July
Apus(Aps), Circinus (Cir), Triangulum Australe (TrA)
For convenience we have grouped these three Southern constellations together. None of them are particularly outstanding, and between these constellations the brightest star is 2nd magnitude. For general interest and completeness we have included them, and hope readrers will enjoy the historical aspects and the releatively small but challenging range of objects available to the amateur;
Apus (pronounced ape-us), The bird of paradise, was included in Bayer's Uranometria of 1603 as "Apus Indica". Bayer apparently had an obsession for exotic birds; his other creations were Grus (the crane), Pavo (the peacock), Phoenix (the phoenix) and Tucana (the toucan). Apus, whose brightest star is only 4th magnitude, rates poorly in objects for the small telescope. However the 5th magnitude, 103 arc second wide, orange pair known as Delta 1 & 2, are easily split in binoculars and make a fine object for small aperture.
Circinus (pronounced sir-sin-us), The pair of Compasses, was another creation of Lacaille in 1752. Lacaille had a desire to fill the sky with as many insignificant and faint constellations as he could. There is only one star brighter than 4th magnitude, and the constellation ranks as the 85th in order of size, (the smallest constellation, Crux, comes in as the 88th), it would have been better included as parts of Centaurus. Two good colour contrasting double stars can be recommended for small apertures, they are Alpha Circini (a wide yellow and red pair) and Dunlop 169 (an even wider pair coloured blue and orange).
Triangulum Australe (pronounced try-ang-yoo-lum os-trail) The Southern Triangle, does indeed look almost like an equilateral triangle, and is the counterpart of the northern Triangulum. The triangle is composed of the constellations brightest stars, Alpha Trianguli Australis at 2nd magnitude and Beta and Gamma both at 3rd magnitude. It is the most recognisable of this months constellations, and was described by Italian navigator Amerigo Vespucci in 1503. Triangulum Australe, is the 83rd constellation in order of size, just slightly larger than Circinus mentioned above.
There are few objects in the South Triangle that
are worthy of telescope time,take open cluster NGC 6025. This fine
group of 30 stars from 7th magnitude down, spread over about 12 arc minutes
of sky. From dark skies the white and yellow stars, associated with the
cluster, appear superb against a very rich background of fainter stars.
If
you want a challenge then NGC 5938 is a galaxy to go after. It is a small
faint hazy glow about 30" in size with a low surface brightness.
Or pehaps the planetary nebula NGC 5979. Small bright disc that responds
well to a UHC filter.
And
then there's NGC 5844 which is fairly large but very faint. A UHC filter
and hight power will help with this one and bring out some of the detail.
There are also some attractive binaries, but most
tend to have small seperations and require large apertures. The exception
would be Iota Trianguli Australis. in an excellent field, these
5.5 and 10th magnitude stars form what is known as an optical double, two
stars close to gether but not physically connected by gravitational attraction.
These stars are different distances from us, and only by chance happen
to be in the same line of sight. In 1836 John Herschel measured the seperation
as 25 arc seconds and the moist up to date measure we could find was 13
arc seconds in 1961. The decreasing seperation is due to the proper motion
of the stars (as they orbit the centre of the Milky Way) and not to any
mutual orbital effects.
Interesting facts:
Apus
1) Ranked 67th in size
2) Contains no Messier objects.
Circinus
1) Contains no asterisms
2) Ranked 85th in size
3) Has no Messier objects
Triangulum Australe
1) Contains no asterisms
2) Ranked 83rd in size
3) Has no Messier objects
Information supplied by
Quasar Publishing P.O Box 234 Strathfield NSW 2135