A brief summary of Michael Hopkins' career in the Air Force and at NASA.
Twice a year, one hemisphere has its longest day of the year while the other has the longest night. These solstices are the astronomical beginning of winter and summer.
Equinoxes occur twice a year when the sun is directly above the equator, and signal herald the beginning of spring and autumn.
Astrobiologists should consider searching for viruses in their quest to find evidence for life beyond Earth, some scientists stress.