船尾座RS星
影像来源与版权:Image Data: NASA, ESA, Hubble Legacy Archive; Processing & Copyright: Rogelio Bernal Andreo (DeepSkyColors.com)

说明:这幅影像中央最亮的星是闪烁的船尾座RS星,它的质量大约是太阳的10倍,平均亮度是太阳的15000倍。实际上,船尾座RS星是一颗造父变星,这类恒星的亮度被用来估计与邻近星系的距离,也是建立宇宙距离尺度的第一步。当船尾座RS星在大约40天时间内有规律的闪烁时,它周围星云的亮度也会延迟发生有规律的变化,这实际上是一种回光现象。通过对星云的时间延迟和角度大小的测量,已知的光速可以使天文学家用几何学确定出船尾座RS星的距离为6500光年,其误差非常小,只有正负90光年。这是恒星天文学的一项显著成就,回波测距也更加精准地确定了船尾座RS星的真实亮度,进而确定其它造父变星的真实亮度,提高了对银河系之外星系间距离的了解。
翻译:北京天文馆

RS Puppis
Image Credit & Copyright: Image Data: NASA, ESA, Hubble Legacy Archive; Processing & Copyright: Rogelio Bernal Andreo (DeepSkyColors.com)

Explanation: Pulsating RS Puppis, the brightest star in the image center, is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid variable star, a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale. As RS Pup pulsates over a period of about 40 days, its regular changes in brightness are also seen along its surrounding nebula delayed in time, effectively a light echo. Using measurements of the time delay and angular size of the nebula, the known speed of light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years. An impressive achievement for stellar astronomy, the echo-measured distance also more accurately establishes the true brightness of RS Pup, and by extension other Cepheid stars, improving the knowledge of distances to galaxies beyond the Milky Way.
Astronomy Picture of the Day 05/17/2019