deepskytraveler
July 16th, 2018, 03:21 AM
Object of the Week July 15, 2018 - NGC 7006
NGC 7006, C 42
Type: Globular Cluster
Constellation: Delphinus
RA: 21h 01m 29.0
Dec: +16° 11’ 18”
Size: 3.6’
Mag(v): 10.6
There are two cataloged globular clusters in the constellation Delphinus. The most prominent one is NGC 6934 which I wrote about as the Object of the Week three years ago here (http://www.deepskyforum.com/showthread.php?766-Object-of-the-Week-August-23-2015-NGC-6934&highlight=7006). The other, less prominent globular cluster is NGC 7006, this week’s Object of the Week.
NGC 7006 was discovered August 21, 1784 by William Herschel and later observed by his son, John Herschel on October 11, 1825. Per W Herschel, “Very bright, small, round, gradually much brighter in the middle. Resolvable.” Per Dreyer, “NGC 7006 (= GC 4625 = JH 2097 = WH I 52, 1860 RA 20 54 58, NPD 74 21.5) is "bright, pretty large, round, gradually brighter middle. The position precesses to RA 21 01 30.3, Dec +16 11 19, well within the outline of the cluster, the description fits and there is nothing else nearby, so the identification is certain.”
NGC 7006 is much smaller and fainter than the more prominent globular in Delphinus, NGC 6934. To a large extent this is due to NGC 7006 being the most distant object of its kind in the Milky Way galaxy, approximately 135,000 light-years from Earth. It was the work of Harlow Shapley that first established the distance of this globular cluster. His observations of 11 RR Lyrae stars in the NGC 7006 showed the cluster to be about five times as remote as M3 or M5, the most distant globulars known at that time (1920s).
Despite its small size of 3.6’ NGC 7006 should be detectable as something other than a star in a 6” telescope. Moving up to a 10” scope, I noticed a slight brightening towards the center of the globular, however there was not noticeable resolution of stars within the cluster. Moving up to a 15” scope, I’m able to discern a smattering of individual stars, however I don’t know whether they are part of the globular or just foreground stars.
Christian Luginbuhl and Brian Skiff in Observing Handbook and Catalogue of Deep Sky Objects provide the following description of the globular NGC 7006. “At a distance of nearly 40 kiloparsecs, this globular cluster is faintly visible in 15 cm. The faint glow is about 1’ diameter with a relatively bright core. With 25 cm it is 1.25’ diameter and shows no resolution even in good seeing. The haze is broadly brighter across the center, exhibiting no sharp central condensation. A mag. 14 par with 20” separation in pa 85° is visible 1.5’ S. In 30 cm the cluster is 1.5’ diameter. A few faint stars are resolved over a granular background at 475 x.”
Brent Archinal and Stephen James O’Meara in Deep-Sky Companions: The Caldwell Objects provide this description of NGC 7006 as observed through the 31” reflector at the Warren Rupp Observatory in Mansfield, Ohio. “The cluster was a scintillating mass of dim starlight. At high power we saw an unresolved, starlike inner core surrounded by a dark ring that defined the inner edge of a finely resolved, though jagged, outer core. With averted vision thin arms radiated out from the stellar ‘hole’ like the limbs of a starfish wrapped around a rock. The outer halo appeared loose and fractured, as if its shell were so old and brittle that pieces of it were flaking off into space.”
3125
12 arcmin wide SDSS image
3126
6 arcmin wide SDSS image
3127
3.2 arcmin wide HST image
For those of you using large aperture you should try for three galaxies that lay less than 8” from the NGC 7006. They are PGC 65907 m15.69(v), PGC 1501723 m16.27(v), and PGC 65908 m16.08(v).
Interesting bit of trivia: NGC 7006 appears in the science fiction novel Beyond the Farthest Star by Edgar Rice Burroughs (written in 1940 but not published until 1964), where it is used as a point of reference by the inhabitants of the planet Poloda to determine the approximate location of Earth.
