Al Thalimain Posterior

This is the second star of the pair called Al Thalimain, the two ostriches, in Aquila. The two entries are not a duplication: the Arabic name is grammatically dual and was always understood to cover both members, and the catalogues list them separately because they stand several degrees apart in ecliptic longitude. Modern identifications usually associate the pair with Lambda and Iota Aquilae, southwest of Altair, though the older lists are not always consistent about which star takes which designation. No single Ptolemaic planetary nature is recorded for either, and the tradition attaches no distinct meaning to them; their interest lies in preserving a fragment of the pre-Islamic Arabian sky within a catalogue otherwise built out of the Greek figures.

That the catalogues preserve both halves of a grammatically dual Arabic name as two separate numbered entries, rather than merging them, is itself informative: it shows the compilers working from formal transliteration rather than from any real fluency in Arabic, since a reader who understood the dual form would have known immediately that al-zalimayn names a pair and requires no duplication to record both stars. Lambda and Iota Aquilae, the stars usually meant here, are both modest, unremarkable points of light whose only real claim on attention is their place within the older Arabian ostrich figure rather than any physical distinction of their own.

The atlas records this star at Capricorn 25 degrees 50 minutes, projected from Aquila, well north of the ecliptic.

It is the further of the two entries carrying the dual name al-thalimayn, the two ostriches. Its partner sits at Capricorn 17 degrees 20 minutes, exactly eight and a half degrees back, so the pair spans more than a quarter of a sign. That separation is what makes them a genuine pair of stars sharing one dual name rather than a duplicate entry, which is the other pattern in this atlas and looks quite different: a duplicate shares a sign, a degree and a minute.

Being deep in the sign, this is among the stars in the table closest to leaving it. On a uniform precession of about fifty seconds of arc a year, one degree in roughly seventy two years, and taking the recorded value for epoch 2000, it entered Capricorn around the middle of the second century of the common era and will cross into Aquarius in something like three hundred years. It has spent longer in the sign than any of the other Aquila entries here and will be the first of them to leave.

The ostrich names belong to the indigenous Arabian sky-lore that survived alongside the translated Greek figures, which is why one region of sky carries both an eagle and a pair of birds coming down to the Milky Way to drink.