Conjunction

A Conjunction is a place in time. First mentioned in Cold Days.

Description
A conjuction are when the stars and planets are aligned enough to support heavy duty magic, among other things.

About / Details

 * The stars and planets are essentially measuring sticks to describe a place in time.
 * Conjuntions do other things besides support heavy duty magic.
 * There is a Conjuntion when immortals are vulnerable, once a year—Halloween.
 * Halloween is when the Kemmlerites attempted a Darkhallow in Dead Beat.
 * Halloween is the only time to do a Darkhallow—Bob believes that Cowl knew that it had to be Halloween.

Darkhallow
In Dead Beat, Necromancers, the Heirs of Kemmler—Cowl, Corpsetaker and Grevane—raced each other to be the first to attempt a dark spell called the Darkhallow on Halloween Night to make themselves into a godlike being.

Halloween
Halloween is a Conjuntion when immortals are vulnerable and can be killed. It is also when they can be created with the Darkhallow.

In the Series Notes
In Cold Days, Harry had to swear on his magic to build Bob a new house if he told him how to kill an immortal. He did. And Bob told Harry that there is a conjunction in which immortals are vulnerable, once a year—Halloween.