes of sand (of about 3,000 feet on a side) on the beaches of California alone, but your estimate on this last point are probably at least as good as mine.

     So by my estimate, there are easily more grains of sand on our planet’s beaches (by at least two, maybe three magnitudes) than there are stars in our known visible Universe.

     Aren’t you glad you asked ? :-)

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