Castor splits in Salinas

by Jamie Dillon

Tonight as sunset there was a clear patch where the crescent moon, Venus and Jupiter were arcing up. Then around 9pm again the sky was largely clear, so Felix Dobson and I rushed out of the garage. The task at hand was splitting Castor. Warmed up with Mintaka and a stretch at M42, where the lanes were clear and the arms of the nebula were unusually long for the this backyard.

This scope has a focal length of 1260mm, so the 7.5mm Celestron Plossl gives out 170x. Funny, after years of holding binocs I had to convince myself that the double star image I was seeing wasn't jitter, that the stars in the surrounding field were crisp. Cranked on the new Televue 2x birthday Barlow and soaked up some A-type photons. Easy to see what all the shouting is about, just lovely those two hot white stars right next to each other, 3" apart.

Learned several useful things:

1. The forehead makes a handy fine altitude adjuster near zenith.

2. Got the turns straight with a Dobs at zenith this way - turning the scope clockwise, imagining looking down on the scope, brings the image to the right. At least for me, this was counter-intuitive, so setting up a verbal prompt was vital to getting myself to move that way at high mag, 340x.

3. Putting the 17.5mm eyepiece on the Barlow made for a nice combo, making for 140x with much better eye relief than the 7.5, more than compensating for the drop from 170x, in this case with a binary in the face of evaporating seeing.

4. When dropping in the Barlow, it was useful to leave the star out of focus while re-centering, to have a fat image rather than a point to chase. Castor was moving fast at zenith at 340x.

Jo came out in time to catch the double. I'd been at the eyepiece without looking up, noticing that the seeing was starting to wash out. Looked up at a complete cloud cover, with about 7 stars visible across 90 deg of sky. Cool to see what a light bucket will do, given that Castor was fading out of naked eye view and still split in the eyepiece.

So Felix went early to bed. However, there was yet one silver lining, when the sky cleared a bit toward midnight, and with the binocs I found M35 for the first time, gorgeous in the 7x50's. Wait'll we catch that beauty in the eyepiece.

Equipment

Date	February 17, 1999
Location	Salinas, CA
Instruments	Celestron Dobsonian, 280mm, f/4.5; Trusty old Swift marine 7x50's on tripod
Oculars	Celestron eyepieces, 7.5 and 17.5mm, Televue 2x Barlow