03 September 2004

The September Sky: Farewell to the summer Milky Way

Paul Curtin

During July and August we described some of the summer Milky Way objects visible from the Northern Hemisphere. September offers a last chance to view these objects before we turn back to the truly deep sky realm of galaxies.

Students or observers who wish to try their hands at astrophotography can take a series of wide-angle shots of the Milky Way. Even relatively short exposures will capture star fields, nebulae, dark lanes and the bulge of the galactic center in Sagittarius.

To the north and east of Cygnus is a large square with a pointed hat. This is Cepheus, which, though fainter than his wife Cassiopea, contains many clusters and interesting star fields best viewed with binoculars.

South of Cepheus is Lacerta, a faint collection of stars rich in nebulae in its northern section. Its southern half, seemingly hanging from the Milky Way, offers little of interest to observers with small to medium aperture telescopes.

Scanning northeast from Altair we see the "tadpole" of Delphinus. This, like the Pleiades, is often mistaken for a "dipper".

East of Sagittarius is Capricornus, a large, smile-shaped group of stars containing a number of deep sky objects. Look for M30 in an otherwise barren section of  eastern Capricornus. M30 is a compact globular cluster that contrasts dramatically with its colleague M13 in Hercules.

Southern observers have already bid farewell to the Milky Way. Early southern spring, like the coming northern autumn, contains few outstanding constellations but is laced with dozens of galaxies for the deep sky enthusiast.

Due south of Capricornus is Microscpium and below is Indus. It is in this region that one can find fields of galaxies in very dark skies. Closer to the south celestial pole these objects peter out and we are left with the truly sparse regions of Pavo and Octans.


The planets this month

Mercury, in Leo, is a great morning object for northern observers. On September 9 it reaches greatest elongation, rising an hour and a half before the Sun.

Venus moves from Gemini into Cancer this month. It rises well before dawn twilight and, at magnitude -4, will be bright enough to cast shadows.

Mars is lost in the Sun's glare this month.

Jupiter is also hidden by the Sun.

Saturn is in Gemini and can be observed in the morning sky.

Uranus is in Aquarius and can be observed throughout the night.

Neptune is in central Capricornus and is thus favorably positioned for observers. Though not visible in amateur telescopes, five new moons have been discovered in orbit around Neptune. For details, see Holman et al. Discovery of five irregular moons of Neptune. Nature volume 430, page 865 (2004).


Bibliography

Burnham, Robert Jr. Burnham's Celestial Handbook. New York: Dover, 1978.

Gupta, R. (ed.) Observers Handbook 2004. Toronto: University of Toronto Press, 2003.

Kepple, G. R., Sanner, G. W. The Night Sky Observers Guide. Richmond, VA: Willman-Bell, 1999.

Webb, T. W. Celestial Objects for Common Telescopes. New York: Dover, 1962.