| Globular Cluster M4 in Scorpius |
The constellation Scorpius houses several globular clusters. The most notable of these are M4 and M80. Because they are so low in the southern sky, they receive less attention
from northern observers than the smaller but more accessible globular clusters M2 and M3. At a distance of 7200 light years, M4 is only a third the distance of the great Hercules
Cluster M13. Also, as one of the most loosely grouped globular clusters, the center of M4 can be resolved visually with backyard telescopes, giving a greater sense of depth at the
eyepiece. The reddish or brownish hue is real, due to tinting by interstellar dust. A larger field of view includes the Rho Ophiuchi Nebula complex. The view from within a globular
cluster must be spectacular. Tens of thousands of nearby stars would fill the night, keeping the sky at a twilight glow. From within M4, John Denver might have written his song as,
"Starshine on my shoulders makes me happy, Starshine in my eyes can make me cry....."
The image above was obtained with 35 minutes red, 40 minutes green, and 50 minutes blue exposures, all unbinned. I no longer shoot clear luminance exposures for targets near
the horizon, as I discussed in my 2010 Sky & Telescope article "Shooting Low". A QSI583wsg camera was used through an Astro-physics 130 mm refractor at f6. A synthetic
luminance was created for added sharpness. Details about creating a synthetic luminance, and imaging near the horizon are discussed in my book, The 100 Best Astrophotography
Targets. The image below was obtained 7 years earlier with 33 minutes luminence, 18 minutes red, and 9 minutes each of green and blue exposures. An ST10XME camera was
used through a TEC140 refractor at f7. Luminence was full resolution, and RGB was binned 2x2.
from northern observers than the smaller but more accessible globular clusters M2 and M3. At a distance of 7200 light years, M4 is only a third the distance of the great Hercules
Cluster M13. Also, as one of the most loosely grouped globular clusters, the center of M4 can be resolved visually with backyard telescopes, giving a greater sense of depth at the
eyepiece. The reddish or brownish hue is real, due to tinting by interstellar dust. A larger field of view includes the Rho Ophiuchi Nebula complex. The view from within a globular
cluster must be spectacular. Tens of thousands of nearby stars would fill the night, keeping the sky at a twilight glow. From within M4, John Denver might have written his song as,
"Starshine on my shoulders makes me happy, Starshine in my eyes can make me cry....."
The image above was obtained with 35 minutes red, 40 minutes green, and 50 minutes blue exposures, all unbinned. I no longer shoot clear luminance exposures for targets near
the horizon, as I discussed in my 2010 Sky & Telescope article "Shooting Low". A QSI583wsg camera was used through an Astro-physics 130 mm refractor at f6. A synthetic
luminance was created for added sharpness. Details about creating a synthetic luminance, and imaging near the horizon are discussed in my book, The 100 Best Astrophotography
Targets. The image below was obtained 7 years earlier with 33 minutes luminence, 18 minutes red, and 9 minutes each of green and blue exposures. An ST10XME camera was
used through a TEC140 refractor at f7. Luminence was full resolution, and RGB was binned 2x2.
Music: Sunshine on my Shoulders, by John Denver
