Re: Naked eye star splitting

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

Date: Tue, 29 Jun 2004 18:01:05 +0000 (UTC)

Tom Wales wrote:
> Thanks Brian, I am fairly new to astronomy and don't yet have a total grasp
> of the whole arcminute/arcsecond thing but I don't understand how these two
> stars are considered 40% of the width of the full moon apart. In my
> telescope they just barely split at 30X, in contrast the full moon is a
> large 3/4 apature filling object at the same power. I'm not questioning your
> knowledge or abilities or even that fact that what you say may be true. Am I
> missing something?

It's possible that you're mistaking Mizar and its close companion in the
telescope for Mizar and Alcor. There should be four stars in the vicinity
at 30x: Mizar, Mizar B, Alcor, and Sidus Ludovicianum (Ludwig's Planet).
They look like this:

.
. + Alcor
.
. * Mizar
. . Mizar B
. ·
. Sid Lud
.

Depending on your telescope, the stars in the field of view may be rotated
or mirror reversed from the map above. Use a constant-width font to view
this. The periods at the start of each line are not stars; they are just
there to keep Google from mangling my ASCII diagram.

Mizar is magnitude 2.2; its close companion, Mizar B, is magnitude 3.9, and
is about 14 arcseconds away, I think. Alcor is magnitude 4.0 and is, as I
mentioned, about 12 arcminutes away from Mizar/Mizar B. (The diagram is
obviously not to scale.) Sidus Ludovicianus is magnitude 7.6. It is named
that because the German astronomer who discovered it in 1723 thought he had
discovered a planet (even though it is way away from the ecliptic) and
dedicated it to his patron, King Ludwig.

Thus, you saw Mizar and Mizar B together in the telescope, but what your
daughter split is undoubtedly Mizar and Alcor. No person can split Mizar
and Mizar B with the unaided eye.

Brian Tung <brian@isi.edu>
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