Distances and the metric system

The prefixes of the metric system are incredibly easy to master.  All the prefixes mean the same, regardless of which unit they precede.
Mega=one million
Giga=one billion
Tera=one trillion
Peta=one quadrillion
Exa=one quintillion
Zetta=one sextillion
Yotta=one septillion
One Parsec is about 30.5 Petameters!
Megaparsecs are distances among galaxies, Andromeda is the only major galaxy under a
megaparsec away
deci=one tenth
centi=one hundreth
milli=one thousandth
micro=one millionth
nano=one billionth
pico=one trillionth
femto=one quardrillionth
atto=one quintillionth
zepto=one sexillionth
yocto=one septillionth

In astronomy, such distances are usually in units of kilometers, but by changing the prefix from kilo-, one may multiply distances by thousands.  The same goes for parsecs, which is the metric unit as well.  Below explains the concept of parallactic seconds.  In this case, galaxies are usually megaparsecs away.  Our Milky Way has a diameter around 30 kpc.  Alpha centauri is about 1.3 pc away.  Vega, my favorite star is 8 pc away.  Its companion appears 40 seconds of arc away, so the distance between them is 8 times 40 or 320 earth-sundistances. 


Use light years for distant galaxies as they retreat from us.

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