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
双语例句
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。
