What is a planetary retrograde? And what connection does it have to astrology? We explain how planets move across the sky.

Skywatchers across the Northern Hemisphere have caught a fleeting glimpse of Mercury as it made one of its final visible appearances of the year. Appearing low on the southwestern horizon just after ...

Turns out, it's as tough to drop inward into the inner solar system, as it is to head outward. The problem stems from losing momentum from a launch starting point on Earth. It can take missions ...

CAPE CANAVERAL, Fla. (AP) – The only spacecraft ever to orbit Mercury ended its four-year tour with a crash landing Thursday. NASA’s Messenger plunged from orbit as planned and slammed into the sun’s ...

(PhysOrg.com) -- MESSENGER scientists will highlight the latest results on Mercury from MESSENGER observations obtained during the first six months (the first Mercury solar day) in orbit. These ...