Perseus Arm

The Perseus Arm begins from the distal end of the long Milky Way central bar.

Recently, scientists in two large radio astronomy projects, the Bar and Spiral Structure Legacy (BeSSeL) Survey and the Japanese VLBI Exploration of Radio Astrometry (VERA), have made great efforts over about 20 years to measure the trigonometric parallaxes toward about 200 water vapor (H2O) and methanol (CH3OH) masers in massive star-forming regions in the Milky Way.

They have employed these parallax measurements to delineate the forms of spiral arms from the Galactic longitude 2 to 240 degrees and extended the spiral arm traces into the portion of the Milky Way seen from the Southern Hemisphere using tangencies along some arms based on carbon monoxide emission.

[3] There is speculation that the local spur known as the Orion–Cygnus Arm, which includes the Solar System and Earth and is located inside of the Perseus Arm,[1] or is a branch of it, but this is unconfirmed.

The Perseus Arm contains the Double Cluster and a number of Messier objects: