The Hubble Space Telescope was launched into orbit on April 24, 1990 – nearly 26 years ago. Ever since, it has been supplying scientists with gorgeous images of the cosmos. The image above, which shows a star "blowing a bubble," is NASA's choice to commemorate the telescope's latest birthday.
The Bubble Nebula (NGC 7635) lies 7,100 light-years away in the constellation Cassiopeia. It's a staggering seven light-years across, formed by a star 20 times as massive as our sun — that bright purple dot just left of center. Previous Hubble images have captured only pieces of the brilliant, ever-growing gas orb, but this latest shot stitches together multiple frames to show the nebula in its entirety.
NGC 7635 is an emission nebula. The bright star at its not-quite-center throws off hot gases, known as stellar wind, that move at 4 million mph. When these hot gases slam into the cold gas and dust of interstellar space, they form an intriguingly symmetrical bubble. The star's intense ultraviolet radiation causes the gases to glow, with different elements heating to different temperatures to form distinct colors: Oxygen is hot enough to burn blue, while hydrogen and nitrogen form a cooler yellow light.
More than a quarter-century into its tenure, the Hubble is still going strong. But its successor will hit the scene soon. The James Webb Telescope, which is set to launch in 2018, will be able to look much deeper into space — and, therefore, earlier into cosmic history — than the Hubble can.