Object: gamma Delphini

Constellation
RA / DEC
Magnitude A / B
Separation
Position angle
Spectral class
Colour A / B
: Delphinus
: 20:46:40 / +16.07
: 4.4 / 5.0
: 9.1"
: 266°
: K1IV / F7V
: yellow / yellowish
Details sketch
Date / Time
Observing Location
Seeing / Transparency
Telescope
Eye-piece
Magnification / Field of View '
: 23/08/08 / 23:45
: Landgraaf
: 3 / 4
: Orion Optics UK 300 mm
: 12 mm Nagler type 4
: 133 / 37
Stacks Image 811
Observing report
This beautiful double was well separated at 133x. The colour of both stars seemed yellow to me, although the A-component is deeper yellow than the B-component. Gamma Delphini lies not in an interesting starfield or asterism, but it does make a very nice couple of double stars, together with Struve 2725.

Struve 2725 is oriented perpendicular to gamma Delphini. The brighter A-component (magnitude 7.5, spectral class K0) is yellow and the fainter B-component (magnitude 8.2, spectral class K0) looks yellow-white. Struve 2725 almost looks like a dimmer duplicate of gamma Delphini. A wonderful sight, these two doubles in one field of view. On the sketch gamma Delphini is at the centre and Struve 2725 lies towards the southwest.
Notes
Smyth describes gamma Delphini as “A beautiful double star on the Dolphin’s head”. The colours he sees are yellow for the A-component and light emerald for the B-component. Webb sees them as “gold and bluish-green”. Haas describes both stars as “grapefruit orange”. I myself see them both as mainly yellow, although the A-component is of a deeper yellow than the B-component.

According to Kaler, the fainter B-component (gamma-1) is white, but because of the contrast with the brighter A-component (gamma-2), which is yellow-orange. Most people also see colour in the white B-component, ranging from yellow to green and even blue. This again proves that colour perception is something very personal. Take five observers and they probably report a five different colours.