56 AUSTRALIAN SKY & TELESCOPE May | June 2017
IVÁN ÉDERWE SEE OUR GALAXY,the Milky Way, as a band of light stretching
across the sky. There’s a ghostly aspect to it; faint streamers of gas and dust extend
far above and below the galactic plane, reaching the galactic pole. This galactic
cirrus— twisted clouds of interstellar dust particles at high galactic latitudes first
observed in the far infrared in 1983–84 by the Infrared Astronomy Satellite (IRAS)
— glows in the dim red region of the spectrum. But the dust also reflects blue light
from countless millions of stars, as shown by amateur astronomer Steve Mandel in- Mandel noticed the subtle blue glow of the spooky dust tendrils associated
with M81 and M82 and captured it in images. These images, which formed
the basis of his Unexplored Nebula Project (galaxyimages.com/UNP1.html),
demonstrated that the dusty interstellar medium could be seen not only in the far
infrared, but in visible light as well.
Mandel called these clouds Integrated Flux Nebulae (IFN), and, taking their cue
from his work, many amateur astronomers use this term whether referring to
galactic cirrus or dusty interstellar medium (ISM) in the galactic plane. Professional
astronomers distinguish more carefully between the two, though the boundary
between them is somewhat, well, nebulous. ISM, the dust and gas between the stars,
is distributed throughout our galaxy, but can be found relatively close by — say 200
light-years from us at its nearest — in the galactic plane. Galactic cirrus, on the other
SROBES OF DUST Galactic cirrus
enshrouds the galaxies M81 (left) and M82
(right) in Ursa Major. It takes commitment
to image these dim structures. This image
represents nearly 25 hours of exposure time
with a 30-cm f/4 reflector.NGALACTIC CIRRUS by Mel Bartels
With the right small scope,
you can track down these
dusty wraiths first
observed in the late
18th century.