| 21. | "' Abell 13 "'is a type 4 planetary nebula in the constellation of Orion.
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| 22. | The first planetary nebula discovered was the Dumbbell Nebula in the constellation of Vulpecula.
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| 23. | The visible planetary nebula is approximately spherical and far older than the 1919 outburst.
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| 24. | "' NGC 2452 "'is a planetary nebula located in the southern constellation of Puppis.
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| 25. | Some of them will end their lifes as Planetary nebula.
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| 26. | NGC 7662 is a popular planetary nebula for casual observers.
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| 27. | The planetary nebula NGC 2438 is superimposed; it is approximately 2900 light-years from Earth.
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| 28. | That case pertains to the planetary nebula PHR 1315-6555 and the open cluster Andrews-Lindsay 1.
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| 29. | It was discovered by William Herschel on April 14, 1789 and misclassified as planetary nebula.
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| 30. | Planetary nebula NGC 3699 is distinguished by an irregular mottled appearance and a dark rift.
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