blood - could it mean the energy we have in our bodies or is it literal as to the blood as it flows through out our bodies much like the path the sun and moon take in our universe.
pulse - could it mean the actual pumping of our hearts or could it relate to the rhythm created by the beating of our hearts much like any rhythm we find in nature, i.e. the rhythm of the wind be it caressing the leaves of a tree or the beating of it upon the waves during a typhoon.
similar - is this separate from the others or is it a link between the characters of the sun; sun and moon; sun or moon; blood to the sun; blood to the moon; blood to the sun and moon; pulse of the blood; pulse of the sun radiating out; pulse of the moon's effects on the earth.
sun - literally the sun above or is this a analogous meaning to something else; sun in relation to the moon; the suns direct influence on the moon; the suns influence on the earth through the moon.
moon - the moon lighting the night to provide guidance in our travels along the path or is this a symbol for some other esoteric meaning; the moon does influence such things as the tides so does it relate to anything that ebbs and flows and has rhythm; does this refer to reflections of the moon in various places to indicate such things as a still mind, body, and spirit or do we need to do more research as to the meaning in the time, place, and person who wrote it.
When we accept this particular meaning how do we interpret it especially since the author does not expand as to their frame of mind and reference. Maybe this is the point so that each of us can use our own perspective, frame of mind, and frame of reference to interpret it for our use.
Maybe that is the intent with the Chinese characters. There are cycles and rhythms cast upon the earth from influences of both the sun and moon. These connections cause the earth to respond accordingly and maybe the meaning of the blood to the sun and moon means that our bodies respond accordingly in a similar manner.