TrevorW
08-07-2010, 09:11 PM
Target: M4, NGC 6121 Globular Cluster in Scorpius
Camera: QHY8 OSC CCD with WO F2 Reducer
Scope: GSO CF RC200
EFR: f/6.4
Mount: EQ6 Pro
Exposure Setting: Prime focus, gain 3 offset 119
Exposures: 9 @ 180s, 9 @ 360s, 2 @ 600s lights taken between 6.25pm and 8:35pm total 1hr 41m 07/07/2010
Seeing: No moon, cool night, usual suburban LP
Guiding: Orion Starshoot Autoguider using PHD with ED80
Focus: Bahitnov mask
Stacking: DSS 2darks 5 flats 5bias frames
Processing: PS CS3 curves, levels, colour, noise etc
Right Ascension 16 : 23.6 (h:m)
Declination -26 : 32 (deg:m)
Distance 7.2 (kly)
Visual Brightness 5.6 (mag)
Apparent Dimension 36.0 (arc min)
Discovered by Philippe Loys de Chéseaux in 1746.
Messier 4 is one of the nearest globular clusters in the sky at an estimated distance of about 7,200 light years. Situated prominently about 1.3 degrees west of Antares, in constellation Scorpius (http://seds.org/messier/map/Sco.html), and being as bright as mag 5.6 visually, it can be detected by the naked eye under very dark skies, and is prominent with the slightest optical aid. Globular cluster M4 was discovered by De Chéseaux (http://seds.org/messier/xtra/Bios/decheseaux.html) in 1745-46 and listed by him (http://seds.org/messier/xtra/similar/deches.html) as No. 19, and included in Lacaille (http://seds.org/messier/xtra/Bios/lacaille.html)'s catalog (http://seds.org/messier/xtra/history/lacaille.html) as Lacaille I.9. Charles Messier (http://seds.org/messier/xtra/history/biograph.html) cataloged it (http://seds.org/messier/xtra/history/m-cat.html#M4) on May 8, 1764 and was the first to resolve it into a "cluster of very small [faint] stars;" this is the only globular cluster he could resolve with his moderate instruments, and thus the first globular cluster ever to be resolved. Only about 20 years later, William Herschel was able to resolve all Messier globulars with his large telescopes.
M4 would be one of the most splendid globulars in the sky if it were not obscured by heavy clouds of dark interstellar matter. Interstellar absorption also reddens the color of the light from the cluster, and gives it a slightly orange or brown-ish appearance on color images. Its angular diameter, seen on deep photographs, is about 36 minutes of arc, more than that of the Full Moon; this corresponds to a linear diameter of about 75 light years. On typical photos it appears somewhat smaller at about 26', and visually it was estiamted at 14 arc minutes. Its tidal radius, determined by the distance where tidal gravitational forces of the Milky Way Galaxy would cause member stars to escape, is estimated at 32.49', or about 70 light-years, so that this globular gravitationally dominates a spherical volume 140 light-years in diameter.
M4 is one of the most open, or loose, globulars, as its classification in concentration class IX indicates. Its compressed central core was measured at 1.66' diameter, or linearly 3.6 light-years. Its half-mass radius is 3.65' or about 8 light-years, so half the cluster's mass is concentrated in an inner spherical volume of 16 light-years diameter. It is receding from us at 70.4 km/sec and contains at least 43 known variables. Its spectral type has been determined as F8, its color index has been measured at B-V=1.03.
Camera: QHY8 OSC CCD with WO F2 Reducer
Scope: GSO CF RC200
EFR: f/6.4
Mount: EQ6 Pro
Exposure Setting: Prime focus, gain 3 offset 119
Exposures: 9 @ 180s, 9 @ 360s, 2 @ 600s lights taken between 6.25pm and 8:35pm total 1hr 41m 07/07/2010
Seeing: No moon, cool night, usual suburban LP
Guiding: Orion Starshoot Autoguider using PHD with ED80
Focus: Bahitnov mask
Stacking: DSS 2darks 5 flats 5bias frames
Processing: PS CS3 curves, levels, colour, noise etc
Right Ascension 16 : 23.6 (h:m)
Declination -26 : 32 (deg:m)
Distance 7.2 (kly)
Visual Brightness 5.6 (mag)
Apparent Dimension 36.0 (arc min)
Discovered by Philippe Loys de Chéseaux in 1746.
Messier 4 is one of the nearest globular clusters in the sky at an estimated distance of about 7,200 light years. Situated prominently about 1.3 degrees west of Antares, in constellation Scorpius (http://seds.org/messier/map/Sco.html), and being as bright as mag 5.6 visually, it can be detected by the naked eye under very dark skies, and is prominent with the slightest optical aid. Globular cluster M4 was discovered by De Chéseaux (http://seds.org/messier/xtra/Bios/decheseaux.html) in 1745-46 and listed by him (http://seds.org/messier/xtra/similar/deches.html) as No. 19, and included in Lacaille (http://seds.org/messier/xtra/Bios/lacaille.html)'s catalog (http://seds.org/messier/xtra/history/lacaille.html) as Lacaille I.9. Charles Messier (http://seds.org/messier/xtra/history/biograph.html) cataloged it (http://seds.org/messier/xtra/history/m-cat.html#M4) on May 8, 1764 and was the first to resolve it into a "cluster of very small [faint] stars;" this is the only globular cluster he could resolve with his moderate instruments, and thus the first globular cluster ever to be resolved. Only about 20 years later, William Herschel was able to resolve all Messier globulars with his large telescopes.
M4 would be one of the most splendid globulars in the sky if it were not obscured by heavy clouds of dark interstellar matter. Interstellar absorption also reddens the color of the light from the cluster, and gives it a slightly orange or brown-ish appearance on color images. Its angular diameter, seen on deep photographs, is about 36 minutes of arc, more than that of the Full Moon; this corresponds to a linear diameter of about 75 light years. On typical photos it appears somewhat smaller at about 26', and visually it was estiamted at 14 arc minutes. Its tidal radius, determined by the distance where tidal gravitational forces of the Milky Way Galaxy would cause member stars to escape, is estimated at 32.49', or about 70 light-years, so that this globular gravitationally dominates a spherical volume 140 light-years in diameter.
M4 is one of the most open, or loose, globulars, as its classification in concentration class IX indicates. Its compressed central core was measured at 1.66' diameter, or linearly 3.6 light-years. Its half-mass radius is 3.65' or about 8 light-years, so half the cluster's mass is concentrated in an inner spherical volume of 16 light-years diameter. It is receding from us at 70.4 km/sec and contains at least 43 known variables. Its spectral type has been determined as F8, its color index has been measured at B-V=1.03.