The color of stars in twilight

Some people see no color in stars. To others the differences are dramatic. But if you;re one of those who have difficulty seeing these color differences, I urge you to try this: Look at some of the brightest, most colorful stars in as large a telescope as you can obtain - and look in twilight when these bright stars are theonly ones visible.

This was driven home to me this morning not because I was looking for color, but because I was using two stars to fine-tune the alignment of the finding devices on a 66mm refractor and the 15-inch Obsession. I've noticed it before when I have been using bright stars to align the computer on the Obsession. When visitors are scheduled to arrive just as it gets fully dark, I take advantage of the twilight time when I'm alone to do the necessary two-star alignment on the computer.

This morning my test star was Arcturus, fairly high in the west. My problem was the fancy Astro-Tech "red ot" sight on the 66mm. Looking for M57 earlier I had discovered it was way, way off. To adjust this little device is one of those good/bad approaches. You neeed an Allen wrench to turn the adjustment screws - but the screw turn firmly - even feels like click stops - and the adjustment moves in fine steps. So it's a pain to dig out and work with the Allen wrench in 27-degree temperatures - and without gloves - but the work does go smoothly.

I adjusted the sight so it centered a star at 80X, then I checked it by switching to Vega. Yepo - right on. I removed the sight from its holder on the telescope, then put it back - something you would do if you put the scope in its case. I swung back to Arcturus. Good!

Having done this, I turned to the 15-inch and decided to fine tune the similar sighting device onit - a Telrad. I pointed it at Arcturus and wham! Screaming ornage star! I mean, how could anyone see this star as anything but orange? As my pulse slowed alittle I made an adjustment in the site - it didn;t need much. Then I pointed it at Vega, high overhead, Bam. Blue as a marble - well blue-white, perhaps, but poh so blue. Back to Arcturus., Orange. Over to the 66mm. Yep - the colros are very visiblke there, but not so vivid. Why? Less light, of course. The 15-inch gathers far more light than the 66mm and our eyes need bright light in order to see color.

What I'm not sure of is why the colors are so vivid in twilight. One obvious answer is they're not. It's simply that during full darkness I seldom - just about never - point the 15-inch at a bright star. But that said, I don't think it's the whole answer. I was looking at Vega briefly earlier this morning when in search of the double. I'm sure the color wasn't so dramatic and I suspect it because these stars dazzle us so when they are seen in contrast to a black sky. The impression is of a lot of light. at twilight the contrast is less and the color more - I think. O need to make some comparisons in full darkness.