The Sagittarius–Carina Arm is the spiral arm just inside the Sun’s orbit, the nearest arm towards the Galactic Centre and home to some of the sky’s richest nebulae.
At a glance
| runs from the centre | 3.5 to 14 kpcmodel |
|---|---|
| width | about 1,100 light-yearsmodel |
| pitch angle | 17.1°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 Sagittarius–Carina Arm
Looking towards the centre of the Galaxy from Earth, the first spiral arm the line of sight crosses is the Sagittarius–Carina Arm. Its name records the two directions in which we look along it: Sagittarius in the northern summer sky and Carina in the deep south. Between those directions it arcs across the inner Galaxy.
It is a minor arm in old stars but a strong one in gas and star formation. The Lagoon Nebula in Sagittarius and the Carina Nebula, with the unstable giant Eta Carinae inside it, both lie in this arm, and its young clusters and glowing clouds make up much of the bright, knotted texture of the Milky Way band in those constellations.
What you see in the piece
From the Sun it is the arm you see most of: its nebulae and star clouds hang in the foreground of the dust that hides the centre. Fly out above the disc and it becomes the next arm in from the Local Spur.
Measured or modelled
The arm’s track, width and pitch angle are the Reid and collaborators fit to maser parallaxes; the arm is well measured near the Sun and extrapolated on the far side of the Galaxy.
Questions
Which spiral arm is closest to the Sun?
The Sun lies in the Local (Orion) Spur. The nearest major arm inward is the Sagittarius–Carina Arm, which in the piece’s model runs from 3.5 to 14 kpc from the centre.
What nebulae are in the Sagittarius–Carina Arm?
The Lagoon Nebula and the Carina Nebula are among its best known. The piece gives the arm a width of about 1,100 light-years and a pitch angle of 17.1°.