The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the red emission nebula seen above and to the right of center in the above photograph. The Horsehead is some 1,500 light-years distant, embedded in the vast Orion cloud complex. About five light-years "tall", the dark cloud is cataloged as Barnard 33 and is visible only because its obscuring dust is silhouetted against the glowing red emission nebula IC 434. Contrasting blue reflection nebula NGC 2023 is visible on the lower left. In this color image, both Horsehead and NGC 2023 seem to be caught in beams of light shining from above -- but the beams are actually just internal reflections from bright star Sigma Orionis, just off the upper edge of the view. The bright star on the left is located in the belt of the familiar constellation of Orion. The horse-head feature is dark because it is really an opaque dust cloud which lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. Also visible in the picture are blue reflection nebulae, which preferentially reflect the blue light from nearby stars. (Text adapted from APOD). Apo TEC140 (140/f7.2) - FLI Proline 16803 - Ha (270m) L (200m) R (120m) G (120m) B (120m) - Warrumbungle Observatory, Coonabarabran, NSW, Australia
A mere seven hundred light years from Earth, in the constellation Aquarius, a sun-like star is dying. Its last few thousand years have produced the Helix Nebula (NGC 7293), a well studied and nearby example of a Planetary Nebula, typical of this final phase of stellar evolution. A total of 16.5 hours of exposure time have gone in to creating this deep view of the nebula. It shows details of the Helix's brighter inner region, about 3 light-years across, but also follows fainter outer halo features that give the nebula a span of well over six light-years. The white dot at the Helix's center is this Planetary Nebula's hot, central star. A simple looking nebula at first glance, the Helix is now understood to have a surprisingly complex geometry (text adapted from APOD). Apo TEC140 (140/f7.2) - FLI Proline 16803 - Ha (630m) OIII (600m 5nm + 240m 3nm) L (270m) R (80m) G (190m) B (170m) - Warrumbungle Observatory, Coonabarabran, NSW, Australia
Interstellar dust clouds and bright nebulae abound in the fertile constellation of Orion. One of the brightest, M78, is just left of center in this colorful telescopic view, covering an area north of Orion's belt. At a distance of about 1,500 light-years, the bluish nebula itself is about 5 light-years across. Its blue tint is due to dust preferentially reflecting the blue light of hot, young stars in the region. Dark dust lanes and other nebulae can easily be traced through this gorgeous skyscape. The scene also includes the remarkable McNeil's Nebula -- a newly recognized nebula associated with the formation of a sun-like star, and the telltale reddish glow of many Herbig- Haro objects, energetic jets from stars in the process of formation (text adapted from APOD). Apo TEC140 (140/f7.2) - FLI Proline 16803 - Ha (420m) L (220m) R (220m) G (150m) B (280m) - Warrumbungle Observatory, Coonabarabran, NSW, Australia
