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The tail of the Corona Australis reflection nebula

Date created: 2001-10-20

Tags: nebula, dust, cluster, globular, reflection

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.

Our picture is about 4.5 degrees across and the extremely faint Corona Australis nebula meanders along the Sagittarius-Corona Australis border, and 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.

By far the largest and densest of the molecular clouds is at the western end of the picture, seen in much more detail here. It is about a degree long, corresponding to eight light years at the 500ly 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 visual binary and a variable star. Other wispy nebulae in the western part of the dark cloud betray the presence of young, hidden stars.

Photograph made from plates taken in 2001, April, May, June, R, B, G. Top left is NE. Image width is about 4.4 degrees.

Credit: David Malin

© Australian Astronomical Observatory