M57
or the popular Ring Nebula in Lyr (NGC6720). Its central star is
a bluish sub-dwarf, very hot 100,000 degrees and likely near its
end. The Ring is at a distance of 1500 l-y and its diameter
about 0.5 l-y. It is estimated that the central star ejected the
nebula approx 20,000 yrs ago, but not in a nova-like explosion.
Spectrographic imaging shows distinct wavelengths in the ring,
while the central star gives just a colored streak.
M46,
OC in Pup, is at 5,000 l-y distance; ringlet nebula, NGC2438, is
3,000 l-y away. The central star is one of the hottest white
dwarfs in our MW, 75,000 degrees K; our Sun is 5,800.
M16,
The Eagle,
is a large star cluster in a large diffuse nebula in Serpens. A
real beauty, but it requires a long exposure. Its center
features the “Pillars of creation”; three denser clouds where
stars are being ‘born’. The Eagle is 8,000 l-y away and located
in the Sagittarius arm of our MW. The Pillars are about 3-6 l-y
in length. Some of the stars are brilliant (several 1000 times
our Sun) and young.
M16,
The Eagle
M8,
Lagoon, is a fine diffuse nebula, just visible with the unaided
eye and easily mistaken for a comet. A photograph reveals its
fine details. Barnard’s nebula B88 and NGC6530 are almost part
of the Lagoon
M17,
The Swan
(Omega is also used), is a diffuse nebula in northern
Sagittarius. Easily mistaken for a comet because of its shape as
a ‘streak’. Imagine the ‘streak’ as the body of a swan, then the
hook at the eastern end can be viewed as the neck and head of a
swan (with some effort). The Swan is almost 6000 l-y away 
M20, Trifid nebula, is only 1 degree north of M8, and consists of three fairly distinct irregular nebulous parts. A bright triple star is near center. A nice nebula and easy to photograph.
portion
The Crescent Nebula, NGC 6888 in Cyg, is only 4,800 l-y
away and is 20’ across in the sky. It has luminous shells around
Wolf-Rayet star WR136. The star’s eruptions (periodic at abt
10,000 years) started 250,000 years ago and the ejected gasses,
blown by the stellar wind of WR136, are colliding with the
surrounding “stuff”. The shockwaves are creating the complex
shell structure and the UV of WR136 ionizes the gas which
creates the luminosity. Soon (few million years) WR136 will
explode as a SuperNova.
M17, or Swan, Omega or Horseshoe Nebula in Sgr (Sagittarius), a large and beautiful diffuse nebula of 45’ x 35’; mag 9 and at a distance of 6,000 l-y.
Bubble Nebula, NGC 7635 Bubble. A longer, 20 times 180 sec,
exposure paid off. Compare with the earlier one.
Our Halloween “special”: VdB141, Sh2-136 or “Ghost Neb”
in Cep is 1,200 l-y away and 2 l-y across.
The star, just visible in the bright portion of the ghost, excites the hydrogen and illuminates the dust of the nebula; it is a young one not even on the “main sequence” yet and still picking up hydrogen.
The star is of the FU-Orionis type (“FUORs”). In 1936 FU-Ori brightened from mag 16 to 10 in a few months; just the opposite of a SN.
The core of the the dark cloud, on the spooky arm farther to the right, shows likely the birth of a binary star. Now it is still a reddish and diffuse dot.
The Horsehead Nebula in Orion, a dark nebula, B33, against IR nebulosity, IC434. The ‘little’ horse head’s size is one l-y or 6 trillion miles!
The star, just visible in the bright portion of the ghost, excites the hydrogen and illuminates the dust of the nebula; it is a young one not even on the “main sequence” yet and still picking up hydrogen.
The star is of the FU-Orionis type (“FUORs”). In 1936 FU-Ori brightened from mag 16 to 10 in a few months; just the opposite of a SN.
The core of the the dark cloud, on the spooky arm farther to the right, shows likely the birth of a binary star. Now it is still a reddish and diffuse dot.
The Horsehead Nebula in Orion, a dark nebula, B33, against IR nebulosity, IC434. The ‘little’ horse head’s size is one l-y or 6 trillion miles!