Now it is your turn. Give it a go and let us know.
NGC 7006, C 42
Type: Globular Cluster
Constellation: Delphinus
RA: 21h 01m 29.0
Dec: +16° 11’ 18”
Size: 3.6’
Mag(v): 10.6
There are two cataloged globular clusters in the constellation Delphinus. The most prominent one is NGC 6934 which I wrote about as the Object of the Week three years ago here (http://www.deepskyforum.com/showthread.php?766-Object-of-the-Week-August-23-2015-NGC-6934&highlight=7006). The other, less prominent globular cluster is NGC 7006, this week’s Object of the Week.
NGC 7006 was discovered August 21, 1784 by William Herschel and later observed by his son, John Herschel on October 11, 1825. Per W Herschel, “Very bright, small, round, gradually much brighter in the middle. Resolvable.” Per Dreyer, “NGC 7006 (= GC 4625 = JH 2097 = WH I 52, 1860 RA 20 54 58, NPD 74 21.5) is "bright, pretty large, round, gradually brighter middle. The position precesses to RA 21 01 30.3, Dec +16 11 19, well within the outline of the cluster, the description fits and there is nothing else nearby, so the identification is certain.”
NGC 7006 is much smaller and fainter than the more prominent globular in Delphinus, NGC 6934. To a large extent this is due to NGC 7006 being the most distant object of its kind in the Milky Way galaxy, approximately 135,000 light-years from Earth. It was the work of Harlow Shapley that first established the distance of this globular cluster. His observations of 11 RR Lyrae stars in the NGC 7006 showed the cluster to be about five times as remote as M3 or M5, the most distant globulars known at that time (1920s).
Despite its small size of 3.6’ NGC 7006 should be detectable as something other than a star in a 6” telescope. Moving up to a 10” scope, I noticed a slight brightening towards the center of the globular, however there was not noticeable resolution of stars within the cluster. Moving up to a 15” scope, I’m able to discern a smattering of individual stars, however I don’t know whether they are part of the globular or just foreground stars.
Christian Luginbuhl and Brian Skiff in Observing Handbook and Catalogue of Deep Sky Objects provide the following description of the globular NGC 7006. “At a distance of nearly 40 kiloparsecs, this globular cluster is faintly visible in 15 cm. The faint glow is about 1’ diameter with a relatively bright core. With 25 cm it is 1.25’ diameter and shows no resolution even in good seeing. The haze is broadly brighter across the center, exhibiting no sharp central condensation. A mag. 14 par with 20” separation in pa 85° is visible 1.5’ S. In 30 cm the cluster is 1.5’ diameter. A few faint stars are resolved over a granular background at 475 x.”
Brent Archinal and Stephen James O’Meara in Deep-Sky Companions: The Caldwell Objects provide this description of NGC 7006 as observed through the 31” reflector at the Warren Rupp Observatory in Mansfield, Ohio. “The cluster was a scintillating mass of dim starlight. At high power we saw an unresolved, starlike inner core surrounded by a dark ring that defined the inner edge of a finely resolved, though jagged, outer core. With averted vision thin arms radiated out from the stellar ‘hole’ like the limbs of a starfish wrapped around a rock. The outer halo appeared loose and fractured, as if its shell were so old and brittle that pieces of it were flaking off into space.”
3125
12 arcmin wide SDSS image
3126
6 arcmin wide SDSS image
3127
3.2 arcmin wide HST image
For those of you using large aperture you should try for three galaxies that lay less than 8” from the NGC 7006. They are PGC 65907 m15.69(v), PGC 1501723 m16.27(v), and PGC 65908 m16.08(v).
Interesting bit of trivia: NGC 7006 appears in the science fiction novel Beyond the Farthest Star by Edgar Rice Burroughs (written in 1940 but not published until 1964), where it is used as a point of reference by the inhabitants of the planet Poloda to determine the approximate location of Earth.
Now it is your turn. Give it a go and let us know.