Daniel Fischer 1 2 3 Hilmar Duerbeck 1 2 3 1. Antofagasta Chile 3. Baltimore USA. Personalised recommendations. Cite chapter How to cite? During the Asymptotic Giant Branch AGB phase, the star undergoes mass loss, emitting a circumstellar shell of hydrogen gas. When this phase comes to an end, the star enters the PPN phase, where it is energized by a central star, causing it to emit strong infrared radiation and become a reflection nebula.
The PPN phase continues until the central star reaches a temperature of 30, K, after which it is hot enough to ionize the surrounding gas.
Many nebulous objects were noticed in the night sky by astronomers during Classical Antiquity and the Middle Ages. The first recorded observation took place in CE, when Ptolemy noted the presence of five stars in Almagast that appeared nebulous in his book.
He also noted a region of luminosity between the constellations Ursa Major and Leo that was not associated with any observable star. On July 4th, , the supernova that created the Crab Nebula SN , was visible to astronomers on Earth, and recorded observations that were made by both Arabic and Chinese astronomers have been identified.
While anecdotal evidence exists that other civilizations viewed the supernova, no records have been uncovered. By the 17th century, improvements in telescopes led to the first confirmed observations of nebulae. In , Swiss astronomer Johann Baptist Cysat also observed the nebula; and by , Christiaan Huygens made the first detailed study of it. By the 18th century, the number of observed nebulae began to increase and astronomers began to compile lists.
In , French astronomer Jean-Philippe de Cheseaux compiled a list of 20 nebulae, included eight that were not previously known. Between and 53, Nicolas Louis de Lacaille cataloged 42 nebulae from the Cape of Good Hope, most of which were previously unknown. The number of observed and cataloged nebulae greatly expanded thanks to the efforts of William Herschel and his sister, Caroline.
In , the two published their Catalogue of One Thousand New Nebulae and Clusters of Stars , which was followed up in and by a second and third catalog. At the time, Herschel believed that these nebulae were merely unresolved clusters of stars, a belief he would amend in when he observed a true nebula surrounding a distant star.
Nebulae are some of the most spectacular objects in the universe, and many have been named after familiar objects, including land animals , insects , aquatic animals , birds , with some even named after ghostly apparitions.
But how exactly does a nebula form in the vast and apparent vacuum of space? Read on and find out! Nature abhors empty space, after all! A nebula subsequently begins to form when a few atoms get close enough to clump together. Naturally, the more atoms that clump up, the stronger their gravitational influence then becomes.
This in turns allows them to draw even more particles towards them and after eons of time you get a large gaseous cloud forming in space.
Furthermore, some parts of the cloud may become even denser than other areas. As more and more matter accumulates, the material mostly hydrogen may then reach a point when it start to collapse in upon itself. This is the beginning of a new solar system.
Several nebulae have been found to be stellar nurseries. The Eagle Nebula, and the Orion Nebula are both sites of active star formation. There are a few nebulae that can be seen with the naked eye and many more that can be detected with a good pair of binoculars. A telescope is required to bring our fine details.
Unfortunately, the human eye is not sensitive enough to bring out the rich colors of most nebulae. It is the photograph that does the most justice to these incredible objects.
Until recently, time exposures on film were the best way to bring a nebula's true colors. Today, digital photography has simplified the process. New tools like the Hubble space telescope are giving us views of nebulae that have never been seen before. Areas of active star formation have been identified in many galaxies that were once thought to be inert.
Perhaps the most well known nebulae is the Orion Nebula, also known as M It is one of the very few that can be seen with the naked eye.
It is a bright emission nebula over 30 light-years in diameter. The nebula is illuminated by a group of stars at its center known as the trapezium. Another popular favorite is the Lagoon Nebula, M8. It is much larger than the Orion Nebula, reaching over light-years across the heavens. The Trifid Nebula, M20, is one of the most colorful. This reflection nebula contains a combination of elements that render it in rich hues of red, blue, and pink.
Dark lanes of dust divide it into three distinct parts, giving rise to its name. One of the most famous planetary nebulae is the Ring Nebula, M This is a beautiful object that resembles a circular rainbow around a small central star.
Another popular planetary nebula is the Dumbbell Nebula, M Its unmistakable bow tie shape gives it its name.
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