What are the ‘nacreous clouds’ lighting up the winter skies? - Business Insider

http://www.businessinsider.com/what-are-the-nacreous-clouds-lighting-up-the-winter-skies-2016-2?nr_email_referer=1&utm_content=COTD&utm_medium=email&utm_source=Sailthru&utm_campaign=Post%20Blast%20%28sai%29:%20Here%20are%20the%20most%20valuable%20companies%20in%20America%20since%201990&utm_term=Tech%20Chart%20Of%20The%20Day