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.