Re: Naked eye star splitting

From: Brian Tung (brian_at_isi.edu)
Date: 06/29/04 

Date: Tue, 29 Jun 2004 17:26:10 +0000 (UTC)

Tom Wales wrote:
> my question is, is it normal for young children to be able to
> see this double star with naked eyes?

Mizar/Alcor? Most certainly. The two stars are 12 arcminutes
apart--about 40 percent of the width of the Full Moon. Alcor, the
dimmer star, is about magnitude 4.0, so it's likely the reason you didn't
see it isn't the separation, but the dimness (in your bright sky). To
you, it was a magnitude 3.5 sky, maybe, but to her, it was at least as
good as magnitude 4.0.

> Now comes the kicker, I decided to look at the M27, after I found it
> I had her look at it. She looked at it through the telescope and then
> went to the Telrad, looked at the position it was in the sky and told
> me she could see a fuzzy blob there without the telescope! She swears
> this to be so, we were pretty well dark adapted and hadn't looked at
> the moon in about 20 minutes. Is this possible given the mag 3.5 sky?
> (as observed by me). I sure wish my eyes were that good!

Gee...well, it seems pretty unlikely to me. I have M27 as magnitude 7.4,
which is considerably tougher than Alcor, especially as M27 is an extended
object (not a point source), and it's not a pristine sky, even if you
haven't looked directly at the Moon for 20 minutes. My guess is that she
saw a star at the limit of her visibility and confused it for M27, but
these kids--you never know.

Brian Tung <brian@isi.edu>
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