APOD: 2024 August 22 - The Dark Tower in Scorpius

Good morning, Rallypoint, and welcome to the August 22nd edition of Astronomy Picture of the Day (APOD). Fans of J.R.R. Tolkien are already familiar with a ground-based "Dark Tower" in the land of Mordor; this dark tower lies in the tail of the constellation Scorpius (The Scorpion) about 5,000 light years away.

A 'globule' is an isolated and relatively small dark nebula containing dense cosmic dust and gas from which star formation may take place. The Dark Tower is a 'cometary globule', where its dust and gas are swept into the shape of a comet by a nearby source (in this case, star cluster NGC 6231 is off frame to the right). The Dark Tower could also be classified as both an emmission nebula and reflection nebula. Why? The radiation from NGC 6231 is ionizing hydrogen gas along the borders of the Dark Tower, and these atoms emit a characteristic red glow. The blue we see is due to visible light from hot stars within the Dark Tower being diffracted and reflected by the dust that is present.