Al Thalimain Prior

Al Thalimain is from the Arabic al-zalimayn, the two ostriches, and it is a dual: the name belongs to a pair of stars in Aquila and not to one. This is the first of the pair as the catalogue orders them by ecliptic longitude. Ostriches are one of the recurring figures of indigenous Arabian star lore, which read the sky quite independently of the Greek constellations and saw in this region birds coming down to the celestial river of the Milky Way to drink. When the Ptolemaic constellations were translated into Arabic, the older indigenous names survived alongside the translated ones and were later carried into Latin and thence into the modern lists, which is why the same stars can hold both an eagle-name and an ostrich-name.

Pre-Islamic Arabian sky-lore of this kind, organised around desert animals coming to drink at the band of the Milky Way, ran independently of the Greek constellations for centuries before the two systems were fused; the ostriches, ravens, gazelles and other creatures of that older tradition were gradually absorbed as alternative names for stars that the translators had already assigned to Ptolemy's eagle, lyre and archer, rather than replaced outright.

The atlas records this star at Capricorn 17 degrees 20 minutes, projected from Aquila, well north of the ecliptic.

The name is a dual, the two ostriches, and it belongs to a pair. The second entry carrying it sits at Capricorn 25 degrees 50 minutes, which is exactly eight and a half degrees away. That separation is the useful fact here: the two stars are not a close pair sharing a name by proximity in the sky, they are more than a quarter of a sign apart in longitude, and any reading that treats the ostriches as a single point is treating an eight and a half degree spread as one.

It also distinguishes this case from the genuine duplicates elsewhere in the table. Deneb el Okab and Deneb Okab share a sign, a degree and a minute, which means one star entered twice. The two ostriches do not, which means two stars sharing one dual name, exactly as the name says.

Precession dates the figure. At about fifty seconds of arc a year, one degree in roughly seventy two years, and taking the value for epoch 2000, this star entered Capricorn in the eighth century and will reach Aquarius in about nine hundred years. Its partner, being further into the sign, entered earlier and will leave sooner.