The head of the Corona Australis reflection nebula
AAO image reference UKS 37a.    « Previous || Next »

 The head of the Corona Australis nebula (NGC 6726, NGC 6727, NGC 6729)
Top left is NE. Image width is 3 degrees
Image and text © 2001-2010, Australian Astronomical Observatory. Photograph from UK Schmidt plates by David Malin.

Corona Australis (the southern crown, CrA) is in the far southern sky but visible from the southern states of the USA. The constellation is small but distinctive. The conspicuous globular cluster NGC 6723 is at the western (right) edge of the photograph, but it is in Sagittarius, and is about 30,000 light years distant, while the wispy dust cloud that dominates the picture is about 500 light years away.

The image above is about 3 degrees across and the faint Corona Australis nebula meanders along the Sagittarius-Corona Australis border in the same E-W direction. Almost all the nebulosity here is starlight, reflected from minute grains of dust, some of which gather into darker condensations ('molecular clouds'), blotting out the background stars. Fainter, more extended features can be seen here.

By far the largest and densest of the molecular clouds is in the centre of the picture. It is about a degree long, corresponding to eight light years at the distance of the nebula and is extremely opaque -- background stars are dimmed by an astonishing 35 magnitudes. However, not all is darkness, and the dusty cloud appears to be tipped by a pair of bright stars, embedded in bright reflection nebulae. The brightest of these is NGC 6726-27 and it contains both a widely spaced visual binary and a variable star. The other bright reflection nebula, IC 4812, is illuminated by rather closer pair of binary stars, while other wispy nebulae in the western part of the dark cloud betray the presence of very young, hidden but still-forming stars.

Related images
AAT 73.     The reflection nebula NGC 6726-27
AAT 106.   The globular cluster NGC 6723
UKS 37.    The tail of the Corona Australis reflection nebula
Constellation of Corona Australis (external site)

For details of object position and photographic exposure, search technical table by UKS reference number.

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Updated by David Malin, 2010, July 25