a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star
planetary nebula的用法和样例:
例句
Many objections can be raised to this picture of planetary nebula formation. 形成行星状星云的这一图象可能会引起许多异议。
This image from the Hubble Space Telescope reveals the Cat&squots Eye Nebula to be one of the most complex planetary nebulae known. 这张来自哈伯太空望远镜的影像,透露出猫眼星云是现知结构最复杂的行星状星云之一。