Where is planetary nebula

Most of them are concentrated toward the plane of the Milky Way's disk, but a few are also know to exist in the halo and a number have been identified in the bulge of the galaxy as well. What's so interesting about planetary nebulae? Astronomers are drawn to study these objects because they provide opportunities to analyze material that was once a part of a shining star. For example, by studying the chemical composition of the nebula we can gain an understanding about the material out of which the star originally formed.

In addition, the abundances of certain elements such as carbon and nitrogen in the nebula reveal details about the physical processes that occurred within the star during its nuclear fusion lifetime. Research on PN advanced significantly with the advent of the Hubble Space Telescope , which revealed their exquisite structures in unprecedented detail.

These characteristics are thought to arise due to a post- AGB evolutionary process that involves the effects of a binary central system, or a local stellar magnetic field, or both. A montage of Hubble Space Telescope images of planetary nebulae. They are extended in size and fuzzy in appearance, and generally show some degree of symmetry.

The nebula is illuminated by a central star, which sometimes is too faint to be seen. Planetary nebulae were discovered by astronomers as early as the 18th century, with four planetary nebulae being included in the catalogue of nebulae by Charles Messier in The most well known planetary nebula is the Ring Nebula in the constellation of Lyra Figure 1 , which can easily be observed with a small telescope in summer from the Northern hemisphere. This turned out to be an unfortunate misnomer as planetary nebulae have nothing to do with planets.

Planetary nebulae are typically one light year across and are expanding at a rate of about km per second. The density in the nebulae is very low, ranging from several hundred to a million atoms per cubic centimeter. Such conditions are better than any vacuum one can achieve on Earth.

The temperature of the gas in the nebula is about 10, degrees Celsius, and the central stars of planetary nebulae are among the hottest stars in the Universe, with temperature in the range of 25, to over , degrees Celsius. The central stars are also very luminous, usually hundreds to thousands of times more luminous than the Sun. However, because of their high temperatures, they radiate primarily in the ultraviolet and are often faint in visible light.

The spectra of planetary nebulae are fundamentally different from those of stars. Instead of a continuous color from red to blue as in the case of the Sun, the spectra of planetary nebulae are dominated by discrete emission lines emitted by atoms and ions. Unlike stars, whose continuous spectra give them a composite white appearance, planetary nebulae have a rich variety of colors. These bright emission lines are powered by the central star, which is the source of energy for the entire nebula.

Ultraviolet light emitted by the central star is intercepted by atoms in the nebula and converted to visible line radiation. First the ultraviolet light removes electrons from the atom in a process called photoionization. The freed electrons then either recombine with the ion and emit a recombination line, or collide with other atoms and ions to cause the emission of a collisionally excited line.

Because of the low density conditions, atomic lines that are generally suppressed under high density conditions as in the laboratory on earth but which can be produced in the low density conditions of planetary nebulae. Our next two targets lie in Aquarius. Through an 8-inch or larger telescope, view NGC with magnifications above x. Its oval disk measures 25" through its long axis. The ringlike extensions that give the nebula its name protrude on each side another 15".

What color do you see in the Saturn Nebula? Whether you see it as mostly blue or mostly green depends only on your color perception. The Helix is one of the brightest hard-to-see objects in the sky.

Although its total light output nearly reaches 7th magnitude, its diameter is 13', so its surface brightness is disappointingly low. For best results, use binoculars that provide 7x to 15x magnification and have front lenses larger than 50 millimeters. The northern and southern edges seem slightly brighter.

Through an 8-inch scope, the Snowball is a small, evenly illuminated disk. Then try to spot the fainter shell that surrounds that ring. The ring is brightest to the northeast and southwest. Pick your favorites and share them with your friends at the next star party. Good luck! Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter. View our Privacy Policy. By signing up you may also receive reader surveys and occasional special offers.

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