Stars in 3D: Overview

Introduction

There are over 100 billion stars in our Milky Way galaxy. Galaxies3D explores two extremes:

• the visually brightest stars, as viewed from Earth, including all stars brighter than ~magnitude 4.5 in each constellation,
• the stars nearest to us.

In these views, Galaxies3D anchors the stars to a grid parallel to the galactic plane.

The Brightest Stars and their Spiral Arm

In showing the brighest stars and star clusters and nebulae in the Milky Way, Galaxies3D makes extensive use of an image of the Milky Way Galaxy by Robert Hurt of NASA and JPL-Caltech, presented at the 212th American Astronomical Society meeting. The image is used to help make clear:

• the particular patch of the Milky Way's vast expanse in the view before us, and
• the spiral arm a particular star resides within.

The NASA/JPL-Caltech map, based on data from the Spitzer Space Telescope, shows the Milky Way with:

• 2 dominant spiral arms: the Scutum Centaurus Arm, and the Perseus arm,
• several minor spiral arms, including the Sagittarius Arm (there is some question whether the Sagittarius Arm is indeed as minor an arm as the Spitzer data seems to suggest).

The Sun lies in a small "spur" or branch arm off the Sagittarius Spiral Arm — the Orion Spur, sometimes also called the Orion Arm. That very small circle marking the position of the Sun in the Orion Spur has a radius of approximately 750 light years. The larger circles are spaced every 5000 light years from the Sun. The lines of galactic longitude radiate from the Sun across the vast galactic disk:

from Milky Way Galaxy annotated, by Robert Hurt of NASA and JPL-Caltech

In front of the Sun in the Orion Spur, towards the galactic center, is the Sagittarius Spiral Arm. In front of the Saggittarius arm lies the large Scutum-Centaurus Spiral Arm. Behind the Sun in the Orion Spur, away from the galactic center, lies the large Perseus Spiral Arm:

The majority of bright stars we see from Earth lie within that small 750 light year radius circle marking the sun in the above images. The Galactic center lies about 26,000 light years from the sun, so the 750 light year radius is about 2.9% of the way to the Galactic center.

To put some numbers on the comment about "the majority" of stars, in exploring the stars of each constellation, Galaxies3D includes all stars brighter than visual magnitude 4.5 — about 925 stars. This magnitude limit includes nearly:

• all stars visible from a dark suburban site, and
• all stars in the common patterns or asterism used to help recognize a constellation in the night sky.

At this limit, 815 visible stars lie within the 750 light year radius circle marking the Sun's position. 110 stars (about 12%) lie outside the circle, most lying within 2000 light years of the Sun and well within the Orion Spur. The notable exceptions are labeled in the image below from Galaxies3D of stars brighter than magnitude 4.5, and farther than 750 light years:

• x Carinae, a G-type hypergiant, about 8,800 light years away, far to our right (if we are facing the Galactic Center), in the Sagittarius Arm,
• α Camelopardalis, an O-type supergiant, about 6,200 light years away, behind us and to the left, in the outskirts of the Perseus Arm,
• 3 Puppis, an A-type supergiant, about 5,500 light years away, far to our right, along Orion Spur,
• ρ Leonis, a B-type supergiant, about 5,500 light years away, far to our right along the Orion Spur,
• κ Cassiopeiae, a B-type supergiant, about 4,600 light years away, behind us and just to the left, in the outskirts of the Orion Spur,
• b Velorum, an F-type supergiant, about 3,200 light years away, to our right, along the Orion Spur,
• μ Sagittarii, a multiple star system, including a B-type supergiant and B-giant, about 3,000 light years away, in front of us, in the outskirts of the Sagittarius Arm,
• τ Canis Majoris, an O-type supergiant, about 3,000 light years away, to our right, along the Orion Spur
• σ Cygni, a B-type supergiant, about 2,900 light years away, to our left, along the Orion Spur
• ι1 Scorpii, an F-type supergiant, about 1,900 light years away, in front of us, perhaps in the outskirts of the Sagittarius Arm

If a constellation's displayed stars (= all stars brighter than magnitude ~4.5) include stars at or outside the 750 light year radius circle marking the Sun's location on the NASA image, Galaxies3D will display the magnified patch of the NASA Milky Way Galaxy image, scaled to the grid, in its 3D view of the constellation. That 750 light year radius circle will often appear highly magnified in the view, as in this image of stars in constellation Centaurus:

If a constellation's displayed stars (= all stars brighter than magnitude ~4.5) are all contained within the 750 light year radius circle, Galaxies3D does not display the NASA Milky Way image, as in this image of stars in the constellation Bootes:

Nearest Stars

In displaying our Sun's "next store" neighboring stars, Galaxies3D paints onto the base galactic plane grid a NASA bitmap of the local interstellar medium:

In this view of all known stars and brown dwarfs up to 16.3 light years from the sun, the color coding of stars by their spectral type helps make it clear that the majority of the stars near the Sun are small, long-lived red main-sequence M-stars. Standing out in this view is the closest star system to the sun, the triple-star system containing α Centauri, a yellow G2 main sequence star just like our Sun, and the blue A1 main sequence star Sirius:

A subset of the above view shows the stars and brown dwarfs within 11 light years of the sun:

Bright Stars and Near Stars

Bright Stars in the Constellations