From the February 2016 issue

Is our solar system within the Milky Way band that we see overhead on a clear night?

Edmund Walendowski, Charlottesville, Virginia
By | Published: February 22, 2016
Milky Way's center
This 340 million-pixel view of the Milky Way’s center was taken from Cerro Paranal in Chile as part of the European Southern Observatory’s GigaGalaxy Zoom project.
ESO/S. Guisard
Yes. Our solar system lies just above the Milky Way disk midplane. The bright band that we can see on a clear night is the disk of our home galaxy, and we are inside it. The brightness comes from the fact that most stars are in this disk. However, it also contains gas and dust from which stars form. Unfortunately, this material blocks our view in some wavelengths, especially in the visible band. In this sense, the development of infrared detectors in recent decades has boosted our knowledge of the galactic structure.

To get an idea of what happens when you look at the Milky Way, picture yourself in a fog. If the fog is not dense, you probably will be able to see nearby objects, but the fog will completely obscure the more distant ones. The dust in the galactic disk is much less dense than a fog, thus you cannot see dust in your neighborhood. For large distances, however, the dust accumulation along the line of sight becomes significant, blocking your view completely. The dust density increases toward the galactic center — the fog becomes thicker.

One final point. The Sun’s location within the dust-obscured disk complicates observations of the structure of our galaxy since we don’t have a bird’s-eye view of the Milky Way.

Denilso Camargo
Federal University of
Rio Grande do Sul
Porto Alegre, Brazil