Explanation:
Narrow band filters and a
false-color palette give these three
nebulae a stunning appearance against the cosmic canvas of
the central Milky Way.
All three are stellar nurseries about
5,000
light-years or
so distant, toward the nebula rich constellation
Sagittarius.
In the 18th century, astronomer Charles
Messier cataloged two of
them; colorful M8, above and right of center, and compact M20 at the
left.
The third, NGC 6559, is at bottom right.
Over a hundred light-years across, M8 is also known as the
Lagoon Nebula.
Divided by obscuring dust lanes, M20's popular moniker is
the Trifid.
In the composite image, narrow
emission lines
from sulfur, hydrogen, and oxygen atoms recorded through the filters, are
mapped into broader red, green, and blue colors respectively.
The color scheme
was made popular in Hubble Space Telescope images.
But for ground-based telescopes, narrow band filters also make it possible
to reject overwhelming light-pollution and capture
compelling images of the cosmos from
urban skies.
