Had a most enjoyable evening looking at double stars in Delphinus. After the delightful and easy double star gamma Del, there are some lesser known double stars in this small constellation that are very rewarding. On this occasion Beta Delphinus , which threw up a couple of nice surprises.

A little history first. According to the Bedford catalogue 1834 this is a most delicate (triple) star of mags 4, 12 and 15. But neither Sir William or Struve saw this as a triple. So as with many early observations, with lesser instruments to that of today, there were many conflicting observation reports,  positioning , separations and magnitudes. But nevertheless a very interesting book.

So on to modern times. We now know this to be a double star of mags 4 and 11, with a separation of 42 arc seconds. So using the 12″ Dobsonian with the Vixen NLW 22mm eyepiece (68x) I centred the object. Despite the wide range of brightness, the wide gap made this an easy double star to split, due to the dimmer star being out the range of the primary. Maybe not a WOW factor double, but very rewarding to see.

But the main and most unexpected reward was the wider view. I could also see the slightly fainter Zeta Delphinus in the same FOV. But my eyes were drawn to a lovely triangle of 8th mag stars in the centre of view, which seemed to have a blue / green tint to them. Looking further into this, I found the top two in the triangle (upside down view through the scope) were in fact another double. The stars are HIP 10700a and HIP 10698b with near equal mags of 8.30 and 8.25. This is a nice wide gap and easy for any telescope. The 3rd star in the small group was HIP 101694, mag 8.65.  So after trying for one double star, I got another one free of charge in the same view. There were also a number of other stars around 10-11th mag to the North of the field, which nearly looked like a mini Delphinus 

Go out and try this lovely grouping of stars for yourself on a clear night. A good scope of 3″ or larger will be needed to see the fainter companion of Beta Delphinus

After dusting off my Bedford catalogue book by Admiral William H.Smith, I felt compelled to start seeking out some of the early observations. 1st on the list was a lesser known double star in Lyra called 17 Lyrae. Many observers go straight to the double double close to Vega for a test of optics. Yet , like with many constellations, there are some lesser known doubles which are hidden gems. So lets have a look at the star 17 Lyrae.

This is an easy object to find, just a star hop from Gamma Lyrae as shown on the image (courtesy star-splitters, word press . com).  According to the older Beford catalogue the magnitudes are 6 and 11 with a gap of 2.9 arc seconds, where one of the latest updates quotes as 5.1 and 9.1 with a gap of 3.5 arc seconds. The combination of a narrow gap, and the large range of magnitudes makes this a challenge for many amateur scopes and the UK seeing conditions.  According to the Bedford catalogue this beautiful and delicate object was discovered with the Dorpat refractor.

So on to my own observation of this double star. To repeat, its an easy star hope from Gamma Lyrae with the finderscope. My telescope used was my trusty Skywatcher 12″ Dobsonian. Once centred, I used my 5mm TMB supermonocentric eyepiece. This gem of an eyepiece is my number one choice for high magnifications. Owned it now for about 30 years and never used a better planetary eyepiece. On the Dob, this gives 300x magnification. The bright glare from the primary, dwarfed the dimmer companion, making this a test of optics. But the gap was clear (if tiny), and I was able to clearly make out the secondary star. I spent some time looking at this double star, which had a few other stars in the same field of around 8th – 10th magnitude, making for a beautiful cluster of stars.

It is looking at objects like this, that remind us about the appeal of visual observations, at a time where many budding astronomers who purchase a new telescope are only interested in astro imaging. Go out yourself and try and capture this double star. I am guessing a well collimated 4″ of greater aperture and 250x magnification will be needed