|Designation:||Multiple star Alpha Crucis (or Acrux).|
|Constellation:||Crux (or Southern Cross).|
|Magnitude: Alpha 1 Crucis:||+1.3|
|Magnitude: Alpha 2 Crucis:||+1.6|
|Apparent separation:||4.2 arc-seconds.|
|Distance:||322 light years.|
|Field of View:||1.56° x 1.03° – up is 260 degrees E of N.|
It appears in the telescope as a double star, with Alpha 1 Crucis and Alpha 2 Crucis easily distinguishable in the above image – but is actually a multiple star system.
Wikipedia attributes six stars to the system but “Annals of the Deep Sky (Vol 7)” by Jeff Kanipe indicates there are at least twelve: two 1st magnitude, one 4th, one 5th and eight 10th – 17th magnitude.
Identifying the components in this complex system is not simple. Astrometry.net doesn’t make any attempt at it. Jeff Kanipe’s book includes a diagram (which I cannot reproduce) but it’s not easy to relate it to the stars in the image. Suffice to say they are not necessarily those closest to the two brightest ones.
I was surprised to see that the two main components are both first magnitude stars (+1.3 and +1.6), they don’t seem as equal as that! In fact Alpha 1 is 1.3 times the brightness of Alpha 2.
|SkyWatcher Esprit 120 mm apochromatic 3-element refractor.|
|840 mm focal length @ f/7 with field flattener.|
|Baader L-Booster UHC-S light pollution filter 2458276.|
|SkyWatcher EQ6-R Pro mount.|
|Camera: ZWO ASI 071 MC Pro (CMOS 28.4mm 16 Mpx)|
|ZWO ASI120 guide camera, using PHD2 software.|