The August Sky

Paul Curtin

Special Events This Month: There is a total solar eclipse on 1 August. Totality can be viewed in Kazakhstan, Mongolia, and China. Observers in Maine, Quebec, Europe and Asia will be able to observe a partial eclipse.

A partial lunar eclipse will occur on August 16. This will not be visible in North America, however.

The August Sky: August in the north is prime Milky Way season. Open clusters, emission nebulae, planetary nebulae, and dense star clouds abound. Cygnus contains all of these. The main section of Cygnus is a large cross shaped figure with bright Deneb at the top. The rest of the stars in the cross are multiple. Beta (Albireo) displays an especially beautiful color contrast. In addition to the open clusters M29 and M39, Cygnus hosts extensive star clouds that can be explored with telescopes of any aperture. In dark skies emission nebulae can be found. The most noteworthy of these are the Pelican, Veil and North American nebulae.

South of Cygnus is the indistinct form of Vulpecula. Look for the asterism Collinder 399, also known as the Coat Hanger. This is best observed in binoculars. Due north of gamma sagittae is the planetary nebula M27, the Dumbbell. The tiny arrow shaped figure east of Vulpecula is Sagitta. There are many faint multiple stars here, but the highlight is the globular cluster M71, roughly midway between gamma and delta. East of Sagitta, just outside the bounds of the Milky Way, is the tadpole shape of Delphinus. Here we find two planetary nebulae, NGC 6891 and NGC 6905, as well as two globular clusters, NGC 6934 and NGC 7006. Perhaps more of an Autumn constellation, yet somehow aligned with Delphinus and Sagitta, is little Equuleus, a tiny inverted Hercules southeast of the Dolphin. It is outside the Milky Way, has few dark sky objects, and reminds the northern observer of what is to come in the following few months.

Moving back to the Milky Way we look west and slightly to the south to the somewhat cross-shaped constellation Aquila. The brightest star here is Altair, which, together with Vega and Deneb, constitutes the Summer Triangle. Aquila hosts a segment of the Great Rift in the Milky Way. See if you can make out the dark divide in the otherwise dazzling star clouds. Look also for the open clusters NGC 6709 and NGC 6755.

West and south of Aquila is Serpens Cauda, the eastern part of Serpens in the grasp of Ophiuchus. Most of this constellation is a rough line pointing north by northeast. There are many nice multiple stars, but the the highlight is M16, the open cluster known as the Eagle nebula. Look for the associated emission nebula IC 4703.

Moving back to the Milky Way south of Aquila we find Scutum, small, not terribly bright but rich in interesting objects. Look for the open clusters M 26 and M11. If you have very good skies, see if you can locate the dark nebulae Barnard 110, 111, and 113.

South of Scutum the galaxy brightens appreciably as the center of the Milky Way comes into view. The main segment of Sagittarius is an inverted dipper that, connected to a triangle to the south, can be construed as a celestial teapot, pouring onto the tail of the scorpion (an unwise recipe in any climate). Sagittarius boasts a huge number of spectacular objects. In binoculars one can see the emission nebulae M20, M8 (Lagoon), M17 north of the open cluster M18, and a host of open and globular clusters.

South of Sagittarius is the small circular shape of Corona Australis, noteworthy perhaps for its lack of interesting sights. To the south is Pavo, containing some interesting multiple stars but outshone by the richer star fields preceding it. Octans, circling the pole, likewise pales in comparison to the southern autumn.


The Planets in August

Mercury is in the early evening sky. Look for it near Venus.

Venus is an evening object. It will become more prominent as the month progresses.

Mars is in the early evening sky. It is slowly slipping into the sun’s glare.

Jupiter is a fine evening object, though it may be too low in the sky for serious observers in the north.

Saturn is visible at twilight at the beginning of the month.

Bibliography

Archinal, B. A., Hynes, S.J., Star Clusters, Richmond, Virginia: Willman-Bell, 2003.

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

Kelly, P. (ed.), Observers Handbook 2007, Toronto: University of Toronto Press, 2006.

Hynes, S.J., Planetary Nebulae, Richmond, Virginia: Willman-Bell, 1991.

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

Tirion, W., Rappaport, B., Remaklus, W., Uranometria Deep Sky Atlas, Richmond, Virginia: Willman-Bell, 2000.

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