A little insight to my headcannon on Eclipse. She is a unicorn, and specialized in Moon Magic. At that point in time, it took several unicorns to raise and lower both the sun and the moon, or an alicorn. Eclipse was trying to become an alicorn, but just wasn't to that point. A few years after Luna was born, she became the last Moon Magic unicorn to raise and lower the moon. She had to expend a great amount of magic and energy to do this every day, and had to dip into her life magic. She and her husband had hope that Luna would be able to help eventually, but the strain of moving the move single-handedly cost her her life early.