On Saturday evening 11th May 2019 I set up my William Optics 158 mm apochromatic refractor in my back garden.
Fluffy clouds broke up after 11 pm local time as I started having a go at splitting some optical and true doubles in Leo.
There was no wind either.
1. Regulus first appeared out of those clouds. The primary is blue -white and its faint true secondary were observed at 40X.
Magnitudes: 1.4 and 8.2. Sep: 175.5". PA: 308 degrees.
2. Algieba was next. Both its deep golden yellow stars are stunning at 112X.
Magnitudes: 2.4 and 3.6. Sep: 4.7". PA: 126 degrees.
3. Denebola has 4 widely spaced optical components coming down from the primary -all seen at 40X. It is a rather nice asterism.
4. Zosma (Delta Leonis) is an optical double. Both stars seen at 40X.
Magnitudes: 2.5 and 10.9. Sep: 204.8". PA: 342 degrees.
5. 90 Leonis I have never observed before. Some observers on Cloudy Nights mentioned it recently and I did find it a very attractive triple.
A and B are both blue -white and are a true binary. C is optical and is yellow -white.
Magnitudes: 6.3, 7.3 and 9.8. Sep: 3.5" and 62.8". PA's: 209 and 235 degrees. I was amazed I could see A and B split at 40X. But the view at 112X was very fine indeed.
6. My next double is the tightest I have ever split. Struve 1517 was split by another observer called Iain some years ago on Cloudy Nights using a large Dobsonian.
I was stunned to see its 2 components barely separated at 320X using at 3.5 mm Nagler and 374X Radian. Sky conditions were extremely impressive!
Magnitudes: 7.5 and 8. The current separation is 0.73". PA: 315 degrees. My previous tightest double was STT 371 in Lyra which I split in August 2018.
But it appears I have now split an even tighter pair. Struve 1517 is very close to Zosma. So maybe some of you might give it a go.
All my figures can be checked on
www.stelledoppie.it
It is just as well the 2 stars of Struve 1517 only have 0.5 magnitude difference between them.
7. One other true binary I have for you is 54 Leonis.
Magnitude: 4.5 and 6.3. Sep: 6.6". PA: 113 degrees.
There seems to be some much controversy regarding its colours.
According to Stelle Doppie, both stars are A class. A1 and A2 in fact.
That means both stars ought to have slight tints of blue.
I do recognise that my William Optics apochromatic refractor should kill false colours.
But I find that the A component has a very slight yellow tinge -with no tint of blue.
Should it not be of F spectral class?
Component B is definitely blue. And that concurs with its spectral class.
8. I had the opportunity to observe Xi Ursae Majoris (Alula Australis).
And I did find simply glorious!
A and B were split at 112X okay.
According to Stelle Doppie, its magnitudes are 4.3 and 4.8. Sep: 2.1". PA: 156 degrees.
I had the desire to check out the colours. So I increased the magnifications up to 280X.
I found A to be slight orange (K9); B as strong yellow (G9).
As it was my first time to study Xi Uma I found myself completely smitten by it.
This true binary is my favourite double star of 2019 so far.
I was delighted that it was positioned quite close to my zenith with my naked eye.
Burnham Celestial Handbook states that both stars are similar to the size of our Sun.
I find that most fascinating!
Stelle Doppie also points out that this magnificent binary is widening and its PA is decreasing.
So it is going to be a must to keep an eye on it over upcoming years.
Its distance its somewhere between 26 light years (Burnham) and 34 light years (Stelle Doppie).
Thank you for reading.
Comments are welcome.
Clear skies from Aubrey.
  