The Local (Orion) Spur is the short spiral feature the Sun lives in, a band of stars and gas lying between the Sagittarius–Carina and Perseus arms.
At a glance
| runs from the centre | 6 to 12 kpcmodel |
|---|---|
| width | about 650 light-yearsmodel |
| pitch angle | 11.4°model |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About Local (Orion) Spur
Every star visible to the naked eye, and the Sun itself, belongs to this stretch of the Galaxy. It is called the Orion Spur after its best-known star-forming region, the Orion complex with the Orion Nebula at its heart, and it is also known simply as the Local Arm. Looking along it from Earth, one direction runs towards Cygnus, where the great Cygnus star-forming clouds lie within it.
For a long time it was thought to be a minor offshoot, a bridge of gas between two real arms. Parallax measurements of masers changed that picture: they showed the Local Arm to be longer and richer in star formation than expected, more like a true arm segment than a short spur.
What you see in the piece
In the piece you start inside it, so its stars fill the sky around you. Zoom out until the arms appear and the Sun is a point on this modest band, out in the suburbs between two larger arms.
Measured or modelled
Its track, width and pitch angle are the maser fit of Reid and collaborators. Whether it is an independent arm, a branch of the Perseus Arm or a bridge between arms is still debated.
Questions
Which spiral arm is the Sun in?
The Sun lies in the Local (Orion) Spur, between the Sagittarius–Carina Arm on the inside and the Perseus Arm on the outside. The piece models the spur from 6 to 12 kpc from the centre.
How big is the Orion Spur?
In the piece it is about 650 light-years wide, with a pitch angle of 11.4°, which makes it the narrowest of the arms the piece draws.