Labels:text | screenshot | universe | space | astronomy OCR: PLANETARY NEBULAS RED-GIANT STARS shed their gaseous outer layers toward the end of their lives. These layers form an expanding shell of glowing gases called a planetary nebula. The name arose because the German-born astronomer William Herschel (1738-1822) thought the shells looked like planets. The gas shell may appear, from the Earth, in the shape of an hourglass, a bubble, or a THE DUMBBELL NEBULA ring. It typically travels outward at This computer-enhanced image shows a about 20 km (12 miles) per second nebula with an hourglass shape produced before dispersing into the interstellar by gas thrown off by the central star. medium after about 35,000 years.
