我们很难发现这类天体，更不用说用光学望远镜研究它们了。
We have trouble discovering those sorts of bodies, much less studying them using just optical telescopes.
从一端到另一端，银河系布满星星的圆盘横跨12万光年，可以用肉眼和光学望远镜观察到。
From end to end, the Milky Way's starry disk, observable with the naked eye and through optical telescopes, spans 120,000 light-years.
这张照片由加那利群岛的北欧光学望远镜的数据合成，显示星云的延伸发射。
Made with data from the Nordic Optical Telescope in the Canary Islands, the composite picture shows extended emission from the nebula.
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