# Billions of stars

Emieno
If there are so so so many stars, in what way can you find out the nearest one to your position?

Staff Emeritus
Visual observation with a telescope and trigonometry (triangulation).

As the Earth revolves around the sun, one can observe stars 6 months apart. The distance then separating the 2 observations (2 astronomical units) forms the base of a triangle (diameter of the Earth's orbit around the sun), and the distance to the star forms the two legs of an isoceles triangle. Knowing the angles of the two observations, one constructs a triangle and determines the distance of the two legs, hence the distance to a star.

For some background - http://en.wikipedia.org/wiki/Astronomical_unit

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Emieno
Thanks, but what if now particles are in place of stars ? From a given particle can you tell me how to find the nearest one ? All particles are supposed to be motionless..forexample :-)

Staff Emeritus
What particles? Do you mean protons, electrons, atoms, molecules, dust particles, . . . ?

Smurf
or are you talking about the cooler particles like Tachyons and Higgs. Btw, nothing (and yet, everything) is 'motionless', anything can be declared at rest.

zoobyshoe
Emieno said:
Thanks, but what if now particles are in place of stars ? From a given particle can you tell me how to find the nearest one ? All particles are supposed to be motionless..forexample :-)

...

Staff Emeritus

Radar is used for weather - as in tracking storms and water droplets.

Lasers can also be used.

Radar and lasers can incorporate Doppler anemometry as well to get not only position, but velocity as well.

Lasers are often used in flow visualization.

There are distance limitations as well.

I would still like to know what particles?

Subatomic particles are subject to Heisenberg's uncertainty principle, and one will never now the position of a quark, neutron or neutrino, or any other neutral particle with much certainty. One knows about neutral particles after they after some interaction.

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