Digital Universe Guide - Hayden Planetarium

3.3. MILKY WAY DATA GROUPS 111
3.3.21 Visible All-Sky Survey
Group Name mwVis
Reference Axel Mellinger (Universitaet Potsdam)
Prepared by Ryan Wyatt (AMNH/Hayden)
Labels No
Files mw-visible.speck
Dependencies mellinger-optmw.sgi
Wavelength 400 nm − 700 nm
Frequency 750,000 GHz − 430,000 GHz
In ancient times, our ancestors knew of the stars, the “wandering stars” (planets), and the Milky Way.
Aside from the occasional comet, “guest star” (supernova), or aurora, these were the only cosmic
features visible to them.
The Milky Way has been the subject of many myths and legends. The Greeks believed it to be a river
of milk pouring from the breast of Hera, the wife of Zeus, and called it a “galaxy,” from the Greek word
for milk. The Romans called it the Via Lactea, or the Milky Way. But it was not until 1610 that Galileo
first observed this faint band of light with his telescope, discovering that it was composed of innumerable
faint stars.
In the past 400 years, astronomers and philosophers have speculated about the nature of this star
system. It was not until the 20th century, though, that astronomers began to understand the nature and
structure of our Galaxy, by looking at that band of light across our sky and comparing it with other
“island universes,” like the Andromeda Galaxy.
Image Features Several features of this band of light become obvious upon inspection (particularly
if you increase its alpha value using the Alpha Slider). You will see the brightest part of the Galaxy if
you look toward Galactic center [turn on the Galactic coordinates (galac) and bring (l, b) = (0, 0) ◦ to
center screen]. In this direction, looking toward Scorpius and Sagittarius, is the center of the Galaxy.
The bright haze is the light from millions of stars; the dark lanes are foreground dust, obscuring our
view. Relative to the rest of the Milky Way band, the center forms what astronomers call a “bulge” of
light (see group bulge for size), whereas the rest of the band appears thinner.
If you turn to look in the opposite direction, toward Orion [(l, b) = (180, 0) ◦ ], you will see that the Milky
Way is not too bright on this side of the sky. Here we look out of the Galaxy through what remains of the
Galactic disk between the Sun and its outer edge.