What is outstanding about this system is that it offers a stunning colour contrast. With a separation of 6.3 arc seconds (PA of 256 degrees) they are easily split in a small 60mm (2.4 inch) telescope at medium to high power. The components are of magnitudes +4.5 and +5.4, with a PA of 326 degrees and a separation 4.5 arc seconds.ĩ5 Herculis / Struve 2264 – 470 light-years distance, is another beautiful double star consisting of two 5th magnitude suns. Rho Herculis (ρ Her) - at 402 light-years away is a pretty double consisting of two white stars, easily resolvable in a small scopes at high magnifications. Manage to do this and you will join a select group of observers.
The separation is currently 1.1 arc seconds with a PA of 165 degrees and requires an aperture of at least 150mm (6-inch) to split the pair. It's a rapid rotating binary with a period of 34.5 years that consists of a yellow primary and an orange companion of magnitudes +2.9 and +5.4 respectively. Zeta Herculis (ζ Her) - 35 light-years distance, is a testing double for large apertures. The distance of Kappa A Herculis is about 390 light-years while Kappa B Herculis may be up to 470 light-years away. Nether the less, it's a wonderful sight in telescopes of all sizes. Recent age and distance measurements hint that this may just be an amazing chance alignment and not a true double star at all. However, there is some doubt about the authenticity of this double star. Kappa Herculis A at magnitude +5.1 is the brighter of the two and is a class G8 yellow giant star, separated by 27 arc seconds (PA of 15 degrees) from its companion, magnitude +6.2 K1 orange giant star Kappa Herculis B. Marsic (kappa Herculis - κ Her) - is a very nice double star easily visible in small telescopes. Regardless of what colours you see, it's a truly striking combination.
Often it looks just white, but on occasions it may seem blue-green or even blue-turquoise. In contrast, the colour of the secondary star is much more difficult to ascertain. Telescopically, even a small 60mm scope at medium magnifications will split the components, with the primary star displaying a very prominent orange colour and sometimes a hint of red. Rasalgethi is also a beautiful double star with a magnitude 5.4 blue-green companion separated by 4.7 arc seconds at a position angle of 103 degrees. The period is of the order of 100 days, although there are much longer variations that may last for about 6 years. Like most red giants it varies erratically - between magnitudes +3.1 and +3.9 - with an average brightness of about magnitude +3.5. It is so enormous, that if Rasalgethi located at the centre of our Solar System it would extend to 1.87 AU and swallow up the Earth and even Mars. With a diameter of 560 million kilometres (350 million miles) it is one of the largest stars known. Rasalgethi (alpha Herculis - α Her) - is a red supergiant star, located at a distance of 380 light-years. Along with marginally brighter Kornephoros (Beta Herculis) these are the only two stars in Hercules above magnitude +3.0.įor deep sky enthusiasts Hercules contains a sprinkle of globular clusters, challenging planetary nebulae and a host of faint galaxies. The brightest of the four, Zeta Herculis, shines at magnitude + 2.81 and is the second brightest star in the constellation. They are all between magnitudes 3 and 4 in brightness. The four stars of the Keystone are Eta Herculis, Zeta Herculis, Epsilon Herculis and Pi Herculis. The centrepiece of Hercules is a trapezoid shaped asterism commonly known as the Keystone. Although easily traceable under dark skies, the constellation can become elusive with just a hint of light pollution or when viewed under a moonlit sky. However, despite its large apparent size it's rather faint. Hercules is the 5th largest constellation and spans an impressive 1,225 square degrees of sky. The constellation of Hercules is one of the original 48 constellations plotted by 2nd century astronomer Ptolemy and remains today as one of the modern 88 constellations.