casting SysTime to ubyte[]

[Laeeth Isharc via Digitalmars-d-learn]

import std.datetime;
import std.stdio;
import std.conv;

void main(string[] arg)
{
	auto a=Clock.currTime();
	auto b=cast(ubyte[])a;
	writefln("%s",b);
}

how do i get the time as a binary representation I can write to a 
file?

Thanks.