Open cluster Messier 6 and Siding Spring – Rolando Ligustri 
Astronomy Picture of the Day

Siding Spring likely formed 4.6 million years ago in the Oort Cloud.  No comet has come anywhere near this close to Earth in recorded history. source

Siding Spring will flyby Mars at a distance of 87,000 miles on October 19. 
That’s one-third of the distance between Earth and Moon.  Siding Spring’s tail could extend from Earth all the way to our moon. Its gaseous coma, the fuzzy head surrounding the nucleus, might stretch halfway to the moon.

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Heads UP  !
GMA