Horsehead & Flame nebula
The Horsehead Nebula, also known as Barnard 33, is a celestial cloud that looks like the head of a horse from Earth. It is one of the most famous nebulae in the sky. It has been observed and recorded for the first time by the Scottish astronomer Williamina Fleming from the Harvard College observatory in 1888. Over thirty years later, the American astronomer Edward Emmerson Barnard cataloged it as Barnard 33. He described it as a “dark mass, diam. 4′, on nebulous strip extending south from zeta Orionis”.
In the photos in this article, we find the Horsehead Nebula on the right of Alnitak: a triple star system and one of the brightest stars in Orion’s belt.
Right below Alnitak, we find the Flame Nebula, also known as NGC 2024 or Sh2-277. It is also a large cloud that is certainly not on fire but looks like a flame from Earth. It was William Herschel who was the first to observe it in 1786.
The Horsehead Nebula and the Flame Nebula are both in the constellation Orion, the prominent winter constellation for the Northern hemisphere residents. The best time to take an image of this iconic couple is between November and February. Conversely, Southern hemisphere residents can observe it during the summer. More precisely, it is located at 05h 40m 59.0s RA and -02° 27′ 30.0″ Dec.
The Horsehead Nebula is a dark nebula, which means a dense cloud of gas and dust that lies at about 1500 light-years from us. This thick nebula blocks the light emitted by an emission nebula (known as IC 434) in the background, as we see in these photos. The Horsehead Nebula is part of the large Orion Molecular Cloud Complex. In the southwestern part of the Horsehead, we find a reflection star-forming nebula named NGC 2023. In this photo, we used an RGB filter for this picture to appreciate the nebula’s true colors. We also used an H-alpha filter to highlight the ionized hydrogen regions in the cloud, which gives it the typical reddish glow. It took three hours of exposure time to collect enough light from the sources to give us this beautiful picture.
Observing towards the Rosette nebula through a pair of binoculars shows the central open cluster (NGC 2244). However, in order to observe the surrounding nebula, we need a telescope, with ideal observing conditions (without light pollution). Even with a telescope, many details cannot be seen. In fact, we need to collect more light from the nebula by increasing the exposure time to let more light reach the camera sensor (see pictures above).
Exploring at X-ray and ultraviolet wavelengths reveal much more information about the nebula. Moreover, spectroscopic observations are gold mines for astronomers. They allow them to reveal the nebula’s deepest secrets, such as its chemical composition, without leaving the Earth.
The Flame Nebula is also a part of the giant Orion Molecular Cloud Complex. It is located at 05h 41m 54s RA and -01° 51′ 0.0″ Dec. It is an emission nebula that is also a star-forming region. With an apparent magnitude of 10, it is not visible to the human eye. It needs a telescope, a camera and a long exposure time. The neighbor trip star Alnitak radiates high-energy ultraviolet light that ionizes the hydrogen by freeing the electrons. When these electrons recombine with the ionized hydrogen, photons are emitted, which is the reason why the Flame nebula is bright, as we see in above photos.
In the heart of the Flame, we find a cluster of hundreds of young stars. Besides, most of these stars have circumstellar disks around them. If we zoom in on the center, we can see a dark lane of dust that blocks the background light. Beside the optical images, X-ray observations revealed that the youngest stars congregate in the central part of the nebula.
The Horsehead Nebula and the Flame Nebula are among the most famous targets in the night sky for observers anywhere in the world. It is always breathtaking to see such large structures where stars are born and evolve. These nebulae have very low visibility. But we are lucky today to have advanced instruments (telescopes, cameras, filters, and processing software) that allow us to enjoy these sceneries.