Astronomy Picture of the Day . ... 20.03.1997 . ... AAC Explanation: Today marks the Vernal Equinox , the first day of Spring for planet Earth's northern hemisphere. ... Gorgeous pictures of the comet with its delightful tails - this one taken March 16 - make this outbreak of "comet fever" understandable. ... However, stretching for millions of miles, awe-inspiring comet tails are actually an extremely tenuous, nearly perfect vacuum and don't pose a danger to life on Earth . ... March 1997 . ...