What is the "cosmic address" of globular cluster M15?
Globular Cluster M15, also known as Messier 15, is a tightly-packed ball of stars orbiting roughly together in the constellation Pegasus. It is a remnant of star growth and activity from the birth of the Milky Way Galaxy, and is visible from Earth with binoculars on clear nights.
The "Cosmic Address" of a stellar object is based in orbits and positions relative to other objects; because most things in the universe are in a constant state of motion, we can only assign a common relative position to an object as long as it is not overtly moving around. For example, M15 is part of the constellation Pegasus, so it hasn't moved outside of that area for a long time. Its position relative to our solar system is about 33.6 thousand light-years; it occupies the NQ4 quadrant of the sky, inside Pegasus, near the bright Epsilon star. If one were to address a letter to M15, the address would read: "Messier 15, 3.5 deg W and 2.25 deg N of Epsilon, Pegasus Constellation, Quadrant NQ4, Milky Way Galaxy" (messier.seds.org).