Explore the Universe - Alpha Librae

Last night was one of the first good nights for astronomy in a long time.  This Spring has recently been giving us 3 or 4 clear nights per month so last night was a treat.  I had a list of targets that I have been saving for a clear night.  I only require two more double stars and four deep-sky objects to complete my Explore the Universe Certificate.  I was fortunate to find two double stars and three deep-sky objects from the list last night.  A complete list of the Explore the Universe items can be found at the link below.

Explore the Universe

The first object on my list was Alpha Librae.  The bright star in the double is also known as Zubenelgenubi.  This name derived from the Arabic الزُبَانَى الجَنُوبِي which means* the 'southern guard' or 'southern police'.  I am assuming this is because Zubenelgenubi is the southernmost of the two bright stars of the justice constellation: Libra. (*Thank-you to a colleague who is well versed in Arabic).

This double star forms the second brightest object in the constellation Libra.  It is an easy naked eye object which made it exceptionally easy to find with a telescope.  When Libra was high in the sky just before midnight I could see Alpha Librae.  I placed my red dot finder onto the target and looked through my 25mm eyepiece.  I could clearly see two bright stars against a field of several dim stars.  I estimated the separation between the stars was approximately 5% across my field of view.  This would give an estimate of 3.13' separation which was close to the accepted value of 3.85'.  My observation record is posted below.

Alpha Librae Observation Record

I recently learned how to type in celestial coordinates to the goto mount and may begin imaging multiple star systems on the list.  They are not incredibly exciting so it may be a while before I attempt it.

The next deep sky objects on the list are either in or near Sagittarius which does rise above the houses until after 1 in the morning.  Messier 16 is more than 10° East of Saturn and would be the next feasible target on the list.  Approaching this target may be difficult as it is about two binocular fields away from an urban naked eye star: Nu Ophiuchi.  The Summer constellation Sagittarius is quite low in the sky and contains many deep-sky objects.  It may require spending a few late Summer evenings at the observatory to get a clearer view of the southern horizon.

It is unfortunate that the clouds seem to be rolling in this evening after an exceptionally clear night.  Long weekend evenings are typically very good for astronomy because you can sleep in after catching some great late night sights!  In future posts this week I will log another double star and three deep-sky Messier objects!