Globular Cluster Messier 2 in Aquarius

A cosmic snowball of around 150000 stars held together by their own gravity. The remnant of a cluster in a small galaxy orbiting the Milky Way. Most of its stars have been lost to the stronger pull of our Galaxy so just this tight core remains.

 

Because its members are so tightly packed together, it has a density classification of II – which is reserved for clusters that are particularly rich and compact.

 

There has been speculation about a dust channel (running from 3 o'clock down to 6 o'clock in this image) caused by dust thrown off from red giant stars in the cluster. Latest measurements suggest this is just asymmetry due to flattening of the "globe" from rotation of the cluster just like Jupiter and the Sun are flattened at their poles.

 

Size is 16 arcminutes

 

ZWO ASI2600MC 61 x 2 minute subs at gain 100, offset 50 at 0c.

Equinox ED 900mm f/7.5 scope x0.85 focal reducer.

IDAS P3 LPS 2" filter in focal reducer.

SkyWatcher EQ6 pro mount with Rowan belt drives.

Guided by PHD2 via PrimaLuce 240mm f/4 guidescope.

 

Atmospheric

Clear throughout. No subs lost.

Light pollution; 20.2 measured with Unihedron SQM (L)

 

Calibration

50 flats (EL panel at 1/4 second)

50 darks at 0c

50 bias at 0c and 1/16000s

 

Processing

PixInsight 1.8.8

 

Polar Alignment:

QHY Polemaster alignment -

Error measured by PHD2= 0.3 arc minute.

RA drift + 2.28 arcsec/min

Dec drift +0.08 arcsec/min

 

Guiding:

PHD2 guiding with ZWO ASI290mm/PrimaLuce Lab 240/60mm guide scope.

RA RMS error 0.80 arcsec.

Dec RMS error 0.65 arcsec.

 

Astrometry:

Resolution ............... 0.988 arcsec/px

Focal distance ........... 785.28 mm

Pixel size ............... 3.76 um

Field of view ............ 43' 9.5" x 36' 2.9"

Image center ............. RA: 21 33 36.101 Dec: -0 52 50.06

Done