December 16, 2015
The night sky on your birthday is never quite the same twice — the planets shift, the constellations drift, the Moon wears a different phase.
The Horsehead Nebula
Birthday · December 16, 2015
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APOD published December 16, 2015. Credit: Jos� Jim�nez Priego. A publication-date match, not a photo taken on your date. Independent of NASA.
The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the red emission nebula in the center of the above photograph. The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will surely alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. On the image left is the Flame Nebula, an orange-tinged nebula that also contains filaments of dark dust. Just to the lower left of the Horsehead nebula featured picture is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars. Free APOD Lectures: Editor to Speak in January in Philadelphia and New York City
Image credit: Jos� Jim�nez Priego