ThePerseus Arm is one of two majorspiral arms of theMilky Way galaxy. The second major arm is called theScutum–Centaurus Arm. The Perseus Arm begins from thedistal end of the longMilky Way central bar.[1] Previously thought to be 13,000 light-years away, it is now thought to lie 6,400 light years from theSolar System.[2]
The Milky Way is abarred spiral galaxy with two major arms and a number of minor arms or spurs.[1] The Perseus Spiral Arm, with a radius of approximately 10.7 kiloparsecs, is located between the minorCygnus andCarina–Sagittarius Arms.[1] It is named after thePerseus constellation in the direction of which it is seen from Earth.
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 (H
2O) andmethanol (CH
3OH) 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. The image clearly presents the Milky Way as a barred spiral galaxy with fairly symmetric four major arms and some extra arm segments and spurs.[3][4]
The Perseus Arm is one of the four major arms. The arm is the length of more than 60,000 lr and the width of about 1,000 lr and the spiral extension in the pitch angle near 9 degree.[3]
There is speculation that the local spur known as theOrion–Cygnus Arm, which includes theSolar System andEarth and is located inside of the Perseus Arm,[1] or is a branch of it, but this is unconfirmed.
The Perseus Arm contains theDouble Cluster and a number ofMessier objects:
