Anticenter shell
{{Short description|Ordinary object}}
{{infobox nebula
|name= Anticenter Shell
|type= supershell
|epoch= B1950.0
|ra= {{RA|06|27}}
|dec= {{DEC|+15}}
|dist_ly= 55 k
|dist_pc= 17 k
}}
The anticenter shell or anticenter superbubble is a region near the anticenter of the Milky Way Galaxy that emits 21 cm radiation. It is located at {{RA|06|27}} {{DEC|+15}}, or l = 197°, b = +2° in galactic coordinates, near the border of the constellations Gemini and Orion. It is a supershell (a very large superbubble) within our galaxy that is spherical in shape and features jets of gas.
Discovered in 1970, this galactic object has subsequently been variously classified by researchers as a spiral arm of the Milky Way in 1972, a nearby tidally-stripped dwarf galaxy in 1975, and a high-velocity cloud in 1979.{{cite journal
| last= Tamanaha
| first= Christopher M.
| journal= Astrophysical Journal Supplement Series
| title= The Anticenter Shell and the Anticenter Chain
| doi= 10.1086/312975 | volume=109
| issue= 1 | pages=139–175
| date=1997
|bibcode = 1997ApJS..109..139T | doi-access= free
}}
The name Snickers for the anticenter shell arose from the description in 1975 by Christian Simonson, a University of Maryland astronomer who believed it to be a small "peanut" of a galaxy just outside the Milky Way.{{cite journal
| last = Simonson
| first = S. Christian, III.
| title = A New Milky Way Satellite Found in 21-Centimeter Line Observations
| journal = Astrophysical Journal Letters
| volume = 201
| pages = L103–L108
| date=1975
| bibcode = 1975ApJ...201L.103S
| doi = 10.1086/181952
}}
| title = Snickers
| work = Astroprof's Page
| date = 2006-02-28
| url = http://astroprofspage.com/archives/117
| accessdate = 2008-02-01
| archive-url = https://web.archive.org/web/20071017213943/http://astroprofspage.com/archives/117
| archive-date = 2007-10-17
| url-status = dead
}}
Simonson's colleagues coined the name Snickers (in reference to the American chocolate bars Milky Way and Snickers) due to its proximity to the Milky Way. Less popularly, the anticenter superbubble is also referred to as 0627-15 from its equatorial coordinates.{{Cite news
|title=Peanuts in the Sky
|newspaper=Time
|date=1975-11-24
|url=http://www.time.com/time/magazine/article/0,9171,913757,00.html
|accessdate=2008-02-01
|archiveurl=https://web.archive.org/web/20080209030517/http://www.time.com/time/magazine/article/0%2C9171%2C913757%2C00.html
|archivedate=9 February 2008
|url-status=dead
}}
The anticenter shell is approximately 55,000 light years (17 kpc) from the Sun. Its dimensions are difficult to determine by radio observation due to its location near the Zone of Avoidance, the regions of the sky obscured by interstellar dust along the galactic equator.