Cephius & Cetus

The primary star of this binary is the prototypical example of a Cepheid Variable Star. The period of variability for this class of star is dependent on its luminosity which enables the stars distance to be calculated with great accuracy. This makes them extremely useful for distance determination when this type of star is found embedded in a distant star cluster or galaxy. The magnitude of Delta Cephei varies from 3.48 to 4.37 over a period of 5.36 days.
Mu Cephei is a Red Supergiant and one of the largest stars known, with a mass 19 times that of the Sun and a radius that would extend halfway between Jupiter and Saturn.
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This popular star field in Cephius contains a triple system and two binary systems- all of them physical.
This nearby physical pair is composed of two low-mass Red Dwarf Stars. The orbital motion of the pair is easily discerned year to year.
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Although Sissy Haas in her book “Double Stars for Small Telescopes” doesn’t explicitly label this pair as a “Showcase Double”, but she does call it her “Favorite Pair”.
Most amateurs’ report needing a magnification of 200x or more to comfortably view this physical pair. I was able to capture the photo above with my C 9.25 f10 SCT at prime focus using a Bahtinov Focusing Mask (which I think helps steady the image) and my Olympus E-M10ii camera. The rainbow shaped spikes on either side of the star are artifacts from the mask. The Micro four-thirds camera sensor has a crop factor of 2x which when coupled to the telescope yields an approximate magnification of 98x.

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The Binary pair BL/UV Ceti is the 6th closest star system to our solar system an is composed of two Red Dwarf stars. The orbital separation of the pair is comparable to the orbital radius of Saturn and with an orbital period of only 26 years its orbital motion is easily apparent year to year.