Galaxies

A larger and unlabelled version of the above map is available here.
I have used the most common names for the spiral arms on this map. But occasionally you may find alternative names being used for the spiral arms. This table lists some of the alternative names:

Common Name	Alternative Name
Norma Arm	3 kiloparsec Arm
Scutum-Crux Arm	Centaurus Arm
Sagittarius Arm	Sagittarius-Carina Arm
Orion Arm	Local Arm
Perseus Arm	-
Cygnus Arm	Outer Arm

Note also that the Orion Arm is not a major spiral arm, but only an enhancement of stars and gas between the Sagittarius and Perseus arms.
It should be emphasized that there are almost as many stars between the spiral arms as in the spiral arms. The reason why the arms of spiral galaxies are so prominant is that the brightest stars are found in the spiral arms. Spiral arms are the major regions of star formation in spiral galaxies and this is where most of the major nebulae are found.