A Sky Full Of Hydrogen
Explanation:
Interstellar space is
filled with extremely tenuous clouds of gas which are mostly Hydrogen.
The neutral hydrogen atom (HI in astronomer's shorthand) consists of 1
proton and 1 electron. The proton and electron spin like tops but
can have only two orientations; spin axes parallel or anti-parallel.
It is a rare event for Hydrogen atoms in
the interstellar medium
to switch from the parallel to the anti-parallel configuration,
but when they do they emit radio waves with a
wavelength of 21 centimeters (about 8 inches) and a
corresponding frequency of exactly 1420 MHz.
Tuned to this frequency
radio telescopes have mapped the neutral Hydrogen in the sky.
The above image represents such an all-sky HI survey
with the plane of our Milky Way Galaxy
running horizontally through the center.
In this false color image no
stars are visible,
just diffuse clouds of gas tens to hundreds of light years
across which cluster near the plane.
The gas clouds seem to form arching, looping
structures, stirred up
by stellar activity in the galactic disk.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings,
and Disclaimers
NASA Official: Jay Norris.
Specific
rights apply.
A service of:
LHEA at
NASA /
GSFC
& Michigan Tech. U.
