ASTRO: Sh2-120 and Sh2-121

sh2-120 and Sh2-121 are a pair of emission nebula in Cygnus about 5
degrees north of the far more well known North American Nebula, NGC
7000. There is a lot of confusion in the catalogs about these two much
to my surprise. SH2-121 is listed as a galaxy in The Sky, PGC 2349711.
SIMBAD misses the position of SH2-120 by about 4 minutes of arc
putting it where nothing is to be seen. Galaxy Map says that both 120
and 121 are at the same distance of 7500 parsecs (24,500 light-years)
under their entry for Sh2-120. Under Sh2-121 they cite another source
as putting it at 4500 parsecs +/- 1000 Parsecs (14,500 light-years +/-
3000 light-years). Then in a third paragraph says it is at a distance
of 6500 parsecs (21,000 light-years). In other words, determining the
distance to these is full of uncertainties. The citation that puts it
at 6500 light-years adds that it is surrounded by an expanding shell
containing about 39 solar masses of gas that is about 650,000 years old.
All this driven by an O8.5 star. Which star that is I don't know.

The H alpha data was mixed using lighten mode with the percentages
shown. I've found this mix retains the color seen in RGB images

14" LX200R @ f/10, L=4x10'+Ha=2x30', R=2x10'+80% of the Ha data,
G=2x10'+5%Ha, B=2x10+20%Ha, STL-11000XM, Paramount ME

Cropped image at 0.8" per pixel.

Rick
--
Prefix is correct. Domain is arvig dot net

Rick,

that's a neat pair. Another target for longer focal lengths in summer.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
...

sh2-120 and Sh2-121 are a pair of emission nebula in Cygnus about 5
degrees north of the far more well known North American Nebula, NGC
7000. There is a lot of confusion in the catalogs about these two much
to my surprise. SH2-121 is listed as a galaxy in The Sky, PGC 2349711.
SIMBAD misses the position of SH2-120 by about 4 minutes of arc
putting it where nothing is to be seen. Galaxy Map says that both 120
and 121 are at the same distance of 7500 parsecs (24,500 light-years)
under their entry for Sh2-120. Under Sh2-121 they cite another source
as putting it at 4500 parsecs +/- 1000 Parsecs (14,500 light-years +/-
3000 light-years). Then in a third paragraph says it is at a distance
of 6500 parsecs (21,000 light-years). In other words, determining the
distance to these is full of uncertainties. The citation that puts it
at 6500 light-years adds that it is surrounded by an expanding shell
containing about 39 solar masses of gas that is about 650,000 years old.
All this driven by an O8.5 star. Which star that is I don't know.

The H alpha data was mixed using lighten mode with the percentages
shown. I've found this mix retains the color seen in RGB images

14" LX200R @ f/10, L=4x10'+Ha=2x30', R=2x10'+80% of the Ha data,
G=2x10'+5%Ha, B=2x10+20%Ha, STL-11000XM, Paramount ME

Cropped image at 0.8" per pixel.

Rick
--
Prefix is correct. Domain is arvig dot net