是什么因素决定了一颗恒星的颜色呢？答案当然是温度。红星温度较低，其表面温度大约只有3000K；蓝星则温度较高，能达到30000K；我们的可爱太阳是黄色的，温度是适中的6000K。在这张试用星迹变焦拍摄技术合成的猎户座趣味照片中，很容易就能分辨出恒星的不同色彩。该图是在逐步变焦的同时连续曝光35次合成的，记录了星星从左到右的移动轨迹，在开始和结束时均未聚焦而中间一张聚焦才创作出这种蝴蝶结形状的星迹图。图中越亮的星星色彩也越饱满。左上角鹤立鸡群的是猎户座α星参宿四（Betelgeuse），它是一颗温度较低的红巨星，温度较高的蓝星则构成了猎户的身体，不属于恒星的猎户座星云在下部中央发出粉红色光芒。图中比较显眼的还有靠近右边缘中间位置的那个较暗星迹，它是温度较低的深红色碳星猎户座W，由于富含碳元素而显得更红。

Explanation: What determines a star's color? Its temperature. Red stars are cool, with surface temperatures of around 3,000 kelvins (K), while blue stars are hotter and can have temperatures over 30,000 K. Our own lovely "yellow" Sun'stemperature is a comforting 6,000 K. Differences in star colors are particularly easy to see in this intriguing composite view of the constellation Orion, made while experimenting with a star trail step-focus technique. In it, a series of 35 consecutive exposures were combined to produce trails of stars moving left to right through the frame, while changing focus in steps. Beginning and ending with the camera out of focus produced a sharply focused exposure near the middle of the series and blurs the star trails into a bow tie shape. For the brighter stars, blurring produces more saturated colors in the images. At the upper left, Orion's cool red supergiant Betelgeuse stands out from the other, hotter, bluish stars composing the body of the constellation. Not a star at all, the Orion Nebula contributes a pinkish tint below center. Also remarkable in the field, the fainter step focus trail of cool, deep red carbon star W Orionis is near the center right edge, its red hue enhanced by a carbon-rich composition.

每日天文一图（APOD）是美国宇航局天体物理学部每日定期发布的天文图片，并配有专业的简短解释，是小子时常光顾的地方，地址为：http://apod.nasa.gov/apod/。现将部分酷图转来并对原文解释做了翻译，英文及天文知识均有限，译错之处敬请各位指正。
秋天的麦兜 2011年2月11日 于济南。