The images below are of the Cresent nebula (NGC 6888) in the Constellation of Cygnus the Swan. This emission nebula is around 5000 light years and is powered a bright Wolf-Rayet star that is ~in the middle of the nebula. Fast stellar winds from this star are colliding with slower gas emitted by the star when it became are Red giant around 1/4 of million years ago and causing it glow. The images below were made using different combinations of filter to bring out the different elements of the nebula. In general, the blue comes from Oxygen energized by the collision. Red comes from Hydrogen gas (except for the Hubble pallet image were the Hydrogen Alpha (Ha) line has been assigned to the green channel).

The first image was made using the third and fourth images and shows why it has the nick name "Brain Nebula".

The second image was made using Luminance, Red, Green and Blue filters and shows why this is called the Crescent nebula.

The Third image was made using a Narrow band Oxygen 3 (O3) filter for the luminance and the Blue channel, a Green filter for the Green Channel and a Narrow Band Ha filter for the red channel.

The fourth image was made using what is known as the Hubble Pallet were a Narrow band Sulphur 2 filter is used for the Red Channel (Note: the yellow in the image where the red and green combine), Ha is used for the Green Channel and O3 is used for the Blue channel.

All the images were taken at F10 with a 4096 mm focal length using an ASI 6200MM pro camera using 1x1 binning, gain set to 100 and cooled to -12C.

Exposure times used per filter
Red -15 exposures at 4 minutes each.
Green -15 exposures at 4 minutes each.
Blue -16 exposures at 4 minutes each.
Luminance -20 exposures at 2 minutes each.
Ha -15 exposures at 500 seconds each.
O3 -15 exposures at 500 seconds each.
S2 -15 exposures at 500 seconds each.