#1# #"parsec"# is equal to #3.26156# #"ly"#.

#1# #"ly"# is the time it takes light in vacuum to travel one year, and is equal to the product of the amount of seconds in one year (#365.25# #"days" = 31557600# #"s"#) and the speed of light in vaccum, #299792458"m"/"s"#:

#1# #"ly" = 31557600# #cancel("s")# #xx 299792458"m"/(cancel("s"))#

#= 9,460,730,472,580,800# #"m"# (exactly)

Thus, #10^8# #"ly"# =

#10^8# #cancel("ly")((9,460,730,472,580,800"m")/(1cancel("ly")))#

#= 946,073,047,258,080,000,000,000# #"m"#