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