Complex sentence: The asteroid has not been observed since 14 March 2000, and 17 February 2014 was the first day that it had a solar elongation more than 90 degrees from the Sun making it easier to recover under a dark sky.
Split into simpler sentences: The asteroid has not been observed since 14 March 2000. During the 2014 approach 17 February 2014 was the first day that it had a solar elongation more than 90 degrees from the Sun making it easier to recover under a dark sky.