It has an apparent diameter of 1 arc minute and a real diameter of about one light year. At magnitude 9.7, its high surface brightness makes it an easy object, even from the city and even with small telescopes, provided a reasonable amount of magnification is used, and you know exactly where to look. The Ring nebula was discovered by Antoine Darquier de Pellepoix in January of 1779. Despite their name, planetary nebulas have nothing to do with planets. They were named originally in the 18th century when their discoverers observed them visually and they did not appear as stellar point sources. Instead, they appeared as small diffuse objects that resembled the planets Uranus and Neptune when seen in a telescope. Planetary nebula are shells of gas shed by stars late in their life cycles after using up all of their nuclear fuel. The star then ejects a significant portion of its mass in a gaseous shell, which is illuminated by its extremely hot central star, which is just the core left from the original star. The star at the center of the Ring nebula has a surface temperature of 225,000 degrees Farenheit or 125,000 degrees Celsius. Our own star, the Sun, is expected to undergo the same process in a couple of billion years. Planetary nebulas do not last long at all in cosmic terms, the shell of gas expands and diffuses, becoming invisible, and the star turns into a white dwarf. The central star in the Ring Nebula has always been an observing challenge for visual observers because of its dimness at magnitude 15.3, and also because it is located in the center of the Ring's faint nebulosity. In this photo, the Ring glows in the blue-green light of doubly-ionized oxygen emission lines at 495.7nm and 500.7nm. An unmodified stock DSLR camera is sensitive to these wavelengths. Because M57 is small, this image is cropped from the full frame to about 100 percent enlargement, in other words, it is cropped a lot. It might look ok here on a computer monitor, but you would not be able to make anything but a very small print with it. This is part of the trade off we are making by using a telescope with a short focal length and small aperture. It does not have much magnification, so fewer shots will be ruined by tracking errors. But this also means that if you shoot small objects, you will really have to crop them to make them prominent in the frame when you display the image. Image Data
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