AL THALIMAIN PRIOR (Lambda Aquilae). It's difficult at best to
fathom why the old-time astronomers, particularly those of ancient
Arabia, singled some stars out for naming (many of which are fairly
faint) while letting other more prominent ones go. Here's a
mystifying pair in Aquila that are not
even all that close together (8 degrees apart!) that share a name,
Al Thalimain, "the Ostriches," which would seem to have little to
do with an eagle and instead reflects the constellations of a different culture.
Confusingly, the name is also applied as a rare alternative to
Lambda and Mu Sagittarii (Kaus Borealis
and Polis). The third magnitude (at 3.44
just barely) western one, which we will call "Al Thalimain Prior"
(as it leads in the movement across the sky), became Bayer's Lambda
Aquilae, while its fourth magnitude (4.36) partner became
Aquilae. Curiously, both are class B stars, Lambda (easier to
write) a B9 hydrogen-fusing dwarf, Iota, a hotter, blue class B6
star. Physically, they have nothing to do with each other. At a
distance of 125 light years, Lambda is by far the closer. With a
temperature of 11,500 Kelvin, it shines with the light (after
allowance for the ultraviolet) of 84 Suns,
from which we deduce a radius 2.3 times solar and a mass 2.8 times
solar. A fast spinner (with a projected, and uncertain, equatorial
speed of 133 kilometers per second), the star makes a full rotation
in under 21 hours, as opposed to our Sun, which takes 25 days.
And, as presaged by its class, the star is indeed a dwarf, and a
young one at that, well under its 425 million year hydrogen-fusing
lifetime. After losing most its mass as an evolving giant, Lambda Aql with die as a
0.7 solar mass white
dwarf. Even a deep examination reveals no companion. There is
one listing of it as a "Lambda Bootis
star," one diluted in metals as a result (we think) of
contamination from metal-depleted interstellar gas, but such a
designation does not seem to be confirmed. The star's primary
importance seems to be as a calibrator for astronomers measuring
angular diameters of other stars through interferometry. It's
sometimes interesting to note the sky from a different perspective.
Were you to travel to Lambda Aql and look back, the Sun would
appear as an inconsequential eighth magnitude G star a few degrees
to the west of Procyon, which itself
would have shrunk to magnitude 6 and be just visible to the naked
Written by Jim Kaler 10/24/08. Return to STARS.