Caption: The multiple-star system Alpha Herculis, popularly known as Rasalgethi, marks the head of Hercules, who kneels upside down in our night sky.
Caption: HERCULES The color contrast makes Alpha Herculis an attractive split.
Near it is the dimmer head of Hercules: Alpha Herculis
or Rasalgethi--a fine orange-and-yellow telescopic double star.
Indeed, in the early 3rd millennium BC when the north celestial pole was near Alpha Draconis, if you looked high in the north from Mesopotamian latitudes when the Kneeler's head (Alpha Herculis
, Rasalgethi) was near the zenith, you would have seen Draco curved out beneath his feet.
I drew up a double-star list and one by one began to bag its targets: Alpha Ursae Majoris, Epsilon Bootis, Alpha Canum Venaticorum, Gamma Leonis, Beta Cygni, Alpha Herculis
, Epsilon Lyrae....
The proper name for Alpha Herculis
is Rasalgethi, which as a child learning the stars I pronounced rass-AL-guh-thi.
In fact, Alpha Herculis is at the lower end of the supergiant class, sometimes categorized as a "bright giant" instead.
Alpha Herculis is one of the prettiest double stars in the sky.
You could begin with Albireo (Beta Cygni) and Rasalgethi (Alpha Herculis
), two of the color-contrast pairs that are very high in this sky.
It must compete with the intensely hued showpiece double Rasalgethi (Alpha Herculis
) and the magnificent Hercules Cluster (Messier 13).
As with most such stars, Alpha Herculis
is an irregular variable; its period is roughly 90 days.
One by one, I began to bag the targets in my double-star list: Alpha Ursae Majoris, Epsilon Bootes Alpha Canum Venaticorum, Gamma Leonis, Beta Cygni, Alpha Herculis
, Epsilon Lyrae, Alpha Geminorum .