Gamma (γ) Delphini is a beautiful double star that marks the tip of the nose of the constellation Delphinus, the Dolphin.
Delphinus is a small but distinctive pattern of stars visible to the east – or left from the UK – of the giant Summer Triangle asterism.
It looks like a diamond with a short tail and in mythology is supposed to represent the head of a bottlenose dolphin, the diamond depicting the creature’s nose and the short tail the start of its neck.
Gamma (γ) Delphini’s two stars
Gamma (γ) Delphini’s components are of magnitudes +5.1 and +4.3, which combine to appear at mag. +3.9 to the naked eye.
They have spectral classifications of F7 and K1 respectively, which means they should appear white and yellow-orange.
However, with a separation of just 9.2 arcseconds, the colours contrast to create the illusion of additional colour within the fainter white star.
Reports of it looking yellow, green, blue and orange are not unheard of.
The stars are physically 2.5 and 7.5 times larger than our Sun and are a true binary pair.
Their orbit is highly eccentric, bringing them as close together as 40 AU and as far apart as 600 AU. The orbital period is 3,200 years.
The brighter yellow orange component, Gamma-2, is in the process of becoming a giant star as it begins to fuse helium.
The Gamma Delphini system lies 104 lightyears from the Sun and is around two billion years old.
Observing
Gamma Delphini is best seen during summer and autumn.
You don’t need a large telescope to enjoy Gamma Delphini and it splits well even at around 50x power.
So the next opportunity you get, go outside and make a note of the colour of the fainter, western component.
An interesting experiment would be to see if the colour appears to change when you use different apertures and magnification.
This article appeared in the August 2018 issue of BBC Sky at Night Magazine