Object: iota Cassiopeiae (Struve 262)

Magnitude A / B / C
Separation A-BC/ AC
Position angle A-BC / AC
Spectral class A / B / C
Colour A / B / C
: Cassiopeia
: 02:29:12 / +67.24
: 4.65 / 6.9 / 8.7
: 2.7” / 7.4”
: 230°/ 114°
: A5 / F5 / K1
: White / Yellow-Orange / White
Detail sketch:
Date / Time
Observing Location
Seeing / Transparency
Magnification / Field of View '
: 23/08/09 / 00:45
: Landgraaf
: 3 / 4
: Orion Optics UK 300mm
: 17mm Nagler + 2xPM
: 184x / 26'
Iota Cassiopeiae

Observing Report

While star hopping towards the Cats Eye nebulae I somehow came across Iota Cassiopeiae, a wonderful multiple star system. I had not observed Iota for a few years, but it surprises me every time I pay it a visit. Iota Cassiopeiae is definitely a showcase triple, just like beta Monocerotis.

At low magnification, Iota Cassiopeia looks just like a single star. I had to use high powers to get a clean split of the two brighter A and B components. The optimum magnification was 184x (17mm Nagler and 2x Powermate) which also was used for making the sketch.

What I like very much is the range in magnitude of the three components (5th-7th-9th magnitude). At high magnification, this huge difference in brightness makes the three stars of Iota Cassiopeiae look like three sparkling gems of different size placed on a black cloth. Wonderful! Besides this magnificent triple star, the rest of the field of view looks rather boring. I decided to sketch only Iota Cassiopeiae itself. I can see no other interesting stars in the field of view. There are no asterisms, and I cannot detect any nebulosity or glow of unresolved stars.

About the colour
The bright A component at the centre of my sketch is sparkling white.
At a position angle of 230°, southwest of the primary star, I see the yellow-orange, B component. The C component, which lies to the northeast off the bright white primary at a position angle of 114°, seems to have no colour. It looks white to me.

The colour of this triple star has always been puzzling me. In my first ever observation of Iota Cassiopeia using the 8-inch TAL 200K at 222x I saw the A, B and C component as a bright white primary with a slight hint of yellow, and two white companions showing a hint of blue. All in all very different from my last observation.

The problem is that star colours sometimes look different, not only for different observers, but also if one observer uses two different telescopes. Even when using only one telescope, I noticed that the colour sometimes can shift a little or become more apparent when using a particular eyepiece (magnification). On top of that, there is the contrast between the colours of stars that can fool you. This makes the perception of colour in double stars very subjective.


Iota Cassiopeiae can be found using the finder chart below. First of all, you must locate the "W" of Cassiopeia. On Jim Kaler's website "Stars" I found a mnemonic to recall the Greek letters (Bayer) of the stars that form the "W" and Iota Cassiopeiae: "BAGDEI". You should read from west to east for the five brightest stars Beta, Alpha, Gamma, Delta, Epsilon (which make the "W") and finish with Iota.Iota

Cassiopeiae can be found by drawing a line from delta to epsilon, and than extend the line with the same length in the same direction. You will need high magnification to split iota Cassiopeiae in its three visual components.

True physical triple star?

In 2003 research using adaptive optics revealed that the A, B and C component are actually not bound by gravity, so I guess this makes Iota Cassiopeiae an optical triple, but nonetheless a beautiful object for amateur astronomers to observe.
Iota Cassiopeiae

Image from Voyager by CapellaSoft

ι Cassiopeiae: Orbit, Masses, and Photometry from Adaptive Optics Imaging in the I and H Bands*
Jack Drummond et al 2003 ApJ 585 1007-1014