An almost-total lunar eclipse was visible before dawn Friday morning. It was the longest in 580 years, dating back to 1440. The Earth cast its shadow on the Moon for just over six hours. If you missed it, you’d have to catch the next one in 2669, another 648 years. It was the longest partial lunar eclipse of the millennium. The entire eclipse was about three hours and 28 minutes. Although the whole length of the eclipse is over three hours, the red color was only visible for less than 20 minutes.